TA.
Price $12.50

The LOWER ANIMALS
Living Invertebrates of the World

By Ralph Buchsbaum and Lorus J. Milne
in collaboration with Mildred Buchsbaum and

Margery Milne

With 315 illustrations, mcluding 144
im full color

‘Eye outstanding teams of scientists here draw on
their rich experience for a fascinating review of the
lower groups of the Animal Kingdom. Together, the
text and pictures form an unsurpassed introduction
to the life of land and water, the creatures of beach
drift, tidal pool and open sea, and the organisms in
living tissue.

Although generally less familiar than such other
groups as mammals and birds, the invertebrates, that
is, animals without a spinal column, are by far the
most diverse. Thus this book ranges from the micro-
scopic radiolarians and other one-celled organisms
to the giant squids that do battle with whales, from
the spider on the highest mountains to the sea
cucumber of the deepest seas. Both text and illustra-
tions present an extraordinary variety of living
things: coral animals that build South Sea atolls,
poisonous jellyfishes (as well as harmless ones), the
earthworms and clam worms that fishermen fancy,
the beauty of mollusk shells that delight the beach-
combers, the scallops, snails, crabs and lobsters
prized by gourmets, and those curious creatures that
have become “living fossils.” There are few more
arresting stories than that of the cuttlefish that es-
cape from enemies by emitting an inky cloud, the
sea worms that swim in a water ballet at the dark
of the moon, or the great clams that raise plants as
food in special “greenhouses.”

As in earlier books in this series, the text is illus-
trated with a matchless collection of 292 photographs
(and 23 drawings) from all over the world.

THE AUTHORS

Ralph Buchsbaum is Professor of Zoology at the
University of Pittsburgh and author of the widely
used textbook, Animals without Backbones. His
wife is also a zoologist and has worked with him in
researches in America, Europe and Southeast Asia.

Lorus J. Milne, Professor of Zoology at the Uni-
versity of New Hampshire, and his wife Dr. Margery
Milne have investigated the role of vision in inverte-
brates in North, Central and South America and in
Africa. Together they have written many books, in-
cluding The World of Night, Paths Across the Earth,
and a popular textbook, The Biotic World and Man.

Jacket design based on a
photograph by ALLEN KEAST

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The Lower Animals

LIVING INVERTEBRATES OF THE WORLD

With photographs by
RALPH BUCHSBAUM
DOUGLAS P. WILSON
FRITZ GORO

and others

Line drawings by

KENNETH GOSNER

3 f
N
oe

INSTITUTION ARCHIVES

W.H.O.1. DATA LIBRARY
WOODS HOLE. MA. 02543

The Lower Animals

LIVING INVERTEBRATES OF THE WORLD

by Ralph Buchsbaum

Professor of Zoology, University of Pittsburgh

and Lorus J. Milne

Professor of Zoology, University of New Hampshire

an collaboration with Mildred Buchsbaum

and Margery M alne

A CHANTICLEER PRESS EDITION

DOUBLEDAY & COMPANY Inc., Garden City, New York

PUBLISHED BY DOUBLEDAY & COMPANY, INC. 1960
Garden City, New York

SECOND PRINTING 1961

PLANNED AND PRODUCED BY CHANTICLEER PRESS, INC., NEW YORK

THE WORLD OF NATURE SERIES

Living Mammals of the World by Ivan T. Sanderson

Living Reptiles of the World by Karl P. Schmidt

and Robert F. Inger
Living Birds of the World by E. Thomas Gilliard
Living Insects of the World by Alexander B. Klots

and Elsie B. Klots
The Lower Animals: Living Invertebrates of the
World by Ralph Buchsbaum and Lorus J. Milne,
in collaboration with Mildred Buchsbaum
and Margery Milne
Living Fishes of the World by Earl S. Herald
Living Amphibians of the World by Doris M. Cochran

Library of Congress Catalog Card No. 60—10650
All rights reserved. Except for brief quotation in reviews, no part of this book may be reproduced
without permission from the publishers. The contents are protected by copyright in all countries

adhering to the Berne Convention.

PRINTED IN THE UNITED STATES OF AMERICA

THIS BOOK IS DEDICATED TO

all those who have helped to found, to maintain,
to direct, and to carry on the work of the field
laboratories of the world. To their efforts we owe
much of our knowledge of the invertebrates.

A few of the larger marine laboratories have become veritable
universities by the seashore, with summer classes, good research
facilities, and fine libraries. They maintain displays of living
animals that are of interest to any serious amateur naturalist
who may stop to visit. The smaller marine laboratories, as well
as those beside fresh waters or located in many terrestrial habi-
tats from the tundra to the tropical forest or desert, have more
modest facilities but are equally hospitable. Large or small,
these field laboratories, or biological stations, make their greatest
contribution by enabling scientists to live and work in places
where animals can be studied in their natural surroundings.

Contents

Preface PAGE

Introduction

he The Protozoans (Phylum Protozoa)

I: The Sponges (Phylum Porifera)

Il. Hydrords, Jellyfishes, Sea Anemones, and Corals (Phylum
Coelenterata or Cnidaria)

IV. The Comb Jellies (Phylum Ctenophora)

Ve The Flatworms (Phylum Platyhelminthes)

VI. The Ribbon Worms (Phylum Nemertea)

VII. A Variety of Animal Groups

VIN. = The Arrow Worms (Phylum Chaetognatha)

IX. The Acorn Worms (Phylum Hemichordata)

xe The Beard Worms (Phylum Pogonophora)

x The Phoronids (Phylum Phoronida)

XU. = The Moss Animals (Phylum Bryozoa or Ectoprocta)

XI. = =The Lamp Shells (Phylum Brachiopoda)

XIV. The Peanut Worms (Phylum Sipunculoidea)

XV. The Echiuroids (Phylum Echiuroidea)

XVI. The Mollusks (Phylum Mollusca)

XVIL. The Segmented Worms (Phylum Annelida)

XVII. The Arthropods (Phylum Arthropoda)

XIX. The Echinoderms (Phylum Echinodermata)

XX. The Invertebrate Chordates (Phylum Chordata)

Bibliography

Index

9
13
16
56

67
115
119
129
33
144
146
148
149
150
154
156
157
158
200
226
254
286
291
293

Preface

ale oldest pictures of living invertebrates that have come down to us, from about 1500
B.C., are of the octopuses that Cretan artists painted on their beautiful vases, and of the
cockles and nautiluses that they worked into the designs of their frescoes and faiences. The
first book illustrations of animals were those of Aristotle, who made many diagrams to support
the descriptions of animal structure in his texts. The diagrams were lost long ago, but many of
them have been reconstructed from his references to them and from his excellent descriptions
in the Historia Animalium. Since Aristotle’s day no better way has been devised for com-
municating details of anatomical structure or embryological development than the well-
designed drawing or diagram.

No diagram, however, could have helped Aristotle to impart to his students the full attrac-
tion of the world of invertebrates that had kept him for much of two years on the island of
Lesbos. He became so enamored of the shore invertebrates that he passed day after day leaning
over the edge of a boat intent on what he could see in the still, clear, shallow, sunlit waters.
The graceful stances, the variety of behavioral postures, the delicate textures, the subtle and
rich colorings, and whatever it is that so completely fascinates those who see invertebrates at
first hand in their natural surroundings—all these are not easily communicated to others.

After Aristotle, interest in marine invertebrates declined; scientific inquiry into animals was
first neglected and then actively discouraged. During the Middle Ages people of religious out-
look tended to look upward, and the birds were of primary interest. Then came the new age of
marine discovery: the sea was once more in fashion, and interest in fishes and in marine
invertebrates returned. From Renaissance to modern times, artists mobilized every skill to
depict living animals as they saw and enjoyed them. Wood engravings, steel engravings, and
color printing inevitably fell far short of the reality. Artistic effort in biological books declined
during the first half of this century, as artists found more lucrative outlets for their skills and as
book-production costs soared. Photographers seemed the natural successors to artists, but
technical limitations made them train their heavy cameras on domestic animals or on the
same big-game mammals of Africa that were already known to us through the displays of zoos.
Not only were the smaller invertebrates more difficult to photograph because of their size and
timidity, but many of the most attractive ones lived below the surface of the sea or were
accessible to a camera only a few days in the year, when the lowest tides happened to coincide
with the sunniest mornings.

More than two decades ago a few photographers rejected the methods of the wire-and-pin
school of nature photography with its long bellows extensions and fixed lighting equipment
used to photograph dead, propped-up insects. Armed with faster lenses and the newest flash-
bulbs, they went whenever possible into the field, turning up logs in the tropical rain forest and
following the tides out on dark, foggy mornings. The black-and-white photographs made by
this group were a vast improvement over earlier ones, and they revived an interest in inverte-
brates and in books on invertebrates. Then suddenly, in the last decade, there was a major ad-
vance in the photography of animals. Faster color films and newly portable electronic lighting
equipment have sent naturalist-photographers into the field in greater numbers than ever. The
aqualung has taken the skin-diving photographer to the ocean bed to bring back beautiful
images of one of the last unexplored “landscapes” on our planet. The aqualung has itself
brought the enchantment of marine invertebrates to many thousands in areas and at depths that

10]

once were accessible only to a handful of swimmers. This has helped to add many to the in-
creasing audience for books on invertebrates. Most of the new books that treat at all of in-
vertebrates are limited to those of the seashore or of shallow marine waters and deal with the
animals from an ecological viewpoint and according to their habitat. This is a much needed
approach, and many such books are listed in the bibliography. But the series of which this is the
fifth volume (earlier volumes have covered mammals, reptiles, birds and insects, and forth-
coming volumes will cover fishes and amphibians) is designed to supply the need for a new set
of illustrated natural histories arranged systematically, group by group, and proceeding from
the primitive forms to the most specialized ones. Thus the present volume is a natural history of
the invertebrates (excepting the insects). But it necessarily presents the animals on a different
scale from that of the other volumes, which dealt with no more than a single class of animals.
The authors have had to cope with the many invertebrate phyla without allowing the extreme
limitations of space for such a project to turn it into a mere catalogue, lacking the vivid detail
and discursiveness that make for readability. The plan adopted here seems a reasonable
compromise: the smaller phyla are covered only in generalized accounts followed by a treat-
ment of a few typical or better-known examples. The large phyla are described in general ac-
counts, as are all of their living classes. Below the level of class the treatment is not completely
systematic; however, where possible, the specific examples are selected so as to give some
representation to all the important orders. Internal structure and embryological evidence are
mentioned only when indispensable for understanding of some aspect of behavior or of an
animal’s position in the evolutionary sequence. For the most part the evidences for classifica-
tion are only alluded to; they cannot be adequately expounded in a book of such broad scope.

It should be noted that the inserts of color plates involve special technical problems and so
do not necessarily adjoin the corresponding text, nor do they in all cases follow exactly the
sequence of the text. The black-and-white photographs accompany the text and follow the
same sequence.

Natural history is the oldest and the most diffuse of all the branches of biology. A realistic
acknowledgement of the written sources of the material in this book would have to begin with
Aristotle, who supplemented his own experience by drawing on every possible source, in-
cluding fishermen, peasants, and mere hearsay. From his time to ours these same informants
have been contributing, along with better-trained or professional observers. This has weighted
down natural history with much unreliable information, but it also has given it advantages in a
day in which most branches of biology have become so specialized and so experimental as to
create an unbridgeable gulf between the professional worker and the interested layman.
Although much of the material of natural history is first published in scientific journals, and
the authors have drawn mostly on these sources as a matter of habit, the field is one in which
original material is also published for the first time in natural history books or even in popular
magazines.

The first half of the text, that covering the protozoans through the entoprocts, was written by
Ralph and Mildred Buchsbaum; the second half, that dealing with the chaetognaths through
the invertebrate chordates was written by Lorus and Margery Milne.

The Lower Anumals

LIVING INVERTEBRATES OF THE WORLD

Introduction

ale develop a really friendly feeling for a jelly-
fish or a flatworm takes a lively imagination. And
even to tell head from tail in many invertebrates one
also needs some information. This poses for the
writer on invertebrates special problems of presenta-
tion that do not arise in quite the same way in books
on the natural history of vertebrates. Show anyone
a vertebrate, even so lowly a one as a goldfish, and
he can immediately identify himself with it, for it
has the same “two-sided” or bilateral symmetry as
himself. He not only knows head from tail but back
from belly and right side from left. He knows where
to approach it with an offering of food, and which
end will go first when it swims away. Gazing into its
two symmetrically placed eyes, he does not doubt
that the fish is looking at him, and he may even im-
agine that his image evokes a psychological response
that is closely akin to his own feeling of relatedness.
Not so with many of the lower invertebrate groups.
Their bodies may be spherical, as in many of the
floating protozoans, or they may be radial in sym-
metry, as in jellyfishes and corals. Even in bilateral
invertebrates like mollusks and insects, the legs may
wrap around the head, the multiple eyes may encir-
cle most of the body, or the ears may be mounted in
the legs. There are groups of invertebrates that su-
perficially are difficult to distinguish from seaweeds
and are almost as unresponsive. Many of the most
fascinating invertebrate groups require the use of a
hand lens or a microscope to be seen at all. Yet it is
the very strangeness of invertebrates—in contrast to
the relative sameness and predictability of the gen-

erally four-limbed vertebrates—that attracts us so
strongly. Whether we are exploring the sea bottom
with an aqualung, eagerly following a receding tide,
or merely wading about in a brook, the constant ex-
pectation of coming upon some hitherto unimagined
living shape or some undreamed-of way of life is an
exciting challenge—but a challenge on a purely aes-
thetic or intellectual level. For there is little emo-
tional warmth to be derived from fondling a beauti-
ful jellyfish or a colorful crab. Though there is great
sensual enjoyment in the kaleidoscopic variety of in-
vertebrate shapes and color patterns, this has its
limits—even with animals as lovely or as bizarre as
are many of the invertebrates.

The inexhaustible possibilities for intellectual en-
richment through contact with invertebrate animals
must come mostly through knowing something of
their habits, their distribution, their role in the nat-
ural communities in which they live, their variety of
structure, the basic relationships of even the most
seemingly diverse forms, their relative structural
complexity, and their origins in the grand scheme of
evolutionary history. The last four matters, it must
be added, can only be touched on in a book of this
kind.

The authors hope only to give the reader, through
both text and photographs, some vicarious familiar-
ity with the external appearance of invertebrates
(excepting the insects) and some understanding of
their habits, their environmental adaptations, and a
few of the more interesting ways in which they en-
ter into our own lives.

What ts an Invertebrate?

The word “invertebrate” is a semantic blanket
that covers most of animal kind and reveals nothing
of the varied shapes that have been thrust under it.
To lift one corner and glimpse a few of the more
familiar invertebrates—worms, starfishes, snails,
clams, crabs, and butterflies—is a mere beginning
toward appreciating a variety of creatures that range
in size and in complexity from microscopic proto-
zoans to giant squids 50 feet long, and that com-
prise 97 per cent of the nearly a million different
kinds of animals that scientists have so far described
and named. About 685,000 of the invertebrate spe-
cies are built very much alike and are grouped to-
gether as the class Insecta. They are treated in a

separate volume in the series of which this book is
a part.

To be called an invertebrate, an animal need have
no one special shape, nor any specific structure, nor
any single positive attribute. It need only, for lack of
a vertebral column or backbone, be excluded from
the select company of the vertebrates. All verte-
brates, including man, have down the middle of the
back a row of articulated bones or sometimes carti-
lages. Each of these pieces, called a vertebra, is
rigid; but since the vertebrae are movable upon one
another, they provide just that combination of high
tensile strength and flexibility needed to support the
large body size, the marked muscularity, and the

ale

speed that characterize the vertebrate way of life.
In contrast, the invertebrate groups generally lack
any kind of rigid internal skeleton to which power-
ful muscles can be attached, and many of the groups
consist of small, soft-bodied, flabby animals that
drift, crawl, burrow, glide, or inch their way along.
Some, like the clams and the arthropods, do have
hard skeletons that support and protect the body and
provide a rigid surface against which muscles can
pull, but these are external encasing skeletons; and
a hard covering that must enclose the whole body
grows disproportionately heavy with increase in body
size. Many invertebrates move swiftly, but mostly in
bodies of very small size.

A striking difference between vertebrates and in-
vertebrates has been apparent to man at least since
the prehistoric time when he was a primitive nomad,
managing a precarious existence as a fisher, a hunter,
and a gatherer of seeds and fruits. We can imagine
him one day stalking a wolf and getting nothing for
all his skill and courage but a few slashing bites from
the sharp teeth of his big, fast, and intelligent verte-
brate adversary. Then, coming out of the woods to a
rocky seashore at low tide, he discovers that the
rocks are covered with a very different kind of crea-
ture—a shelled animal that neither flees nor turns on
its attacker but lies quiet and defenseless within its
hard shell until this is split open, with a rock, to ex-
pose the soft, flabby, deliciously edible, bite-size in-
vertebrate within. Seashores in many parts of the
world bear witness to such scenes of long ago as this.
On the shores of Denmark, for example, there are
huge mounds that are filled mostly with the shells of
mussels, periwinkles, and cockles, but also contain
charred bones, stone tools, and other kinds of refuse
discarded in these prehistoric kitchen middens.
There is no difficulty for us today in distinguishing
invertebrate remains from vertebrate, for no sub-
stance quite like bone is found in any invertebrate
group (though they do sometimes have cartilage-
like materials). The texture and detailed structure
of bone is unique to vertebrates; and even the de-
posited salts, of calcium phosphate, are seldom
found in invertebrate skeletons, which are typically
of calcium carbonate.

In radially symmetrical invertebrates there is no
head, and the central nervous system is a ring of tis-
sue encircling the animal. But in the much more nu-
merous bilateral invertebrates the central nervous
svstem is a pair of solid nerve cords that run along
the midline of the belly (not the back, as in verte-
brates). Each cord has swellings, the nerve ganglia,
that are concentrations of nerve cells and that act as
nerve centers. In those invertebrates that have heads,
the largest ganglion is in the head, where the sense
organs are concentrated, and it is called the brain.
The small invertebrate brain has room for few cells

14]

that are free to do much except coordinate the mus-
cles and relay information from sense organs to mus-
cles. Even if the tiny brain were capable of handling
much learning, there would scarcely be time for such
a luxury in the great majority of invertebrates, for
most have brief life cycles. They usually feed, grow,
reproduce, and die within a few weeks or, at most,
months. To do this, they must come into the world
equipped with instinctive behavior patterns, and
these are promptly elicited by the stimuli of their en-
vironment. Only to a very limited extent can they
take advantage of the adaptive possibilities and of
the flexibility of learned behavior. Though we can
demonstrate, even in the one-celled protozoans,
some capacity to modify behavior as a result of ex-
perience, it is instinct, not learning, that dominates
behavior in the invertebrate world. This is true even
in the generally highly developed line of evolution
that led to the insects.

All invertebrates are cold-blooded; that is, they
have no mechanism for controlling their internal
body temperature, which in turn controls the rate at
which bodily activities can take place. At all seasons
they must adjust to the temperature of the external
environment—living actively when temperatures are
moderately high, becoming dormant or dying when
temperatures are very low or very high. None has
the capacity to be up and about at either of the tem-
perature extremes to which a warm-blooded verte-
brate like man can adjust. This does distinguish
them from the warm-blooded birds and mammals—
but not from the lower classes of vertebrates, the
fishes, amphibians, and reptiles, which also are cold-
blooded. In a desert at high noon or on an arctic
tundra in the dead of winter, we would see none but
birds and mammals on the move. Only in tropical re-
gions, where cold-blooded animals can remain ac-
tive at all seasons, or in all the great seas of the
world, where the water masses themselves act as
thermal regulators for the animals that live in them,
is it readily evident that ours is indeed an inverte-
brate world.

One may seriously question whether it is logical
to divide the animal kingdom into animals with and
animals without backbones, since there are only
some 55,000 species of vertebrates and nearly a mil-
lion known species of invertebrates—perhaps several
million when zoologists have finally named and de-
scribed all of them. The vertebrates are admittedly
a highly successful group; and many of them, such as
man, are big, cunning, aggressive, and noisy, and at-
tract an undue amount of attention to themselves.
From the viewpoint of a zoologist, though, the five
kinds of vertebrates—fishes, amphibians, reptiles,
birds, and mammals—are all so similar that they
must be considered only as five of the classes of one
major phylum or group, the phylum Chordata. Shar-

ing the same phylum with the vertebrates (in most
classifications) are three small subphyla of inverte-
brate chordates built on the same basic body plan
but lacking the vertebrated backbone and other in-
ternal bones.

The union of invertebrate animals, on the other
hand, is not a natural grouping but merely a con-
venient device for talking about at least twenty-eight
different phyla—some say more—with as many
different basic designs for living. The discrepancy in
number of phyla results from differences of opinion
as to just what constitutes a body plan distinctive
enough to entitle a group to a phylum of its own.

Classifying animals in neat cubicles labeled with
long, resounding names tends to obscure the fact that
such names designate phyla of very different size
and importance, and that the characteristics used to
differentiate the groups are not always of equal mag-
nitude. To emphasize these points, the list of phyla
given below has apposed to it rough approximations
of the number of living species and also a few sub-
headings that indicate either deep cleavages or broad

Subkingdom Metazoa
(continued )
Phylum Entoprocta: 60
Phylum Chaetognatha: 30
Subkingdom Metazoa Phylum Hemichordata: 100
Phylum Coelenterata: Phylum Pogonophora: 22
9,000 Phylum Phoronida: 15
Phylum Ctenophora: 80 Phylum Bryozoa: 6,000
Phylum Mesozoa: 7 Phylum Brachiopoda: 260
Phylum Platyhelminthes: Phylum Sipunculoidea:
9,000 250
Phylum Nemertea: 570 Phylum Echiuroidea: 60
Phylum Nematoda: 10,500 Phylum Mollusca: 40,000
Phylum Rotifera: 1,200 Phylum Annelida: 6,000
Phylum Gastrotricha: 100 Phylum Arthropoda (ex-
Phylum Kinorhyncha: 30 clusive of insects): 65,000
Phylum Priapulida: 6 Phylum Echinodermata:
Phylum Nematomorpha: 80 5,500
Phylum Acanthocephala: Phylum Chordata (exclu-
400 sive of vertebrates): 1,320

Subkingdom Protozoa
Phylum Protozoa: 30,000
Subkingdom Parazoa
Phylum Porifera: 4,500

bonds. The numbers given here are only tenta-
tive and all of them are subject to change as
new forms are found, described, and named. Occa-
sionally a group even loses a species or two because
a specialist finds that two or more named species are
really variants of the same species. In practice it is
not easy to decide how much variation can be al-
lowed within the bounds of a single species or of
higher ranks in the classificatory scheme, so that the
“Jumpers” and the “splitters” among taxonomists
often engage in spirited arguments over criteria. If
there are difficulties even at the species level, where
the specialists are dealing with the more or less natu-
ral category that we think of as “a kind of animal” —
a man or a dog or a honeybee—it is little wonder

that the disagreement increases as we approach the
larger and more arbitrary groupings.

It is apparent that the “great divide” in the animal
kingdom is not that between vertebrates and inver-
tebrates, even though this distinction was first made
by Aristotle. He did not use those terms, but mistak-
enly divided the animal kingdom into the “enaima”
(“bloody animals”) equivalent to our vertebrates,
and the “‘anaima”’ (“bloodless animals” ) correspond-
ing to our modern concept of invertebrates. In his
limited experience with invertebrates he did not hap-
pen to examine one with red blood, and the colorless
blood of invertebrates he did not recognize as blood
at all. Though he also recorded that “all sanguineous
animals have a backbone,” his error of classification
stood for more than two thousand years. Then in the
early part of the nineteenth century Lamarck used
the terms “vertebrate” and “invertebrate,” and his
fellow Frenchman, the great comparative anatomist
Cuvier, made the correct distinction based on the
fundamental difference in body plan.

The really wide gap in the animal kingdom, how-
ever, is that which separates the one-celled animals,
the Protozoa, from the other phyla which we call
the Metazoa because they are many-celled. More
will be said of this in the next chapter. Here it is also
important to point out the setting apart of the many-
celled sponges, or Porifera, as a phylum so different
from other Metazoa that we feel it must have had a
separate origin from the Protozoa. Among metazo-
ans an important distinction sunders the two-layered
coelenterates and ctenophores from all the groups
which have three well-developed primary embryo-
logical layers. This third layer appears between the
original two, and it produces those firm and bulky
tissues which are so conspicuously lacking in the
more fragile kinds of coelenterates.

The pattern of animal evolution is not a ladder on
which the various groups have ascended rung by
rung, but a three-dimensional tree with branches
that diverge at various levels. For lack of evidence
we cannot make out the exact connections of some
of the branches. But looking up along the main trunk
of the tree we see clearly that it soon splits into two
main branches. One of these is the main line of in-
vertebrate evolution, which gives rise to the seg-
mented worms or annelids; to the two largest inver-
tebrate phyla, the mollusks and arthropods; and also
to most of the smaller groups. The other main branch
is a minor diversion as far as invertebrates go, for it
has only one sizeable invertebrate phylum, the Echi-
nodermata, which includes the starfishes and their
allies. These are sluggish creatures, lacking a head,
losing their two-sided symmetry, and possessing the
most feeble kind of nervous system. Yet from this
stock, man and the vertebrates appear to have come.

[15

CHAPTER I

‘The Protozoans
(Phylum Protozoa)

alee protozoans belong to a microscopic world
into which we may peer, but only through a glass
darkly. We have no hope of coming face to face with
the problems of their microcosm because our faces
are too big and our sense organs are scaled accord-
ingly. This difference in size, however, does not de-
ter the protozoans from entering very importantly
into the natural economy of which we are a part, or
from invading our bodies and living there as para-
sites Or as uninvited commensal guests that share
the organic matter we ingest. For many thousands of
years men have been dying of protozoan-caused
amebic dysentery and African sleeping sickness. The
Roman Empire is often said to have fallen victim
not so much to political events as to the protozoans
that cause malaria. Again and again epidemics of
protozoan-caused disease have returned to decimate
the animals that man has taken into his economic
household, causing widespread distress among those
who tend silkworms, honeybees, or domestic flocks
and herds. Yet the microscopic organisms—at least
100,000 kinds of them, protozoan and otherwise,
and many of them occurring on everything men

16]

Radiolarians, a paramecium (upper cen-
ter) and three flagellates

touched or ate—went unknown and unsuspected
during almost all of man’s long history on earth.

Then, in 1674, a minor Dutch official named
Leeuwenhoek trained a simple lens of his own mak-
ing on some water from a small inland lake near his
home in Delft and became the first to observe and
describe living protozoans.

By 1816, when Baron Cuvier was putting together
Le Regne Animal, the first important modern work
on animal classification, he had to write in his pref-
ace that “infusorians, offering no field for anatomical
investigations, will be briefly disposed of.” By in-
fusorians he meant protozoans and rotifers (p. 137),
because they were the most numerous of the micro-
scopic forms to be found in infusions, standing water
containing decaying organic matter. He disposed of
the infusorians in two and one-half pages in a book
that ran to about two thousand. Today our knowl-
edge of protozoans is a major branch of biology and
fills many hundreds of published volumes. The in-
troduction of achromatic lenses for the microscope
has made it possible to see the detailed structure of
Leeuwenhoek’s “very little animalcules,” whose ex-

traordinary variety and complexity first fascinated
and then overawed the earlier microscopists. Though
some workers delineated the protozoans in superb
engravings which we still admire, they also put curi-
ous interpretations upon what they saw, because
they tried to find stomachs and intestines and kid-
neys in little animals that they visualized always in
terms of vertebrate anatomy. Only when it was re-
alized that protozoans are not miniatures of the
larger beasts but animals organized in a very differ-
ent way from all the other groups did biologists begin
to make real headway. Now we understand the
protozoan body to consist of a minute bit of a com-
plex mixture of substances known as protoplasm,
bounded externally by a membrane and containing
at least one formed body, the nucleus. In all other
animals the body is built up of a very large number
of such nucleated units of protoplasm, called cells.
Whether to think of a protozoan as a single cell, or
to consider it noncellular (or acellular) because
the body is not partitioned up into units as in the
many-celled metazoan groups, is a matter still de-
bated by specialists. For our purpose it is enough to
keep in mind that a protozoan is not comparable to
a single cell of a man but to his whole body.

Size is not the criterion for putting protozoans
into a special subkingdom Protozoa apart from all
the animals of the other subkingdoms. As we shall
see later, there are groups of metazoans that are en-
tirely microscopic, and some as big as lobsters that
have free-swimming microscopic stages when they
first hatch from the egg. The larger protozoans regu-
larly capture and devour adult metazoans related to
the lobster, though sometimes not without a truly
heroic struggle. The important distinction, as has
already been pointed out, is that of body design. And
it is at least as remarkable that protozoans are able
to carry on all the complex processes of life within a
single microscopic globule as that many-celled ani-
mals can do the same thing through the combined
activities of vast numbers of walled-off and special-
ized units.

Having just settled the protozoans comfortably in
their place, it seems a little belated to point out that
some zoologists have tossed them out of the animai
kingdom altogether. The problem of their status be-
gan to puzzle microscopists from the moment that
Leeuwenhoek first saw green globules swimming un-
der their own power. Today many zoologists still
maintain that green unicellular forms that move
about actively are properly members of the irritable,
restless animal kingdom. Equally firm are the bota-
nists who claim that such forms belong to the plant
kingdom, since the green color is that of chlorophyll.

Those who feel less sure about what to do with
sedentary one-celled plants that have actively swim-
ming sex cells, or where to place swimming green

forms that can lose their pigment and feed like any
animal when conditions change, decline to take sides
in this tug of war. They prefer to set up a third king-
dom of living organisms, the Protista, that admits
any form not divided into separate cells. Colonial
forms are included because they do not show enough
division of labor among the aggregated cells to be
considered truly multicellular.

The very existence of modern plant-animals that
are green but swim actively and that can shift from
plantlike to animal-like feeding habits suggests that
there was at one time a primitive stock of green mo-
tile organisms, perhaps very much like modern green
flagellates (p. 22) from which both plant and ani-
mal kingdoms have arisen. Because this book is about
animals, it is more convenient here to put flagellated
organisms that swim about actively, whether green or
colorless, in the phylum Protozoa. This first great
grouping in the animal kingdom, as mentioned ear-
lier, is set aside in a special subkingdom of its own.

Numbers

The protozoans or “first animals” deserve their
name in more than just the chronological sense. Ev-
ery larger animal that we carefully examine turns
out to harbor one or more species of protozoans, and
protozoans themselves may play host to even smaller
uninvited protozoans. So it is quite safe to guess that
the number of individual protozoans in the world
exceeds by far that of all other animal species com-
bined. In the seas, which cover three-quarters of the
globe, free-living protozoans occur from top to bot-
tom. The billions upon billions of protozoans in such
masses of water are really incomprehensible to our
simple mammalian minds.

Despite the inconceivable numbers of protozoans
in all bodies of water and in all surface soils, and the
intimate association enjoyed by some twenty-five
different species of protozoans that live in man, no
large grouping of animals is so unfamiliar at first
hand to all but professional biologists. In the nine-
teenth century in England and on the Continent,
every gentleman of wealth who had any pretensions
to intellectual curiosity displayed a microscope in his
living room and perhaps belonged to a microscope
club in which he could exchange his latest observa-
tions with like-minded friends. This has gone out of
fashion, and the only microscopes found in most
homes are toylike versions for children. The almost
incredible fairyland of beautiful and bizarre crea-
tures that swim, feed, pursue each other, and re-
produce—unabashed by the gaze of anyone who
chooses to look at them through a microscope—may
some day again become a source of entertainment
and intellectual satisfaction after we have pushed
most of the bigger animals to near extinction. For
protozoans are accessible to anyone who can spare

el

Long and slender Spirostomum, a
giant among protozoans, dwarfs the
smaller, slipper-shaped Paramecium.
Two rotifers in this same microscope
field are many-celled animals, yet are
barely larger than the paramecia.
(General Biological Supply House,
Chicago )

the space for a jar of water from a bird bath, a stag-
nant pool, or the plant-invaded edge of a pond.
There are known to us roughly thirty thousand spe-
cies of protozoans, and new ones are reported almost
every day. But there are also presumably respect-
able ones that are suddenly dispossessed of their
status and have to move in with their relatives be-
cause they are shown not to be different enough to
be considered separate species.
Size

Protozoan predominance in number loses some of
its overwhelming impressiveness when we consider
that almost all protozoans are minute and that most
of them are microscopic. The smallest forms, para-
sites that live within other animal cells, are only 2
microns (1 micron = 4%; 999 of an inch) in their
longest diameter. To learn much about the structure
of such animals is difficult even for the most experi-
enced microscopists using the best microscopes. For-
tunately, most of the free-living forms come in larger
packages, but even these are invisible to the naked
eye except when a colored species multiplies so fast
that through sheer density it colors sea water pink,
a rain pool blood-red, forms green scum on ponds,
or gives a pink or greenish cast to large snow banks.

18 |

Paramecium caudatum is of moderate size (180 to
300 microns or 4459 to 4499 of an inch) and can
barely be seen by the unaided eye as a white speck
darting about in a dish of pond water. Ten times
larger than this are such fresh-water giants as Spi-
rostomum and Stentor, which often measure more
than *4, of an inch. Even these are dwarfed by the
shelled foraminiferans of marine waters. If we ad-
mit to the phylum Protozoa the slime molds (the
Mycetozoa), which many botanists classify as fungi,
then these super-amebas, with hundreds of nuclei
but without cellular partitions, are by far the largest
protozoans. During the multinuclear stage the ame-
boid body may extend for several feet as it crawls
slowly over a rotten log on the forest floor. The size
of any particular protozoan may vary with nutri-
tional state and with changing conditions in the en-
vironment. It depends also upon consistent heredi-
tary differences that mark the many races or strains
of any one species. So size is not always a depend-
able criterion for identifying a protozoan. Neverthe-
less, a fairly definite adult size does characterize
each species, as well as each stage of its life cycle.

Gross Structure

Though it will save time to consider the protozo-
ans as a whole before going on to separate accounts
of the classes, generalizations come hard about a
group that matches all of the rest of the animal king-
dom in its range of sizes, shapes, habitats, structural
specializations, feeding habits, and life cycles. Only
the basic body plan brings all of these extraordinarily
varied creatures into a single grouping. The body
consists of one undivided mass of living substance,
or protoplasm, bounded by an external membrane
that regulates exchanges of materials with the out-
side environment. Near the center of the proto-
plasm is a formed body, the nucleus, which is in con-
trol of essential chemical processes. If an ameba is
deprived of its nucleus by accidental or experimen-
tal manipulation, the part without the nucleus may
move about for a time, but it cannot feed and it
soon dies. There is usually only one nucleus, but
when there are two or more, no one nucleus is in
sole charge of any particular portion of the proto-
plasm. In some species the division of the original
mass results in a group of cells that remain attached
to each other as a protozoan colony. Such a colony
differs from a multicellular body in that the cells are
usually all alike except during reproduction and in
that any one can live independently of the others.

Body Symmetry

Protozoans come in every major type of symmetry
known in the animal kingdom. In this they differ
from all other groups, for in each multicellular phy-
lum the members are consistent in having some one

kind of symmetry. The freely floating protozoans,
such as the radiolarians, are likely to be spherically
symmetrical, with organs of locomotion and feeding,
or protective spines, projecting from the whole sur-
face and meeting life in every direction. Bottom-
living forms that grow attached by a stalk are usu-
ally radially symmetrical, with a mouth at the free
end surrounded by a ring of food-trapping organs.
The fast swimmers, various ciliates and flagellates,
are usually bilaterally symmetrical, with front and
rear end, top and bottom surfaces. They may have an
asymmetrical spiral twist at the front. Finally, many
protozoans can be described only as asymmetrical.

Habitats

Protozoan habitats are all essentially aquatic,
though the amount of water required by a micro-
scopic animal may sometimes be no more than the
merest film between particles of damp soil or of rain-
moistened desert sand. Parasitic protozoans find ad-
equate moisture between or within the living cells of
their plant or animal hosts. The free-living protozo-
ans abound in all bodies of water, large or small: in
puddles of standing rain water and in rain-filled tree
holes or hollow stumps; in bird baths or flower urns;
in ditches and canals; in brooks and rivers; in
swamps, ponds, and lakes; and in all the seas of the
world. Even the melting surfaces of icebergs, gla-
ciers, and snow banks have active populations of
flagellates, as one can tell at a distance by the green-
ish or reddish cast of such snow. At the other tem-
perature extreme are the protozoans that live in hot
springs (at up to 133°F. in one place in Japan).
This is highly exceptional, of course, and most pro-
tozoans die when their external environment reaches
temperatures between 97°F. and 104°F. They lack
the internal controls that enable a warm-blooded
(really temperature-constant) animal like man to
keep his body temperature from rising much above
98.6°F. even when his surroundings rise to tempera-
ture levels that kill living protoplasm. The optimum
temperature range for activity and growth of proto-
zoans seems to be between 61°F. and 77°F.

Distribution

The common protozoan species are ubiquitous. A
schoolboy who scoops up pond water in Australia is
likely to find the same species of Paramecium as will
a boy in Germany or California. Soil samples all
the way from Greenland to Argentina have yielded
Amoeba proteus. Apparently, animals that are as
small as protozoans and have the habit of encysting
(encasing themselves in a dormant condition within
a waterproof, resistant wall) are readily transported
about the world by wind, animals, and the slightest
movement in bodies of water. Thus protozoans, and
especially those that live in large bodies of water,

show very little of the limitations in geographic dis-
tribution that are due to mechanical barriers and
that we expect in dealing with the larger animals.
This does not mean that protozoan species do not
differ where conditions of life make different de-
mands. In the seas there are characteristic species
of warm and of cold waters, of shallow and of deep
waters, of surface waters and of sandy or muddy
bottoms. Where fresh waters move rapidly, protozo-
ans are sparse; but where such water is slow-mov-
ing or stagnant, especially if there is much organic
matter present, protozoans come into their own.

The numbers of protozoans, contrary to what
many people suppose, are greatest in arctic and ant-
arctic waters, which are richest in the nitrogenous
compounds necessary for protoplasmic growth.
Tropical seas are home to a great variety of species,
including most of the really bizarre protozoans, but
these do not occur in the dense populations that
make cold waters a kind of protozoan soup.

The salt content (salinity) of waters also deter-
mines what species will be found there. Especially
versatile species are at home in marine, brackish,
and fresh waters; but most are restricted to one of
these habitats, or even to a particular level of salt
content. Brine pools or large salty bodies such as
Great Salt Lake contain some species of flagellates,
amebas, and ciliates that are not found elsewhere.

More critical than salt content for many protozo-
ans is the acidity or alkalinity of the water or moist
soil in which they must thrive. A few species are reg-
ularly found in extreme situations, such as in the
highly acid drainage from mines, but most grow best
under conditions that hover close about the neutral-
ity point. If grown above or below their most favor-
able range, some species are not only smaller but
have a very different body shape.

In soils protozoans live mostly within six inches of
the surface, but they can be found in small numbers
even at depths of several feet. Their numbers vary
mainly with the supply of bacterial food, and in
moist, rich soils the density of amebas and flagel-
lates may reach a million per gram of soil, even
though you cannot see anything alive about the soil
as you pass it through your fingers. Whether proto-
zoans play a role in enriching the soil, or whether
they are harmful to the soil by destroying soil-enrich-
ing bacteria, we do not really know, even though this
is a matter of great economic importance.

Encystment

Where the sun beats down on desert sands proto-
zoans are scarce. They stay quietly within their cyst
walls except immediately after a rain, when they
emerge to feed actively—perhaps for no more than
a single hour during a whole year. As the sand dries
the protozoan rounds up and appears to lose its spe-

[19

cialized structures. It extrudes any undigested food,
and then shrinks by expelling water. Finally it se-
cretes around itself outer and then inner cyst walls.
Many encyst also when they are regenerating in-
jured parts, reproducing, or simply digesting a big
meal. Dry cysts have in extreme cases been shown to
be capable of returning to active life again at any
time during half a century if proper conditions are
supplied. For most species the period of viability
lasts only for several months to several years. En-
cystment is characteristic of parasitic protozoans,
for these must temporarily leave their comfortable
berths inside moist and nutritious hosts in spreading
the species from one host to another. In the oceans
encysting protozoans are rare, for the tremendous
volume of the marine habitat acts as a great stabiliz-
ing mechanism against changes of any kind. Bodies
of fresh water are smaller and so less stable as
aquatic environments. In temporary ponds and
marshes protozoans regularly encyst and excyst with
the round of dry and wet seasons. Not all forms can
do this, and among the exceptions, as far as we
know, is the familiar Paramecium caudatum.

The capacity to encyst has opened to protozoans
a tremendous assortment of land-based but irregu-
larly moist niches which would otherwise be too un-
reliable for aquatic organisms. Such are the bark on
the shady side of trees, the cavities of insectivorous
plants and of cup-shaped flowers, the axils of leaves,
the crevices in beds of moss, and the surfaces of
grasses and other vertical vegetation that are regu-
larly wet by dew. A special fauna inhabits the freshly
laid feces of animals, remaining active until the sun
bakes the feces dry, then encysting again.

Nutrition

The protozoan approach to nutrition runs the en-
tire gamut of possibilities. There are green flagel-
lated forms able to use the energy of sunshine to
synthesize their food, like any green plant, from sim-
ple materials in water and soil. And there are color-
less protozoans that roam, chase, and capture prey
like any carnivorous animal. Between these wholly
plantlike or wholly animal-like methods are a series
of intermediate solutions to the problem of earning
a living. Some forms absorb already synthesized and
dissolved foods through their external surface and
are known as saprozoic feeders. These include many
free-living flagellates as well as most of the parasitic
protozoans. Others turn from “independent” or pho-
tosynthetic habits to saprozoic feeding when occa-
sion permits, thus availing themselves of an alterna-
tive source of food whenever it presents itself. By
far the greatest number of free-living protozoans
earn their living by ingesting whole organisms or
large particles of organic debris. They feed on bac-

20 ]

teria, yeasts, algae, wood particles, and small ani-
mals, either other protozoans or certain small meta-
zoans.

Reproduction

Reproduction in the protozoans is essentially the
same as in the multicellular groups, for in all animals
the basic process is cell division. Sexual processes
are widespread among protozoans, and in some spe-
cies must take place at intervals or the strain will die
out, but they do not occur in all species. As far as
we have been able to determine, Amoeba proteus,
for example, has only asexual reproduction. When
the animal has reached a certain size and maturity,
it divides into two cells, each containing half of the
nucleus and of the hereditary materials of the nu-
cleus. This division of the parent cell into two halves
(binary fission) is the most common method of re-
production in protozoans. Two other main types of
asexual division are known. One is budding, in which
the parent cell retains its individuality while produc-
ing, by division, one or more “daughter” cells, usu-
ally much smaller in size and less differentiated than
the parent. Either before or after it is freed, the bud
grows to resemble the parent in size and structure.
Budding is typical of the Suctoria but is rare in other
groups. Multiple fission, or sporulation, is an asexual
process in which the nucleus divides many times,
and then the protoplasm divides into as many off-
spring as there are newly formed nuclei. This is the
protozoan version of mass production, and it results
in extremely rapid multiplication. It is seen espe-
cially in forms like the sporozoans. Through the vari-
ous asexual processes a species is assured rapid mul-
tiplication and the maintenance of its numbers.
Through sexual processes there arises a steady sup-
ply of new variants, individuals with new combina-
tions of hereditary characteristics. Each sexually pro-
duced individual has the possibility of being better
adapted in some way than were either of its parents.
Thus sexual processes provide the hereditary varia-
tions upon which natural selection may act. Their
significance for adaptation and evolution is the same
in the protozoans as in higher animals. In animals as
small as protozoans growth and reproduction take
place on a time scale measured in hours, not years.
Paramecium may undergo binary fission as often as
three times a day, the smaller ciliate, Glaucoma,
eight times a day.

Behavior

Anyone who observes the speed with which pro-
tozoans dart backward after striking an obstruction,
or the persistency with which they squeeze through
a narrow passageway between two algal filaments,
or the ingenuity with which a sluggish ameba cap-
tures a fast-moving ciliate, will want to credit proto-

zoans with a full share of the irritability and modi-
fiability that are characteristic of all living proto-
plasm. Whether this involves “consciousness” is
something we can only guess about. A single cell
cannot provide the complex sense organs or nervous
system that we see in higher animals, but protozo-
ans apparently do use flagella, pseudopods, and cilia
as tactile organs, and probably also as chemorecep-
tors to detect food or chemical changes in the water.
Near the front end of many green flagellates there is
a specialized photoreceptor in connection with the
red-pigmented eyespot or stigma. Many ciliates, in-
cluding Paramecium, have been shown to have a
neuromotor system, a counterpart, within the cell, of
a nervous system, which conducts information from
one point to another and which coordinates the beat-
ing of the cilia. Nevertheless, we know that percep-
tion, conduction, and responsiveness can all occur in
what appears to be undifferentiated protoplasm.
Protozoans in general probably are sensitive over
the entire surface of the cell to such stimuli as light,
contact, excesses of heat and cold, concentration of
chemicals, or presence of food. And when they re-
spond, they usually do so by a movement of the
whole animal. The responses of protozoans are ster-
eotyped, but no more so than the reflexes of higher
animals. And they are not invariable.

Body Structure

In touching briefly on the ways in which protozo-
ans move about, feed, grow, and reproduce, we are
reminded again that they perform all of the same
life activities as do the other animals among which
they must live and compete. The clear implication
is that the “simple protozoans” are not as simple as
they appear to the human eye, even though some of
them have little visible structure. There are, more-
over, some protozoans that are among the most com-
plex cells known. One ciliate, Epidinium ecaudatum,
displays at least forty-eight protoplasmic structures
that can be described and named. This exceeds the
complexity of some of the lower metazoans. The
endless variety of protozoan structural specializa-
tions can hardly be discussed adequately in any-
thing less than a good-sized treatise. Those merely
alluded to here are the ones that are visible in the
accompanying photographs.

The nucleus is the one structural specialization or
organelle that is consistently present and indispen-
sable. It is not always easy to see in the living pro-
tozoan, especially in a photograph. In a stained
preparation it usually stains much darker than the
unspecialized protoplasm or cytoplasm. The nucleus
may appear quite different during the various stages
of the life cycle. A protozoan that has recently fed
contains conspicuous food-filled globules, the food
vacuoles. These are not specialized structures but

merely droplets of water containing ingested food in
various stages of digestion. The surrounding proto-
plasm secretes digestive enzymes into these food
vacuoles, and as the food body undergoes digestion
it gradually dissolves, the dissolved substances pass-
ing into the protoplasm to be used there for supply-
ing energy or growth needs. Flagellates that manu-
facture their own food by photosynthesis have no
food vacuoles (with rare exception), but instead
have one or more prominent pigment bodies, the
chromatophores (“color-bearers”). These may be
bright green, yellow, green, or brown—depending
upon how much yellow or red pigment is present to
mask the bright green color of the photosynthetic
pigment, chlorophyll. A conspicuous organelle is the
contractile vacuole, a pulsating clear globule that ac-
cumulates and expels to the exterior excess fluid
from the protoplasm of many protozoans, espe-
cially fresh-water species. Such vacuoles are usually
absent in marine or parasitic forms other than cili-
ates. In ciliates the feeding habits tend to increase
the amount of fluid taken into the body. There is no
very good evidence for supposing that the contractile
vacuole also acts as a special device for ridding the
organism of metabolic wastes, in the manner of the
vertebrate kidney. And in any case this could not be
its major role, since so many protozoans are able to
do without a contractile vacuole. Usually there is
only one such vacuole, as in Amoeba proteus, but
Paramecium has two, and some protozoans have
many. The locomotor organelles, and an extraordi-
nary array of skeletal structures that encase or sup-
port the delicate protoplasm, especially of the flagel-
late and ameboid types, will be described in connec-
tion with the groups in which they occur.

The Flagellates

(Class Flagellata or Mastigophora)

The flagellated protozoans or “‘whip-bearers” are
the most widely distributed of the protozoans, occur-
ring in every place that it is moist, from hot springs
to the melting surfaces of glaciers. In all seas the
greatest portion of the protozoan component of the
floating surface population consists of flagellates. Al-
most any bit of unlovely green scum from the surface
of a pond, when mounted in a drop of water on a
microscope slide, will suddenly become transformed
into a field of shimmering, green, ovate creatures
that swim rapidly but with a jerkiness that distin-
guishes them from their more smoothly gliding cili-
ated relatives. The jerkiness is not due to an inter-
mittent supply of power but to the rotation and gyra-
tion of the flagellate body as the flagellum is thrust

(21

forward with a whiplike motion that draws the ani-
mal along. It usually cuts a spiral path in the water
but moves in a fairly straight line.

Now that spindles are no longer so common as
they used to be, words like “fish-shaped” or “sub-
marine-shaped” are replacing “spindle-shaped” in
descriptions of these little animals, which tend to
be widest in the middle and tapering toward both
ends. The front end may be more rounded than the
rear, or just the reverse. In either case the end that
goes first in locomotion has some sort of depression
into which the flagella (usually one to four in num-
ber, but sometimes eight or many) are inserted.
The outer layer of most flagellates is firm enough to
maintain a constant body shape. The surface cover-
ing may be a stiff pellicle handsomely sculptured
with spiral or longitudinal ridges, or it may be thin
and plastic and allow for squirming “euglenoid
movements,” named for the familiar fresh-water
Euglena in which they are most often seen. A com-
pletely constant shape is shown by those dinoflagel-
lates that are enclosed in hard skeletons. When a
hard surface layer is absent altogether, the animal
may be ameboid, at times even losing the flagellum
and moving about by extending pseudopods.

The flagellates are the only group in either plant
or animal kingdoms that utilizes all three main meth-
ods of feeding: photosynthesis, saprozoism, and in-
gestion of solid food. Even a single flagellate species
may use the whole repertoire. The photosynthetic
flagellates feed like plants, and all have pigmented
bodies containing the green pigment chlorophyll; but
the green may be masked by additional pigments
that make it appear red, yellow, or brown. Even flag-
ellates that lack chlorophyll may show, in the proto-
plasm, refractive bodies which contain reserves of
starch or a similar substance. These have a pale blu-
ish green tinge and should be easily distinguishable
from the bright green color of chlorophyll. Food re-
serves also include oil and fats. Photosynthetic flag-
ellates usually have a pigmented eyespot or stigma,
near the base of the flagellum, that partly shades a
highly light-sensitive region of the protoplasm and
enables these animals to orient readily to light and to
remain as much as possible in the degree of light in-
tensity at which they carry on photosynthesis most
advantageously. Parasitic flagellates are entirely sap-
rozoic, absorbing dissolved nutrients through the
body surface. Most free-living colorless flagellates are
animal-like feeders that take in solid food.

Reproduction is almost entirely asexual in flagel-
lates, though some species do show sexual reproduc-
tion. In the usual asexual method the body splits
lengthwise down the middle, beginning at the front
end and proceeding toward the rear. Often this oc-
curs at a definite hour of the day. Some always di-
vide while in an encysted state; others reproduce

22]

within cysts only at certain times. Resistant cysts
are formed readily if conditions change. Colony for-
mation is widespread, especially among green forms,
and in such colonies there may be division of labor
between ordinary feeding individuals and those that
can reproduce, and between reproductive cells that
form male or female sex cells.

Some of the green (zoochlorellae) and the much
more common yellow or brown algalike cells (zoo-
xanthellae) seen in the bodies of a great variety of
protozoans and metazoans, most of them marine,
have been shown to be modified flagellates. These
live imprisoned within the bodies of their hosts and
escape as free-living forms only at certain times.
Within the transparent host body they enjoy a place
in the sun, yet they are well protected and have all
about them a steady supply of carbon dioxide and
more especially of other waste products of the host.
From these they can obtain the nitrogenous com-
pounds that are at such a premium in the tropical or
warm waters that are home to most of such flagel-
lates. The host receives oxygen and probably bene-
fits from the removal of its wastes. Whether it also
receives food or uses the pigmented cells as a food
reserve is not clear in most cases.

As a group the flagellates lie somewhere between
the algae and the amebas, overlapping somewhat at
the edges with both groups. The nature of the over-
lap makes it quite plausible that the green flagellates
are the ancestral group from which both plant and
animal kingdoms have been derived. The ancestral
group has remained, on the whole, the most primi-
tive of the five classes of protozoans, but particular
members are among the most complex protozoans
that we know about. There are many different orders
of both plantlike and animal-like flagellates, but
only some examples can be given, of species most
commonly seen or of some interest for the ways in
which they benefit or annoy man.

THE PLANTLIKE FLAGELLATES

(Subclass Phytomastigina)

THE CHRYSOMONADS

Typical of the chrysomonads (“golden units”) is
the oval Chromulina, with two large pigment bodies
in which the golden-brown color masks the green
chlorophyll. When it is abundant enough in fresh
waters, the water appears brown. Any single indi-
vidual, however, is less than 14 9,999 of an inch long.
Its one flagellum whips the water, pulling the body
along in the fast vibratory glide characteristic of
flagellates; but there are times when it uses pseudo-
pods to move like an ameba. Dinobryon has two un-
equal flagella which protrude from the transparent,
vase-shaped cellulose case that encloses the animal.
It lives either as a solitary individual or as a branch-

ing attached colony, and if abundant in water reser-
voirs, imparts a fishy odor to the water, like that of
cod-liver oil. Also colonial is Synura, with the indi-
viduals attached at their inner ends and the flagellar
ends extending out radially in all directions. Synura
may be very numerous under the ice of ponds in
winter. When it is the dominant form in a pond,
the water has an odor like that of ripe cucumbers or
muskmelon and tastes both bitter and spicy. The
odors and tastes imparted by flagellates are due to
aromatic oils stored as food reserves and liberated
when the animals die. One part of oil from Synura
can be detected in twenty-five million parts of water,
so that it may be necessary to filter the water or to
add to it minute quantities of copper sulphate which
inhibits the growth of the small organisms without
doing readily detectable harm to man or other ani-
mals. Marine chrysomonads often are enclosed in
beautiful latticed cases or have the body surface coy-
ered or embedded with secreted plates of calcium
carbonate called coccoliths. These range from flat
oval disks to plates ornamented with long rodlike
or trumpetlike extensions. The coccoliths of bottom
deposits from tropical and subtropical seas were
well known to biologists long before the living flagel-
lates that produced the skeletons had ever been seen.
The disintegrated skeletons continue to be deposited
at a rate that is estimated for an area in the North
Atlantic, at a depth of 7200 feet, to be sixty billions
of shells per square meter (about ten square feet)
annually. They add their bulk to the more numer-
ous and more durable shells of ameboid protozoans
(forams and radiolarians ).

THE CRYPTOMONADS

Cryptomonas, of fresh water, is a photosynthetic
cryptomonad with two flagella protruding from a dis-
tinct opening at the front, and two yellowish or
brownish green pigment bodies. The very similar but
colorless and saprozoic Chilomonas is the common-
est and most familiar cryptomonad of stagnant fresh
waters. We know a great deal about its remarkable
nutrition. It can synthesize protoplasm from inor-
ganic material provided that certain chemicals are
present.

THE DINOFLAGELLATES

The numerous dinoflagellates are distinguished by
the two flagella seen in all the typical forms. In
these a long flagellum trails downward with the long
axis of the body from a hole in a longitudinal
groove, and another flagellum undulates in steady
waves in a groove that encircles the body at right
angles to the upright axis. They swim in a bouncy
sort of way, and occur in incalculable numbers, pro-
viding the nutritional basis for the surface-floating
animal populations in all seas and in ponds and

lakes. Some cause the destructive “red tides” re-
ferred to below. Most of them are photosynthetic,
usually have an eyespot, and have green, yellow, or
brown pigment bodies. The single nucleus is very
large. Some dinoflagellates live as floating rounded
forms that look like algae. Many are believed to be
the yellow alga-like bodies seen inside marine proto-
zoans, especially in tropical radiolarians. Others are
external or internal parasites. The colorless forms
engulf small organisms in ameboid fashion.

Marine dinoflagellates, Ceratium tripos, with three
long spines on the encasing armor, are tremendously
abundant in surface waters. One extrudes a long fla-

gellum. (England. D. P. Wilson)

The typical dinoflagellates, all with two grooves
and two flagella, may be either armored or unar-
mored, the latter kind either naked or enclosed in a
cellulose membrane. Most are marine, but some
genera are also numerous in fresh waters. Gymnodi-
nium brevis, a marine species, suddenly “bloomed”
in 1947 in concentrations higher than five million to
a quart, causing a “red tide” off the Florida coast.
The toxin provided by such large numbers of dino-
flagellates killed coastal marine animals over a wide
area, and littered the beaches for many miles with a
hundred pounds of rotting fish per running foot. Off
the southern and Lower California coast destructive
red tides are caused in certain summers by the rise
of Gonyaulax polyhedra, a heavily armored dino-
flagellate whose toxin kills fishes, shrimps, crabs,
barnacles, oysters, and clams. Similar dinoflagellate-
caused red tides also occur off the Atlantic coast of
Spain and Portugal, and either red or yellow tides
cause serious local problems in many other parts of

[23

Luminescent dinoflagellate, Nociiluca scintillans, is
noted for tinting the sea surface pink in the daytime,

lighting it at night. (England. D. P. Wilson)

the world. On the California coast several epidemics
of shellfish poisoning in men have been attributed to
the eating of a common California mussel, Mytilus
californianus, which may in summer become loaded
with Gonyaulax catenella, known to produce a very
toxic substance.

The most significant of all dinoflagellates are the
typical genera Peridinium and Ceratium, of both
fresh and salt water, which have large numbers of
species and of individuals. Ceratium has three spines
on its enclosing armor, and these tend to be short and
thick in cold, highly saline waters and very thin and
long in warm, less salty waters. The greater surface
of the longer, thinner spines retards sinking in the
less dense low-salinity warmer water, so that it is
actually easier, in certain oceanographic studies, to
use the species of Ceratium as a “biological indi-
cator” of salinity than it is to make actual measure-
ments of salt content.

Noctiluca is one of the largest, most aberrant, and
most conspicuous of the flagellates. What is usually
considered a single species, preferably called Nocti-
luca scintillans (“night light that scintillates”), oc-
curs off oceanic shores all over the world. The pin-

24]

head-sized, nearly spherical, and mostly gelatinous
bodies are colorless, pale pink, or yellowish, and
when dense can make extensive areas of the sea ap-
pear, in the daytime, like pale tomato soup. At night
this protozoan is a major cause of the luminescence
of seas. As ships plow through the water, disturbing
billions of Noctiluca, the waves that they set up
flame in the darkness, and the trailing wake scin-
tillates with minute flashes. Where Noctiluca-laden
waters are thrown with great force against steep
rocky shores, the nighttime displays are truly spec-
tacular, suggesting fireworks set off under water,
though this bioluminescence, or animal light, gives
off no measurable heat and dissipates little of the
animal’s energy. In marine waters that enter plumb-
ing installations, the luminescent effects can be start-
ling. Inshore winds may compact Noctiluca to a sur-
face crust on the waters and also bring them ashore,
where they are seen, on sand beaches, as a red scum
at high tide mark. A noctiluca was once described
by T. H. Huxley as looking like a little peach, with a
waving, finger-like tentacle as long as the body,
emerging from the place where the stalk of a peach
might be. Under the microscope we see that the curl-
ing tentacle emerges from one end of a pouchlike
depression. The animal floats mostly with the feed-
ing pouch down, and the tentacle wafts diatoms and
dinoflagellates toward the mouth, or even manages
to cram in the larvae of copepods or other crusta-
ceans, which distort the enclosing Noctiluca body.
Digestion goes on in the protoplasmic mass that lies
at the bottom of the pouch, and that branches and
rebranches into fine filaments radiating out through
the thin gelatinous bulk that adds to the buoyancy of
the animal. Organisms too small to be easily strained
out of the water by larger animals are thus converted
into packages of Noctiluca size. These are then avail-
able to small crustaceans, which form the next links
in the chains of animals of increasing size that make
up the network of animal feeders of the seas.

THE EUGLENOID FLAGELLATES

Distance lends no enchantment to Euglena in the
mass, and to many people a green pond scum of this
flagellate is not pleasing. But close up, under the
magnifying powers of a microscope, a single eu-
glena, propelled gracefully across a lighted micro-
scope field, rich green in color and often beautifully
sculptured with surface ornamentation, is as lovely a
sight as any living organism. In the various species of
Euglena the pellicle may be striated, or ridged with
rows of spines or knobs, often spirally arranged; and
it is highly elastic, permitting the wormlike creeping
“euglenoid” movements named for this common ge-
nus. In euglenoids of other genera the pellicle may
be rigid. At the front end of a spindle-shaped eu-
glena is a flasklike depression, the gullet, and from

the narrow neck of the flask there emerges the single
long flagellum. Into the rounded base of the flask a
large contractile vacuole discharges its fluid content
at frequent intervals. No one has ever seen a green
euglena take particles of food into its gullet, but if
placed in the dark the animal does lose its green pig-
ment, chlorophyll, and lives by absorbing nutrient
material through the surface. Next to the gullet is a
bright red eyespot, and if a dish of euglenas is placed
near a window they gather quickly in the lighted side
of the dish if the light intensity is not too great. They
are negative, however, to very strong sunlight.

This special sensitivity to light plays a major role
in the life of animals that must use the energy of sun-
light to synthesize their food supply. Euglena gracilis
is small as euglenoids go, 15) of an inch, and the
flagellum is shorter than the body. It is one of the
most common species, apparently because it can
adapt to a wider range of acid or alkaline conditions
than can others. Euglena rubra contains thousands
of red granules, which may be concentrated in one
central area, allowing the green color of the pigment
bodies to predominate, or which may be distributed
through the protoplasm, covering the green bodies
and giving a red color to the animal and to the scum
it forms on barnyard ponds, especially in very hot
weather. During sunlight hours a pond may appear
red, then turn green when the sun goes down. Color-
less euglenoids live by devouring bacteria, algae,
diatoms, and the smaller protozoans. Reproduction
in Euglena is by asexual fission only, with the body
splitting down the middle and parallel to the long
axis of the body. Division may occur in the free-
swimming animal, but the encysted reproductive
stage is so common that it may be the sole content of
the green scum covering a pond. If examined under
a microscope it looks more like an alga.

THE PHYTOMONADS

The most plantlike of the flagellates are the phyto-
monads (“plantlike units”), which resemble algae in
having, typically, a rounded shape, a rigid cellulose
wall, and grass-green pigment bodies. Chlamydo-
monas is common in ponds and ditches and often so
numerous there as to render the water an almost
opaque green. Especially abundant in waters con-
taminated by manure, it probably supplements its
mostly photosynthetic nutrition with saprophytic
feeding, absorbing dissolved nutrients through the
body surface. It is small (14559 of an inch), ovate,
has two equal flagella protruding through the cellu-
lose cell membrane, a red eyespot, and a large cup-
shaped pigment body. Carteria resembles Chlamy-
domonas but has four flagella. It is probably a
species of this genus that lives in the tissues of the
marine acoel flatworm Convoluta roscoffensis (Plate

Euglena, in the midst of dividing, shows a split front
end, each half with a long flagellum. A smaller flagel-
late, Peranema, is at the right. (Ralph Buchsbaum)

36). Haematococcus looks like a reddish Chlamy-
domonas with a loosely fitting outer wall that is at-
tached to the organism by radiating threads of proto-
plasm. Its red hematochrome granules may be so
numerous as to mask the green, giving a red color to
standing rain water or to fresh-water ponds in which
Haematococcus abounds. In the Alps and in the
American Rockies Haematococcus is well known for
imparting a reddish or pinkish color to melting snow
drifts.

Colonial phytomonads, all fresh-water forms, are
remarkable for the way in which the various species
can be arranged in a series showing every stage from
a simple flat disk of four cells, as in Gonium, that
look alike and reproduce in the same way, to com-
plex colonies of many thousands of cells, as in Vol-
vox, where cells differ in appearance and in function
yet are coordinated into a single behavior unit.
Though developed to a lesser degree, these are cer-
tainly the beginnings of the multicellularity and the
individuality we see in higher plants and animals.
Volvox is large enough (144 of an inch in diameter)
to be seen in fresh-water ponds as a small green ball
that rolls smoothly through the water. Under the mi-
croscope this rolling motion (volvere is Latin for

[25)

Colonies of Volvox, with small daughter colonies
showing within the parental spheres. (General Bio-
logical Supply House, Chicago )

“roll”) comes to be understood as the coordinated
beating of thousands of flagella protruding outward
from the surface of a fluid-filled gelatinous ball. Each
flagellated individual imbedded in the outer layer of
the jelly ball is something like Chlamydomonas,
with an oval body, two equal flagella, a large cup-
shaped pigment body, and a red eyespot. If the fla-
gella were not in some way coordinated, such a ball
could get nowhere and would simply tumble this way
and that. If we watch carefully we see that the same
end of the sphere is always the one that goes for-
ward, and careful study has indeed revealed proto-
plasmic strands that traverse the jelly and connect
the individual flagellates with each other. Only par-
ticular zooids in the rear half of the sphere can divide
asexually, while still others produce small motile
sperms or large food-laden eggs. Tumbling about
within the fluid-filled interior of a Volvox colony are
usually to be seen small asexually-produced daugh-
ter colonies, which are released to a life of their own
when the mother colony breaks down after the spring
period of rapid asexual multiplication. In sexual re-
production eggs and sperms are not produced at the
same time in any one colony, so that whether the
species has both kinds of sex cells in one colony or
not, fertilization occurs only between sex cells from
different colonies. The resulting fertilized eggs de-
velop a thick, spiny covering, often orange or deep
red. They lie dormant during the winter months, but
in the spring the covering bursts, releasing the young
colony.

26]

THE ANIMAL-LIKE FLAGELLATES

(Subclass Zoomastigina)

For admission to the clearly animal-like flagellates
(the technical name means “animals with whips”) a
species must lack photosynthetic pigment bodies and
must not be otherwise practically identical with one
of the green flagellates. It must never store starch or
starch-related carbohydrate reserves, and often it
will have more than the two flagella that are char-
acteristic of most plantlike flagellates. In this group
of flagellate orders are many of the important para-
sites of man and his domestic animals.

Most likely to be seen are the free-living Monas
and Bodo, abundant among decaying vegetation and
in the infusions examined by students. Extremely
small, and active in a microscope field, they do not
make for easy examination and are usually dismissed
quickly as “common monads.” Both have two un-
equal flagella, but in Bodo the longer one trails be-
hind and is used for temporary anchoring. Food is
ingested at a spot near the base of the flagella. Oi-
komonas, of fresh waters and of soil, is similar but
has only one flagellum. Also with one flagellum are
the choanoflagellates (“collar flagellates”), which
are generally fixed by a stalk, either singly as in
Monosiga, or by a branching stalk that unites many
zooids as in Codosiga. There is a large, delicate pro-
toplasmic collar around the base of the flagellum.
Food particles attracted by currents set up by the
flagellum adhere to the outside of the collar and are
ingested at its base.

Important from the human point of view are the
trypanosomes, many of which cause serious or fatal
disease in man and in his domestic animals. An
African form of trypanosome disease has been
known to us at least since the days when the slave
traders learned not to accept as captives any Negroes
with swollen neck glands, an important symptom of
African sleeping sickness. A similar disease in cattle
is known as nagana. These are not the same as the
epidemics of virus-caused sleeping sickness that
strike in the United States during certain summers.
The African trypanosomes have no doubt been in-
troduced into the Western Hemisphere many times,
and only the lack of their insect carrier, the tsetse
fly, prevents our part of the world from suffering the
dreadful human and economic losses that so heavily
afflict Africa. Large parts of Africa have long been
uninhabitable for men and for any of their domestic
animals except poultry because of certain trypano-
somes and the flies that carry them. It has been a
long, seesaw struggle, with men now gaining control
after many years of intensive medical and ecological
work by many investigators. But it remains a stag-

gering problem. As recently as 1949 about a fourth
of Africa was still completely denied to man.

The African disease in man begins with anemia
and fever as the flagellates begin to multiply, and
then manifests itself as swollen lymph glands, ex-
treme lethargy, and finally coma as they invade the
lymph glands and then enter the fluids surrounding
the spinal cord and the brain. After this last stage
death may ensue. Two closely related forms of the
human disease are known: one caused by Trypano-
soma gambiense, and another more acute form of
the disease caused by Trypanosoma rhodiense.
Whether these are really separate species of Trypa-
nosoma, or whether both are only variant strains of
Trypanosoma brucei, which causes nagana in cattle,
is not yet settled. If we examine the blood of a vic-
tim we see long, slender flagellates propelled about
among the red corpuscles by a delicate ruffled mem-
brane along one side of the body. The single long
flagellum is attached along the outer border of this
undulating membrane, and it may extend free like a
little tail at the front end of the animal, the end that
goes first as it swims. Many years of patient investi-
gation have shown that the flagellates in human
blood are injected into the blood stream with the sa-
liva from the bite of the tsetse fly (Glossina). The
same flagellates are also found in the blood of almost
all the large wild game of Africa. In the wild hosts,
such as antelopes, however, there are no obvious
signs of disease. And we can only conclude that an
amicable relationship has been worked out between
antelope and flagellate, who were introduced to each
other a very long time ago. They have had ample
time to adjust, apparently by a steady elimination of
the most susceptible hosts and also of those trypano-
somes that abused their hosts too severely and so
were killed when their hosts died. Where unbalance
occurs, such that a parasite kills its host, it is likely
that host and guest have been very recently intro-
duced and have not yet worked out the biological
amenities.

Trypanosomes probably infested only inverte-
brates at first, and many still do, but in their long
history some have come to use their invertebrate
hosts as a means of gaining entrance to the bodies of
vertebrates. In the Western Hemisphere, where there
are no tsetse flies, Trypanosoma cruzi, of South
America, can be transmitted to man from its natural
hosts (armadillos, opossums, rodents) and also from
cats, dogs, monkeys, and other mammals, by the
bite of triatomid bugs that regularly live in houses,
like bedbugs, and suck blood from the human inhab-
itants. Having gained entrance to human tissues,
Trypanosoma cruzi causes the anemia and the nery-
ous symptoms of Chagas’s disease in scattered areas
from northern Argentina to Mexico. In some parts
of Brazil, Bolivia, Chile, and Argentina, 10 to 20

per cent of the population is infected. The same
flagellate is found in many species of triatomid bugs
in the scrub woods and farms of Texas and in the
deserts and canyons of Arizona and California; but
natural infections, if they occur, must be rare. Some
trypanosomes have dispensed with the invertebrate
host altogether and can be transmitted directly; for
example, Trypanosoma equiperdum, which is passed
from horse to horse in coitus, and causes dourine
disease. It is found in all regions except Australasia.

The family Trypanosomidae also includes such
forms as Herpetomonas, parasitic in the intestine of
invertebrates, and Leishmania, which causes kala
azar and Oriental sore in people living in warm parts
of the world. Phytomonas, from the milky latex of
many plants, can be found abundantly in our com-
mon milkweeds, and infection is carried from one
plant to another by sucking bugs that visit the plants.
For the amateur wishing to see trypanosomes, an
easily obtained form is in the blood of frogs and of
crimson-spotted newts. The transmitting agent for
flagellates that live in such aquatic hosts is often a
pond leech. Fortunately, flagellates parasitic in the
lower vertebrates do not infect man. Details about
such disease-causing protozoans are best sought in
the specialized books on human parasitology or on
the parasitology of domestic animals, as listed in the
bibliography. Information on the protozoan parasites
of animals other than man or his pets and flocks will
be found in books on protozoology.

The most highly organized of the flagellates are
the polymastiginads, which usually have more than
three flagella, often many. The trichomonads are
common in the digestive tracts of vertebrates, and
also in the urinogenital passages. They are pear-

Trypanosomes among red blood cells in a stained
blood smear. Those shown here, Trypanosoma gam-
biense, cause African sleeping sickness. (General
Biological Supply House, Chicago )

shaped, and have at the front end several flagella,
one of which extends backward along the edge of an
undulating membrane. The body is supported by an
internal stiff rod, projecting at the rear, which also
anchors the animal in feeding. Trichomonas vaginalis
is found in the vagina of from 20 to 40 per cent of all
women examined and in 50 to 70 per cent of those
who complain of leucorrhea. It sometimes causes ir-
ritation and discomfort, but whether it does more
serious harm we do not definitely know. Since the
flagellate does not thrive in the acid condition of the
normal vagina, weak acetic acid is the usual treat-
ment; but it does not always help, and then various
drugs or antibiotics are tried. This flagellate also oc-
curs in the male urinary tract, in the urethra and in
the prostate. Trichomonas tenax lives in the mouth
of man and may be involved in some way in pyor-
rheal conditions. Trichomonas hominis is present
suspiciously often in cases of human diarrhea.

The diplomonads, which have paired sets of or-
ganelles and look as if two simpler flagellates were
joined together in the middle, include Giardia intes-
tinalis and other species of Giardia that live in all
kinds of vertebrates. They inhabit the upper part of
the small intestine instead of the large intestine,
which attracts the other intestinal protozoans. Seen
from the side, Giardia looks like a half-pear with the
broad end directed forward and the flat side indented
by a concavity, which helps the animal to adhere
tightly to the intestinal lining. The eight flagella, at-
tached at the middle and at the hind end, are in ac-
tive use when the animal is seen in the liquid feces
that attend the diarrhea it apparently causes. The
lashing of these flagella was vividly described by the
indefatigably curious Leeuwenhoek. Ill with mild
diarrhea, he was not content merely to complain,
like the rest of us. Instead he set about to examine
his watery feces and in them saw Giardia. In the ab-
sence of diarrhea, only the cysts of Giardia are found

An ameba is never the same from moment to moment as it
moves along by protoplasmic flow. (Ralph Buchsbaum)

in the feces. In one case a single stool was estimated
to contain 14 billion cysts, but in a moderate infec-
tion the number would be closer to 300,000,000.
An effective cure for Giardia-caused diarrhea is
atebrin or other drugs used also for malaria. A group
of related flagellates, the hypermastiginads, which
live in the gut of termites, cockroaches, and wood-
roaches, are certainly among the most remarkable of
protozoans both in the complexity of their structure
and in their habits. Trichonympha campanula, from
the gut of termites, is pear-shaped, with the fore end
narrower than the rear, and is covered with hundreds
of long flagella. The front end of the body is very
complex and composed of structurally specialized
layers. The large, rounded rear end has thin proto-
plasm and engulfs the minute wood particles that
surround the animal in the termite gut. The flagellate
has enzymes that digest the cellulose in wood to
soluble carbohydrates. These are then shared with
the termite host, which eats wood but cannot digest
its chief constituent, cellulose, without the interven-
tion of its protozoan guests. Such mutualistic rela-
tionships, in which two organisms are so closely asso-
ciated for mutual benefit, are fairly unusual in the
animal kingdom, but they are common in this group
of flagellates that inhabit wood-eating insects.

The Ameboid Protozoans

(Class Sarcodina or Rhizopoda)

The word “‘ameba” is derived from a Greek word
meaning “change,” and the ameboid protozoans are
those that move about and capture their food by
means of “false feet” or pseudopods, temporary ex-
tensions of the body, that may never appear the
same from moment to moment, or may appear stiff
and fixed yet show a constant streaming of the proto-
plasm. Members of this group never move by flagella
in the principal phase of the life cycle, though they
may have flagellated stages or sex cells. Most are
free-living in fresh and salt waters and in soil. Some
are parasitic or live as supposedly harmless commen-
sals, mostly in the digestive tracts of larger animals.
A few very small amebas live as parasites within the
bodies of other protozoans.

THE LOBOSE AMEBAS

The lobose amebas have no fixed shape and move
along by extending lobose or finger-like pseudopods,
now at one point, now at another. As new pseudo-
pods form, the old ones flow back into the general
mass of protoplasm, and the animal appears to flow
about in irregular fashion with no permanent front
or rear. Lobose amebas may at times have long,
pointed pseudopods, especially when they are float-
ing in water. But typically they are bottom-dwellers

that glide over the substrate or on vegetation or de-
caying organic debris in fresh and salt waters. Most
of the soil amebas are members of this group.
Amoeba proteus is one of the largest (15, of an inch)
of the common pond amebas. It has a disk-shaped
nucleus, longitudinally ridged pseudopods, and the
habit of advancing through a flow of all the proto-
plasm into the leading pseudopod. Pseudopods are
used not only in moving about but also in engulfing
food and in taking it into the body, surrounded by a
minute quantity of water that then forms the food
vacuole we see within the protoplasm. Anyone
tempted to speak of “the simple ameba” should
watch one moving about and capturing prey. If the
food is a motionless algal cell, the ameba’s body
flows closely about the alga as a flowing drop of oil
might surround a glass bead. But if the food is a
rapidly swimming protozoan, something quite dif-
ferent occurs. The ameba sends out long pseudopods,
in a wide embrace, but at no point in contact with
the prey until it has been completely surrounded on
the sides and over the top so that it is trapped against
the substratum. Only then is it closely enveloped and
finally incorporated into the body. Amebas can also
tell food particles from nonnutritive ones and show
a preference for one species of prey over another.
The giant ameba, Pelomyxa carolinensis, has several
hundred small nuclei and may be up to !5 of an inch
long when moving actively. Though rarely found in
nature, it is readily obtainable from biological sup-
ply houses and is very convenient to watch because
of its large size. It ingests paramecia, one after an-
other, as many as twenty in one food vacuole. (The
naming of the fresh-water amebas is still being de-
bated, quite unknown to the amebas themselves, so
that you may find them called by different names in
different books. )

About half a dozen species of naked amebas live in
man; but only one, the dysentery ameba, Entamoeba
histolytica, is unquestionably harmful. Small and
very active, it is able to dissolve the intestinal lining
and to enter the connective tissue and muscle layers
of the large intestine; and when present in numbers
it causes abscesses, diarrhea (liquid feces) and dys-
entery (bloody feces). Human amebiasis is a world-
wide disease—not confined to the tropics as many
people believe—and it is spread by the contamina-
tion of food or of drinking water with the resistant
cysts of an ameba that is itself too delicate to be
passed around. We do not have immunizing tech-
niques for amebiasis, as we do for typhoid, and when
traveling in countries where soil is likely to be ferti-
lized with human manure, or water contaminated
with human sewage, or food handled by people with
unsanitary habits, it is best to avoid foods that can-
not be peeled or cooked. Ordinary chlorination of
drinking water will not always kill the cysts. Ame-

biasis is better avoided than cured, but we do have
several drugs that are effective in most cases. Enta-
moeba coli is a harmless commensal that lives in the
human colon, feeding mostly on bacteria but occa-
sionally on intestinal protozoans that come its way.
The mouth ameba, Entamoeba gingivalis, does not
form resistant cysts so can only be spread directly
from mouth to mouth in eating or in kissing. Even
so, by the time they are forty years old about 75 per
cent or more of the human population have managed
to obtain some of them. These amebas feed on bac-
teria and loose cells, and when pyorrhea is present
they cluster about the bases of the teeth, probably
aggravating the condition.

Closely allied to the naked amebas of fresh wa-
ters are the shelled amebas which have single-cham-
bered coverings. The covering may be vase-shaped
or bowl-shaped, and has an opening at the bottom
through which the lobose, in some cases filose (long
and thin), pseudopods are protruded. Some cover-
ings are soft and gelatinous; others harden after they
are secreted. They may consist entirely of secreted
silicious plates or prisms, or they may be constructed
of foreign particles, such as sand grains or diatom
shells cemented together by a secretion. These
shelled amebas live mostly in somewhat foul fresh-
water ponds, in sphagnum bogs or peaty soil, and in
animal feces. Most often seen is Arcella vulgaris,
which lives in the ooze and vegetation of stagnant
water and also in damp soil. It secretes about itself a
hard, bowl-shaped, yellow or brown transparent cov-
ering. Viewed from above, the covering appears
circular, and the animal is seen not to fill the interior
completely but to be attached to the walls by thin
protoplasmic strands. Two nuclei, several contractile
vacuoles, and numerous food vacuoles are visible in
the protoplasm. Viewed from the side, the hemi-
spherical covering is seen to have a concave funnel-
shaped opening at the bottom, through which pseudo-
pods extend. When an Arcella divides, one daughter
inherits the cover; the other has to secrete a new one.
Also likely to turn up in organic ooze in fresh water
is Difflugia, which at first glance may be mistaken
for a little mass of sand grains. This ameba gathers
sand grains and cements them about itself into a
pear-shaped (in some species vase-shaped) cover-
ing into which it can withdraw completely whenever
necessary.

THE FORAMS

The “pore-bearers” or foraminiferans (called
“forams” for short) are amebas with shells that typi-
cally are many-chambered and perforated all over
with small pores through which extend long and fine
branching pseudopods. These fuse and fork over and
over again, forming a spreading network of living,
sticky threads that entangle and digest small organ-

[29

When enlarged under the microscope and viewed by
transmitted light, foraminiferan shells of certain spe-
cies look like snail shells. (West Germany. Kurt
Herschel )

isms. The protoplasm extends not only through the
pores but out of the mouth of the shell as well, pour-
ing out in all directions and flowing over the surface
of the shell. In the pseudopods, granules can be seen
streaming constantly toward the tips and then return-
ing along their outer edges.

In contrast to the predominantly fresh-water ame-
boid protozoans just discussed, forams are almost ex-
clusively marine. Most of the species move about on
the ooze of the muddy bottom or attach themselves
loosely to debris on the ocean floor, usually in shal-
low waters but sometimes at depths of even 18,000
feet. Of more than twelve hundred living species,
only about twenty-six are pelagic and float in the
surface waters of the seas, mostly in the warmer
parts of the world, where the high alkalinity of the
water facilitates the extraction of calcium carbonate
from the sea. But these are the most prolific of the
forams, and when they die their innumerable shells
fall in a steady rain to the ocean floor, contributing
about 65 per cent by weight to the gray mud known
as “Globigerina ooze,” from the genus of forams
that predominates in its formation. The most com-
mon foram species in the ooze is Globigerina bul-
loides, but shells of other species of Globigerina are
well represented, as are other foram genera, other
shelled ameboid protozoans, and especially the skele-
tal parts, called coccoliths (p. 23), which make up
nearly 30 per cent by weight of the ooze. Globigerina
ooze occupies nearly fifty million square miles of the
deep-sea bottom. Below fifteen thousand feet, how-
ever, the lime content of the ooze begins to thin out
because the calcite shells of the common foram spe-
cies become dissolved, and below eighteen thousand
feet calcareous shells are rare.

30]

The presence of Globigerina in fossil beds has
been used as an indication that the beds were de-
posited originally at a depth of between about three
thousand and twelve thousand feet. Operculina shells
indicate a depth of less than 180 feet. The rate of
deposition of Globigerina ooze has been calculated,
for some areas, to be about four-tenths of an inch in
a thousand years. Though this is a rate in modern
times, it gives those who can comprehend such stu-
pendous figures some idea of the time it must have
taken to deposit the marine beds that, when uplifted,
form such great chalk formations (as much as 90
per cent calcium carbonate) as the white cliffs of
Dover in England, the chalk beds of Europe, and
the thousand-foot-deep chalk beds of Mississippi and
Georgia in the United States. Modern species of
forams are for the most part just visible to the naked
eye (14; of an inch), but many are of the size of a
pinhead and the largest one has a long, slender, tube-
like shell that may be 2 inches long. In geological
times past, when forams were more abundant than
at present, some members of the genus Nummuilites
had shells several inches across. Many large forms
flourished on the sea bottom in Tertiary times, and
their fossil shells, mostly about as big and flat as a
United States quarter-dollar, can be seen in lime-
stone now exposed in Asia, in the Alps, and also in
northern Africa, where such limestone was used to
build the pyramids of Gizeh, near Cairo.

Limestones are produced instead of chalk when
foraminiferan ooze is deposited in waters close
enough to shores to become admixed with deposits
washed in from the land. The gradual change in
foram species from Tertiary times to the present
makes their shells very valuable as index fossils for
paleontologists trying to determine the age of various
sedimentary rocks. And because of their minute size
foram shells can be recovered undamaged, from
rocks far below the surface, in the borings made by
oil-well drills. By comparing the species of shells
brought up from different levels with species from
layers known to be oil-bearing, paleontologists are
able to direct oil-well drilling operations.

A detection scheme on a much grander scale is
now unfolding in many laboratories around the
world, where foram shells are being used in studies
of world-wide glaciation, for piecing together the jig-
saw puzzle of the evolution and distribution of ani-
mals, and for understanding long-term climatic
trends.

Globigerina bulloides has a shell (about 14; of an
inch) of spherical chambers spirally arranged and
perforated by many pores. When the foram is alive
and near the surface the shell is covered with long,
needle-like spines; these dissolve away when it later
falls to the bottom and is found in the ooze. The
protoplasm is said to be a rosy pink color when seen

through the shell of an animal that has withdrawn on
being lifted out of the sea in a tow net. When un-
disturbed it spreads its pseudopodial network in sur-
face waters and feeds on diatoms and algae, other
protozoans, and occasionally even larger animals.
Elphidium crispa is another pelagic form, and is a
giant among modern species. Its flattened, spiral,
sculptured, many-chambered shell reaches a diam-
eter of ‘4 of an inch and superficially resembles a
small snail shell, so that originally it was classed as a
mollusk. Leeuwenhoek first found this genus in the
stomach of a shrimp, but Elphidium can ingest, along
with its unicellular plant diet, the small copepods
that are relatives to the shrimp.

Many forams harbor green or yellow bodies be-
lieved to be modified flagellates. Reproduction in
forams takes place by multiple division and involves
an alternation of asexual and sexual forms. In the
typical many-chambered species the forms that re-
produce asexually have shells of small size, those that
reproduce sexually have larger shells. The sex cells
are usually flagellated but sometimes are ameboid.
The life cycles of forams are marvelously complex,
but details must be sought in advanced treatises.

THE HELIOZOANS

The “sun animalcules” or heliozoans, found mostly
in fresh waters, are spherical ameboid protozoans
with stiff radiating pseudopods that serve only for
feeding, not for moving about. The pseudopods are
supported by stiff internal protoplasmic rods and
covered with thin, clear, streaming surface proto-
plasm. In many species the body has a gelatinous
covering in which foreign particles or secreted plates
or needles of silica are imbedded. Or it may be en-
closed, as in the common but lovely Clathrulina, in
a spherical latticed cage. Clathrulina is fastened by a
stalk to the substrate, and the pseudopods protrude
through the lattice openings. The more typical free-
floating forms are motionless or move only very
slowly. Passing organisms that happen to touch the
outstretched stiff pseudopods adhere to them and are
quickly paralyzed, as if by a toxin. The pseudopods
may shorten and carry the prey to the main body
mass, or several may surround the victim first and
then slowly withdraw into the main body. The two
most familiar heliozoans of pond water are both
free-floating. The small Actinophrys sol has one nu-
cleus and a body that is not clearly divided into two
regions. The much larger Actinosphaerium eich-
horni, visible to the naked eye, has a distinct outer
layer surrounding a granular interior in which one
can usually see recently eaten diatoms or other algae,
and small protozoans or crustaceans. A number of
small heliozoans may unite temporarily when they
capture and ingest large prey. Asexual reproduction
is by fission or budding.

THE RADIOLARIANS

The radiolarians are all marine and pelagic ame-
boid protozoans, abundant especially in warm seas.
They nearly always have siliceous skeletons, many
of these so exquisitely shaped that Haeckel, the great
German biologist and student of the radiolarians,
once called them the miniature jewelry of the abyss.
Mostly spherical, they extend long, fine, usually
stiff raylike pseudopods from which they take their
name. The pseudopods are sticky and capture dia-
toms, protozoans, and copepods that adhere to them.
Radiolarians are of large size as protozoans go. The
giant Thalassicola nucleata is about 1 of an inch in
diameter, and its closely related colonial relatives
reach | inch or more in length. Thalassicola has no
skeleton, but in most radiolarians siliceous needles
are fused into a beautifully symmetrical latticework.
The lattice is most often spherical, and in some spe-
cies there are a number of concentric latticed spheres,
one within the other, like the balls made to show off
the skills of Chinese ivory carvers. There is also a
bewildering variety of helmet-shaped, disk-shaped,
and bell-shaped lattices—all combined in every pos-
sible way with beautiful and bizarre ornamentations
of spines, hooks, branching thorns, and long, grace-
fully curved extensions. The almost endless differ-
ences in radiolarian skeletons, each produced in a
consistent inherited pattern by what appears to be a
relatively formless blob of protoplasm, makes one
wonder if this protoplasm is as unorganized and as
similar in the various species as its appearance in the
naked amebas might lead us to believe.

A great variety of shell shapes can be seen in many
samples of foraminiferan material. (Otto Croy )

Radiolarians can be distinguished from their fresh-
water counterparts, the heliozoans, by the definite
membrane that separates the outer highly vacuo-
lated protoplasm from the inner more granular pro-
toplasm—though these are continuous with each
other through pores in the membrane. The outer
layer is gelatinous, with large fluid-filled vacuoles
(none of them contractile) that give it a frothy ap-
pearance; and it usually contains yellow bodies,
which are thought to be flagellates that exchange
favors with their hosts.

When the weather grows rough or the temperature
rises too high, the buoyancy of radiolarians is said
to be reduced by a withdrawal of the pseudopods and
a bursting of some of the fluid-filled vacuoles in the
frothy layer. Surface-living animals can thus descend
into deeper water, restoring their vacuoles later.

Radiolarian shells are exquisite lattices of silica. In
life, the protozoans that secrete the shells extend stiff
pseudopods from many openings. (Otto Croy )

Some species regularly float at great depths (six-
teen thousand feet or three miles). In the deeper
parts of the ocean, where the calcareous shells of
foraminiferans soon dissolve, the bottom ooze may
contain siliceous skeletons only: radiolarian lattices,
sponge spicules, and diatom cases. When the radio-
larian content reaches at least 20 per cent, bottom
deposits are called “radiolarian ooze.” In the Pacific
and Indian oceans such ooze covers almost three mil-
lion square miles of ocean bottom. Upon being up-

32]

lifted, radiolarian beds become sedimentary rock
layers on land, and the small but well-preserved ra-
diolarian skeletons, like those of the foraminiferans,
serve as convenient index fossils for dating rock lay-
ers and for guiding oil-well digging operations. Ra-
diolarian deposits occur as siliceous inclusions in
other rocks, forming flint or chert. And radiolarian
skeletons contribute to the abrasiveness of the “Trip-
oli stone” used in metal-polishing powders.

The Spore-Formers

(Class Sporozoa)

The sporozoans include some of man’s worst ene-
mies, the spore-forming parasitic protozoans that
cause malaria, various cattle fevers, coccidiosis in
chickens, diseases of halibut, salmon, and other
fishes, epidemic death in cultivated honeybees and
silkworms. Yet one hesitates to hold a grudge against
a whole class of animals that is itself so impartial
as to parasitize every major group in the animal
kingdom, not excepting other protozoans. Each spe-
cies of parasite is more or less limited to a specific
host or to a few closely related hosts, and the para-
site lives within or between the host cells, absorbing
food through its body wall. Feeding in this way,
sporozoans can take only dissolved food, sometimes
that digested by the host but more often the dissolved
protoplasm or body and tissue fluids of the host it-
self. An animal that lives protected from the external
environment and surrounded on all sides by mate-
rials for abundant feasting has little or no need to
move about, and the adult or main feeding stage of
sporozoans has no external organs of locomotion.
Besides this negative criterion, which is used to sep-
arate them from other protozoans, all sporozoans
share the habit of producing very large numbers of
spores as transfer stages to new hosts, and this has
suggested the name of the group. The young transfer
stage produced by sporulation is usually enclosed in
a resistant wall, but in the blood-inhabiting species,
like the malarial parasite, the spores are naked and
they are never exposed to the rigors of the external
world, being transferred from one final host to an-
other by a blood-sucking intermediate host. The life
cycles of sporozoans can be extraordinarily complex,
involving both asexual and sexual processes, each of
these with one or more cycles of multiple fission.
The nucleus splits repeatedly by rapidly ensuing di-
visions, and each new nucleus becomes surrounded
by a tiny share of the protoplasm, so that when the
cell finally breaks up there are as many offspring
as there were nuclei. The simultaneous hatching of
billions of slender parasites in each such cycle is

[continued on page 49 ]

1. The breadcrumb sponge, Halichondria panicea, can
be crumbled like stale bread. The thin patches that en-
crust shaded rocks on the shore are usually greenish but

may be creamy or orange. (Brittany, France. Ralph
Buchsbaum )

2. This globular commensal sponge, Suberites, overgrows the shells inhabited by c
tain hermit crabs. It repels predators by its distastefulness, and benefits from being
carried about to new feeding grounds. (Banyuls, France. Ralph Buchsbaum )

2 * -
2
a &
+
*

“ Ps

s
oe ¥
: ee ¢
‘ ,
on P 4
a
fe
7 Rg
on? *

3. A yellow branching sponge,
Axinella, and an irregular red-
dish-orange sponge, Polymastia,
are both common in the shore
waters off South Devon, Eng-
land, at depths of sixty feet or
more. (D. P. Wilson)

4. The club-headed hydroid,
Clava squamata, forms little col-
onies on shore seaweeds. The
inch-long pink polyps stretch
their tentacles to ensnare small

prey. (England. D. P. Wilson)

5. A colony of oaten-pipes hy-
droid, Tubularia larynx. It gets
its name from the yellowish
tubes that encase the stems hold-
ing aloft the many flower-like
but carnivorous polyp “heads.”

(England. D. P. Wilson)

6. A hydrozoan medusa, Polyorchis, common on the American Pacific coast, is shown
here about three times natural size. The trumpet-shaped feeding tube, with the mouth
at its tip, is mostly obscured by the stringlike sex organs. At the bases of the tentacles

are pigmented sense organs. (Woody Williams)

7. A true or seyphozoan jellyfish, Dactylo-
metra pacifica, whose lovely appearance be-
lies the danger of its stringing threads. Some
members of this genus can cause illness or
death. (Sagami Bay, Japan. Y. Fukuhara)

romeareonpanenncntiarinstaasisim
—~

—_— ge OT SSS

ee a

8. The Portuguese man-of-war, Pliysalia,
was probably named by English sailors who
first sighted its floating bladder, up to a foot
or more long, in Portuguese waters. T he
trailing tentacles of this coelenterate usually
ensnare fishes and can inflict fatal stings on

(Florida. Charles Lane)

swimmers.

9. Sea fingers, a kind of soft coral, deserves its name when seen, as here, with the body
limp and the polyps withdrawn. Compare this contracted colony of Alcyonium palma-
tum with the fully expanded sea pen overleaf. (Banyuls, France. Ralph Buchsbaum)

10. A simple kind of sea pen, Veretillum cynomorium,
with fully expanded polyps arising from its fleshy
body. To its right is a white sea squirt, Phallusia
mamillata. (Banyuls, France. Ralph Buchsbaum)

11 and 12. A common sea fan of European waters,
Eunicella verrucosa, still attached to a small boulder,
is shown just after being dredged from the sea bottom
off Plymouth, England. (Ralph Buchsbaum.) Below,
the enlarged portion shows the many polyps, each
with eight feathery tentacles. (D. P. Wilson)

13. The aggregated anemone, Anthopleura elegantissima, is the commonest anemone
of the American Pacific coast. About 3 inches across when fully expanded, it lives in
dense beds, often attached to rock in sand. (Woody Williams)

14. The snakelocks anemone, Anemonia sulcata, is
usually pinkish brown but may be a soft apple green,
from the algal cells in its tissues. Unlike most anem-
ones, it displays its snaky tentacles in the sun. (Brit-
tany, France. Ralph Buchsbaum)

15. A commensal anemone of European waters, Cal-
liactis parasitica, attaches to whelk shells inhabited
by the large hermit crab, Eupagurus bernhardus.
Here five anemones cling to one shell. (Banyuls,
France. Ralph Buchsbaum)

16. The p

liferating anemone, Epiactis prolifera, seems to be pinching off tiny

anemones around its waist, but these young are not asexual buds. They first shelter
within the body (*% inch wide) of the parent, then emerge and complete their de-
velopment on the outer surface, (San Francisco. John Tashjian at Steinhart)

17. The dahlia anemone, Tealia, is often pale in color
when found in deep water. (See shallow-water Tealia
in Plate 20.) The column is covered with wartlike
tubercles to which bits of stone and shell adhere.
(Oregon. Ralph Buchsbaum)

18. The plumose anemone, Metridium senile, may
in deep water grow as large as 8 inches tall and
5 inches broad; but those found in rock crevices
at ordinary tides are usually small or young speci-

mens. (Plymouth, England. D. P. Wilson)

19. The opelet anemone is another name for the
snakelocks, Anemonia sulcata (Plate 14), which
at low tide does not withdraw its tentacles but
only shortens them as it droops in the sun. (Ros-
coff, France. Ralph Buchsbaum)

20. The dahlia anemone, Tealia felina, uses its
robust tentacles to push rather large prey into its
mouth. It feeds in great part on small crabs in
rocky crevices. (England. D. P. Wilson)

21. The gemmed anemone, Bunodactis verrucosa,
closes tightly at low tide, crowding a greenish
disk and some fifty delicately banded tentacles
into a contracted body measuring about | inch
across. (Roscoff, France. Ralph Buchsbaum)

22. The plumose anemone, Metridium dianthus, is widely distributed and is one of
the commonest anemones of the northern half of the American Atlantic coast. Young
specimens have a simple disk which has not yet developed the deep lobes and frills

typical of larger members. (New Jersey. David C. Stager)

A solitary cup coral, Caryophyllia clavus, dredged from the Bay of Biscay,
abounds in the deeper waters off England, France, and Spain, and also in the coastal
Mediterranean mud zone. If shell or gravel is lacking it is held in the mud by its
pointed base. (D. P. Wilson) j

24. An orange-colored coral, Astroides culy-
cularis, here shown at about natural size,
carpets rocks along the coasts of It ily, often
just below the water line. Only at the base
of the colony, where some of the polyps
have died, can one see the gray limestone
skeleton, pocked with cavities that housed
the polyps. (Naples Aquarium. D. P. Wilson)

25. The smooth, gently lobated living edge of a
Porites coral platform is dotted with minute
polyps hose combined efforts produce coral plat-
forms up to forty feet across. These support other
corals on their exposed and eroded centers. (Great

Barrier Reef. Allen Keast)

26. These coral polyps, here
greatly enlarged, are part of a
colony of Phyllangia americana,
a reef-building West Indian stony
coral. One polyp has just opened
its mouth to receive a fragment of
clam meat. In nature it captures
living prey. (Jamaica. Thomas
Goreau)

= «
at Bas

27. A large brain coral, Lobophyllia, originally dome-shaped, which has been killed at
its center by exposure. (Green Island, Great Barrier Reef. Allen Keast)

28. Globose masses of reef coral with relatively
large twelve-tentacled polyps appear green from
the plantlike cells that live in their tissues.
(Bimini. Fritz Goro: Life Magazine)

‘ “we
i Ste DY

29. A prickly colony of soft coral from Micronesian

waters. (Jerome M. and Dorothy H. Schweitzer)

30. A zoanthid colony, Epizoanthus wri
several times enlarged, resembles a of the
related sea anemones. Brought up by a free-swim-
ming diver from a depth of eighty-four feet off
the South Devon coast of England. (D. P. Wilson)

{ continued from page 32 ]

what ruptures so many red blood cells all at one time
and produces the periodic chills and fever of malaria.
A loss of locomotor organs, and the development of
complex life cycles with incredible numbers of off-
spring, are common to the parasitic way of life. So
that sweeping all the odds and ends of protozoan
parasitism into one big hodgepodge and calling it the
Sporozoa does tidy up the rest of the protozoan clas-
sification, but it creates a group with members that
really have very little in common and that do not
represent a single branch of protozoan evolution.
The several subclasses of Sporozoa include many
important parasitic groups such as the myxosporid-
ians of fish disease, the microsporidians that kill
honeybees and silkworms and other higher inverte-
brates, and the haplosporidians that parasitize many
groups from rotifers to fish. Even the sarcosporidians,
which invade the muscle tissues of lizards, birds, and
also mammals, especially sheep, used to be placed
here. Now they are usually classed as fungi. Only
one of the subclasses, the Telosporidia, seems to be a
natural grouping of related orders, and as these
include many animals of importance to man they
will be briefly considered.

THE GREGARINES

The gregarines are mostly wormlike protozoans
that infest the digestive tracts and body cavities of
many invertebrates, but not of vertebrates. The
young form usually lives within a host cell, but as it
feeds and matures it protrudes from the cell, re-
maining attached only by the front end or leaving
altogether and moving about in the intestinal cavity
or one of the body spaces. Gregarines can be found
by teasing out on a microscope slide, and then dilut-
ing with water, the content or the lining of the in-
testine of a cricket or a grasshopper. It is likely one
will see the wormlike feeding stage gliding slowly
by means that are not evident, perhaps by slow
and inconspicuous muscular contractions. In this
group of gregarines the body is divided by a parti-
tion into a small front segment by which it can attach
to the host tissue, and a larger hind segment which
contains the nucleus. One may also see two individ-
uals attached end to end, the “gregarious” habit for
which the group is named. It is an indication that
sexual reproduction will ensue, with the front indi-
vidual as the female, the one at the rear as the male.

THE COCCIDIANS

The coccidians excite little notice as human para-
sites, though species of the genus Jsospora are com-
moner in human feces than one would suspect from
the few cases of diarrhea actually reported. The bad
reputation of the group rests mostly on the damage
inflicted by Isospora, and more especially by the
genus Eimeria, on domestic animals. Coccidiosis

takes a heavy toll of chicken flocks and other poul-
try; and rabbits and cattle may also be seriously af-
fected, the latter having bloody feces, becoming ema-
ciated, and often dying. Practically any farm animal
may suffer from coccidian attacks, and so may dogs,
cats, and even canaries. In addition to these verte-
brate hosts, coccidians live in annelids, mollusks, and
arthropods. The feeding stage usually resides within
the lining cells of the intestine or of the organs that
connect with it, often the liver. The virulence of
many coccidial diseases is due to the tremendous
numbers of parasites that result from the multiple
fissions.

Gregarina is a parasitic sporozoan likely to be found
in the intestine of a grasshopper, cricket or cock-
roach, Pairs of cells often remain together, each one
subdivided into a small portion and a larger. In mat-
ing, the front individual will be the female, the rear
one the male. (General Biological Supply House,
Chicago )

THE HEMOSPORIDIANS

The hemosporidians live within the blood corpus-
cles or other cells of the blood system of verte-
brates, and all of them require a blood-sucking inter-
mediate host during part of their very complex life
cycle. In human malaria, as everyone knows, the
intermediate host is a mosquito of certain species of
the genus Anopheles. For lack of this bit of knowl-

[49

Three of these oval red blood cells contain a common
sporozoan parasite of birds, Haemoproteus, here made
more visible by use of a dye. The parasite is trans-
ferred from one bird host to another by a blood-suck-
ing fly, in whose body the parasite goes through a
sexual part of its life history. (General Biological Sup-
ply House, Chicago. )

edge, which was not finally established until 1898,
the course of human culture was long deeply influ-
enced by the sporozoan that we now call Plasmo-
dium. No human tyrants, nor all the wars in human
history, have taken the toll of misery and death ex-
acted by the malarial parasite in those warm or tem-
perate parts of the world where anopheline mosqui-
toes are infected with Plasmodium. Malaria was well
known to the Greeks twenty-five hundred years ago,

50]

but perhaps it was introduced, after they had already
achieved their fine civilization, by soldiers returning
from military triumphs or by slaves brought in to do
their menial work. Whether malaria came to the New
World with the Spaniards or was already here when
they came, it was one of the major hazards, less men-
tioned but probably more important than either hun-
ger or Indian attacks. Malaria may have been the
disease that in 1607 killed half the settlers at James-
town, and malaria epidemics are recorded for Mas-
sachusetts as early as 1647. It was one of the chief
burdens of the pioneers who moved westward into
the Mississippi Valley, and as late as the 1930’s was
still widespread in the southern part of that valley.
If the history of man had not in the past been written
to so great an extent by militarily and politically
minded writers, it might tell a very different sort of
story. The southern part of the United States has lost
much of its strength to a disease that annually, until
World War II, debilitated at least a million Ameri-
cans and killed several thousand. During the war,
when quinine ran out among the men at Bataan, 85
per cent of every regiment developed acute malaria.
And in the South Pacific campaign there were five
times as many casualties from malaria as from com-
bat. Up to the end of the war there were in all the
world some 350,000,000 cases of malaria annually,
of which about 3,500,000 resulted in death each
year.

Since that time a dramatic change has come. New
therapeutic drugs, spraying of houses with DDT, bet-
ter control of mosquito breeding places, and better
organized health care have wiped out malaria in the
United States and brought it completely under con-
trol in parts of Europe, especially Italy, where it was
so long a heavy drain on the life of the people. A vast
improvement has been made in a great many parts of
Africa and of Asia. But to assume that man has
necessarily consigned malaria to his unhappy past is
naive. Our control of malaria depends upon the
proper functioning of a complex civilization that can
break down as others have in the past, while the
biological potential of mosquitoes and sporozoans is
built firmly into the species. Long before there were
men about, hemosporidians were living in lizards,
birds, bats, small rodents, monkeys, apes, and others.
Much of what we know about human malaria was
first learned from studies in birds, whose malaria is
transmitted by mosquitoes of the common genus
Culex and certain related genera. There are four
species of Plasmodium that cause malaria in man.
P. ovale is rare but found in many separated parts
of the world. P. vivax, P. malariae, and P. falciparum
are common and widespread, and each causes a
distinctive set of cyclic symptoms corresponding to
forty-eight-hour, seventy-two-hour, and forty-hour
cycles of development respectively.

The Ciliates (Class Ciliata)

The ciliates are mostly free-swimming forms that
row themselves about by the beating of many cilia,
so named for their resemblance to eyelashes. Abun-
dant in all fresh and marine waters, ciliates flourish
best where there is much decaying organic material,
for most of them are bacteria feeders. Any water
dipped up from the weed-grown edge of a stagnant
pond, especially if it contains organic debris or frag-
ments of vegetation, will on microscopic examina-
tion reveal a miniature community in which ciliates
play many of the leading roles. Of all the protozoans
they will be the most conspicuous, move the most
rapidly (almost one-tenth of an inch per second, in
some of the fastest species), and occupy the greatest
variety of niches. They may be difficult to appraise
at a glance, for they cross the field at all angles in a
fast, powerful glide that can usually be slowed only
by using anesthetics or such a barrier as cotton fibers.

The familiar Paramecium is often best seen when
anchored to a bit of debris and quietly feeding on
bacteria. This slipper-shaped animal has a conspicu-
ous groove at one side of the body, and this is lined
with cilia whose beating wafts bacteria and minute
particles of organic material through the mouth open-
ing into a funnel-shaped gullet. There special tracts
of cilia compact the bacteria into a food ball, which
is passed on, surrounded by a minute droplet of wa-
ter, as a food vacuole. Successive vacuoles are
launched into the fluid interior protoplasm and circu-
late in a regular path. One experimenter kept close
watch on some individuals of Tetrahymena, a small
relative of Paramecium, and estimated that each
food ball was an accumulation of about a thousand
bacteria and that a vacuole was sent out on its course
once every six minutes. The spent vacuoles were
eliminated some four hours later. A really large cil-
iate, Stentor, when placed in a rich suspension of
euglenas, was observed to down these flagellated
organisms at the remarkable rate of about a hundred
per minute.

But not all ciliates feed by ciliary currents. Some
are predatory, actively seeking out their prey and
attacking it with a ferocity that matches anything
seen in higher animals. Didinium feeds mostly on
paramecia, devouring them whole, as many as eight
in one day. It has no difficulty in opening its mouth
wide enough to swallow any individual not too much
larger than itself, but if greatly outclassed in size the
didintum may have to struggle longer, and the vic-
timized paramecium continues to swim about ac-
tively with the attacker grimly hanging on. In
clearer waters, where oxygen content is high, bacteria
feeders are few and carnivorous ciliates attack small
herbivorous ciliates that feed on green or blue-green

algae or on diatoms. Such carnivores may in turn be
fed on by larger ciliated carnivores, and when the
carnage is all over, fragments of dead plant and ani-
mal tissue will be cleaned up by scavenging ciliates.
In this highly competitive microworld others have
turned to exploiting both the external surfaces and
internal cavities of invertebrates and vertebrates.
Ciliates may themselves harbor smaller parasites or
commensals, or they may live in a mutually beneficial
relationship with alga-like flagellates that carry on
photosynthesis within the ciliate body.

The firm shape of most ciliates is maintained by a
stiff but flexible outer covering, the pellicle, and by
the outer clear gelatinous layer of protoplasm that
lies beneath the pellicle. Within the firm outer layer
is a more fluid, granular protoplasm in which the nu-
cleus floats, the food vacuoles circulate, and the con-
tractile vacuoles work away at pumping out the
excess water that accumulates more especially in the
particle feeders. The cilia protrude through holes in
the pellicle, which is handsomely marked with longi-
tudinal or diagonal lines of ciliary attachment. At
their bases, in the outer protoplasm, the cilia connect
with the fibrils of the neuromotor system that coordi-
nates ciliary movements. Much of the time the cilia
beat so fast that all we can see is a flickering at the
edge of the body. They move like the flexible arms
of a swimmer doing the crawl, reaching forward in
the relaxed part of the stroke and then striking back-
ward through the water in a forceful sweep—not
straight backward, but obliquely so that the animal
rotates and describes a spiral path as it continues on
a straight course. Aside from the ciliation of the
body, which serves both locomotion and feeding,
most members of this class share a unique nuclear
situation that distinguishes them from other proto-
zoans. The functions of the nucleus are divided be-
tween two separate bodies: a large nucleus con-
cerned with the chemical processes of feeding and
growth, and a small nucleus concerned with repro-
duction.

Asexual reproduction occurs, as in other groups,
by a division of the protoplasm and each of the two
nuclei between two daughter cells. But sexual repro-
duction usually takes place by a special kind of con-
jugation. The individuals become sticky and pair off,
each couple adhering together by apposing their
mouths and forming a protoplasmic bridge. This
lasts for several hours, during which the nuclei un-
dergo complex changes and a portion of each small
nucleus migrates to the opposite member of the un-
ion. Thus the essential part of sexual reproduction
is accomplished—the recombining of hereditary ma-
terials so as to produce offspring with new hereditary
possibilities. In Paramecium, where it has been most
studied, the two conjugants do not appear to our eyes
to be visibly differentiated. But they are physiologi-

[51

cally distinct, as it has been shown that pairing oc-
curs only when the two members are from different
strains.

Only a little of the behavior of ciliates is of the
kind that we see in higher animals as they move di-
rectly toward some favorable object or situation in
their environment. Ciliates secure very little warning
of what surrounds them, beyond what current feed-
ers can detect as they sample the water ahead, so
that mostly they find the best conditions for existence
by a kind of trial-and-error method, as we do when
fumbling about in the dark. A paramecium does not
react when entering a favorable situation but only
when it starts to leave such an area. That is, on
reaching a place where it can detect physical obstruc-
tion, too high or low a degree of acidity, or too high
or low a temperature, it backs up by reversing the
ciliary beat, and then changes its course slightly. If
it meets the same unfavorable stimulus it backs up
again and again shifts its course. We have named
this the “avoiding reaction,” and it can be repeated
any number of times until the animal at last finds a
free passageway or is turned back into the more fa-
vorable region in which it has been moving. Unlike
those people who go about boasting that they know
what they like, ciliates seem mostly to know only
what they do not like. And they make their way
about in life by getting “trapped” in those areas
where they are best adapted to live.

As a group the ciliates are the most highly special-
ized of the protozoans, with a variety of feeding
structures and of elaborate locomotory and coordi-
nating systems that defy brief description. The cili-
ation of the body ranges from an even covering over
the whole body, as in the holotrichs, to a few large
cilia on the lower surface, as in the hypotrichs. On
the basis of the distribution of the cilia, the class has
been divided into a number of orders.

THE OPALINIDS

The opalinids, named for their beautiful opales-
cent appearance, are all mouthless parasites, mostly
of the large intestines of amphibians. When removed
from the rectum of the frog or toad, they will be seen
swimming about by what appear to be short cilia
that clothe the whole body. Opalina is oval, flattened,
and has many similar nuclei. In the spring, at just
about the time that frog eggs are hatching into tad-
poles, Opalina produces cysts that pass out in the
feces. Those that happen to be swallowed by a tad-
pole hatch and give rise by a sexual process (not the
conjugation seen in other ciliates) to a new genera-
tion of opalescent adults that absorb food in the frog
intestine. In spite of their superficial appearance
they are often put with the flagellates, which they
resemble in many ways, notably in the habit of di-
viding lengthwise—instead of crosswise, as the cili-

52]

ates do. Moreover, their nuclei, which number from
two to many, are all alike instead of being of two
kinds, as in most ciliates.

THE HOLOTRICHS

The holotrichs typically have simple cilia, usually
short and of equal length, that cover the whole body
in lengthwise rows, as in Paramecium. Or the cilia
may be restricted to certain areas of the body, as in
the two or more ciliary girdles that encircle the bar-
rel-shaped Didinium, and the rows of cilia that
emerge between the plates of the armor that enclose
its near relative Coleps. To follow the group tradition
is to earn a living by bacteria feeding, and most have
a ciliated groove or depression that funnels food into
the always open mouth, reversing the ciliary beat if
what comes in is undesirable. Some are predators,
however, and Didinium and Coleps have at the front
end a mouth that can be opened wide to swallow
large prey. In Didinium nasutum the mouth is at the
top of an extensible proboscis which is not fully pro-
truded as the animal swims about, barging full on
into anything that comes in its way. Didinia have
been seen to strike the glass walls of aquaria, algae,
euglenas, rotifers, the giant ciliates Stentor and Spi-
rostomum—all without success. When, however,
they happen to strike Paramecium or another com-
mon _ holotrich, Colpoda, the proboscis penetrates
and fastens onto the victim, drawing it whole into
the widely spread mouth. Vorticella, a bell-shaped
ciliate, also gives way to the snout, as does frontonia,
though this last is a very large holotrich and has to
be eaten in installments. Mast, a leading American
student of feeding in protozoans, saw one frontonia
attacked in fifty-eight places by many didinia, but
until it died after forty minutes it kept closing its
wounds and swimming about actively, growing
smaller and smaller all the time. Apparently the
choice of food in didinia depends not on toughness
of exterior or on size but on particular physical or
chemical properties of the prey.

When a didinium attacks its usual food, a para-
mecium, the victim may shoot out a barrage of trich-
ocysts, long, sticky threads extruded through pores
in the outer covering. The undischarged trichocysts
lie as a layer of carrot-shaped bodies in the outer
protoplasm; and many physical or chemical stimuli,
especially irritants, will cause their discharge. They
may be defensive devices, but they make a didinium
stand back only briefly. In the end the paramecium,
enveloped in gelatinous threads, goes down the hatch.
It takes more than trichocysts to discourage an ani-
mal like the didinium that was seen to devour two
conjugating paramecia at one time. In a parame-
cium, at least, the trichocysts seem most useful as a
means of anchoring the animal as it quietly feeds on
bacteria. Though common in holotrichs, trichocysts

are rare among other ciliates. Holotrich feeding hab-
its also explore many other ways of getting along in
the world. Paramecium bursaria harbors green flag-
ellates, and it is said that the animal can survive on
its green cells if bacteria are not available. The
astomate (mouthless) holotrichs live in the digestive
tracts of annelids, the livers of mollusks, the body
cavities of annelids and crustaceans. Parasitic forms
with mouths raise pustules in the skin of fishes or
may be found on the gills of tadpoles. Many live as
relatively harmless commensals, sharing the food of
their hosts by taking up posts in the mantle cavities
of bivalve mollusks or the intestinal tracts of sea
urchins or mammals.

THE SPIROTRICHS

The spirotrichs have, leading to the mouth, a
downward-curving zone of membranelles, large tri-
angular plates of fused cilia that create powerful
feeding currents. Spirotrichs may be divided up into
heterotrichs, oligotrichs, and hypotrichs, according
to their patterns of ciliation. The heterotrichs are
covered all over with short cilia, and they include
such well-known forms as the huge, trumpet-shaped
stentors, named for the Greek herald in the Trojan
War, who, according to Homer, had a loud trumpet-
like voice. Stentor lives attached by the narrow end
of the “trumpet,” but may detach and swim about
with the muscular body partly contracted. The large
blue species, Stentor coeruleus, with the fully ex-

panded body showing alternate stripes of white and
Bhi from the white muscle fibers that underlie
the blue-pigmented layer, and with the large mem-
branelles of its feeding disk steadily wafting small
flagellates and ciliates into the mouth, is one of the
finest sights in the animal kingdom. It is quite impos-
sible to leave the eyepiece of a microscope when such
an animal is performing. Also in this group is the
long, slender Spirostomum, about the length of
printed dash—and one of the largest of fresh-water
protozoans. Often seen in dark, shady pools, it may
when numerous whiten the surface of the water.
Balantidium coli normally parasitizes pigs but may
shift (when its cysts get into the food or drink of
people who handle pigs) to the human intestinal
wall, causing diarrhea.

The oligotrichs have the body cilia reduced or ab-
sent. Such are Halteria, familiar to those who exam-
ine pond water, as the minute form that seems to
bounce like a ball across the field of the microscope;
the marine tintinnids that secrete about themselves
vase-shaped cases; and the many commensals of
hoofed animals, including the astoundingly complex
Epidinium ecaudatum.

The hypotrichs include many of the most com-
mon and most amusing ciliates that turn up in the
fresh and salt waters usually examined. Oval and

A fully expanded large blue stentor, Stentor coeruleus,
with membranelles beating around the edge of the
feeding disk. (P. S. Tice)

flattened, they have the cilia confined almost entirely
to the flat undersurface, on which they creep about
in a characteristic jerky manner. The cilia do not
beat but are fused into a number of stout projections
that act like little legs. The upper surface is convex
and has only a few stiff sensory bristles. Well known
are Oxytricha, Stylonychia, and Euplotes, as well as
Kerona, a curious little commensal that crawls about
on the outer surface of hydras.

THE PERITRICHS

The peritrichs typically are bell-shaped or vase-
shaped forms that live attached by a long, spirally
contractile stalk, and that have no cilia except those
on the feeding disk that occupies the broad end of
the bell. The cilia occur in circlets, and cling loosely
to each other to form a kind of continuous undu-
lating membrane that sweeps food particles into the
mouth. When the animal is feeding the bell is held
aloft, fully expanded, and the ciliary membrane
sweeps in bacteria by creating a whirlpool or vortex,
which suggested the name of the common genus,
Vorticella. At the least alarm the stalk contracts like
a coiled spring and the contractile bell folds its edge

In Stylonychia, many of the cilia are fused in groups
and are stout organs, easy to see as the animals move
about on them. Stylonychia is flattened, with definite
upper and lower surfaces. (General Biological Sup-
ply House, Chicago)

54]

over the cilia. Any bell can develop a girdle of cilia,
break loose, and swim away to a better neighbor-
hood. When vorticellas conjugate, one of the mem-
bers is of very different size. Vorticella grows singly
or in dense clusters; and Epistylis is colonial, with
stalks that are noncontractile. Both occur in marine
waters but are most familiar from fresh waters ev-
erywhere, for they form whitish patches on sub-
merged sticks and stones and in some streams are
found springing from the body of almost every
aquatic insect or crustacean. Carchesium colonies,
in which the individuals contract their stalks inde-
pendently, grow nearly 4% of an inch long on the
underside of sticks and stones in fresh-water streams.
Zoothamnium is like Carchesium except that there is
a single branching system of contractile fibers, so
that the whole colony contracts at one time. A freely
moving peritrich is Trichodina, often seen moving
about on the bodies of hydras by means of a posterior
circlet of cilia. The round squat body has a concave
undersurface bearing a horny ring, usually with
curved hooks, by which it clings to the hydra and
also to a variety of other aquatic hosts such as
sponges, flatworms, frog tadpoles, other amphibians,
and fish.

The Suctorians (Class Suctoria)

The suctorians have staked out a new claim in the
protozoan world, and established a whole new class
of animals, through their development of long,
sucking tentacles that enable them to capture and
feed on prey without either moving about or produc-
ing feeding currents. Though obviously derived from
ciliates, the adult suctorians have been able to dis-
pense with cilia altogether. Only the young are cili-
ated, and this helps them to move a little distance
before settling down and competing for food with
their parents, who live attached by a stalk to vegeta-
tion, to other animals, or to any solid object in fresh
and salt waters everywhere. Tokophrya has a long,
noncontractile stalk that holds aloft a club-shaped
body. From the free end of the club it rigidly extends
a number of very long and slender hollow tentacles,
knobbed at their tips. When a ciliate sails unaware
into one of these tentacles it is seized and held fast
by a number of tentacles, while from three to ten of
the hollow tubes in some way penetrate the surface
covering and suck up the protoplasm. About fifteen
minutes suffice for sucking dry a euplotes. The vic-
tim may thrash about and struggle mightily to escape,
but it rarely does, even though held by only a few
delicate-appearing tentacles. A specialist on sucto-
rians watched many trapped paramecia in their
death struggles without ever seeing one extrude trich-

Vorticellas attached by their long, coiling stalks to a piece of plant debris. (P. S. Tice)

ocysts. During one of these uneven battles between
suctorians and their victims, another observer once
saw a stylonychia achieve a partial triumph. It un-
derwent fission and one of the daughters escaped!
Dendrosoma is a branching suctorian that has been
found on many aquatic plants, rotifers, bryozoans,

and crayfishes in fresh waters. When suctorians di-
vide asexually they may split into two equal daugh-
ters or may bud off small individuals that swim about
by cilia, then settle down, lose the cilia, and grow to
full size. The process of sexual reproduction involves
conjugation.

CHAPTER II

The Sponges
(Phylum Porifera)

See are more widely known from their
cleaned and dried skeletons than they are as living
creatures that flourish in all the seas of the world or
encrust rocks and sticks in fresh waters. Familiarity
with sponges through enjoying the luxury of a fine
soft Mediterranean bath sponge or scrubbing a wall
with a sturdy but elastic sheepswool sponge from
Florida waters is hardly good preparation for recog-
nizing such animals in the flesh. Peering over the
edge of a boat in twenty feet of water, one sees on
the clear, sunlit bottom an ugly black ball, somewhat
larger than a grapefruit and with an uneven bumpy
surface. If there is someone aboard who can manipu-
late a twenty-five-foot pole without being pulled
overside, it becomes a simple matter to hook onto
the sponge with the curved metal prongs that pro-
trude from the far end of the pole and to pull the
living animal from its firm mooring on the sea bot-
tom, delivering it wet and glistening into the boat.
Now it is seen to have a number of large openings
through the jet-black leathery membrane that coy-
ers the surface. And if the sponge is sliced open the
halves reveal cut surfaces that look like nothing so
much as raw, slimy, dark-brown beef liver. What
superficially resemble bile ducts are tangential sec-
tions of the main channels through which water is
ejected out the large openings noted at the top of the
sponge. Not apparent except on very close examina-

56]

Limy and glass sponges

tion are the millions of microscopic pores that pierce
the whole of the outer surface and through which
water is sucked into the sponge when it is on the sea
bottom and feeding by straining microscopic plants
and animals out of the water. The steady stream that
passes through the body into the many small pores
and out the few large vents at the top also serves to
bring oxygen to the internal cells of the sponge and
to carry away their wastes.

The volume of water filtered by a good-sized
sponge is tremendous. One estimate set the rate of
active flow for a Bahaman wool sponge at about two
quarts a minute, and perhaps several hundred gal-
lons in twenty-four hours. To add one ounce to the
weight of a growing sponge, as much as a ton of wa-
ter may have to be filtered. The rate of flow can be
diminished or stepped up, depending upon the condi-
tion of the water, by contraction of the vents or by
opening them wide. The surface pores are less re-
sponsive than the vents and usually close only under
injurious conditions.

The external pores, for which the phylum of
sponges has been named the Porifera or “pore bear-
ers,” are represented in the dried bath sponge only
by the few large vents, the small apertures having
been stripped away with the removal of the flesh.
And the extraordinary porosity of the skeletal net-
work represents only the remnants of the complex

system of internal channels and feeding chambers,
for the bleaching of the skeleton has destroyed all
the delicate fibers that supported the actual canals.
In the simplest sponges the feeding cells completely
line one vase-shaped internal cavity, while in com-
plex sponges like the bath sponge they are restricted
to innumerable little special feeding chambers inter-
posed between the incurrent channels and the excur-
rent ones. In either case the cells that trap the food
particles as they go by are also the cells that produce
the food-bearing currents. These important and al-
most unique cells are called “collar cells” because
they have, at the free end that projects into the
cavity of the chamber, a single long, hairlike fla-
gellum surrounded at its base by an erect and deli-
cate protoplasmic collar. Food particles brought to
the cell by the beating of the flagellum adhere to the
sticky collar and slide down its outer surface to be
engulfed by the cell. The many collar cells all feed
quite independently, so that a sponge cannot digest
any particle too large to be taken into a single cell.
No matter how massive the sponge, its diet is re-
stricted to minute organic particles, bacteria, micro-
scopic algae, the smaller protozoans, and the many
eggs and other single sex cells set free in the water
by various plants and animals.

Sponges constitute the simplest of the well-defined
groups of many-celled animals, and the only one in

which the largest opening into the body is not a
mouth and the feeding machinery has entrances that
are less conspicuous than the exits. They are also
alone among many-celled forms in having collar
cells, though there are collared flagellates among the
protozoans. For these reasons, and others besides,
the phylum Porifera is removed from the ranks of
the Metazoa (p. 15) and set aside in a separate sub-
kingdom of animals, the Parazoa.

In quiet shallow seas one can sometimes detect a
“boiling” of the water where the outgoing current is-
sues in a jet from a large sponge. If the edge of a
vent is struck sharply, it may be seen to close slowly,
perhaps almost imperceptibly. There may even be,
in some sponges, contraction of the whole body; and
the early naturalists noted that these curious growths
did “sometimes seem to shrink from the hand that
tried to seize them.” For the most part, though, the
ceaseless inner turmoil of the steadily pumping
sponge is masked by the deceptively quiet exterior.
And to the casual observer sponges are as unrespon-
sive as the rocks to which they grow firmly affixed.
During various periods in the past, sponges were
classed as plants, as plant-animals, and even as non-
living secretions produced by the great variety of
animals that take shelter in the numerous cavities of
a sponge. Not until the middle of the nineteenth cen-
tury were sponges finally assured of an unquestioned

Living horny sponge, Hippospongia, sliced in half on being brought up from the bottom off
Batabano, Cuba. This is a commercial species; after the living tissue has been removed the
horny skeleton is used for washing walls and automobiles. (Ralph Buchsbaum)

right to stand in the ranks of animals. This was after
the last skeptics had been satisfied that sponges could
feed like any animal without having to move about
to gather their food. “The poor creatures,” wrote one
naturalist, “receive their nourishment from the wave
that washes past them; they inhale and respire the
bitter water all their lives.”” He could have saved his
sympathy, because sponges were enjoying great
prosperity at least half a billion years before man
appeared on the scene. Vaselike fossil glass sponges
and masses of fossil glass needles from the support-
ing framework of such sponges are found in the ear-
liest fossil-bearing rocks we know.

An elaborate skeletal framework permeating the
entire body is very important to an animal in which
gelatinous material holds together loosely organized
masses of delicate cells which must be firmly sup-
ported to keep the extensive network of canals and
chambers from collapsing and so interfering with the
vital circulation. Yet every group has its exceptions,
and there are a few sponges without skeletons. The
soft elastic framework of the bath sponge and its rel-
atives makes these few aberrant forms useful to us,
but such support without hard particles in addition
is rare among all the thousands of kinds of sponges.
Most are much too hard and scratchy, too brittle or
friable, whether alive, dead, or skeletonized, to be of
much use to man. Their bodies are usually thor-
oughly permeated with microscopic hard particles, or
spicules, which either are simple needles or have a
number of rays in a variety of configurations. In one
class the spicules are calcareous, or chalky, but in
most sponges the spicules are siliceous and like mi-
nute splinters of glass. If a fibrous network is present,
it is usually combined with hard spicules. Those
sponges in which long spicules protrude from the
surface are quite bristly. As if to make doubly sure
that no animal will be attracted to their flesh, many
sponges have noxious odors. Little wonder, then, that
sponges have so few enemies and that the bodies of
the less compact forms give shelter to many hundreds
of kinds of invertebrates, especially crustaceans and
worms, and even to fishes. Among the few animals
definitely known to feed on sponges are certain sea
slugs (nudibranchs), limpets, and periwinkles—all
of them mollusks. But perhaps there are others.

The known number of sponge species has been
estimated as high as 4500, but of these only about
150 species, all members of the family Spongillidae,
live in fresh waters. The rest are marine, and these
grow most abundantly in warm shallow seas but are
widely distributed also in temperate and cold waters
and at all depths. During the Galathea expedition
sponges were recorded from the sea bottom at nearly
21,000 feet below the surface. Fibrous sponges pre-
dominate in shallow tropical waters but give way to
calcareous and siliceous sponges in cold water. The

58]

glass sponges (p. 60) are deep-water forms. The
favored substrate is rocky or hard bottom along the
seashores or in coral-reef lagoons, though some
sponges are found encrusting pilings, shells, or even
the backs of certain crabs (Plate 2). A few forms lie
free at the bottom, but all the rest are firmly secured
in some way, either fastened to a solid object or on
muddy bottom anchored by a long tuft of glassy
spicules. An occasional hardy species, like Terilla
mutabilis, which lives in the mud flats of estuaries
in southern California, can somehow manage to sur-
vive the temperature changes, pollution, and sus-
pended sediments of such a habitat. But sponges as
a group are especially vulnerable to suspended par-
ticles that could clog their labyrinthine channels; and
they grow best in very clear waters, thriving on mud
bottoms only in deep or very quiet waters where the
mud is seldom or never in suspension.

The sizes and shapes of sponges vary from minute
urns only a fraction of an inch long to erect vaselike
or branching types 5 or 6 feet tall, or broad, squat,
irregular or rounded masses big enough for several
people to sit on. The simpler and smaller sponges are
often radially symmetrical cylinders or vases, fas-
tened at the lower end, with a single large opening
at the top. But most sponges are colonial and have no
special symmetry. They continue to spread out in-
definitely in a plantlike manner and with little indi-
viduality. If a single vent with its contributory chan-
nels represents an individual in the diffuse colony,
then it is difficult indeed to tell where one individual
stops and the next one begins. Over long periods
sponge colonies do change their patterns on rocks,
almost as if they were moving about, by a constant
reorganization of the cells around the periphery. As
they meet other colonies of the same species they co-
alesce. The most common shapes are irregularly mas-
sive, encrusting, or branching, and the many large
excurrent openings may be on the tips of branches or
elevated cones, or sunk into craters. The same species
may grow erect branches in quiet waters and cling
matlike, molded to the substrate, where the surf is
strong. In fresh waters and on temperate rocky
shores encrusting sponges are most common. After
a storm a beach may be strewn with decaying sponge
fragments torn from the rocks, or with sponge-cov-
ered mollusk shells hurled in from offshore bottoms.
On a beach in Panama we once saw hundreds of
empty scallop shells cast up by a storm, and every
one bore a finger-like sponge several inches tall. The
finger-like, vaselike, and fanlike sponges are charac-
teristic of warm, quiet seas or of the deep ocean bot-
tom. In such quiet-water habitats many sponges
have fairly regular growth forms, and in more elegant
times than ours they were given common names like
the fan, the trumpet, the bell, the lyre, the peacock’s
tail, Neptune’s goblet, the sailor’s nest, the feather,

the mermaid’s glove, the elephant’s ear (p. 64),
and Venus’ flower basket (p. 61). Sponge colora-
tion is extremely variable, even in the same species.
Deep-water forms are likely to be drab grays or
browns, sometimes white; but in shallow waters many
of the encrusting sponges tend to take on brilliant
hues: sulphur yellow, bright pink, scarlet, deep reds,
all shades of purple, and beautiful greens. Both ma-
rine and fresh-water sponges often harbor algal cells,
and a fresh-water species that appears green in full
sunlight is colorless on the underside of the same
rock. The horny sponges of commerce shade from
light browns to jet black.

All sponges are capable of sexual reproduction,
and though most produce eggs and sperms in the
same body, they do so at different times, so that
cross-fertilization occurs. The small motile sperms
enter other sponges with the ingoing current, and the
food-laden fertilized egg develops into a tiny flagel-
lated larva that leaves with the outgoing jet. After
swimming about for some time the larva attaches
and grows into a young sponge. This serves to dis-
tribute the wholly sedentary sponges to new habitats
and gives the young an opportunity to move over a
bit before setting up shop in competition with their
parents and relatives.

Animals as loosely put together as the sponges can
be expected to have exceptional capacity for asexual
reproduction and for the regeneration of injured or
lost parts. Any part of a sponge can grow into a
whole animal, though the process is slow and the at-
tempts to raise commercial sponges from small pieces
have met with only limited success (p. 66). When
sponges with very high regenerative powers are
squeezed through silk bolting cloth, the separated
cells come together in small clumps, then in some-
what larger masses, and finally grow into complete
sponges. All fresh-water sponges, and some marine
ones too, regularly produce asexual reproductive
bodies, called gemmules (p. 64). When conditions
of life become unfavorable many sponges constrict
off the tips of their branches or simply disintegrate
and leave behind little masses of cells. These round
up, remain dormant for a while, and with the return
of better times regenerate into new sponges. Small
sponges may not outlast a single year, but it is hard
to believe that some of the largest sponges can attain
their magnificent size without continuous growth over
twenty-five or even fifty years or longer.

Most zoologists are repelled by the prospect of try-
ing to identify sponges that fit their shape to the sub-
strate on which they grow, vary in size according to
the local prosperity of a spot they attached to when
still a larva, and vary in color for reasons that are not
always clear. Rare sponges dredged from deep wa-
ters are often easier to identify superficially than are
the compact encrusting types found between tide

marks. Sponge specialists have resolved the problem
by basing the identification of species mainly on the
chemical composition and geometrical configuration
of the skeletal parts, which are consistent, highly dis-
tinctive, and readily preserved. It is relatively easy
to set aside two of the classes: the simpler and mostly
smaller forms, the calcareous sponges, and those sili-
ceous sponges that we call glass sponges. All those
siliceous and horny sponges left over are put into a
third and much the largest class, which is less homo-
geneous and which has been divided up in somewhat
different ways by the various specialists. The names
of even the largest groupings are not yet stabilized.

The Calcareous Sponges
(Class Calcarea)

The calcareous sponges, as biologists call them—
or the chalky or limy sponges, as they are popularly
named on English-speaking shores—have spicules
that are largely of crystalline calcium carbonate.
They are all small marine sponges, ranging in length
from about ’% of an inch to 5 inches at most. Usu-
ally white or of drab color, these inconspicuous little
vases or tubes, often of bristly texture, grow singly,
in clusters, or as branches of a bushy or compacted
colony. Some of the genera are widely distributed
about the world in shallow waters, except where the
salt content is too markedly lowered by admixture
of fresh water.

Whether or not a sponge has spicules of calcareous
content can easily be determined by teasing apart a
bit of sponge on a microscope slide, adding a drop of
acid, and watching through the eyepiece to see if
the spicules dissolve with the effervescence of carbon
dioxide released from calcium carbonate.

Around the opening or vent at the top the cylin-
drical body is constricted a little, and often bears an
erect fringe of especially long needle-like spicules.
On the body, however, the most common type of
spicule is three-rayed, with the rays at equal angles,
T-shaped, or Y-shaped. Three-rayed and less nu-
merous four-rayed spicules are distributed through-
out in such a way as to strengthen and support the
fragile structure of nonliving gelatinous matrix and
delicate living cells. The surface may be strength-
ened by a special layer of spicules or by a parallel
arrangement of the rays of many body spicules. Of-
ten long, hairlike spicules protrude through the body
surface, giving it a hairy or bristly texture.

The simplest of shore sponges belong mostly to the
genus Leucosolenia, a name that means “white
pipes.” But these sponges are so small and incon-
spicuous that they have never attracted much atten-
tion from fishermen and others who bestow common

[59

A cluster of calcareous sponges, pulled from their
attachment on wharf piling. Three vaselike ones at
left are Sycon coronatum, about 1 inch long. Much-
branched mass at right is Leucosolenia complicata.

(England. D. P. Wilson)

names. Widely distributed on rocky shores near low-
tide mark, they favor well-aerated spots where the
water is in motion without being really surfy. Leuco-
solenia grows only in colonies of little vertical tubes
connected by horizontal tubes or by a complex net-
work of branching tubes. An upright branch encloses
a single cavity, completely lined with flagellated, col-
lared feeding cells, and opening at the top by a single
vent. The colonies spread in tide pools or over the
underside of stones as small fungus-like patches
about 42 of an inch high. Or they hang as bushy
growths, which have been compared to miniature
bunches of bananas, from wooden wharf pilings or
from the stems of the brown seaweed Fucus. One

60 |

species, in which the tubes are compacted into an
encrusting meshwork of twisted tubes, may be yel-
lowish, pink, red, brown, or bluish gray. The colonies
are somewhat stiff, because the fragile structure of
nonliving gelatinous matrix and delicate living cells
is strengthened and supported throughout by both
scattered and interlacing spicules.

The urn sponge, Sycon, is also called the crowned
sponge, because the fringe of giant needles that rims
the constricted opening at the top of the urn looks
like a little crown. In one species from deeper wa-
ters the fringe is as long as the body itself. Crowned
sponges have a more complex internal structure than
do the little sacs of the Leucosolenia colony, but ex-
ternally most species display a simpler growth form.
The single cylindrical individuals, dull gray or yel-
lowish, and usually about 1 inch in length, spring in
small clusters from a single attachment. These are
widely distributed, but they are best known on north-
ern Atlantic shores. A colonial species with finger-
like branches is an inhabitant of southern seas. They
flourish where wave action is not too strong, and at
low tide can be seen in tide pools, under stones, and
hanging from wharf pilings or from the brown sea-
weed Fucus or the green eelgrass Zostera.

The purse sponge, Grantia, is named for R. E.
Grant, who first really understood the structure and
workings of sponges, gave them their phylum name,
and cleared up the uncertainties about their status as
animals. Now his work is recalled whenever we refer
to the light gray or creamy white sponges that hang

“as little bags with the somewhat compressed opening

down, and when the tide is out collapse to flattened
purses. So abundant on certain English beaches as to
occur by the tens of thousands in a few hundred
yards, they hang in rocky crevices, or among the
delicate red algae that droop from rock overhangs,
or from the blades of eelgrass. Each is usually about
1 inch long; but D. P. Wilson, writing of Grantia
compressa in They Live in the Sea, says that in Eng-
lish harbors where food is plentiful and wave action
subdued the flattened sponges may be almost as
large as one’s hand. They are rarely the neat little
bags drawn in books, but are much folded and
twisted upon themselves. The manner in which they
split along these folds, dropping fragments that at-
tach and grow into new sponges, has been vividly
described by Maurice Burton in Margins of the Sea.

The Glass Sponges
(Class Hexactinellida)
The possession of six-rayed spicules distinguishes

the glass sponges from all others. Composed chiefly
of silicon dioxide, the spicules show a variety and

complexity far beyond anything seen in calcareous
sponges. The rays may be covered with spines, their
tips branched like brushes or feather dusters, or ex-
panded into umbrellas or recurved anchors. They oc-
cur as separate particles, and in most members of
this class are also hooked together into loose skeletal
networks or firmly fused into rigid lattices of open
structure that support delicate cellular complexes.

Most glass sponges are radially symmetrical and
grow as solitary cylinders, vases, cups, or funnels,
drab or white in color. Some are branching or have
the branches fused into latticework. They are of mod-
erate size, from 4 to 12 inches, but there are species
3 feet long; and a form like Monoraphis is much
longer if we count its tremendously extended anchor
(6 to 9 feet long and almost 1 of an inch thick).

The beachcomber will find no glass sponges. They
are all deep-water forms, reaching their peak of
abundance on bottoms three thousand feet or more
below the surface, and then tapering off in numbers
as they extend down into the great abyssal regions of
the oceans. The glass sponges are among the finest
rewards of dredging in the great deeps off the West
Indies, the Philippines, the Molucca Islands, and Ja-
pan. N. B. Marshall, in Aspects of Deep Sea Biology,
quotes from Alcock’s recollection of trawling in the
Indian Ocean: “As the trawbag came clear of the
sea, it seemed at first sight as if it had fouled a sunken
haystack, for there stuck out on all sides things that
looked like bundles of hay, with here and there a
bird’s nest attached, which on closer inspection
turned out to be great Hexactinellid sponges.” In the
deep waters to the west of the European coasts Le-
Danois has found the cup-shaped Asconema and the
vaselike Pheronema to be quite common, as are also
species of the glass rope sponge Hyalonema. The
name means “glassy thread,” but the dried skeleton
of a Hyalonema is better described as looking like
an upturned bell-shaped wad of glass wool with a
long, opalescent handle of spirally twisted spun-glass
fibers. The tuft is a bundle of greatly elongated
spicules that end in recurved hooks; and it splays out
at the end, anchoring the living sponge firmly in the
soft ocean floor. At its upper end this column of fi-
bers protrudes into the body of the sponge and may
even push up the perforated exhalant surface into a
projecting cone, eliminating any sort of cavity in the
upturned bell. Off the New England coast a species
of Hyalonema is found in only thirty to forty-five
feet of water, but even such forms have been, in the
past at least, inaccessible as living sponges to anyone
who could not manage to be on deck when a glass
sponge was dredged up. To most professional zoolo-
gists, glass sponges are known only from preserved
specimens or dried skeletons.

The unvarying climate and the slow, continuous
current of deep waters are usually called upon to ex-

The beautiful skeletons of Venus’ flower basket,
Euplectella, are all that most of us ever see of glass
sponges. (American Museum of Natural History )

plain the adaptations of glass sponges, and especially
of such a form as Venus’ flower basket, or Euplec-
tella, which is brought up from depths of fifteen hun-
dred to fifteen thousand feet off islands in the western
Pacific, especially the Philippines and Japan. As dis-
played in the showcases of museums, the elegant skel-
eton of Euplectella is a foot-long curved tube of glis-
tening siliceous open latticework. Strengthening the
upper end is a perforated convex sieve plate; and
bearding the lower end is a tuft of fibers that root the
living sponge. From top to bottom the tubular lattice
is wreathed with projecting ledges of fused siliceous
spicules that strengthen the framework and add to its
rigidity as well as to its loveliness. Within the closed
cylinder there usually is to be found a pair of

[61

shrimps, male and female (of the genus Spongicola).
These enter when very minute and then cannot es-
cape because of the sieve plate over the exhalant
opening. Such a glass sponge, with its pair of im-
prisoned dried shrimps, was long used in Japan as a
wedding gift symbolizing the wish that the marriage
would see the happy couple “together unto old age
and into the same grave.”

The Siliceous and Horny
Sponges

There is more than one way to gain admission to
this big and heterogeneous class, which includes four-
fifths of all sponges. Members may have skeletons of
siliceous spicules alone, of horny fibers alone, or of a
combination of the two. A few genera without any
skeleton at all have been slipped in, but they have
the complex internal channels and the multiple,
small, round, flagellated feeding chambers character-
istic of the Demospongiae.

Sponges with skeletons composed entirely of sili-
ceous spicules, or those which have in addition to
such spicules a framework of fibers, are referred to
as siliceous sponges (Plate 3). The ones with both

(Class Demospongiae )

Fresh-water sponge, Spongilla, common in both run-
ning and standing waters. It may occur in either
branching or encrusting form. (Vermont. William H.
Amos )

spicules and fibers are the most numerous of all
sponges. Those entirely devoid of spicules and sup-
ported by horny framework alone are called horny
sponges. In either case the horny fibers are composed
of spongin, a protein secretion chemically related to
the connective-tissue fibers of human skin. The
spongin is often impregnated with rock fragments
and other minute foreign particles, so that most horny
sponges are not soft enough to be of commercial use.

The siliceous sponges are divided into two main
groupings. The Tetractinellida have no spongin but
have four-rayed spicules. They are small to moder-
ately sized, drably colored, rounded sponges which
attract little attention. Among them is Tetilla, men-
tioned earlier. In the second grouping, the Monax-
onida, members may or may not have spongin but
they have one-rayed, needle-like spicules. Here are
found most of the common and abundant marine
sponges of shores and shallow waters, and the whole
of the relatively small fresh-water fauna. A few ma-
rine monaxid sponges grow in deeper waters, some
even at fifteen to eighteen thousand feet.

Among the monaxids are the largest of all sponges.
Neptune’s goblet, Poterion, and the cake-shaped log-
gerhead sponge, Spheciospongia, of the Gulf of Mex-
ico, may be 2 to 6 feet tall or broad. In the cavities
of one large (185,000 cu. cm.) loggerhead sponge
at Tortugas, Florida, A. S. Pearse once found more
than seventeen thousand animals, about sixteen thou-
sand of them shrimps of the genus Synalpheus.

The breadcrumb sponge, Halichondria panicea,
(Plate 1) is a cosmopolitan species, especially abun-
dant on all English and other northern European
shores and on the New England coast north to the
Arctic Ocean, but somewhat spottier in occurrence
on the American Pacific coast. It is reported also from
places as far apart as Alaska, Ceylon, and Nova
Zembla. Usually greenish in color, but also yellowish
or orange, patches of different color may grow side
by side. The fairly smooth surface is patterned with
more or less regularly spaced miniature “volcanoes”
through which the spent water issues. The colony
grows as an encrusting sheet in rocky clefts, under
rock overhangs, and under masses of brown sea-
weeds—in almost any firm spot that will not be ex-
posed for long to the sun when the tide is out. In
deeper water the sponge grows more massive, with
higher, more slender “volcanoes.” On the American
Pacific coast it often encrusts beds of California
mussels and gooseneck barnacles, along with the
violet-colored Haliclona, which is common on some
Australian shores. Also splashing color across shaded
rocks on both sides of the Atlantic and on the Pacific
coast are thin, shiny, brick-red or coral-red blotches
of Ophlitaspongia (Plate 47). Usually more orange-
red are patches of Hymeniacidon, with a rough sur-
face that is puckered with grooves. On Atlantic

beaches the red species is very abundant; the Ameri-
can Pacific coast species is yellow-green and grows
in quieter waters, often on oyster shells. Encrusting
practically all scallop shells in Puget Sound are yel-
lowish brown growths of Ectyodoryx parasitica, less
often of Mycale adherens. North of Puget Sound and
into Alaska, mollusk shells, especially those of the
rock oyster or jingle shell, may be honeycombed to
the crumbling point with the tunnels of the yellow
boring sponge, Cliona celata, a cosmopolitan species.
Farther south, as in Monterey Bay, it bores in abalone
shells but is not so generally widespread. In the Gulf
of California Ricketts saw it growing, beyond tidal

range, in its nonboring, massive form as reddish pink
vases several feet in diameter. On the American east
coast it is well known from South Carolina north-
ward; and it is common in European waters. The yel-
low massive form with wartlike vents occurs off-
shore; the boring type tunnels in limestone pebbles
and shells in shallow water. The activities of Cliona
are important in disintegrating the empty shells that
accumulate on the sea bottom, but we appreciate
them less when the sponge weakens the shells of edi-
ble clams or scallops and becomes a pest in oyster
beds by making oysters more vulnerable to their
many enemies.

Finger sponge, with both spicules and horny matrix, from San Francisco Bay. Two tiny hermit
crabs explore its surface. (Woody Williams)

Horny skeleton of the elephant’s-ear sponge, from the
Mediterranean, a fine-textured commercial sponge
valued by potters. (Ralph Buchsbaum)

The family Clionidae has other well-known borers,
some of them busy in coral reefs. Most are sulphur
yellow, a few green or purple. Some members of the
family Suberitidae encrust the snail shells inhabited
by various hermit crabs, and certain species are
never found except on such shells, growing until they
completely enclose the shell. When the shell disap-
pears the crab continues to occupy the spiral cavity
formed by the sponge, and it is presumed that both
members benefit, the sponge by being carried about
during its feeding, the crab by protection from preda-
tors (Plate 2).

The redbeard sponge, Microciona, is a bright red
colony that grows as a low incrustation or, in deeper
waters, as an erect mass of red branches perhaps 6
inches high. It is well known from South Carolina to
Cape Cod, and has been much used in experiments
on the dissociation and reintegration of sponge cells.
A different species occurs in European waters.

The family Spongillidae comprises all of the fresh-
water sponges. It consists of about 150 species, of
which about 30 are known from ponds, lakes, and
slow streams in the United States. Typically, they
form inconspicuous matlike incrustations on rocks,
logs, sticks, or leaves in the water, but they may also

64 |

be lobed or branched. Most of the species that grow
on the upper side of objects are greenish from the
algal ce!ls that they contain, but those on the under-
sides of rocks or in fairly deep water have no chloro-
phyll to mask their lack of color or their drab shades
of tan, brown, or gray. Some species are not green
even when growing in light. The colonies spread as
small, thin patches perhaps an inch or two square,
but in the best spots may be more than | inch thick
and cover 40 square yards. They are most abundant
in clear, quiet waters less than six feet deep, but
some species tolerate deep water, or running water,
or a small amount of pollution. Sexual reproduc-
tion occurs during the summer growing season; and
in addition, fresh-water sponges characteristically
produce asexual bodies, the gemmules, which lie dor-
mant all winter and hatch into new sponges in the
spring. They are easily seen in the fall as small balls
of cells coated with a protective layer of anchor-
shaped spicules. No predator is known to feed on
fresh-water sponges, but the larvae of Spongilla flies
(insects of the family Sisyridae) pierce the sponge
cells and suck out their contents. Fresh-water sponges
are of no economic importance except when they oc-
casionally block water conduits or reservoir drains.
The decay of sponges may give water what is known
as “swamp taste.” An excellent account of American
forms may be found in Pennak’s Fresh-water In-
vertebrates of the United States.

The horny sponges, the Keratosa, are typically
shallow-water forms of tropical or subtropical seas,
but some species extend even into polar waters.
Though they all lack sharp spicules, the spongin fi-
bers are usually impregnated with hard foreign ma-
terials, and only a dozen or so species are soft enough
for commercial use.

The best commercial sponges were for centuries
brought up by divers from the shores of the Mediter-
ranean, so it is not surprising that the earliest uses of
sponges known to us were among the ancient Greeks,
and that in Greek mythology Glaucus of Anthedon
was a sponge diver. In the Odyssey, before a dinner
party for Ulysses, the maids were instructed to wipe
off the tables with sponges. When Ulysses had fin-
ished with his wife’s suitors, sponges were used to
mop the blood from the floor. While Greek mothers
sponged their houses clean and Greek fathers went
off to the wars with sponge padding in their helmets
and leg armor, Greek babies were bathed with
sponges and pacified with bits of sponge dipped in
honey. In Roman times sponges were used also as
paintbrushes and were carried by soldiers as a sub-
stitute for a drinking cup, so it is understandable that
Christ on the cross should have been offered vinegar
in a soaked sponge. Today the sponge in the bath-
room is more likely to be a marvel of modern
chemistry, because overfishing of sponge grounds, in

Reef scene at Nassau. Many sea whips in foreground, two sea fans near center,
and lobed masses of the coral Montastrea annularis dominating background
(Fritz Goro: Life Magazine )

mee Nyt
az oe. ‘Sa

ag. a

a world in which people are multiplying faster than
sponges, has made sponges more and more difficult
to collect. Men must now use special diving equip-
ment and go farther and farther from shore, so the
price has risen accordingly. The more exacting pro-
fessional users continue to buy the finest Mediter-
ranean sponges for surgical and hygienical prepara-
tions, for dressing leather, for applying glaze to pot-
tery, and for scouring and sponging cloth. Fine
sponges are also used by jewelers, silversmiths, and
lithographers. The great bulk of commercial sponges
like the sheepswool, which are used for cleaning
walls and automobiles and railroad cars, have in our
century come mostly from the Gulf of Mexico and
from the Caribbean grounds. Some sponge fishing is
done in the Philippines, but it is of minor importance
in the world market. An excellent and accessible ac-
count of commercial sponge fishing and sponge prep-
aration, with a list of the chief commercial species
and the areas from which they come, is P. Galtsoff’s
article in the Encyclopaedia Britannica.

The last “normal” year for sponge fishing was
1938, when more than two million tons of sponges
were harvested, about 30 per cent of them from the
United States fisheries in the Gulf of Mexico. In that
year a disease struck at the 180,000 cultivated

66]

sponges that were being grown from sponge cuttings
fastened down in artificial beds at Water Cay in the
Bahamas. From there the disease rapidly spread to
the natural beds of Cuba, northwest Florida, and
British Honduras, where 700,000 sponge cuttings
were killed. When the authors visited a Cuban fish-
ery in June of 1939 the local fleet of sponge-fishing
boats was tied up in the harbor, and the townspeople
were desperately anxious for someone to minister to
their dying source of livelihood. One old man brought
us a sick sponge in a bucket of sea water and handed
it over as tenderly as if it were an ailing child. When
we went out with several fishermen to hook a few
sponges from the sea bottom, we had difficulty in
finding a healthy one. The disease was finally diag-
nosed by biologists as being due to a fungus, though
some doubts remained. Useless sponges like the log-
gerhead were unaffected, but the valuable commer-
cial species were all but wiped out. After reaching a
mortality as high as 95 per cent in the worst areas, the
disease began to subside. But the damage to the in-
dustry was long-lasting. Synthetic sponge competi-
tion was encouraged, and rising costs in overfished
beds did the rest. In recent years sponge production
in the United States has been as low as 6 per cent
of the 1936 value.

CHAPTER III

Hydroids (at left) and jellyfish

Hydroids, Jellyfishes, Sea Anemones,

‘Roper symmetrical, often gorgeously col-
ored, and festooned with one or more circlets of
graceful tentacles, coelenterates are indeed the “‘flow-
ers of the animal kingdom,” but they are animals
nevertheless, and carnivorous at that. Their elegant
symmetry is an effective design for snaring prey from
any direction and passing it on to a centrally placed
mouth.

Fleshy sea anemones hang tentacles downward
in rocky grottoes or hold their delicate petaled disks
upright in tide pools or on shaded rocks. Their coral
allies rise, like minute anemones, from rigid cups of
limestone, either singly or in massive colonies that in
tropical waters form huge reefs. Feathery sprays of
delicately colored hydroids soften rocky crevices and
tide pools or are seen as bedraggled brown plumes in
the beach flotsam.

In warm temperate waters the sea floor below
low-tide mark is a colorful garden of foot-high sea
fans, sea whips, and sea feathers, displaying plume-
like or latticed branches of vivid reds, pinks, yel-
lows, and purples. Soft corals thrust up spongy lobes
like ghostly hands, and a little farther out the lovely
sea pens anchor by their fleshy quills in the sand or
mud. The deeper waters are a fairyland of tall and
flexible gorgonians that sway with the currents.
Through every opening and into every crevice of
these coelenterate thickets dart fishes and inverte-
brates of all kinds, seeking food and taking shelter
as do the animals in our woods. In the water above,
jellyfishes pulse gently about or drift with the cur-

and Corals

(Phylum Coelenterata or Cnidaria)

rents as minute little saucers or frighteningly large
bowls of jelly.

At night the sea is lighted with new splendor by
the many coelenterates that luminesce when stimu-
lated. Millions of small jellyfishes flash with every
wave, making the dark water sparkle. Now the sub-
marine gardens reveal themselves as softly lighted,
scintillating pathways that fade and then sparkle
anew as the sea pens and other sessile coelenterates
react to the touch of wandering fishes and bottom
creatures.

Of more than nine thousand species of coelenter-
ates, only a few small members, all belonging to the
most primitive class, the Hydrozoa, have managed to
invade fresh waters. These include the little hydras
of ponds and streams, an uncommon hydroid, a tiny
parasite in the eggs of the sturgeon, and two small
jellyfishes that turn up sporadically. Some hydroids
and sea anemones penetrate into brackish waters,
where sea water is diluted by fresh, but the coelen-
terates as a group, and the reef corals in particular,
flourish only in fully marine habitats and are notice-
ably absent near the mouths of rivers.

The great banks of reef-forming corals, and the
luxuriant growth of other coelenterates that live on
these reefs, are not found outside the tropics and
subtropics. Yet many coelenterates, and even cer-
tain kinds of tall branching corals, are so abundant
in temperate and cold waters that one can hardly
think of this as a warm-water phylum.

Beyond the depths to which the aqualung or diy-

[ 67

ing suits can take us, coelenterates are very much at
home, even in the deepest trenches of the ocean floor.
There they have been reached only by the instru-
ments and dredges, and at lesser depths also by the
cameras, of specially equipped oceanographic ex-
peditions. The matchless English Challenger expedi-
tion (1872-1876) and the superbly equipped Dan-
ish Galathea expedition (1950-1952) dredged
many lovely and bizarre coelenterates that were still
alive and often still able to luminesce even after
rough upward trips from fifteen thousand feet or
more.

All of the attached and cylindrical coelenterates,
whether they be large fleshy anemones or minute and
glassily transparent members of a hydroid or coral
colony, are called polyps, from. the French word
poulpe, for octopus. The term goes back to the Greek
for “many-footed,” and refers to the agile tentacles
that capture and pass food to the mouth, but in a few
species can be used for moving about. In the jelly-
fishes the tentacles have been pushed out, by a
spreading of the body, to the rim of the umbrella.
Where the handle of an umbrella would be, there
hangs a tube with the mouth at its tip, directed down-
ward, in contrast with the usually upright polyps. In
either group, polyps or jellyfishes, some members
may take up the opposite stance, and this is not sue-
prising, for when we come to examine them closely
we see that the two kinds are built on the same basic
plan and that both fixed polyp and free-swimming
jellyfish types may occur as stages in the life history
of a single species. In both, the body is a sac with
only one opening, which doubles as entrance for
food and as exit for indigestible residues and body
wastes. The main body cavity (“coel”) is the in-
testine (“enteron’”’), and the saclike digestive cay-
ity, or coelenteron, lends its name to the animals de-
scribed in this chapter.

The digestive lining secretes juices that break
down the food into a thick broth and the fluid food
then circulates about the whole animal, or through
branches to other members of a colony. Some cells
lining the cavity engulf the small particles protozoan-
fashion, and complete the digestion of what appears
to be in most cases wholly animal food.

The phylum Coelenterata at one time included
the sponges and the comb jellies. Then it was real-
ized that the main cavity of sponges is a water pas-
sage, not a digestive cavity, and the sponges were
removed. The coelenterates and the comb jellies still
share the same phylum in many books, for they
have the coelenteron in common. But they differ in
several important ways, notably in the absence in
comb jellies of the microscopic thread capsules, or
nematocysts, which are characteristic of coelenter-
ates and which they use to sting and to hold prey.
More will be said of these later. In dividing the coe-

68 |

lenterates from the comb jellies it would be most log-
ical to discard the old phylum name and to call the
group the phylum Cnidaria (cnidos = “thread’”) to
indicate the basis for distinction from the comb jel-
lies, which (with one possible exception) have no
thread capsules. Some leading students of coelenter-
ates have already done this, but the name “coelen-
terate” is so well established and so widely used
that it has seemed best not to change it here.

The outer surface of the coelenterate body is a
protective epithelium, only one cell layer thick, so
that the most fragile coelenterate bodies consist only
of two microscopic layers of cells held together by a
secretion of nonliving jelly. Jellyfishes acquire bulk
and buoyancy by a tremendous increase in the
amount of secreted jelly, and in the more advanced
(scyphozoan) jellyfishes the jelly is invaded by cells
and strengthening fibers. Even more cellular ele-
ments take over the gelatinous layer of sea anem-
ones. Nevertheless, the extraordinary diversity in
external form that we see in coelenterates consists
only of superficial variations on one simple structural
theme.

The phrase “spineless as a jellyfish” is meant to
epitomize the flabby invertebrate way of life, and
the animal it describes has little resemblance to the
firm, muscular, and speedy fish. Zoologists prefer the
name “medusa” for the jellyfish type. It was sug-
gested by a fancied resemblance to the snaky tresses
of the Gorgon Medusa, the mythological maiden
whose hair was turned into serpents that petrified
anyone who looked on them. Small animals are in-
deed paralyzed when they approach or are ap-
proached by coelenterates, for the heavy armature
of stinging thread capsules, especially on the ten-
tacles, makes them highly deserving of their rep-
utation as “the stinging nettles of the sea.” The oval
capsules contain coiled hollow threads that can be
discharged when properly stimulated. There are
many kinds of such capsules in the group as a whole,
and usually more than one kind in a species. Some
are adhesive and used to attach the tentacles in cer-
tain modes of locomotion; others adhere to prey;
still others wind like tiny lassos around the bristles
of small animals and hold them fast. The largest and
most important kind has a thread that penetrates
small prey and injects a paralyzing poison. The dis-
charged threads of the common anemones of tem-
perate seashores have little effect on the relatively
big, horny hands of human beings. At the most, one
senses a sticky feeling as the tentacles adhere to a
probing finger. Likewise many of the commonest
jellyfishes of temperate seas either are quite harm-
less or only slightly annoy swimmers by producing
strong prickling sensations. This is no comfort to
those who tangle with cyaneas in Atlantic waters or
with certain tropical jellyfishes for they are lucky to

come away with no more than painful red welts. The
real danger is pain or cramps so severe as to cause
panic and prevent one from reaching shore, and this
is especially true of encounters with one of the most
dangerous coelenterates of all, the floating colony
called the Portuguese man-of-war.

Isolated instances of the use of stinging capsules
in certain species of flatworms and nudibranch
mollusks have ceased to puzzle zoologists, since it
has been shown that these are always obtained by
feeding on coelenterates and then manipulating the
captured capsules into positions on the surface where
they can be used in the same manner as in the ani-
mals that produced them.

Coelenterates on the whole show little promise as
a direct source of food for man. Sea anemones have
long been eaten in France, Italy, and Greece, and in
some of the Pacific islands. As late as the nineteenth
century they were regularly sold in Mediterranean
markets and brought a good price in Bordeaux. Some
of the green anemones were especially popular, and
after being boiled in sea water were said to acquire a
firm and palatable consistency, excellent with any
sauce. Wrote one early naturalist gourmet, “They
are of an inviting appearance, of a light shivering
texture, and of a soft white and reddish hue. Their
smell is not unlike that of a warm crab or lobster.”
Some cooks prepared anemones as they would oys-
ters, and often served the two together. Dahlia anem-
ones are still eaten on the Continent but in England
they are used only as bait with long fishing lines.

Certain jellyfishes are regularly eaten in Korea,
Japan, and China. When these turn up in large shoals
they are dried and cut into strips, which can be re-
constituted with water whenever desired. The chief
contribution of jellyfishes to the human diet, how-
ever, is indirect and is appreciated only by fisheries
experts. Certain species of jellyfishes, says L. A.
Walford in Living Resources of the Sea, are among
the most valuable marine animals from man’s view-
point because they provide portable shelter for the
young of commercially valuable fishes such as hake,
haddock, cod, horse mackerel, and butterfish. The
young fishes accompany their host in the floating sur-
face plankton, feeding around it within a radius of
several feet and darting quickly to safe harbor be-
neath its spreading umbrella whenever danger threat-
ens. The relationship may even be an essential stage
in the life cycle of some fishes, and the fingerling that
fails to find a jellyfish host within a certain time may
not long survive among the hungry predators of the
sea. This is not to deny that some jellyfishes take a
great toll of the juvenile fish population.

Red corals are fished from Italian and other
Mediterranean coasts, and also in Japan, for manu-
facture into jewelry and various ornaments. Dried
sea fans, sea whips, sea feathers, and especially

“Soe 6 oee oem

A common trachyline jellyfish of shore waters is Goni-
onemus vertens, shown here swimming actively. (Eng-
land. D. P. Wilson)

dried and bleached coral skeletons, all of them highly
decorative, are sold in the same shops that sell many
tons of mollusk shells every year. Even the delicate,
horny skeletons of sheathed hydroids have some
economic value. In England, centering in the Thames
estuary, there is a small “whiteweed industry.” Boats
drag iron rakes over shell-and-sand bottoms, pulling
up feathery colonies of Sertularia argentea, some-
times other species or other genera. The processed
hydroid plumes are dyed green or other colors and
sold for decorative purposes, mainly in the United
States, as “ever living house plants” or as “sea
ferns.”

Parasitism by coelenterates is rare, though even
hydroids can parasitize fish; but the group as a whole
has a notable talent for sitting down uninvited at the
table of other invertebrates, or for living associated
with snails, crabs, and a great variety of other crea-
tures in a relationship which may possibly be of some
benefit to the host as well as to the coelenterate
guest. Playing the role of host, on the other hand, are
the many jellyfishes and large tropical anemones
that shelter fishes, all the large attached coelenterates
that provide a place for myriads of tiny invertebrates
to hang onto in a restless ocean, the coral crevices
that shelter hundreds of kinds of fishes and crabs and
worms, and—most important of all—the widespread
mutualistic ties of coelenterates with green or yel-
lowish brown algal cells. Certain hydras of fresh wa-

[69

ters and many anemones of temperate and cold
marine waters look green from the plantlike cells
that live in their tissues. But in warm shallow seas
such relationships are the rule rather than the excep-
tion. On coral reefs almost all coelenterates, jelly-
fishes included, harbor colored cells; and we believe
that this contributes to their astounding success in
warm waters.

Reproduction is both sexual and abundantly asex-
ual. Like the sponges or any other group that readily
reproduces by asexual means, coelenterates have ex-
traordinary capacity to regenerate lost tentacles or
branches, to grow by budding, or to reproduce by
rupture of the body. Some species can regroup their
cells and grow again even after the tissues have been
dissociated experimentally by being passed through
fine cloth, thus giving us answers to many problems
dealing with the enviable adaptability of tissues less
specialized than our own. When both polyps and
jellyfishes appear in the life cycle, the reproductive
chores are divided between a polyp that reproduces
asexually by budding off medusas, and a medusa
that reproduces sexually by shedding eggs or sperms
into the water. The medusa may be free-swimming,
or it may never be set loose, remaining always at-
tached to the polyp or polyp colony. The fertilized
egg of marine coelenterates develops into a little oval

or elongate free-swimming larva, called a planula,”

which swims about for a time, then settles down, at-
taches to the bottom, and grows into a polyp or,
by budding, into a polyp colony. Many modifications
and short cuts occur in this typical scheme.

Of the three classes of coelenterates, the first or
most primitive one is the Hydrozoa, in which many
species have both polyps and medusas, often equally
developed, in the life history. The Scyphozoa have
minimized or dropped the polyp, staking their for-
tunes on larger and better jellyfishes. The Anthozoa

Feather hydroid, Kirchenpaueria (Plumularia) pin-
nata. About 2 to 3 inches high. (England. D. P.
Wilson)

have gone off in the other direction and have given
up the medusa altogether, the sea anemones per-
fecting a larger and more muscular polyp, the corals
specializing in great skeletal works.

Hydrozoan Polyps and
Jellyfishes

Hydrozoans are named from the resemblance of
their polyps to the little solitary hydras of fresh wa-
ter, but members of this class may also have a me-
dusa stage. We are not always able to match the pol-
yps we find attached on the bottom to the properly
related little gelatinous medusas that swim and feed
at the surface and reproduce sexually. Often polyps
and medusas are separately described and named,
and their relationship as stages of a single life cycle
sometimes emerges only when we happen to see the
medusa released, by an asexual process, from a
polyp confined in an aquarium.

This is an important group, with close to three
thousand species, and almost all are entirely marine;
but it does include those few little polyps and me-
dusas that live in fresh waters. The tentacled polyps
of hydrozoans differ from those of the other classes
in having a simple digestive cavity, undivided by
ridges or partitions. The hydrozoan medusa can usu-
ally be readily told from the true or scyphozoan jel-
lyfishes by its smaller size and by its possession of a
velum, a transparent and muscular circular shelf
that projects inward from the rim of the gelatinous
umbrella (or saucer, or deep bowl, or bell, or what-
ever name best fits the variously shaped medusas).

Hydrozoans are notable in the animal kingdom
for the many shapes that members of a hydroid col-
ony assume. Aside from the division of reproductive
chores between polyps and medusas, the polyps
come in a variety of body forms, each specialized
for its share of the colony housekeeping. Tentacled
feeding polyps and club-shaped reproductive polyps
are a frequent combination, but some colonies have
one or more kinds of mouthless polyps that serve
only for stinging prey or for protection. In other spe-
cies there may be in addition a striking difference
between the reproductive polyps that produce female
medusoid individuals and those that produce male
medusoids, both bearers of sex cells.

THE HYDROIDS

The hydroids are called “sea firs” in England and
sometimes “‘sea plumes” in the United States. These
names indicate the branching patterns of some com-
mon colonial forms, but they are rather misleadingly
grand designations for most hydroids, which are

(Class Hydrozoa)

small and inconspicuous and seldom recognized as
among the most abundant animals of the seashore.
The plumelike colonies that rise to heights of 6 feet
from their moorings on the sea bottom at depths of
three thousand feet, and the equally tall solitary
polyp, Branchiocerianthus, which has been dredged
up from fifteen thousand feet below the surface, are
conversation pieces. The vast majority range from a
fraction of an inch high to several inches, with 8 to
12 inches as the upper extreme; and they are largely
confined to the shores and to shallow waters, where
they form delicate white, pink, violet, or brown tufts
on rocks and wharf pilings, on seaweeds, and on
many animal stalks and shells.

Hydroids are often mistaken for minute seaweeds
because of their plantlike growth forms, though
there the resemblance ends. The “flower heads” of
solitary polyps or those at the free tips of branching
colonies are voracious feeders on minute crustaceans
and worms, eggs and larvae, or even on fishes. Few
things are more beautiful than a microscope field
filled with row upon row of elegantly shaped, glassy
hydroid chalices, each with a circle of graceful trans-
parent tentacles—or more potentially lethal. A small
animal swimming through has as much chance of
making it safely as a ship would have in sailing
through waters so heavily mined that the detonating
devices were almost touching. At the slightest alarm
the outspread tentacles are whisked in with a liveli-
ness that at once betrays their animal nature.

Favored and protected positions are acquired by
hydroids that attach to the branches or stalks of ses-
sile animals like sponges, sea whips, or sea pens—
or that are constantly carried to new pastures on the
shells inhabited by hermit crabs. Many hydroids
share in the host’s feeding currents by fastening to
the outside of mollusk shells or worm tubes near the
water intake. Some even live within the mantle cav-
ity of certain oysters or other bivalves, and in the
sievelike branchial cavity of certain tunicates.

There are two main types of hydroids, divided ac-
cording to the extent of the transparent yet protec-
tive horny covering that the polyp or polyp colony
secretes about itself. Most familiar of the fully
sheathed hydroids is the cosmopolitan genus Obelia,
with species on almost all shores. Some form delicate
little white sprays that rise 1 or 2 inches above the
creeping runners that attach to rocks, seaweeds, mus-
sels, wharf pilings, or floating wood. In shallow wa-
ters below low-tide mark, yellowish species of Obelia
grow 8 to 12 inches long. The various species are
alternately branched or have stems that zigzag, with
tentacled polyps arising at the angles and lodged in
goblet-shaped transparent cups. From the axils
formed by the stalks of these feeding polyps arise
urn-shaped reproductive polyps enclosed in trans-
parent containers of the same shape. At intervals

these bud off little medusas that swim away. Though
they are barely visible to the naked eye, their jerky
pulsations are familiar to those who examine plank-
ton under the microscope. The muscular shelf that
characterizes hydrozoan medusas is aborted during
development, but otherwise the Obelia medusa is
typical of the little flattened saucers allied to the
sheathed hydroids. It has four digestive canals ra-
diating from the central digestive cavity to the rim of
the umbrella, and to these canals are attached the
sex organs.

Besides the campanularian or bell-like hydroids,
to which Obelia belongs, the many kinds of sheathed
hydroids include such widespread families as the
sertularians, in which the cups are not stalked but
are set directly on long, graceful stems that branch
to look mosslike or fernlike. A species of Sertularia
was referred to earlier as the “whiteweed” of a small
industry in England. In the plumularians the cups
are also set directly on the stems, but the branches

Portion of a hydroid colony, magnified through a
microscope, shows the many polyps with outspread
stinging tentacles that lie in wait for small passing
prey. (Bermuda. Ralph Buchsbaum)

wy

The minute jellyfish stage, Lizzia blondina, of a hy-
droid colony. (England. D. P. Wilson)

come out in only one plane, so that they resemble
every kind of plumage from small feathers to long
plumes, some growing up to 6 feet in very deep wa-
ters. The ostrich-plume hydroid, Aglaophenia, which
looks like stout brown feathers, often about 3 inches
long, is especially common, after storms have washed
it loose, in the beach drift on the American Pacific
coast. Other species are known from the Atlantic
coast and European and many other shores as well.
The podlike structures conspicuous among the
branches are protective flaps covering the reproduc-
tive polyps.

In the naked hydroids, the horny covering is ab-
sent or scanty or extends only as tubes that stop at
the bases of the feeding and reproductive polyps.
These include a number of common genera that
grow as rather large single polyps or as clumps or
mats of vertical colonial polyps; they are mostly pink
or rosy in color. Corymorpha is a solitary polyp up
to 4 inches long that lives in mud flats. It is related to
the solitary giant polyp, Branchiocerianthus, men-
tioned earlier as a deep-water form. Clava and Tu-
bularia grow in long-stemmed clumps (Plates 4 and
5). Hydractinia, sometimes known as “hedgehog hy-
droid” because of the spininess of the encrusting mat
formed by the basal stalks that unite the colony, is
noted for the diversity of its several kinds of polyps,
and also for its habit of encrusting shells adopted by
hermit crabs. Whether it actually shares the host’s
food we do not really know; in any case it can live
on rocks and wharf pilings, quite independent of the
crabs.

Related to Clava and the other naked types is
Cordylophora lacustris, the fresh-water colonial hy-
droid. In brackish inlets on marine coasts it is seen
as white, bushy, treelike colonies, a few inches high,
on stones, eelgrass, or wharf piles. When found in
rivers and lakes it seldom exceeds 1 inch in height.

72)

Of the medusas allied to the hydroids, few are as
big or as cosmopolitan as Aequorea, or better known
from their summer swarms. White or pale bluish
ereen and somewhat flattened like the other medusas
of sheathed hydroids, it has many radially spreading
digestive branches, in some species more than a hun-
dred. The tentacles are a short fringe when con-
tracted, a long curtain of slender strands when fully
extended. The polyp is minute and not known for all
species. Stranded aequoreas, masses of jelly often
about as big as one’s hand, sometimes much bigger,
are as well known to Japanese beachcombers as to
those of American or European coasts. The lumines-
cence for which they are noted can be rubbed off on
the hands as luminescent grains, then dabbed on the

faces and hands of unsuspecting friends, creating
weird effects in darkness. It may be added that all the
hydroids mentioned earlier are also luminescent,
though not so bright as Aequorea.

Medusas allied to the naked hydroids are usually
deep-bodied little bells, like Sarsia, Lizzia, and Po-
docoryne. Many have never been matched to their
polyps. The need of the larva to attach to some kind
of solid substrate in those forms that have a fixed
polyp stage keeps most hydrozoan jellyfishes tied to
shore waters. Bigelow once observed that in the deep
and open waters ten miles off Bermuda only 3 per
cent of the jellyfishes he collected were of species
with a fixed stage in the life cycle.

Hydras are naked little fresh-water polyps that

abound in unpolluted streams, ponds, or the shore
waters of lakes, living attached to submerged stones,
twigs, vegetation, or debris. Yet they rarely come to
the attention of anyone who does not deliberately
seek them out, for when disturbed they contract into
all but invisible little knobs. Even when fully ex-
tended the cylindrical body is as fine as sewing
thread, only % of an inch long or so, and has gos-
samer tentacles that barely match the body in length,
or in some species are three or four times as long.
Their regular occurrence in certain favored spots
makes them the only living coelenterates readily and
dependably accessible at great distances from the
ocean. Though to the naked eye the hydra may ap-
pear as an insignificant little creature, under a hand
lens or a microscope it becomes a spectacular beast
that fully deserves to be named after the mythical
monster slain by Hercules. Hydra had nine heads,
and when Hercules cut one off, two grew in its place.
Hydra’s small namesakes are renowned for their
ability to replace injured tentacles, grow a new
“head” if beheaded, grow two heads on one body, or
reproduce asexually by budding off new individuals
from the sides of the body. In sexual reproduction
the egg develops into a little embryo that may lie
dormant during the winter but in spring develops di-
rectly into another polyp without any kind of free-
swimming stage.

The green hydra, Chlorohydra viridissima, which
harbors algal cells of the genus Chlorella, and the
brown hydra, Pelmatohydra oligactis, in which the
slender basal stalk is more obviously set off from the
main part of the body than in other hydras, are cos-
mopolitan species, found on many continents. All
the other species are limited to particular continents
or continental regions. When green coloring occurs
in Pelmatohydra oligactis it is always due to eating
green food, such as green chironomid larvae. Starved
animals lose their color, while well-fed ones on the
usual diet are brownish or even black. Hydra circum-
cincta is a lovely orange-red if fed on ostracods or red
copepods, and a rich color advertises the prosperity
of its bearer.

Most large libraries have the original Memoire by
Trembley on the behavior and regeneration of hy-
dras. To read about his long romance with the little
“polypes d'eau douce en forme de cornes” is to want
to see the creatures feed, bud, and regenerate. For
readers who prefer English, John Baker’s book, also

Left. A hydra opens its mouth wide to swallow a wa-
ter flea. The minute crustacean victim is already para-
lyzed by the stinging threads. Right. The daphnid has
been swallowed and is in the hydra’s digestive cavity;
the body outline and the large eye can be seen through
the body wall. (Eric Grave)

hes

listed in the bibliography, tells of Trembley himself
and of his work with hydras and other microscopic
animals of fresh water. Hydras may be readily col-
lected in nature or purchased from biological supply
companies, and they can be cultured in the home if
kept in pond water, maintained at temperatures be-
low 75°F., and fed on small crustaceans such as
daphnias. Detailed directions for rearing many kinds
of invertebrates are given in the Galtsoff book listed
in the bibliography.

THE TRACHYLINE MEDUSAS

A jellyfish in fresh water once seemed as anoma-
lous as did a black swan to the ancients. Yet the
black swan eventually turned up in Australia. And
in 1880 a fresh-water jellyfish was discovered in the
tank in Kew Botanical Gardens, near London, in
which were kept the giant water lilies from the Ama-
zon. It was named Craspedacusta sowerbyi, and af-
terward more were found in other botanical gardens
in Europe, confirming the impression that it had been
brought with water lilies from Brazil. During recent
decades it has turned up on other continents, and is
frequently but sporadically reported from all over
the United States. Either it is becoming more wide-
spread, or more people are aware of its existence and
are keeping an eye out for it, especially in the most
likely season, from July to October. It seems to favor

The commonest jellyfish encountered by amateur
yachtsmen along the Atlantic coast of America is
Gonionemus murbachii, whose tentacles and dark
sense organs around the rim of the bell mark a circle
as much as an inch in diameter. The cross-shaped
marking in the dome of each bell is produced by the
ruffed reproductive organs. (Massachusetts. Lorus
and Margery Milne)

artificial bodies of water or those of limited size, such
as aquaria, ditches, old flooded quarries, impounded
streams, and small ponds, perhaps because it does
best where plankton is very rich; but it has been
found also in small lakes. No written account or col-
ored plate of a beautiful or bizarre coelenterate from
the ocean deeps can substitute for the thrill of look-
ing over the edge of a rowboat, a thousand miles
from the nearest salt water, and seeing little trans-
parent hemispheres, 1 inch across at most and usu-
ally smaller, pulsating in the water. Removed to a
large jar or an aquarium, where one can watch them
at leisure, they are seen to have several sets of ten-
tacles and to hold one group erect or obliquely up-
ward, the others horizontal or extending downward.
There is a shelflike velum extending in from the um-
brella, and four radial digestive canals. From each of
these hangs a baglike sex organ that looks like a little
pistol holster. Though usually seen in small groups,
all of one sex, they may occur by the thousands.
They are known to feed on rotifers and various small
crustaceans. The polyp stage, originally described
and named as Microhydra ryderi, lives on the bottom
as a minute (14, to 1% of an inch) colony of several
polyps lacking tentacles. A good account can be
found in Pennak’s Fresh-Water Invertebrates of the
United States. Limnocnida, a similar jellyfish, is
known from lakes and streams in Africa.

The fresh-water jellyfishes seem to be allied to the
trachyline medusas, a marine group that differs from
the hydrozoan medusas mentioned earlier in having
a very minute polyp or none at all. It also differs in
the nature of the sense organs found around the rim
of the umbrella, which are thought to have a balanc-
ing function. A well-known marine member is Go-
nionemus, familiar to all students of biology from
laboratory experience with preserved specimens. In
nature it uses the adhesive pads near the tips of the
tentacles to cling to the eelgrass among which it lives.
When the light is not too bright or too low, Gonio-
nemus fishes for its food by swimming in rapid pul-
sations to the surface, turning upside down, and then
coasting slowly downward with its tentacles out-
spread in a wide net.

THE HYDROCORALS

The hydrocorals are a wholly marine group that
includes the “‘stinging corals,” likely to be long re-
membered by any inexperienced collector in warm
waters who tries to break off what may look like an
innocent and beautiful bouquet of light pink branch-
ing coral. They used to be lumped with the hydroids,
which they resemble in many ways, but hydrocorals
secrete massive skeletons of limestone, either erect
and branching or leaflike, or low and encrusting.
The millepores, which are white or of pale fleshy or
yellowish tones, contribute a good share to the for-

mation of many coral reefs and are very abundant
in reefs of the western Atlantic. Another group of
hydrocorals, mostly of deeper hues of pink, red, vio-
let, or purple, also do best in warm waters but extend
into temperate seas as branching species in deep wa-
ter or encrusting ones in the more surfy shore waters.
A lavender or purple encrusting form, Allopora por-
phyra, occurs as calcareous patches encrusting rocks
at very low tide levels on the southern California
coast. Its white polyps may be glimpsed in the small
starlike craters that pock the surface of the massive
colony.

THE SIPHONOPHORES

The siphonophores are floating hydrozoan colo-
nies of great beauty, in which several kinds of polyp-
like individuals and a variety of medusa-like indi-
viduals are all combined into a single functioning
complex that swims or drifts its way about, dangling
drift nets of stinging tentacles to catch living prey.
Most common in tropical and semitropical waters,
they are to be found, especially in summer, drifting
even in polar seas. On the Danish cruises of 1908 to
1910, an hour’s tow in the Atlantic or Mediterranean
brought in from six hundred to one thousand of these
delicately transparent, milky, or subtly shaded colo-
nies. Feeding polyps, contractile stinging tentacles,
reproductive individuals, swimming bells, floating
medusoids, protective flaps, and still other kinds of
coelenterate units share the food netted from the rich
animal plankton of surface waters. But many sipho-
nophores can release gas from their floats in rough
weather and sink below the surface, and some regu-
larly live at greater depths, down to nine thousand
feet. Even those at the surface are usually incon-
spicuous in the water and may escape notice despite
their occurrence in immense swarms brought together
by winds or currents. Around the globe, tropical and
semitropical waters have much the same component
of common siphonophores; those restricted to one
ocean are the exception. In all warm seas Hippopo-
dius trails delicate strings of polyps from a small
cluster of swimming bells at the surface. A little more
compact is Physophora, also circumglobal in warm
waters but in summer carried northward by currents
to southern Greenland, Iceland, and the Barents Sea.
Superficially resembling little medusas are the tiny
blue or greenish disks of Porpita, which from the
deck of a liner in tropical waters can be seen by the
thousands, dotting the ocean for many miles.

The only two siphonophores that are really well
known, however, are the usually sky-blue “by-the-
wind sailor,” Velella (called the “purple sailor” in
areas where it tends to be violet), and the even more
vividly blue “Portuguese man-of-war,”’ Physalia,
which may also be tinted with bright pink or orange.
In certain years both are carried northward in the

Atlantic by steady winds and become stranded in
great numbers on British, Belgian, French, and
American Atlantic shores, far beyond their usual
range, where their novelty attracts much attention.
The same sort of thing happens in the southern hem-
isphere, Dakin says in Australian Seashores. There
Velella, Porpita, and Physalia are stranded on the
beaches of New South Wales, where the local name
for the last is “bluebottle.””

Velella looks like a single flat medusa, 1 to 3
inches long according to age or species, with a trans-
parent iridescent sail set diagonally across the long
axis of an oval float stiffened with horny material.
From beneath the transparent gas-filled float is sus-
pended the blue or pale purple body, with a single
large-mouthed feeding tube at its center and this sur-
rounded by rows of reproductive bodies and a circle
of stinging bodies that look like tentacles. Their sting
is innocuous to man. At intervals of several years
countless numbers are washed up on the beaches of
Florida, Oregon, California, Sicily, and many other
mild parts of the world. Fleets of Velella are accom-
panied and fed on by certain mollusks such as the
floating purple snail Janthina janthina, and by nudi-
branchs such as Fiona. Great shoals of Velella may
at times furnish the main food of the giant sunfish,
Mola mola, which is said to live entirely on floating
coelenterates. As Velella is swept northward along
the American Pacific coast, even sometimes to north-
ern Washington, the big fish follows, far beyond its
usual range.

Physalia (Plate 8) occurs in middle latitudes in
the Atlantic, Pacific, and Indian oceans. For all the
blue and pink iridescent beauty of the gas-filled float,
the tentacles trailing downward for 40 to 60 feet, or
perhaps even as much as 100 feet, pack a sting that
can disable or kill a swimmer. Fatal injuries are said
to be due to allergic shock in people who have be-
come strongly sensitized by earlier experiences with
the proteins of the large stinging threads. Neverthe-
less, all swimmers in warm waters should give this
most dangerous of coelenterates a wide berth, and
even those who examine Physalia from a boat or
when the colony is stranded on a beach should use
care. So many may accumulate on beaches as to turn
the sand blue, and people suffer painful stings from
the dead tentacles in beach sand or on fishing gear.
We well remember the fiery welts on the arms of a
laboratory helper in Bermuda who cleaned an aquar-
ium that had housed a physalia weeks before and
apparently still contained tentacle fragments that
had dried on the walls. Oddly, there are animals that
can exploit Physalia without suffering harm. A small
fish, Nomeus, has never been found except in the
company of Physalia, venturing away briefly, but al-
ways darting back to the safe harbor of the tenta-
cles so deadly to other fishes, even those as big as the

[75

mackerel. A Japanese observer has seen Nomeus
nibbling on the tentacles of its host, and perhaps it is
in this way that it develops immunity to the stings.
Whether Nomeus lures bigger fishes to the tentacles,
as some say, we do not really know, but Physalia
does feed on fishes—some accounts say mainly on
flying fishes. This is not hard for us to believe, as our
own first experience of Physalia was in the Carib-
bean, where for some eight or nine sunny hours our
ship sailed through water seemingly alive with flying
fishes and dotted to the horizon with a great flotilla of
Physalia. Even from the deck of the small ship one
could see the crest changing its shape and the float
dipping from side to side in the quiet air. Douglas
Wilson, who has studied physalias that occasionally
come to Plymouth, in England, has suggested that
this habit serves to keep the delicate float wet in hot,
calm weather. A physalia kept in an aquarium will
eat a proferred fish, first stinging and entangling it in
the tentacles and then hauling it up under the float.
There feeding polyps stretch down to spread their
thin, transparent lips until they overlap, completely
enveloping the fish as they pour out digestive juices
and dissolve the flesh. The food particles are drawn
up into the colony, further digested, and shared.
Physalias fall prey to petrels and albatrosses, and
fishes too, if we believe one old account that tells of
an albacore swallowing a physalia and its accom-
panying little fishes. On tropical beaches ghost crabs
nibble at stranded physalias from below, thus help-
fully burying them.

The common jellyfish of all seas, Aurelia aurita. Here
the saucer-like umbrella is seen from below. (Eng-

land. D. P. Wilson)

Vivid accounts of pelagic invertebrates, including
Physalia, are to be found in D. P. Wilson’s Life of
the Shore and Shallow Sea and in Hardy’s The Open
Sea. The only place known to us where living sipho-
nophores have been regularly displayed to the public
is the Naples Aquarium. In the past, at least, Phy-
sophora, Forskalia, and Hippopodius were shown in
the tanks whenever quiet weather made them avail-
able. Sea anemones, sea pens, and other sessile coe-
lenterates are on display in many seaside public
aquariums.

The ‘True Jellyfishes

(Class Scyphozoa)

Almost all of the larger jellyfishes one sees in ma-
rine waters or washed up on the beaches as shapeless
blobs of jelly are true or scyphozoan jellyfishes.
Most familiar of these is the moon jelly, Aurelia,
which can be seen in great shoals from the deck of an
ocean liner. The milky saucers drift along together
or swim slowly by rhythmic pulsations. The giant
among jellyfishes is Cyanea arctica, sometimes 8
feet across, with long, trailing tentacles that extend
downward for 200 feet. In the cold waters where
these occur no swimmer could last long anyway, so
we can only imagine what it would be like to be stung
by such a monstrous coelenterate. Of more real con-
cern are the 12-inch Cyaneas of temperate Atlantic
waters, for these do turn up off beaches in summer,
and they can cause painful red welts that remain dis-
colored for many hours. Since some people also de-
velop generalized symptoms or disabling muscular
cramps, any swimmer stung by a jellyfish should
promptly go ashore. There seems to be disagreement
over whether there are any fatalities known to be
due solely to Cyanea poisoning or to the painful
stings of Dactylometra quinquecirrha, both common
in the Atlantic. In tropical waters scyphozoan jelly-
fishes can be more dangerous. A sea wasp, Chiro-
psalmus quadrigatus, of the South Pacific and Indian
oceans, is said to have caused deaths in from three to
eight minutes. Such reports do not always rule out
death from other possible causes, but the bad reputa-
tion of this cuboidal jellyfish is probably deserved. A
swimmer or diver who feels uncertain about a mass
of jelly coming his way should give it plenty of lee-
way, remembering that it is probably trailing long
tentacles for some distance.

After a great storm, tropical waters or even beach
sands may be filled with tentacle fragments still cap-
able of dealing painful stings. Any jellyfish stranded
at ebb tide should be examined with a stick or turned
over with the toe of one’s shoe, but not touched with
bare skin unless readily recognized as of a harmless
species. Having set down all these warnings, it is
only fair to point out that of the two hundred or so

Stalked jellyfishes attached to seaweed. At left, Haliclystus auricula; at right, Craterolophus
convolvulus. The bigger one is less than 1 inch across. (England. D. P. Wilson)

species of scyphozoan jellyfishes, some are harmless
and many can cause only mildly annoying prickling
or burning sensations. Moreover, there really is no
poison that is not another man’s meat, for in the Gil-
bert Islands sea wasps are considered a delicacy. The
natives collect great shoals of them and scrape away
the tentacles and umbrella, retaining little but the
reproductive organs. Writing of this in Margins of
the Sea, Maurice Burton says that boiled sea wasps
taste like tripe—those first dried and then fried in
deep fat, like pork cracklings. Jellyfishes are relished
also by other peoples of the Pacific (p. 80); in Naga-
saki one may buy the large Rhopilema esculenta in
the market. Among the scyphozoans important in
sheltering young commercial fishes is Cyanea, which
gives cover to young whitings.

Scyphozoan jellyfishes are usually easy to tell from
their tiny hydrozoan relatives because of their mod-
erate to large size and because they lack the trans-
parent shelf (velum) that projects inward from the
margin of the umbrella in the hydrozoans. In addi-
tion, scyphozoans may have fringed mouth lobes, a
scalloped rim, and a complex pattern of digestive
canals that contrasts strongly with the four simple
canals that radiate to the margin in the hydrozoan
medusas.

A conspicuous four-sided symmetry shapes the ex-
ternal form and internal structure of most scypho-
zoans. The four stomach pouches and the four repro-
ductive organs often show through the translucent
body, and externally there are often four long, frilly
mouth lobes that entangle food organisms and direct

[77

them into the mouth. Little sense organs may occur
in four notches in the scalloped margin, or in eight
notches, or in some higher multiple of four. Tentacles
may also occur in marginal notches, alternating with
the sense organs, or in other positions as well. Some-
times they form a fringe of indefinite number.

The jelly of scyphozoan medusas can be very
bulky, and it contains many cells and strengthening
fibers. Sometimes it is almost of a cartilaginous tex-
ture, so firm that one can jump on such an animal
without crushing it. Even the firmest ones, however,
are at least 94 per cent water.

The jellyfish is always the predominant stage in
the scyphozoan life history. The polyp stage either is
very small or is missing altogether. When present, it
may transform directly into the adult; or it may elon-
gate into a trumpet-shaped polyp with tentacles and
then undergo a series of successive crosswise con-
strictions until it resembles a pile of saucers. One by
one these little saucers are pinched off from the par-

ent polyp and swim away as little medusas, each
growing into an adult jellyfish.

The true jellyfishes are usually divided into five
orders, and the first of these is sometimes set off as a
separate subclass because the members are not free-
swimming like the rest but live attached.

THE SEDENTARY OR STALKED
JELEVERISHES

These are the simplest scyphozoans, the stauro-
medusas or lucernids, which live attached by a
sucker, usually at the tip of a stalk that springs from
the center of the outer surface of a trumpet-shaped
or goblet-shaped umbrella. They inhabit sheltered
waters in the colder parts of the oceans, clinging to
eelgrass in sheltered coves or bays, to algae in rock
pools, or sometimes to rocks or shells. The margin
of the umbrella may be circular, but typically it is
drawn out into eight lobes, each tipped with a cluster
of twenty or more short, knobbed tentacles. Such

The giant jellyfish, Cyanea capillata, stranded at low tide. (Maine. Ralph Buchsbaum)

The sea nettle, Dactylometra quinquecirrha, is visibly dotted with wartlike clusters of stinging
cells. Golden tentacles partially veil the pink flounces of the mouth lobes. Up to 8 inches
across. (Delaware Bay. William H. Amos)

stalked medusas are only too easy to overlook, for
most are only | inch or so across the open flaring
end of the umbrella, and are the same brownish or
greenish color as the seaweeds to which they cling.
A few come in prettier shades of blue, violet, pink,
or orange. The pendant mouth stalk is four-cornered,
with little lobes, and ingests small animals that come
its way. If the food supply runs low, some stalked
jellyfishes can glide to new stations, adhering to solid
support by the tentacles and by adhesive pads that
alternate with the clusters of tentacles around the
margin of the umbrella. They are said to breed at all
seasons, and the egg develops into a stalked, trum-
pet-shaped adult without going through the splitting
stage typical of many scyphozoans. Best known of
the stalked jellyfishes are Haliclystus and Lucernaria.

THE CUBOIDAL JELLYFISHES OR
SEA WASPS

In tropical or subtropical bays or harbors, or some-
times in the open sea, sea wasps had best be recog-
nized by their cuboidal shape, not by testing their
highly venomous sting. The colorless body has four
flattened sides, and from each corner springs a ten-
tacle or a group of tentacles, these often with some
color. Feeding mostly on fish, they back up their vo-
racious appetites by the strongest swimming habits
known among jellyfishes. The cuboidal umbrella
may contract up to 150 times a minute. Though many
are only | or 2 inches high, some measure as much as
10 inches from margin to top of umbrella. The best-
known genus of sea wasps, Carybdea, is luminescent.
In spite of the evil reputation of Carybdea alata in
the tropical Pacific, Atlantic, and Indian oceans, it is
members of this genus that are relished in the Gilbert
Islands (p. 77). The most fearsome genus of all is
Chiropsalmus, especially in Philippine waters. Phil-
ippine and Japanese fishermen call this the “fire me-
dusa” and keep their distance. Chiropsalmus quadri-
gatus, notorious for its rapidly fatal sting, is known
from northern Australia, the Philippines, and the In-
dian Ocean. A related but less dangerous form oc-
curs in the Atlantic from North Carolina to Brazil,
and also in the Indian Ocean and northern Australia.

THE CORONATE JELLYFISHES

The coronate or crowned jellyfishes are recognized
by a prominent horizontal groove that encircles the
umbrella. Below this crowning groove the umbrella
margin is furrowed by vertical grooves, each ending
in the middle of one of the lobes of the often deeply
scalloped edge. The beautiful sculpturing of these
masses of jelly reminds one of some of the gelatin
desserts that have been shaped in grooved, domelike
metal molds. Coronate jellyfishes may measure 6
inches across, but most are under 2 inches. Though
this is chiefly a deep-water group, some species, like

80]

the flattened Nausithoé, are common in all warm,
shallow waters. Nausithoé is often seen in the Baha-
mas and in Florida, and is carried northward along
the American Atlantic coast. It occurs also in more
northern Atlantic waters. Periphylla hyacinthina,
with a high, narrowly pointed umbrella and a beau-
tiful purple color, is common in deep waters all over
the world and is often seen at the surface.

THE DISK JELLIES

Not all the members of this group are as disklike
as the common name suggests, but compared with
other scyphozoans they do have flattened umbrellas
when relaxed. They look hemispherical when con-
tracted in swimming. Large and bulky kinds, espe-
cially Cyanea, are often called sea blubbers. The
technical name, Semaeostomeae, makes a poor han-
dle for these most typical of scyphozoan jellyfishes,
which are the ones most likely to be seen in temper-
ate waters. All are of moderate to large size, ranging
from 2 inches to 2 feet across. The giant Cyanea, re-
ferred to on page O00, is exceptional. Disk jellies oc-
cur in all coastal waters, especially warm and tem-
perate ones, often in great shoals of many thousands
of individuals, usually at seasonal intervals. The um-
brella margin is often scalloped into eight lappets,
sometimes more. The four corners of the mouth are
drawn out into four long, frilled lobes, each folded
down the middle and forming a trough to direct food
into the mouth.

Unfettered by a fixed stage, the lovely Pelagia is
the only disk jelly free to roam the open seas. The
purple-rose umbrella, shading into blue, is 2 inches
or more across, and the scalloped margin has sixteen
notches, eight tentacles, and eight sense organs; the
tentacles and sense organs alternate in the notches.
When Pelagias glide past a ship at night they glow
like white balls of fire. Seen at a distance, they show
as large winking spots instead of as the even glow
caused by billions of luminescent protozoans. Pelagia
noctiluca is abundant in the Mediterranean, and it is
probably the same species that is swept up the Amer-
ican coast by the Gulf Stream and that delights Scot-
tish observers whenever it arrives in the North At-
lantic Current.

Also luminescent is the graceful compass jellyfish,
Chrysaora hysocella, strongly marked on the um-
brella with radiating V-shaped streaks. Toward the
end of summer it appears in great numbers in Euro-
pean Atlantic waters.

Most widely distributed of the true jellyfishes is
the moon jelly, Aurelia aurita. In all oceans, and
from polar waters to the equator, it seems to vary
little, though probably there are several subspecies
that breed at different times and require different sea
temperatures. When relaxed and drifting it is a shal-

[continued on page 97 ]

31. The staghorn coral, Acropora, abounds on reef flats but grows tallest and most branch-
ing in sheltered lagoons. At low tide, and in bright light, the delicate polyps draw back
into the coral cups on the surface of the colony. (Great Barrier Reef. Allen Keast

32. The tube anemone, Cerianthus, lives in a tube of hardened slime, down
which it retreats when disturbed. It is common off European shores and has
close relatives on other coasts. (Roscoff, France. Ralph Buchsbaum)

WANS
ATRIA A

34. Delicate spirals of the branching bryozoan, Bugula,
hang exposed in rocky crevices at low tide. (Brittany,
France. Ralph Buchsbaum)

33. Lacelike patches of the
bryozoan sea mat, Membrani-
pora membranacea, grow over
the broad fronds of seaweeds.
The chambers of all the sepa-
rate individuals stand out clearly
long after the occupants have
died. (Roscoff, France. Ralph
Buchsbaum )

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35. The leaflike flatworm, Pseudoceros, which has many drab-colored polyclad rela-
tives in temperate marine waters, shows the gay coloring common in tropic: ul animals.
sreat Barrier Reef. Fritz Goro: Life Magazine)

37. A marine ribbon worm, Tubulanus polymorphus, exposed
at low tide. Stretched out, it measured 6 feet. (Oregon. Ralph
Buchsbaum )

36. A dense aggregation of minute acoel flatworms,
Convoluta roscoffensis, shown much enlarged. When
the worms rise to the surface sand at low tide, they
se to the sun the green algal cells that pack their
bodies. (Roscoff, France. Ré ph Buchsbaum )

39. The black tunic of Katherina
tunicata overgrows the eight
plates that are more fully ex-
posed in other chitons. Katherina
stands strong surf and does not
retreat from sunlight. (Oregon.
Ralph Buchsbaum)

38. The hairy chiton, Mopalia, like many of its rela-
tives, avoids light at low tide and must be sought
under rocks on partially protected coasts. (Oregon.
Ralph Buchsbaum)

40. The common mussel, Mytilus, grows in
dense masses. Each mussel is attached by strong
threads to rock or to other mussels. (Brittany,
France. Ralph Buchsbaum)

41. The queen scallop, Chlamys opercularis, a common edible
species of European Atlantic waters. It lies on the bottom
with valves agape, and here displays along the lower mantle
edge a row of black-pigmented eyes alternating with delicate
tentacles. (Roscoff, France. Ralph Buchsbaum)

42. The blue-eyed scallop, Pecten irradians, the common edible scallop of the American
east coast. Close-up view of shell gape shows its blue eyes and numerous tentacles,
which screen incoming feeding and respiratory currents. (Woods Hole, Massachusetts.
Roman Vishniac)

43, The great scallop, Pecten maximus, with
convex valve below and flat valve above, is
larger than the queen scallop and not so
agile a swimmer. It is the most relished of
European Atlantic scallops. (England. D. P.
Wilson)

44. The file shell, Lima, has a rasplike covering of spiny
ribs. The brightly colored sensory tentacles are contrac-
tile but cannot be withdrawn completely into the shell.

(Marineland, Florida)

45. File shells are able to
swim about slowly, clap-
ping their valves, which
are held vertically. (West

Fritz Goro: Life

46. File shell (West In-

dies. Fritz
Magazine)

Goro:

Life

ts
y

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aati we,

S ae”

A keyhole limpet, Diodora aspera, 3
inches long, uncovered at a very low tide.
By means of its muscular foot it clings to
the rock, even in strong surf, from Alaska to
Lower California. The ribbing of the shell
is obscured by a calcareous growth. (Ore-
gon. Ralph Buchsbaum)

48. In the giant keyhole limpet, Megathura crenulata, 7 inches long, the
black, velvety mantle partly covers the oval shell. Found on the open coast,
it is shown here in an aquarium. (Cy La Tour and Marineland of the Pacific)

This giant land snail, Achatina fulica, with a shell 5 inches long, was brought
from Sierra Leone in Africa to the London Zoo. It was spread by man eastward from
India to Hawaii. Freed of natural enemies, it is now a plant pest in the Pacific.
(Ralph Buchsbaum )

50. The garden snail, Cepaea hortensis, native to Europe and introduced into eastern
v England. Half an inch high and about as broad, it shows five dark bands. It

Nev
lives in little
table gardens. (Bavaria. Otto Croy)

colonies in moist places, and eats weeds but sometimes attacks vege-
g

51. The spider conch, Lambis lambis, is a voracious camivore fairly common on coral
reefs. The sharp-edged operculum attached to the rear of the foot closes the shell
like a door. (Great Barrier Reef. Jerome M. and Dorothy H. Schweitzer)

53. A Brazilian olive shell, Olivancillaria, from the
coast near Santos. When the snail is plowing
through sand the lustrous shell is covered by two
folds of the large mantle. (Othmar Danesch)

52. The painted top shell, Calliostoma zizy-
phinum, of European Atlantic shores, does
not come above low-tide level except in
favorable spots. (Roscoff, France. Ralph
Buchsbaum )

54. Wrinkled purples, Thais lamellosa, named for the purple
dye they excrete, fasten their vase-shaped egg capsules to the
undersides of rocks. They are the American west coast coun-
terpart of the purples, ‘or dog whelks, of Atlantic shores.
(Oregon. Ralph Buchsbaum )

56. The flat periwinkle, Littorina littoralis, of
temperate and cold Atlantic shores, depends
on large seaweeds for food and for keeping
moist when the tide is out. (England. Ralph
Buchsbaum )

55. The largest moon snail of the American Pacific coast, Polinices lewisii, averages
more than 4 inches long. The fleshy foot envelops most of the shell as the animal pushes
through sand and feeds on other mollusks. (Cy La Tour and Marineland of the Pacific)

57. The bubble shell, Hydatina physis, is a snail with a shell only about 1 inch in length,
but the mantle and head shield are voluminous. It lives on sandy and muddy bottoms,

though here it is crawling on organ-pipe coral. (Australia. Jerome M. and Dorothy H.

Schweitzer )

58. The tiger cowrie, Cyprae tigris, about
4 inches long, has a lustrous shell that has
long made it the most sought after of South
Pacific marine snails. (Great Barrier Reef.
Jerome M. and Dorothy H. Schweitzer)

59. The marbled cone, Conus marmoreus, ranges from Polynesia west to the Indian
Ocean. Despite its lovely shell, a favorite of collectors, it is one of the most dangerous
of poisonous cone shells. The tube at the front (right) is the respiratory siphon; the
proboscis that deals the sometimes fatal bite is retracted. (Great Barrier Reef. Jerome
M. and Dorothy H. Schweitzer)

[continued from page 80 ]

low saucer, with extremes of size from 3 inches to 2
feet; but most are from 6 to 10 inches in diameter.
The tentacles are short and extremely numerous,
forming a fringe around the margin. Readily visible
through the top of the milky white or bluish umbrella
are four horseshoe-shaped reproductive organs, of-
ten colored violet or pink. From the underside hang
four long, tapering, somewhat stiff mouth lobes. This
is a relatively harmless jellyfish, and it feeds on mi-
nute organisms, chiefly copepods, which are collected
in mucus on the umbrella surfaces and then licked
off by the mouth lobes and carried by ciliary currents
to the mouth.

Dactylometra quinquecirrha, with a long name
and a bad reputation for painful stings, belongs to
the same genus as certain dangerous jellyfishes of the
tropical Pacific. (A Pacific species is shown in Plate
7.) It is seen from the Azores and New England to
the tropics, and from West Africa, the Indian Ocean,
the Malay Archipelago, and the Philippines to Japan.

The common sea blubber, Cyanea capillata, whose
huge arctic variant has been referred to several times,
is also called the pink jellyfish—probably by people
who have not felt its fiery stings. In England it is “the
hairy stinger” or “the lion’s mane,” the last name
serving in the Sherlock Holmes story about a fatal
case of Cyanea poisoning, “The Adventure of the
Lion’s Mane.” Most individuals are not over 3 feet
in diameter, with tentacles extending down for 75
feet, and 12-inch disks are most common. The color
showing through the thick disk varies from a rosy
pink to a brownish purple, and the yellow or reddish
tentacles hang down in great bunches, the gaps be-
tween bunches revealing the frilled purplish mouth
lobes. Cyanea capillata is abundant in the cool and
cold waters of both the Atlantic and the Pacific
oceans. Other stinging species are found in the tropi-
cal and temperate Pacific. This is another of the
scyphozoans that are known to luminesce.

THE MANY-MOUTHED JELLYFISHES

There is no widely used common name for this
group, and it helps little to say that the technical
name, Rhizostomeae, means “root-mouthed.” The
rhizostomes have no single large mouth as do other
jellyfishes, but feed through numberless small open-
ings in the mouth lobes. Each of the four lobes is sub-
divided, elongated, lobed, and folded, so that in some
members they suggested a bundle of eight long roots
hanging from the lower surface. There are no tenta-
cles around the margin, and these jellyfishes feed
mostly on microscopic organisms drawn into the tiny
mouths by ciliary currents. The 7-inch Stomolophus
of the southeastern American coast and the larger
Rhizostoma of European waters have a high, mush-
room-shaped umbrella. Most interesting is Cassio-
peia, common in quiet, shallow mangrove bays in

Florida and in the tropics. Thousands of them lie
disk to disk, on their backs, the voluminous and
branching mouth lobes exposed to the gentle food-
bearing currents that sweep across. This relaxed
feeding habit also displays to the sun the myriads of
green cells that live in the tissues. Presumably the
green guests utilize nitrogenous and gaseous wastes
of the jellyfish and in return make it possible for Cas-
siopeia to live densely crowded in stagnant waters.

Sea Whips, Sea Fans,
Anemones, Corals, and

Others

The anthozoans (“flower animals”) are most fa-
miliar as the solitary sea anemones of temperate
seashores, or as the corals, sea fans, and sea whips
known to most people from their beautiful dried skel-
etons. This is by far the most conspicuous and most
successful class of coelenterates, comprising more
than six thousand species, all of them marine and
most of them living in shore or shallow waters. All
are cylindrical polyps, with no trace of a jellyfish
stage in the life history. A little free-swimming plan-
ula larva serves to distribute many of those that live
permanently attached. A few, like the sea anemones
and sea pens, do move about at times. The free end

(Class Anthozoa or Actinozoa)

The many-mouthed jellyfish, Rhizostoma, feeds
through countless small openings in the pendant
mouth lobes. (Naples Aquarium. Ralph Buchsbaum)

The Cassiopeia at the left is swimming, and the one at the right is lying on its back in feeding

position, with the |

ching many-mouthed lobes gathering food particles. (Lerner Marine

Laboratory, Bimini. Fritz Goro: Life Magazine )

of the polyp is not conical, as in many hydrozoan
polyps, but is expanded into a flat disk that has an
oval or slitlike mouth at the center and bears one or
more circlets of hollow tentacles. The external cover-
ing layer turns in at the mouth to form a tube, the
gullet, which hangs into the digestive cavity. The gul-
let is lined with beating flagella and usually has one
or two flagellated grooves that direct currents of wa-
ter to the inside. Unlike the simple cavity of hydro-
zoans, that of anthozoans is divided by membranous
partitions, all or some of which extend from the body
wall to the hanging gullet.

The class Anthozoa is divided into two groups:
the alcyonarians or octocorallians, in which all the
parts are based on a plan of eight; and the zoanthar-
ians or hexacorallians, in which the body is based on
a plan of six, or of a multiple of six, or on some

98 |]

other number, but not on a plan of eight simple re-
peated parts.

THE ALCYONARIANS

(Subclass Alcyonaria)

Alcyonarians are all colonial growths, often color-
ful and luminescent, and they are especially conspic-
uous in warm seas. At a distance they show great va-
riety of shape, most of them arising from the bottom
as fleshy lobes or as slender branched feathers or
fans. Except for the gorgonians, they are mostly
rather insensitive to light, and they respond to touch
only locally, though in a few forms the stimulus
spreads for some distance over the colony. Those
that are not permanently attached, like the sea pens,
are the most responsive. Some that pay no heed to
probing fingers will react to chemical or electrical

stimulation. The stinging capsules are very small and
cannot penetrate the human skin, so alcyonarians
can be handled with impunity. If we examine them
closely when the polyps are fully expanded we see
that the feeding polyps are all remarkably alike and
have a single circle of eight feathery tentacles. These
are widest at the tips and somewhat flattened, and
bear rows of side branchlets. The oval or elongate
mouth may have one ciliated groove at most, and it
opens into a gullet that has attached to it eight parti-
tions readily visible in transparent polyps.

Many alcyonarians have a second kind of polyp
without tentacles, and these may be concerned with
circulation of water, which plays a large role in the
expansion and contraction of the colonies as well as
in respiration. Between the external covering layer
and the thin digestive lining is a thick jelly layer that
adds bulk to the body, and this is invaded by cells
that secrete the skeleton of calcium carbonate or of
horny material, either in little spicules of distinctive
shape or as amorphous substance. Even when loosely
scattered, the spicules give firmness to the flabby
body; and those alcyonarians in which the spicules

are densely packed or fused may contribute no small
share to coral reefs. Also in the jelly are the digestive
canals that unite the many polyps. The sex cells de-
velop on the digestive partitions and are shed to the
outside through the mouth.

THE SOFT CORALS

The soft corals, or alcyonaceans (Plate 9) with
only scattered spicules stiffening the body, are
best known in temperate waters from the flesh-col-
ored, white, or orange-colored lobed masses called
“dead men’s fingers” in England and something less
mentionable in France. Alcyonium digitatum, abun-
dant in European waters, lifts its spongy, gelatinous
lobes, like bloated fingers, as much as 8 inches high
from gravelly bottoms below low-tide mark. In dull
light the numerous and delicate transparent ends of
the polyps form a white furriness over the surface as
they project beyond the opaque lobes. At the slight-
est disturbance the little feeding disks are pulled in
by special muscles, and the rest of the delicate col-
umns follow, turning the formerly exposed parts of
the polyps inside out, like the fingers of a glove, and

Dead men’s fingers, Alcyonium digitatum, a fleshy colony of soft coral that extends delicate
polyps. (England. D. P. Wilson)

= Me al «*
- #. -
: = aN My i aint
ae ~ = Opal
“a a “ > ~~ ~o wh
Cie 2 ae Wa an ar . \
A . ye —<
on -” 6
~

into the safety of the digestive cavity imbedded in
the main mass. In New England waters and north-
ward, species of the related Gersemia have salmon-
colored or reddish branches, or clusters of slender
lobes. Anthomastus, which looks like a red mush-
room with polyps strewn over the fleshy cap, is often
dredged up by fishermen on the New England coast,
and another species is known from deep waters off
California. Though some soft corals extend into po-
lar waters, this is largely a warm-water group with its
great center the Indo-Pacific Ocean. There, in shal-
low waters, the flabby masses of what look like leath-
ery seaweeds are alcyonacean colonies of moderate
size and of drab shades of yellow, brown, or olive.
Some run to dull reds or purples or other hues, and
in deeper waters they grow more treelike and are
stiffer (Plate 29).

THE ORGAN-PIPE CORAL

The organ-pipe coral, Tubipora, is a spectacular
aleyonarian coral, with emerald-green polyps that
emerge from brick-red limestone tubes. In some trop-
ical waters it is an important reef-builder, though the
massive layers of tubes, laid down over many gener-
ations, are not secreted as solid limestone as in true
reef corals, but consist of fused spicules and lie within
the living tissue of the coral. Tubipora belongs to
the stoloniferans, a group with some small members
in temperate waters that are the most primitive of
alcyonarians. In these the polyps are not fused to-
gether but arise separately from a basal mat of run-
ners. In the organ-pipe coral, however, the vertical
limestone tubes that house the polyps are joined at
intervals by horizontal platforms in which run con-
necting digestive canals. As the colony grows, the
lower levels of the tubes are abandoned, and they be-
come great tenements housing worms, small crabs,
and innumerable other little animals (Plate 54).

THE BLUE CORAL

The blue coral, Heliopora, which does not look
blue when the brown polyps are fully extended, is
found on the coral reefs of the Indo-Pacific. The blue
color of the broadly lobed calcareous skeleton is said
to be due to iron salts, and the limestone mass is
composed not of fused spicules as in other aleyonar-
ian corals, but of fibers of crystalline calcium carbon-
ate (aragonite) fused into sheets. The polyps live
only in the surface portions of the cylindrical cavities.

THE GORGONIANS

The gorgonians or horny corals include the sea
whips, sea fans, and sea plumes, which have a flexi-
ble skeletal core of a horny material called gorgonin.
Of plantlike growth form, and colored vivid shades
of yellow, red, orange, and purple, they furnish most
of the “blossoming shrubbery” of Atlantic shores,

In the shallow waters of Indo-Pacific reefs the soft
corals are mostly great flabby masses of what look
like leathery brown seaweeds. (Great Barrier Reef.
Fritz Goro: Life Magazine )

adding much to the invertebrate lure that brings so
many skin divers to the shallow waters of Mediterra-
nean, Caribbean, and Florida coasts. They are really
most abundant in the tropical Indo-Pacific, but there
they are inconspicuous in shore waters compared
with the soft corals or the true reef corals.

Though mostly coastal or from waters no more
than three thousand feet deep, gorgonians occur at
all depths. Many are luminescent, and when the
Challenger expedition in the 1870’s was discovering
so much that was new that everything since has been
anticlimax, all the alcyonarians dredged from deep
waters were seen to be brightly luminescent as they
came on board, one shrublike gorgonian glowing
with a soft pale lilac light. The larger deep-water col-
onies may reach 9 feet; and in the deep waters of
Norwegian fjords the bright scarlet Paragorgia at-
tains treelike growths. The shallow-water Lopho-
gorgia chilensis is seen by aqualung divers on the
rims of underwater canyons off La Jolla, California,
as sparsely scattered, low-branching, coral-colored
shrubs with white polyp “blossoms.” Common in the
same places is the reddish purple Eugorgia rubens.
Typically, gorgonians have slender whiplike branches
arising from a short main trunk that is firmly fastened
to the bottom. When the stems have side branches

[101

————

A deep-water soft coral, showing the lovely treelike form typical of alcyona-
ceans from the deeper waters of the Indo-Pacific region. (Aquarium of Nou-
méa, New Caledonia. René Catala)

Sea whips, a kind of flexible but horny gorgonian
coral, are a dominant feature of the coral reefs of
the western Atlantic. These were growing off the
Virgin Islands at a depth of twenty-eight feet. (T.
Parkinson: National Audubon)

the colonies may resemble feathers or great plumes.
Having established a sure anchorage in the moving
water, gorgonians are a standing invitation to settling
larvae of invertebrates such as sponges, hydroids,
bryozoans, and brachiopods, to hop on and take
hold, later obscuring the host polyps or even, in the
case of certain little crustaceans and worms, stimulat-
ing the host to pathological growth as it adjusts to the
guests. Gorgonians are very sensitive to strong light,
and they expand their polyps fully only at night or
on dull days.

In shallow European waters, in many of the same
places that support the fleshy hands of Alcyonium,
we find the graceful little sea fan, Eunicella verru-
cosa (Plates 11 and 12), in which the treelike
branches are flattened and grow all in one plane. It
has a horny black branching skeletal core covered
with orange, pink, or white fleshy tissue and innu-
merable little white polyps. The dried colony retains
its lovely form, but the orange-pink color of the gay-
est specimens dries to a dull white, because the pig-
mentation is not in the spicules, as in most alcyonar-
ians, but in carotenoid droplets in the living cells.
Less disappointing when dried is the larger sea fan,
Gorgonia, of semitropical waters, in which the flat-
tened branches have cross-connections that convert
the colony into a lattice of yellow, lavender, or pur-
ple “lace,” with lasting color in the scattered spicules.

The red or precious coral, Corallium, has a differ-
ent kind of skeleton, completely lacking the horny
gorgonin. Highly prized since ancient times, the hard
and entirely calcareous red or pink branching core
lies hidden within the colonial tissue, which is fleshy

102 ]

and yielding though stiffened and colored by red, cal-
careous, evenly scattered spicules. The surface of the
living colony is raised into little protuberances from
which arise the pure white blossom-like polyps.
Smaller elevations house a diminutive kind of polyp
without tentacles._

Commercial fishing of coral was for centuries car-
ried on off the coasts of Corsica, Sardinia, and Sicily,
the south coast of France, the north coast of Africa
from the Straits of Gibraltar to Tunis, and in the At-
lantic from the Cape Verde Islands. A similar red
coral, though inferior in beauty and texture, is also
collected and worked in Japan. The coral colonies
are strongly affixed to the rocky bottoms and slopes,
and in the Mediterranean were collected by boats
towing large wooden crosses dangling old nets and
frayed rope mops that entangled and broke off the
lovely red branches. The difficulties of coral fishing,
especially with hand labor in past times, so enhanced
the value of the coral that it was traded to the In-
dians and Chinese for emeralds, rubies, and pearls.
The early Celts in Britain, before the Roman con-
quest, obtained coral by barter from the Gauls, and
used it to decorate shields and other valuables. Its
rarity and blood-red color inevitably suggested ther-
apeutic powers, and to the end of the eighteenth
century physicians made great use of powdered red
coral in prescriptions. In our own century rural Eu-
ropeans have continued to attribute special thera-
peutic value to coral necklaces and have given them
to adults suffering from debilitating diseases or to
children cutting teeth, for which they must serve as
well as any other smooth, hard surface. Now the
coral “trees” that once thickly covered whole areas
of the Mediterranean are mostly smashed or gone.
Only in specially protected areas or in recesses and
grottoes do they survive in great numbers. In The
Silent World, J.-Y. Cousteau presents colored photo-
graphs of red branches of Corallium hanging from
the ceiling of a cave and “accumulating like stalac-
tites.” From such places it can be gathered only by
divers, to whom the red coral branches, seen at
depths below 120 feet, appear blue-black.

THE SEA PENS AND SEA PANSIES

The sea pens, or pennatulaceans, were named in
the days when a pen still suggested the feathered
quill of a bird. The fleshy, feather-shaped bodies add
color to the same warm bottoms favored by their
alcyonarian relatives, and also extend with them into
temperate or cold waters. Sea pens, however, are re-
stricted to soft bottoms, in which they anchor by
means of the expansible bulbous tip of an elongate
stalk. In size they range from a few inches to 3 feet
or more. Their varied shades of yellow, orange, red,
brown, and purple result mostly from the pigmenta-
tion of spicules scattered in the flesh, though many

have dark pigments in the cells also. A horny central
axis usually adds mechanical support. This group is
noted for its bright luminescence, usually blue or vio-
let, sometimes greenish or yellowish. The slime se-
creted by pennatulids contains luminescent granules;
the dried slime will glow when water is added, but it
cannot be stimulated in other ways. The intact ani-
mal, or pieces of a colony, luminesce only on stimu-
lation. In the more primitive forms, like Veretillum,
common in the coastal muds of the Mediterranean
and also found in the Altantic, the upper part of the
body is a stout fleshy club with flowerlike polyps
strewn over the surface in no obvious order (Plate
10). More like a quill pen is Pennatula phosphorea,
which lives somewhat farther from shore but often
comes up in fishermen’s nets. The stalk is yellow-
orange, and the expanded upper part, which bears
rows of polyps on each side as a feather bears its
barbs, is purple. The polyps glow a bluish green,
and when they are stimulated repeatedly, waves of
light run the length of the region bearing the polyps.
After this response the colony contracts and expels
water. In the same Mediterranean and Atlantic hab-
itats as Pennatula, and as far north as Norway, dredg-
ing brings up the related wandlike Virgularia, with a
slender body up to 2 feet long and polyps closely
packed in rows on either side at intervals along the
stem. Pink, rose-colored, red, and purplish red va-
rieties of Pennatula are widely distributed along
the New England coast, growing more abundant as
dredging proceeds to deeper and deeper water, even
to six thousand feet. One species may be only 4
inches long, but the other, the great sea pen, well
known to halibut fishermen, attains a length of 20
inches. Also present in these deeper waters are sev-
eral tall wandlike forms related to Virgularia. They
grow 3 feet high and may bend from the weight of
sea anemones that live on the long basal stalk. On
the American Pacific coast, in the mud of shallow
bays from San Francisco to San Diego, are two com-
mon sea pens: Stylatula is rough to the touch and
about 1 foot long; Acanthoptilum is smooth to the
touch and up to 2 feet long. In Between Pacific Tides,
Ricketts and Calvin tell of rowing in Newport Bay at
low tide and looking into the shallow water at a
pleasant meadow of waving green Stylatula pens
“like a field of green wheat.” When they reached
down with an oar to unearth one, the feathery pens
instantly snapped down into the sandy mud, leaving
only their very tips to betray their presence. Entirely
deep-water or abyssal are pennatulid families like
the Umbellulidae. Umbellula has a very slender
bare stem, perhaps 2 feet long, topped by a cluster
of large orange-red or purplish flowerlike polyps.
One that emitted a bluish light was hauled up from
about fifteen thousand feet by the ship Galathea.
The sea pansy, Renilla, a very different kind of

A pale orange sea pen, Leioptilus, from deeper shore
waters of the American Pacific coast. The stalk is
partly imbedded in sand. Large specimens may be
2 feet long. (Ralph Buchsbaum)

pennatulid, is common in the West Indies and on
warm American shores, extending northward to the
Carolinas and to southern California. Related forms
are known from the Red Sea and from Australian
and other coasts. Though named for its kidney shape
and violet color, it may be heart-shaped or of a rosy
pink tint. It lies with the short stalk buried, and the
flattened disklike body bears on its upper surface two
kinds of polyps, arranged in a regular pattern. Sea
pansies may occur in a muddy bay by the hundreds
or even by the thousands, the lovely color obscured
by a thin coating of sand or mud. Transferred to a
dish of clean sea water and left undisturbed, the disk
may expand to several times its contracted size and
the polyps may open. If they are kept in the dark for

[103

several hours and then poked, a wave of soft bluish
light spreads over the whole surface of the colony
from the point touched. Renillas feed on small ani-
mals and larvae, stinging and swallowing them after
the prey has become entangled in a mucous net se-
creted over the surface. They are themselves known
to be eaten by nudibranch mollusks, one of the few
animal groups with a taste for the coelenterates.

SEA ANEMONES AND CORALS

(Subclass Zoantharia)

This somewhat heterogeneous group includes the
sea anemones, solitary and without a skeleton; the
true or stony corals, with a skeleton and usually co-
lonial; the black corals; the zoanthids; and the “tube
anemones” or cerianthids. Not all fit the most com-
mon body pattern of parts repeated in multiples of
six; but none fits the neat aleyonarian model of just
eight feathery tentacles and eight internal partitions.

THE SEA ANEMONES

Though named for the lovely “windflowers” of
mountains and woodlands, the familiar anemones of
tide pools and rocky ledges more often suggest dahl-
ias and chrysanthemums. There are about a thou-
sand species of sea anemones, and most have a
broad, flat, rayed disk crowning the free end of a
stout muscular body. At the center of the rayed disk,
which gives the group its order name, Actiniaria, is
an elongate mouth, usually with a flagellated groove
at each end for directing a current of water to the in-
terior. Surrounding the mouth are one or more circles
of tapering hollow tentacles that belie their harmless,
petal-like appearance, wafting minute animals into
the mouth or cramming it with worms, crabs, and
fishes.

The common colorings in temperate waters are
white, tan, salmon pink, orange, brown, olive, or
green, but temperate-zone anemones may also be
vividly red or striped and dotted in contrasting and
breath-takingly beautiful geometric patterns of reds,
blues, grays, greens, and purples. Even in tropical
waters, where all groups put on a spectacular show,
the anemones distinguish themselves by their bril-
liance of color.

Sea anemones unfold their disks in every sea,
growing larger and more numerous from the poles to
the equator, though any one species may not con-
form to the general trend. Mostly creatures of shore
and shallow waters, they extend to all depths. Un-
derwater photography has revealed an area 2100
feet deep, off the American Atlantic coast, where sea
anemones are the most abundant form of life. On
such mud bottoms they are anchored by a bulbous
base, attached to manganese nodules on the floor, or
cling to shrublike gorgonians or tall branching corals.
The Danish Galathea expedition hauled up a hith-

104 ]

erto unknown anemone from the Philippine trench,
about 30,000 feet down, and very appropriately
named it Galatheanthemum. From 15,000 feet the
Galathea dredge yielded white anemones attached
to the long stalks of Hyalonema-like glass sponges.

Entirely tropical are the floating minyads, many
of them a lovely blue color like that so often seen in
other floating coelenterates of warm surface waters.
The giant stichodacytyline anemones are also ex-
clusively tropical. These include Stoichactis, with a
disk up to 3 feet across, a full complement of plant-
like cells in its tissues, and an interesting set of small
crustacean and fish friends. Best known of its animal
commensals is the little pomacentrid “damsel fish,”
Amphiprion, that darts among the tentacles of Stoi-
chactis in Indo-Pacific waters. Vividly banded in
black and orange, with fins edged in black and white,
it is very conspicuous as it plays about its anemone
host; and it is said to lure other fishes to the host’s
disk or even to bring in offerings of food. At the least
threat the fish darts quickly to the safety of the way-
ing tentacles. The fish is apparently immune to the
anemone’s stings and perhaps becomes so by its
habit of mouthing and nibbling the tentacles. In any
case, a fish once acclimated to its host no longer in-
cites the discharge of stinging cells on contact with
the tentacles. Working at the Marineland of the Pa-
cific, an exhibition aquarium in California, and using
Stoichactis and Amphiprion imported from the Phil-
ippines, Davenport and Norris found that the protec-
tion of the fish seemed to reside in the mucous cover-
ing of its skin. The Dutch investigator Verwey, who
studied this anemone from Djakarta Bay, off Java,
has shown that at least in the conditions of an aquar-
ium, the big anemone does not flourish without its
small fish associate. Stoichactis is the upper limit of
the size range. At the other extreme are minute pol-
yps only a fraction of an inch long, some of them also
tropical, like Gonactinia prolifera of the eastern At-
lantic, which swims by waving its tentacles.

In temperate waters few anemones are as wide-
spread as the plumose anemone, Metridium, which
lives mostly below low-tide mark. The soft, rounded,
feathery masses of tentacles, colored white, pink,
orange, or brown, decorate wharf pilings and the un-
derside of floating docks, or rise on broad muscular
bodies, usually of the same color, in rocky caves or
crevices where they can be seen at the very lowest
tides. The large lobed and frilled feeding disk, cov-
ered with many hundreds of tentacles and with very
little bare area around the mouth, is vaguely sugges-
tive of the many-petaled chrysanthemum (Plate 18).
Fine tentacles capture only minute plankton animals,
which are swept toward the mouth by beating cilia on
tentacles and disk. Metridium extends pretty well
around the world in the northern hemisphere. It
flourishes in cool European waters, and on the Amer-

ican Atlantic coast it is one of the largest and most
familiar anemones from Labrador to New Jersey
(Plate 22). On the Pacific coast it extends along the
shallow shore from Alaska to Monterey, California.
As far south as La Jolla it has been seen on the rims
of underwater canyons by skin-diving, aqualung-
equipped biologists, like Conrad Limbaugh of the
Scripps Oceanographic Institute, who are learning to
know the anemones and other invertebrates of deeper
shore waters as we now know those of tide pools.
In the Bay of Morlaix, in Brittany, where perhaps
a third of the bay is difficult or impossible to dredge,
Pierre Drach, of the Biological Station at nearby
Roscoff, is diving with open rubber suit and aqua-
lung on the steep rocky slopes. To the study of such
slopes he is bringing the same careful methods of ob-
servation that we use so much more easily on land
for studying exactly how animals are associated with
each other. This is something we cannot learn from
the jumbled masses brought up by the dredge from
flat bottoms.

Favoring deeper waters and northern seas, around
the globe, is the dahlia anemone, Tealia, which is
large and stout and has short, somewhat blunt tenta-
cles that taper from wide bases. In the variety of
Tealia felina that is common on northern European
shores the column is often red spotted with green,
and the tentacles are strongly banded with reds,
blues, grays, and olives. The deep-water variety,
with a disk 1 foot or more across, is less strongly
marked and likely to be buff, yellow, or orange. On
American coasts the dahlia anemones are similarly
bright red, and often also pink, and in Maine one
has been called the thick-petaled rose anemone.
They are common below low-tide mark as far south
as Cape Cod on the Atlantic coast, and southward
to California on the Pacific coast (Plates 17 and 20).

Rocky bottom is the favored substrate of anemo-
nes, and in protected areas every crevice is jammed,
every tide pool carpeted, with anemones crowded
disk to disk. Some burrow in sand or mud, then lie
with the long, slender column completely buried and
only the feeding disk outspread on the surface, as
Peachia and Milne-Edwardsia on European shores,
Edwardsia in New England, Edwardsiella and Hare-
nactis on the southern California coast. Many anem-
ones hang from wharf pilings or floating wood, cling
to seaweeds or eelgrass, or attach to shells and stalks
of sessile animals, especially if on soft bottoms. Oth-
ers lead a mobile life affixed to jellyfishes and comb
jellies, the backs of crabs, the shells of living marine
snails, or the snail shells appropriated by hermit
crabs.

The classical alliance between anemone and her-
mit crab is that of Adamsia palliata on the hermit
crab Eupagurus prideauxi in European waters. The
crab seeks out a young anemone and holds it until it

A group of plumose anemones, Metridium, from north-
ern European waters. Some are expanded, spreading
their great lobed and frilled disks. Two are con-
tracted; the large one in the background, which has
pulled in its disk, resembles a plump tomato. (Ginter
Senfft )

attaches to the shell just below the mouth parts of
the crab. As the anemone grows, the base of its col-
umn extends upward in two lobes that meet and fuse,
embracing the shell. The anemone secretes a horny
membrane that roofs over any holes in the shell and
extends beyond the shell margin, enlarging its ca-
pacity and so minimizing the number of times the
growing crab must change houses. When it does
move to a new shell, the crab transfers its associate,
which submits readily instead of clinging stubbornly
to the old shell as it does if we try to remove it. The
anemone receives scraps of food from the crab’s less-
than-neat feeding, and the crab is protected by the
stinging tentacles and also by the stinging filaments
of the anemone. These last are long filaments that
extend freely in the digestive cavity from the swollen
glandular edges of the internal partitions. They are
richly endowed with stinging capsules, and when the

[105

anemone contracts they are extruded through the
mouth and through special holes in the body wall,
the cinclides. Many anemones, including Metridium,
extrude stinging filaments; but it is interesting that al-
most all the anemones that live on hermit crabs do
have them. Adamsia palliata apparently cannot live
without its crab host, but other anemones so associ-
ated are less dependent. Calliactis parasitica lives
on Eupagurus bernhardus (Plate 15) in Europe, and
Calliactis tricolor on hermit crabs along the Ameri-
can southeast coast and in the Gulf of Mexico.
Other species of Calliactis and other anemones,
however, are reported to have similar habits in all
parts of the world, mostly in fairly warm waters, as
of the Gulf of California, Chile, Hawaii, Japan, the
Indo-Pacific, the Great Barrier Reef, East and South
Africa. In the tropics certain reef crabs go about
brandishing an anemone in each claw, presumably
as defensive and food-catching devices, for the crabs
are said to reach up and take food from the disks of
the anemones.

Apparently contented anemones have been ob-
served to hug the same crevice for more than thirty
years. Others move occasionally, especially if their
posts turn out to be too surfy or on the sunny side;
and the more restless species walk about frequently
by a slow kind of muscular gliding. The minyads,
mentioned earlier, have the basal disk expanded into
a rounded float. The tiny Gonactinia was mentioned
earlier as one of the few anemones that can swim by
stroking the water with its tentacles. Undulating the
whole body produces brief swimming excursions for
some bigger forms, and Stomphia coccinea in Puget
Sound frees itself and swims about by muscular un-
dulations whenever it is touched by certain starfishes.
This may be a rapid-escape mechanism, as at least
one of the starfishes involved has been seen to feed
on anemones. For the most part, however, sea anem-
ones have few predators besides those intrepid eaters
—sea slugs and men.

Anemones expand their column and tentacles
by taking in water, and they are very vulnerable to
drying. Most live below low-tide mark where they
never have to face this problem, but shore anemo-
nes usually pull in their tentacles and contract until
the tide returns. The beadlet anemone, Actinia
equina, of European waters, is bright red with a row
of blue beads around the column just below the ten-
tacles, but it occurs also in less common brown and
green varieties. At Helgoland in the North Sea red
and green Actinias literally carpet the rocks. On
British and French shores one sees them on exposed
spots where others cannot brave the surf and at high
shore levels where more delicate anemones could not
survive the long intervals of dryness. As the tide ebbs
the beadlet contracts into a formless blob of red jelly

106 |

that in hot weather dries to a leathery knob before
the water comes surging back to restore its elegant
form, translucent coloring, and delicate texture. Ac-
tinias are the commonest of British shore anemones,
and their habits of feeding on jellyfishes, small fishes,
and other sizable prey are known to few people as to
Douglas and Alison Wilson. They were surprised one
day, however, to come upon a unique sight—a rocky
ridge in a Devon bay that at low tide was covered
with beadlets, each with a long, silvery sand eel
protruding from its mouth. A shoal of fishes had run
into the ridge, and there were the anemones, each
striving to cope with prey much too long to be swal-
lowed, while other animals were managing bites of
the protruding bodies.

Suddenly contracting anemones often eject water
from the mouth or through special holes in the body
wall. At low tide one sees jets of water issuing un-
expectedly from closing anemones, and hears the
squshing sounds made by luckless ones that have
been stepped on. Kneel beside a tide pool and poke
almost any anemone, and it will hug your finger as
the discharge of stinging threads makes the tentacles
cling and as the folding disk pulls in. Then, as in a
string pouch being closed by a tightening of the cord,
the anemone may contract a ring of circular muscle
around the opening and leave your intruding finger
outside. One of the few anemones that does not close
up and that rarely retracts its tentacles is the “opelet”
or “snakelocks,” Anemonia sulcata, a dull green or
pinkish brown anemone common on European shores
(Plate 14). In the sunny spots shunned by most
anemones, it spreads its long, snaky tentacles, often
tipped with mauve, where they best display to the
light the green algal cells within the tissues. Perhaps
it has little need to retreat, for its stinging capsules
are especially large and numerous and it is often
something of a feat to disentangle the clinging tenta-
cles from one’s fingers. Also green with contained
algal cells are the two common anemones of the
American Pacific coast, the solitary “big green
anemone,” Anthopleura xanthogrammica, and the
“aggregated anemone,” Anthopleura elegantissima
(Plate 13). Like the snakelocks, they feed in full
light. When darkness comes and most other anem-
ones begin to unfold their disks and feed, the an-
thopleuras draw in their tentacles and rest.

The big green anemone is known from Japan, the
North Pacific, and down the American Pacific coast
from Alaska to Panama in the very low tide zone or
in well-aerated tide pools. Flourishing specimens
growing in brilliant sunlight are a beautiful emerald
green, often marked with purple, and as much as 10
or even 16 inches across. In spite of their large size,
their sting causes only a slight tingling. Under
wharves, in caves, or in shaded spots they are pale

green or even white, perhaps tinted with pink or lay-
ender. The aggregated anemone, green with pink or
lavender markings, is by far the more abundant of
the two species, but it has a less extensive range and
peters out south of San Luis Obispo and north of
British Columbia. Aggregated anemones live in
densely crowded beds higher up on the shore, often
attached to rock in sand; they survive much sand
deposition and scour. Perhaps they are helped by
their patchy armor of adhering pieces of shell and
gravel, which makes them look so much like the
background that one often sits or walks on them un-
wittingly and then hears—or feels—their squashy
wetness. Both species of Anthopleura, as well as
many other anemones, have vertical rows of warts
that cover the column. In some anemones these
have no function we can discover, but in Antho-
pleura, Tealia, Bunodactis (Plate 21), and others
the protuberances are glandular and sticky, and hold
sand or shell fragments close about the column.

If green anemones that contain green algal cells
are more deeply colored in full light than in shaded
areas, we can see why this should be so, but what of
other green anemones or the green varieties of Ac-
tinia that have no algae? These are also found to be
more densely colored in brighter situations, and so
are many red dahlia anemones. If we explain this by
saying that the pigment acts as a screen against
light too strong for the delicate tissues, this will not
do for Metridium senile. The ones examined on Brit-
ish shores are, if anything, more likely to be white in
the most lighted situations. This species of plumose
anemone has an especially striking array of color
varieties, even in those found living side by side. Fox
and Pantin, working at Cambridge with specimens
of Metridium from all over England and from Scot-
land, described the varieties as white, simple red,
simple brown, brown with gray, simple gray, red
with gray, red with brown, and red with brown with
gray. The notation “simple red” covered red, orange,
or salmon-pink hues, or even yellowish varieties,
since these shades depend upon the intensity of the
red pigment, or perhaps several pigments. The con-
clusion they drew was that the color varieties may be
due to random variations in heredity and may be re-
lated to biological processes taking place within the
animal. When the resulting colors are vivid, they may
have no special value as coloration, but indicate only
that bright color is no great handicap to an anemone
and is therefore not eliminated by natural selection,
as perhaps it is in drab-colored groups that match
their surroundings. In some anemones the color is
clearly related to the food supply. If the tentacles of
a red Actinia equina are amputated and the animal
eats the usual diet of red shrimp, the tentacles grow
back red. If instead the anemone is fed on colorless

The aggregated anemone of the American Pacific
coast, Anthopleura elegantissima, in the final stage of
reproduction by body rupture. Only a thin strand of
tissue still connects the two daughter anemones.
(California. Woody Williams )

pieces of fish, the regenerated tentacles are colorless.

The responses of anemones are not always the
ones we would make to the same kinds of stimula-
tion, but they do seem suited to the life of an anem-
one. When taken into the laboratory by C. F. A.
Pantin and his many students at Cambridge, Calli-
actis parasitica appears undisturbed by contact with
an electrically heated wire that burns the skin of the
column. Yet the tentacles twitch at the slightest tap
on the walls of the aquarium or when waves are set
up in the water by any object, whether or not it is an
offering of food. To mechanical prodding the disk
and tentacles are four thousand times as sensitive as
the column.

Often it is impossible to pry an anemone loose
without inflicting injury or leaving pieces behind. In
nature there are species that treat themselves in this
same way, either because of the roughness of the
rock over which they move or because of incoordi-
nation. The plumose anemone is one of these, and it
turns tragedy into triumph, because the fragments

[ 107

round up and regenerate into new anemones. Dia-
dumene luciae, a small, slender, greenish anemone
striped with yellow or orange, common on both
American coasts, expands the basal disk and at-
taches it firmly, then pulls up the central portion,
leaving behind a ring of small pieces that may re-
generate into as many as a dozen or more anemones.
It also has a more brutal approach to asexual repro-
duction—rupture of the whole body into halves that
regenerate. This rapidly spreading anemone prob-
ably came originally from Japan, where it repro-
duces sexually as well.

Of the many genera that reproduce asexually,
only Gonactinia is known to split across the body;
all the others rend themselves lengthwise. This is an
unsettling habit at best, and things do not always get
divided neatly, so that anemones which divide asex-
ually often have unconventional numbers of tenta-
cles or mouth grooves or internal partitions. When
matters really go astray, an anemone may end with
ten or more mouth grooves instead of the more usual
two.

The aggregated anemone, mentioned earlier,
forms its colonies by asexual division of the body.
The round anemone becomes elliptical and one end
keeps moving outward until the stretched anemone
is connected in the middle only by a narrow strand
that finally breaks. Only uncrowded individuals di-
vide, so that in a cluster only the ones around the

Brain coral in light, with polyps retracted. (Great
Barrier Reef. Fritz Goro: Life Magazine )

edge pull apart, and small colonies spread out even-
tually into large, crowded beds.

Regeneration in anemones takes place most read-
ily in primitive forms like Harenactis, the burrowing
anemone, which can produce both disk and base
from almost any slice of the body. When Metridiuin
is cut across the column, the lower piece regenerates
a new disk with tentacles; but the upper portion can-
not readily produce a new base. Severed tentacles do
not usually regenerate, but in Boloceroides, a Japa-
nese anemone, the whole set of tentacles is shed and
then replaced; and each cast-off tentacle becomes a
new anemone.

It is a memorable day or sunset hour when one
comes upon anemones spawning in a tide pool and
sees the water turn cloudy with wave upon wave of
ejected eggs, or in some species ejected larvae. The
little free-swimming larva, oval or pear-shaped, of-
ten looks grooved along the attachments of the in-
ternal partitions. It develops a mouth but usually
does not push out tentacles until after it settles down.
Retaining the developing eggs in the digestive cavity
to the larval stage or even beyond is only one method
for prolonging maternal protection of the young. A
small red sea anemone, Epiactis prolifera, common
on eelgrass in Puget Sound but known all down the
American Pacific coast, is frequently found with a
complete circle of juvenile anemones in special brood
pouches around the middle of the external surface of
the column (Plate 16).

Usually we can only guess at the age of an anem-
one, for extended observations on particular anem-
ones in nature are rare. The late W. K. Fisher, when
he was director of the Hopkins Marine Laboratory
at Pacific Grove, California, did observe some large
green anemones that occupied the same crevice for
at least thirty years. But the laurels for known lon-
gevity all go to captive anemones tended by me-
thodical Scots. In The Great Barrier Reef, Dakin
tells of Dalyell, a Scottish laird and fine naturalist,
who about 1827 collected an Actinia from a rock
pool at North Berwick and kept it in a little bowl,
feeding it on bits of oyster or mussel and changing its
water regularly. Finally known as Granny, it outlived
Dalyell and three successive caretakers; and when
things finally went wrong and it died, it was given a
newspaper obituary notice half a column long. An
even more famous batch of anemones, long identi-
fied as Sagartia and later as Cereus, were said to
have been collected as full-grown anemones some
time prior to 1862, and for many years lovingly
tended by a lady who fed them fresh liver. They were
finally given to the Department of Zoology at the
University of Edinburgh, and there they thrived and
budded until something went amiss and they were
all simultaneously found dead in about 1940 or
1942. At that time they were at least eighty years

old, more likely ninety, but they had undergone no
obvious changes during all the years of observation.

THE TRUE OR STONY CORALS

The graceful sprig of white coral on the mantel-
piece, rudely broken from its firm attachment on
some coral reef, is little more than a brittle limestone
cast of coralline symmetry. In life it was veiled with
delicate flesh of pink, heliotrope, purple, red, yellow,
green, or golden-brown hue; and it held blossom-like
polyps secure in its sheltering craters. Though many
tons of coral skeletons are every year distributed all
over the world to ornament homes far from the trop-
ics, the great economic importance of coral polyps
lies in the serious hazards to navigation erected by
their limestone-secreting habits. So rapid is reef
growth in some parts of the South Seas that navi-
gation charts more than twenty years old are said to
be useless. Much modern research on living coral
reefs is contributing toward a more successful ap-
proach to drilling for oil in fossil reefs left from ear-
lier geologic periods when the extent of warm seas
on our watery planet was far greater than it is in
our time.

There are some twenty-five hundred species of
true or stony corals (technically called scleractinian
or madreporarian corals), and all have similar pol-
yps that look like tiny and delicate anemones sitting
in limestone cups. The polyps may be widely spaced,
each occupying a separate cup; or the cups may be
so close together as to have common walls; or the
polyps may be joined together in rows and occupy
grooves in a rounded skeletal mass. In the “brain
corals” so common on coral reefs, sinuous skeletal
grooves are fringed on each side by a continuous
row of tentacles and have along their bottom a row
of spaced mouths.

Relatively few corals are solitary, and these oc-
cupy isolated little cups or disklike skeletons several
inches across. All the rest are colonial and join their
small but numerous forces to secrete large coral tene-
ments. The rounded boulder-like corals are hardier
and predominate at the surf-beaten seaward face of
most reefs. The branching antler-like corals (Plate
31) of shallow waters are more typical of the pro-
tected rear areas of a reef. Sometimes the same spe-
cies of coral grows rounded or softly lobed in exposed
situations and intricately branching farther back on
the reef. Deep-water coral colonies have a treelike
aspect, with narrow branches well suited to shed sed-
iments that fall from above.

In the daytime coral polyps remain more or less
contracted, then expand and feed at night, when
plankton animals rise to the surface in greatest num-
bers. Corals with very small tentacles entangle mi-
nute crustaceans and other animals in strands of mu-
cus and waft them to the mouth by beating cilia. The

larger polyps with long tentacles grasp small prey,
sometimes even tiny fishes, and drop the food onto
the mouth or push it in (Plate 26).

The skeletons of stony corals are not laid down
within the living substance, as in the alcyonarian
corals described earlier, but are secreted by the outer
layer of cells and lie completely outside the coral
animals. Each polyp secretes about itself a limy cup
filled with radiating ridges that alternate with the
internal partitions. As the ridges grow by steady ac-
cretion, they push up the underside of the body into
folds that conform to the hard ridges. Except for
some of the orange-red or red solitary and deep-
water forms, corals have no pigments in the skeleton
itself, so that dried reef corals are various shades of
off-white until they are bleached white by the sun or
by those who prepare pieces of decorative coral for
sale. Many reef-coral “heads” look red or green
when broken open, but only because the old layers
of porous colonial skeleton are thoroughly permeated
by colored algae.

Corals live firmly cemented to the bottom, but
some of the solitary forms, though attached when
young, are freed later in life to shift about on sandy
bottoms or to become imbedded in mud by a pointed
base. The mushroom coral, Fungia, found mostly on
tropical reefs, has a single large green or brownish
polyp that may be 5 inches across or more. The fully
extended tentacles stretch 2 or 3 inches beyond the
disk. The young mushroom coral expands at the
mouth end into a disk which is eventually set free.
The original stalk then repeatedly produces and
sheds disks until a number lie scattered about, and
still growing, upon the bottom. The beautiful convex
disk with its many large radiating ridges looks like
the underside of the cap of a gilled mushroom; it is
familiar to collectors of shells and corals. A free-
living coral, Heteropsammia, provides shelter for a
sipunculid worm; when the coral topples over, the
worm sets it upright.

The subtle or gorgeous colorings of living corals,
which make coral reefs as exquisitely beautiful as
any flower garden, are provided in part by the
golden-brown plantlike cells that live within colorless
polyps, as well as by the many pastel tints lent by
pigments in the flesh. The gayest contrasts often
come from the other animals that throng all coral
reefs, either attaching firmly to maintain a foothold
on these biological oases in a vast, shifting ocean, or
moving about freely from one coral crevice to an-
other in the almost spongelike porosity of old coral
layers. Gaily colored fishes dart in and out of coral
thickets, and some of them browse on the coral to get
at the worms in coral cavities. Little coral-gall crabs
live within the branches of certain corals, the young
female settling in the fork of a growing branch and
becoming imprisoned as coral growth continues. In

[ 109

the perforated coral chamber it maintains respiratory
and feeding currents, and when mature it is visited
by a minute male able to make its way through the
small openings in the coral.

Sediments would clog the delicate ciliary-mucus
feeding apparatus of corals were they not constantly
removed by reversing the ciliary feeding currents to
carry foreign particles to the outer edge of the feed-
ing disk and drop them off. Some polyps simply
shake off sand by rising up in their little cups. De-
spite this steady grooming, rapidly settling sediments
in shallow waters seriously limit the distribution of
reef corals by smothering the little settling larvae and
by making the water too turbid to admit sufficient
light for the plantlike cells in adult tissues.

The classification of corals cuts across such differ-
ences as solitary and colonial habit, distribution over
the seas, and whether or not the coral is an im-
portant reef-builder. It is based on the finer structure
of the skeleton. Since it is not possible here to take
up the many kinds of corals group by group, we shall
consider them in two categories which are convenient
for readers who live on temperate shores and which
do have real significance in the mode of life of the
corals.

Corals Extending into Temperate or Cold Waters

The solitary cup corals (Plate 23) and the tall
branching colonies considered here belong to groups
represented on tropical coral reefs and in deep tropi-
cal waters, but they are not restricted to such waters,
and many do best in subtropical or cool seas all
over the world. Nor are they limited to shallow wa-
ters, as reef corals are. Delicate branching forms
that occur at great depths in the tropics, even to
24,000 feet or more, can be dredged at lesser and
lesser depths as we move to cooler latitudes. Most of
these corals do not harbor the plantlike cells that play
so great a role in the life of reef corals, and they are
quite negative to light. Where they do not keep to
deep waters they grow in dim rock pools, on the un-
dersides of stones, or in the shade of neighboring
corals on a reef. The yellow, orange, red, brown,
and black pigments which color the soft tissues of
many may in bright situations help to screen the
strong light.

The little orange-red solitary cup coral, Balano-
phyllia elegans, is abundant in shaded situations in
Monterey Bay in California and northward to Puget
Sound. When the delicate flesh is so tightly con-
tracted that it forms a mere veil over the hollowed
cup and its radiating ridges, it measures 44 to 2 of
an inch across. Fully expanded, the little polyp rises
much higher than the cup and extends long, tapering
transparent tentacles covered with wartlike batteries
of stinging cells. On southwestern British shores
Balanophyllia regia, with bright yellow warts on the

110]

tentacles, is called “the red and gold star coral.”
Close to shore it is rare, but in deeper waters its cups
are found in great numbers.

The “Devonshire cup coral,” Caryophyllia smithi,
is found at low-tide mark in southwest England, and
is often dredged from the continental shelf south of
Ireland and at all depths in the English Channel,
where it attaches to rocky outcrops on the soft bot-
tom. The white or pinkish disk, about 34 of an inch
across, is ringed with chestnut brown around the
mouth; the transparent tentacles have brown mark-
ings and silvery white knobbed tips. On the Ameri-
can Pacific coast Caryophyllia is a shore form in
Puget Sound, and occurs deeper farther southward.

A larger fan-shaped solitary coral, Flabellum, is
common on Mediterranean bottoms alongside Bal-
anophyllia, and also on deep mud bottoms in the
Atlantic. A salmon-colored species, about 4 inches
across, comes up in dredges from Newfoundland to
Florida. Flabellum is attached when young but later
may lie loose on the bottom or with the tapering
base imbedded in the mud.

The “star coral” of American coasts is Astrangia,
which forms small encrusting colonies with closely
spaced cups. The knobbed tentacles, dotted with
warts of stinging cells, catch tiny crustaceans and
even minute fishes. Astrangia danae, with colonies
usually 2 or 3 inches across, has white or pinkish
polyps less than 2 of an inch high. It encrusts rocks
from Cape Cod to Florida. This is a hardy species,
and when brought in to an aquarium, even after be-
ing shipped hundreds of miles from the sea, it can be
maintained for some time on bits of raw meat. A spe-
cies in southern California, once said to be common
in pools near La Jolla, was described as orange or
coral red, with lighter tentacles ending in white
knobs.

In deep Atlantic waters the tall, branching colo-
nial corals that dominate whole areas of the conti-
nental shelf, especially on its sloping edge, have large
blossom-like polyps that are widely spaced on the
shrublike or treelike branches. Dredging reveals
slopes of the northeastern Atlantic, from six hun-
dred to six thousand feet, where the bottom is
covered with open or dense thickets of yellow Madre-
pora and Lophelia. A species of Lophelia is even
better known from the deep Norwegian fjords, es-
pecially Trondheim Fjord, where at about six hun-
dred feet the rocky bottoms support great banks of
Lophelia and Amphihelia. These differ from typi-
cal coral reefs in that they never come to the surface.
Also scattered over the continental shelves and slopes
are great patches of Dendrophyllia.

All these deep-water branching colonies are en-
crusted with small solitary corals and with some three
hundred species of other invertebrates that are fas-
tened permanently and grasp their food out of the wa-

ter that flows by, or that creep about on the branches
safe above the smothering sediments of the soft sea
floor.

Dendrophyllids are also well known in the Medi-
terranean for their lovely yellow or red polyps. As-
troides (Plate 24) forms an orange-colored belt
below the water line. A similar coral is Tubastrea,
a bright red dendrophyllid that is widely distributed.
On Jamaican reefs the red flesh of Tubastrea stands
out in sharp contrast with the reef corals that take
their soft green and golden-brown colorings from
plantlike cells contained within the transparent and
colorless tissues.

Corals Restricted to Shallow Tropical Seas

Nearly all shallow-water corals of warm waters—
and this includes all the true reef corals—are abun-
dantly filled with plantlike photosynthetic cells
(called zooxanthellae and thought to be modified
dinoflagellates ). The chemical partnership that links
animal and plantlike cells apparently makes possible
the close spacing of the polyps of huge reef com-
munities, in which millions upon millions of individu-
als are crowded together in great honeycombs of
coral, further congested by myriads of hangers-on.

Reef corals do not digest their plantlike cells even
though these always occur in the digestive lining. If
starved or placed in the dark, the corals eject the
little guests. Nor is oxygen usually in short supply on
the wave-beaten surface of a reef. The most in-
formed guess, that of C. M. Yonge, who during the
Great Barrier Reef Expedition in 1928 performed
many carefully controlled experiments on living reef
corals, is that the corals benefit most from the rapid
removal of their carbon dioxide, and especially of
their nitrogenous and phosphate wastes—and that
this rapid turnover of materials promotes the prolific
growth of tropical reefs. This means that true reef
corals are limited in their distribution to conditions
under which the plant-animal bond remains intact.

Rate of growth varies with species, location, depth,
and other factors. Some corals measured in the
1890’s by Saville-Kent on Thursday Island, in the
Great Barrier Reef area, were measured again
twenty-three years later. A brain coral had increased
from 30 to 74 inches in diameter, and a specimen of
Porites (Plate 25), a very dense coral, from 19 feet
to 22 feet 9% inches. The East Indian reefs, below a
depth of fifteen feet, grow upward as much as 4
inches a year.

A map of coral-reef distribution reveals that the
reefs occur in a great warm belt that engirdles the
middle of the globe, roughly between latitudes 30°N.
and 30°S., so that the reefs of the western Atlantic
extend for about the same distance north and south
of the equator as do those of the Indo-Pacific. Within
this belt temperatures average 21°C. (about 70°F.)

Each polyp of the coral colony (Astrangia) is about
¥%% inch high. It produces new individuals by bud-
ding, thus enlarging the colony. Astrangia tolerates
the cold waters off Cape Cod, Massachusetts, but
does not form reefs there. (American Museum of
Natural History )

or higher, and never drop lower by more than a few
degrees or for very brief periods. The most flourish-
ing growth and the greatest variety of species is in
waters that average 25° to 29°C. (77° to 84°F.),
and most of the antler-like branching forms are in
this narrower zone. Below an average temperature
of 23.4°C. (74.3°F.), the species are dominated by
the more resistant rounded forms.

A closer look at the map brings out great gaps in
the distribution of corals where cold currents from
the Antarctic stream north along the western coasts
of continents. The western coasts of Africa and South
America have almost no reef corals. Neither western
Mexico nor California have any true reefs. Warm
currents, on the other hand, make a small bulge in
the reef belt at Bermuda, where the northward-flow-
ing warm waters of the Gulf Stream support beauti-
ful if not typical reefs at 32°N. The southernmost
Atlantic reefs are those at the latitude of Rio de
Janeiro (23°S.). In the Pacific the reefs extend
northward to the southern shore of Japan, while in
the southern hemisphere the reefs farthest from the
equator are those of Queensland, Australia (about
24°S.). Other great gaps occur at the mouths of
rivers, where fresh water and silt are fatal to the
growth of reef corals.

Thus the lesser of the two great centers of reef-
building, that of the Caribbean and adjacent waters,
includes the reefs of Bermuda, the Bahamas, the
West Indies, southeastern Florida, and parts of the
coast of Brazil. Diving expeditions have found some
reef growth on the western or Gulf coast of Florida,
at depths of 50 to 150 feet. But only the southeastern
shore of the peninsula of Florida has good reefs, and
these can be seen a few miles south of Miami. Some

[111

Elkhorn coral formation off the Virgin Islands. This is the only stony coral listed among
“venomous coelenterates.” It is a menace to skin divers off the Florida keys and the West
Indies. (T. Parkinson: National Audubon)

of the smaller coral species are accessible to anyone
who wades out in many places along the Florida
keys, even as far north as the shores of Elliot Key or
on the bars south of Biscayne Key. F. G. Walton
Smith’s Atlantic Reef Corals will be helpful to any-
one visiting the Florida shore, and it has brief sug-
gestions on where to see the better-developed reefs
of the Bahamas and Cuba. He lists nineteen spe-
cies for Bermuda and forty species from Florida
waters. Thomas Goreau has in recent years collected
forty of the forty-one species recorded for Jamaica,
and he reports that the density of growth is often
comparable with that on the great Indo-Pacific reefs
even though the number of species is far less. The
Atlantic reefs are mostly bank reefs built on flat shal-
low platforms. They are farther from shore than true
fringing reefs, but the lagoon channel that separates
them from the shore is not nearly so deep as in the

112]

barrier reefs of the South Seas. They are often some
distance inward from the edge of the platform, so
they do not slope off into very deep water as do
atolls and barrier reefs.

The most densely crowded communities of animal
species found anywhere on land or in the sea are
those of the great coral reefs of the Indo-Pacific re-
gion, from the Red Sea and the east coast of Africa
at one extreme to the islands of Hawaii, Tahiti, the
Marquesas, etc. at the other. The reefs of the African
east coast and of the island of Madagascar are fring-
ing reefs, which lie close to shore in shallow water
and continue to grow actively only on the wave-
beaten seaward side, which slopes steeply downward
into deep water. At low tide one can wade out to the
partly exposed platform. Such fringing reefs are also
well developed at Java, the Solomon Islands, and the
Carolines, but grow less well at Hawaii and other

islands that are near the outer edge of the Indo-
Pacific coral region.

Barrier reefs consist of lines of reefs paralleling a
mainland but separated from it by a lagoon channel
deep enough to accommodate large ships. These are
not well developed in the Indian Ocean but in the
Pacific are found at the Society Islands, the Fiji Is-
lands, New Caledonia, to the southeast of New
Guinea, and at many other spots. The largest and
best-known of barrier reefs is the Great Barrier Reef
of northeastern Australia, which parallels the coast
of Queensland for 1250 miles, though it is inter-
rupted by many passages.

Atolls are the coral islands that romantic dreams
are made of. These ring-shaped or horseshoe-shaped
islands, surrounding a central lagoon with sheltering
palm trees and mangroves, are dotted like oases over
the vast Indian and Pacific oceans in waters thou-
sands of feet deep.

Below the depths at which there is sufficient light
for the photosynthesis carried on by their content of
plantlike cells, reef corals cannot live. They grow
best near the surface and are most abundant in the
upper 60 feet of water, though many extend through
the water layers down to 150 feet. Only a few man-
age to grow as low as 270 feet.

The best-developed reefs of the Bahamas, Ja-
maica, and Florida, according to Norman Newell, a
leading student of Atlantic and other reefs, usually
have three coral zones, which are determined by
differences in depth and turbulence of water: an
outer zone of massive corals, especially of yellow-
brown Montastrea annularis lying at depths of thirty
to sixty feet; a middle zone of brownish yellow stag-
horn corals, Acropora palmata, at five to thirty feet;
and an inner rocky shoal rising to low-tide level.
This last zone is characterized by the velvety yellow-
orange or brown “stinging coral,” Millepora alcicor-
nis (not a true stony coral but a hydrozoan coral),
encrusting coralline algae, sea fans, and small
rounded corals. In the Indo-Pacific many reefs re-
ceive much greater contributions of limestone from
the coral-secreting algae, and also in certain places
from hydrozoan reef-builders like the organ-pipe
coral and blue coral.

THE ZOANTHIDS

Without skeletons and with a marginal circlet of
unbranched tentacles, zoanthids superficially resem-
ble small anemones, except that most of them are
colonial and are united at their bases. This is a small
group, found in both shallow and deep waters and in
cold and warm latitudes, but especially in warm
shallow seas. Most zoanthids regularly grow on the
surfaces of other animals, often on very specific
hosts. Certain species of Epizoanthus occur only on
particular glass sponges; others fasten to the shells

inhabited by hermit crabs, dissolving away the crab’s
shell and finally coming to enclose the crab directly.
Other genera live on sponges, hydroids, gorgonians,
corals, bryozoans, and worm tubes (Plate 30).

THE BLACK CORALS

The black or thorny corals, or antipatharians, are
slender, branching, attached colonies of plantlike
form ranging from an inch to several feet high. Most
are known to biologists only as preserved specimens
dredged from deep or abyssal waters, especially of
the tropics and subtropics. The horny internal
skeleton is black or brown and beset with thorns.
According to Russel and Yonge, in the excellent ac-
count of products of the sea which concludes their
book The Seas, the skeletons of certain black corals

The star coral, Montastrea, grows into yellow-brown
boulder-like masses, 5 feet or more across, in Florida,
the Bahamas, Bermuda, and the West Indies. The
individual cups are only a fraction of an inch across
and show the ridges supporting the internal parti-
tions. (Fritz Goro: Life Magazine )

are used in China, Japan, the Malay Archipelago,
and the Indian Ocean for making bracelets that are
worn to ward off rheumatism, drowning, and other
perils. Black corals occur also in the Mediterranean,
the Red Sea, and the Persian Gulf, but having no
decorative value they are no longer worked by Euro-
peans as they were in ancient times.

THE TUBE ANEMONES

Like long, slender, muscular burrowing anemones
are the tube anemones or cerianthids, which live
buried in sand almost to the feeding disk. The slender
tentacles arise in two distinct sets—an inner smaller
set encircling the mouth, and a marginal set, each
composed of one or more circlets. The body is sur-
rounded by a tube formed of a hardened slimy se-
cretion and lined with cast-off stinging capsules or
imbedded with sand grains and other foreign parti-
cles. The feeding disk cannot be retracted into the
column as in most anemones, but when disturbed it
disappears down the protecting tube. The Medi-
terranean Cerianthus is well known to visitors to the
Naples Aquarium, where fine specimens have been

114]

on display at least since the 1880's. In 1882 a small
green individual was placed in a tank when it was
only 14% inches long and 2% inches thick. In 1924,
forty-two years later, it had increased ten times in
size, and the crown of gracefully extended drooping
tentacles had a diameter of 10 inches. Species of
Cerianthus are also common in the English Channel
(Plate 32) and along the American Atlantic coast.
A brown species up to 6 inches long occurs from
Cape Cod to Florida in shallow water. A larger
northern species, with a rough tube up to 2 feet long,
housing an anemone that stretches 18 inches, occurs
in deep water from southern New England north-
ward at least to the Bay of Fundy. On the Ameri-
can Pacific coast Cerianthus estuari is well known
from sandy mud flats (alongside the burrowing and
true anemone Harenactis ) in Mission Bay. The outer
set of transparent, delicately banded tentacles is
spread out on the sand in a circle 4 or 5 inches
across. A bigger species, which does not live inter-
tidally north of southern California, may have a
tube 6 feet long. Most cerianthids are tropical or sub-
tropical.

CHAPTER IV

Sea walnut and Venus’ girdle

The Comb Jellies

@ N a smooth stretch of wave-washed sandy
beach one’s attention is easily caught, even at some
distance, by little oval balls of clear jelly that glisten
in the sun like crystal beads. “Cat’s eyes,” fishermen
on the American Pacific coast call them, and on
many other shores such stranded comb jellies are
known as “sea gooseberries” or, in the case of some
of the slightly larger species, as “sea walnuts.” If
they are not too far gone the little sea gooseberries
will revive in sea water, regain their gossamer loveli-
ness, and swim about like paddle boats, propelled
by the rapid beating of eight vertical rows of ciliary
combs that radiate over the rounded body like the
lines of longitude on a globe. The delicate trans-
parency of comb jellies makes them all but invisible
in the water, so that often they reveal themselves
only in the rippling iridescence of the rows of beating
combs as they diffract the light. Unless the water is
smooth as glass they are likely to remain below the
surface, and even when they come within one’s
reach they slip between the fingers or tear to shreds
at the touch of an oar. Such diaphanous creatures
are best gathered by towing a net behind a boat, but
a few may be dipped up in a small net or container.

The daytime play of rainbow colors is replaced at
night by luminescent waves of an intensity that is
matched only by some of the deep-sea fishes. On
summer nights the waters beneath a jutting wharf
may shine with hundreds of languidly gliding
comb jellies, which at the slightest disturbance light
up along the eight comb rows. Dipped up and taken
in a jar of sea water to a lighted room, they cease to

(Phylum Ctenophora)

glow. Then, if the room is darkened for at least
twenty minutes, they shine again with a bluish or
greenish light.

The phylum name, Ctenophora, means “comb-
bearers,” and the swimming paddles are made of
large cilia that are fused at the attached end like the
teeth of a comb. They are regulated and coordi-
nated in their movements by a network of nerve cells
that connect with a tiny sense organ housed in a
glassy little dome atop the upper pole, the one oppo-
site the mouth. Presumably the sense organ is con-
cerned with balancing and helps to orient the ani-
mal as it swims.

The more primitive comb jellies, like the little sea
gooseberries, have two long tentacles with which they
fish for food. At times these are drawn up into
knotted, stringlike masses, at other times stretched
far out in graceful sweeping curves, the side
branches that fringe one edge lending a plumelike
elegance. The more advanced groups of comb jellies
have only fringes of short tentacles or lack them al-
together. When present, the tentacles or their side
branches are thickly studded with special adhesive
cells, unique to ctenophores and not to be confused
with the thread capsules of coelenterates. The pro-
truding heads of the adhesive cells are very sticky
and cling to prey. At their inner ends they are at-
tached to spirally coiled contractile filaments that
yield to the pull of struggling prey but cannot be
wrenched loose.

This is an exclusively marine group, though some
do flourish in bays and estuaries with a salt content

[115

only one-third that of full oceanic salinity. Of more
than eighty species, almost seventy can be found in
warm seas, three live only in arctic and northern
waters, three are deep-sea forms. Two species—the
sea gooseberry, Pleurobrachia pileus, and the flat-
tened thimble-like Beroé cucumis—are cosmopoli-
tan and found from pole to pole. Distribution varies
with temperature changes, and many comb jellies
migrate from surface to deeper waters and back
with the round of seasons, as Pleurobrachia pileus is
known to do in the Black Sea. During the cool of
spring it feeds at the surface, then descends gradually
to about 110 feet as warm weather arrives, and re-
mains below until winter weather returns, having
followed water temperatures that remained always
at about 52°F.

In stormy weather comb jellies sink below the sur-
face: but their feeble swimming powers are of no
avail against wind-whipped waters or strong currents
and tides, so that they often accumulate in great
swarms. Then they decimate the small animals
that float near the surface, including the fry of com-
mercially important fishes. Off the New England
coast feeding comb jellies are a menace to cod eggs
and young. And in England the fisheries experts
have ‘good reason to believe that swarms in certain

Swimming sea gooseberries, Pleurobrachia pileus. In
some the two long tentacles are extended, in others
withdrawn. (England. D. P. Wilson )

years wreak such havoc on small herrings as to be
one of the important factors in determining the sizes
of herring broods in the different years. The transpar-
ency of comb jellies readily reveals the truly formi-
dable meals they make on copepods, tiny fishes, lar-
vae, and eggs.

In warm seas ctenophores often have a yellowish
cast from the yellow-brown, plantlike cells which
they harbor. The relationship is apparently like that
seen in many tropical protozoans, sponges, and coe-
lenterates, which was discussed earlier.

The biradial symmetry of ctenophores is a two-
sided modification of radial symmetry, and the basic
body plan reminds us strongly of scyphozoan jelly-
fishes. The main cavity of the body is a digestive sac
with branches. Though fine particles can be elimi-
nated through two small pores near the upper pole,
the main opening of the digestive sac is still the
mouth, which serves also for ejecting fish heads and
other sizable wastes. Between the fragile digestive
lining and the delicate outer covering is a great bulk
of secreted jelly which lends firmness and buoyancy,
and in the jelly are various cells including long mus-
cle fibers. Comb jellies do not pulsate like jellyfishes,
but the elongated forms swim by gentle undulations
of the whole body, and the aberrant flattened ones
can creep about. When dropping vertically or ac-
tively moving along, the mouth end precedes. Rest-
ing or feeding comb jellies, however, often hang from
the surface with the mouth up.

Both ovaries and testes occur in all individuals;
they can usually be seen through the transparent
body as they hang from the walls of the eight diges-
tive canals that run below the rows of combs. The
eggs and sperms are shed through the mouth, and
the egg, fertilized in the open water, develops into a
little free-swimming larva, the cydippid, which looks
like a miniature of a sea gooseberry, with combs and
two long tentacles. In the more highly developed
ctenophores the cydippid must undergo reduction or
loss of the tentacles, besides many other changes, be-
fore it achieves the adult form.

The ctenophores are usually divided into two
classes, one with tentacles and one without.

Comb Jellies with
Tentacles

(Class Tentaculata)

THE CYDIPPIDS

The comb jellies that have departed least from the
primitive ctenophore stock are the cydippids, the lit-
tle globular, egg-shaped, or pear-shaped relatives of
the sea gooseberry. Pleurobrachia pileus, referred to
earlier as having a world-wide distribution, has an

egg-shaped body less than 1 inch long and about 12
of an inch wide. It loops through the water sweeping
two long tentacles, which can extend twenty times
the length of the body or can be completely with-
drawn into the two pouches from which they emerge.
Each tentacle is fringed along one edge with short,
sticky side branches that adhere to floating fish eggs,
copepods, crab and oyster larvae, arrow worms, and
tiny fishes. As the prey is caught the tentacle shortens
and wipes the food off onto the rim of the narrow
mouth, where beating cilia on the lips carry it swiftly
inward to await its turn in the digestive sac—perhaps
already crammed full with undigested little fishes.

During winter storms this comb jelly is driven
southward along the eastern coast of America and
can be seen in the waters of Long Island and New
Jersey, but in early summer it is most abundant off
southern New England, trailing orange-tinged tenta-
cles. As the water warms it vanishes there and ap-
pears in great swarms, one individual almost touch-
ing another, over wide areas off Maine and Nova
Scotia, the Arctic Sea, and northern Europe. Another
species, P. brunnea, with purplish touches on the ten-
tacles, abounds off the New Jersey coast in the fall.
The little ovate spheres are also well known in the
Pacific and the Antarctic. From San Diego north-
ward along the whole of the Pacific coast the beaches
are strewn with stranded P. bachei; but to see these
little sea gooseberries maneuvering about in the wa-
ter, with red-tinged tentacles sweeping every inch,
there are few places that compare with Puget Sound,
an arm of the Pacific Ocean that extends into north-
western Washington, offering protection to a great
profusion of invertebrates.

A common “sea walnut” is Mertensia ovum, about
2 inches long and with the mouth at the more pointed
end of the somewhat flattened but egg-shaped body.
A delicate pink color tinges sense organ, tentacles,
and comb rows. Though Mertensia can in winter
wander as far southward as New Jersey, its south-
ward extension in summer is Massachusetts Bay, for
it cannot tolerate warm water. Great summer swarms
are seen off Maine, but the center of distribution
seems to be the Labrador coast, where it has been
seen to feed on little sculpins. On the contrary, Hor-
miphora plumosa, a warm-water species of the Med-
iterranean and tropical Atlantic, is seen north of its
normal habitat only as the warm flow of the Gulf
Stream carries it up the American coast or to English
waters. Species of Hormiphora and Mertensia occur
also on the American Pacific coast.

THE LOBED COMB JELLIES

The lobed comb jellies have compressed bodies
drawn out on two sides into large lobes. After starting
in life as cydippid larvae that look like tiny sea goose-
berries with two long tentacles, they transform into

The lobed comb jelly, Mnemiopsis, common along
the American Atlantic coast, may be seen in great
swarms in summer. When disturbed, as by the pass-
ing of a boat, it glows brightly along the eight rows
of swimming plates. Large specimens are 4 inches
long. (Massachusetts. George G. Lower)

adults without tentacle pouches and with tentacles
reduced to short filaments and fringes close to the
mouth. They can snare fishes longer than themselves,
holding them fast with the short but powerful tenta-
cles and closing them in, by means of the lobes, until
they are safely inside the mouth. Usually they satisfy
their voracious appetites on crustaceans and larvae
small enough to be entangled in mucus and wafted
into the mouth by ciliated grooves. Mnemiopsis leidyi
is pear-shaped, slightly translucent, and up to 4
inches long. It feeds mostly on copepods and mollusk
larvae, and when it is present in numbers bodes no
good for the oyster industry, since it can down a hun-
dred or more oyster larvae at a time. The summer
swarms of lobed ctenophores are especially noted for
lighting up New England waters with a greenish light
of great intensity. From Cape Cod to South Carolina,
Mnemiopsis readily adapts to marked changes in
salinity and temperature. Individuals that in winter
invade the coastal waters of New Jersey have been
seen with combs continuing to beat until they finally
freeze fast in the ice. Another species, often greenish

[117

amber in color, extends from South Carolina into the
tropics and in summer is common around Jamaica.
Its jelly is more rigid than in most, and it can be
lifted by hand without injury, or readily maintained
in an aquarium.

From north of Cape Cod into arctic waters the
common lobed form is Bolinopsis, also well known
from Scottish and northern European waters and
from the cool waters of the American Pacific coast.

THE CESTIDS

The cestids (“girdle-like”) are a somewhat sur-
realistic version of the lobed ctenophores. The body
is a gelatinous ribbon, greatly flattened and elongated
in the plane at right angles to that of the mouth and
sense organ, so that these remain no farther apart
than in lobed comb jellies. The tentacles are reduced
to a tuft alongside the mouth and a row of short fila-
ments along the edge bearing the mouth. They swim
by graceful undulations of the body as well as by the
beating of elongated comb rows. The well-known
“Venus’ girdle,” Cestum veneris, shimmering with
blue and green iridescence in the sunlight and some-
times reaching a length of 4% feet, easily deserves
the compliment of its name. The genus Cestum and
the similar Velamen, both known from the Mediter-
ranean and limited to warm waters, are represented
by species that turn up around Florida.

THE FEATTENED CREEPING

COMB JELLIES

The creeping ctenophores are an aberrant flat-
tened group, often colored on the upper surface in
dull reds or greens. Most are warm-water forms.

118]

Ctenoplana, with combs and two tentacles, can creep
on the bottom but usually floats at the surface off the
shores of Sumatra, New Guinea, Indochina, and Ja-
pan. Coeloplana, leaflike and also with two tentacles
but without combs in the adult, was discovered in
the Red Sea, is abundant off Japan, and occurs also
off Florida. It creeps about on particular alcyonar-
ians. A curious cold-water form, Tjalfiella, also with-
out combs, is found in Greenland waters creeping
about on the deep-water pennatulid Umbellula. Rec-
ognizing a nearly sessile comb jelly that has no combs
is a challenge even to the specialist. The affinities of
Tjalfiella were revealed when little cydippid larvae
were found in brood pouches on the upper surface.

Comb Jellies without
Tentacles

The beroid ctenophores, so called from the name
of the most important genus, Beroé, have no traces
of tentacles, either in adult or larva. They are some-
what flattened, and are variously described as thim-
ble-shaped, barrel-like, or mitre-shaped. The many
fine branches of the digestive canals make a con-
spicuous and decorative pattern. At the open end is
a very large mouth, and as the animal propels itself
about by the beating of its combs, it sucks in sizable
prey, often comb jellies nearly as large as itself.
Beroé is thimble-shaped and up to 6 inches long. It
is found in all seas, and in cold waters is of a delicate
pink or lavender color.

(Class Nuda)

CHAPTER V

Free-living turbellarian, tapeworm and _ fluke

The Flatworms

Oe may easily pass a lifetime without ever see-
ing a flatworm. The smallest ones are microscopic,
and the largest ones, the ribbon-like tapeworms that
may grow up to 50 feet or more in length, develop
and pass their adult lives safely hidden within the
bodies of their human or other vertebrate hosts. They
are seen only when they die or are rudely removed
by medical treatment. Best known, perhaps, are the
Ya-inch planarians used in classroom study and in
zoological research. In nature these live unobtru-
sively in springs, streams, and ponds, crawling about
on the vegetation or under stones. After gathering
wild watercress one may have to rinse out little pla-
narians. On marine shores the oval and leaflike poly-
clads, some of them 2 inches long and colorful or
beautifully striped, may be seen by turning over boul-
ders or peering into sheltered rock overhangs when
the tide is out. Tantalizingly hard to find are the land
planarians of moist temperate woods; by their noc-
turnal and retiring habits they elude even the serious
students of flatworms. The occasional land planar-
ian that turns up in temperate gardens or in green-
houses is usually an import from tropical lands,
brought in with exotic plants.

Yet for all this, free-living flatworms are abundant
and widespread; while the importance of the para-
sitic kinds in human history and in modern economic
and political problems can hardly be exaggerated.
One kind of parasitic flatworm, the blood fluke Schis-
tosoma, lives in the blood vessels of more than a hun-
dred million people. In World War II it helped to de-

(Phylum Platyhelminthes)

termine the outcome of many military actions in the
South Pacific. Parasitic flatworms are still very much
a part of the African and Asian pattern of disease,
low productivity, and poverty. If the pattern is to be
broken, the flatworm parasites that flourish espe-
cially—though by no means entirely—in tropical
countries will have to be more widely understood and
coped with. Some things that we think of as progress
in many countries, such as the building of dams to
supply irrigation canals, tend to increase the spread
of blood flukes. To understand why, one needs to
read the brief account that will be given of the life
cycle of such flukes. In temperate latitudes Euro-
peans and Americans, their pets, and their livestock,
are still subject to infestation with flukes and tape-
worms, though some of these have been brought un-
der control. Many people who think of such para-
sites as occurring only under very unsanitary condi-
tions have had “swimmers’ itch” caused by the larval
flukes that develop in numerous lovely lakes favored
as Summer resorts.

There are three classes of flatworms, roughly esti-
mated to include almost nine thousand known spe-
cies, only a fraction of the number that actually exist.
The first consists almost entirely of free-living little
worms. The other two classes, the flukes and the
tapeworms, are exclusively parasitic and far more
numerous. These are not attractive animals to the
average layman, and when Aristotle became fasci-
nated by the various worms that live in man, he felt
obliged to justify his curiosity in these words: “In all

[119

natural objects there is some marvel, and if anyone
despises the contemplation of lower animals, he must
despise himself.” From Aristotle’s time to our own
there have always been some minds that feel chal-
lenged by whatever is unknown, especially if it causes
vast human suffering. The unraveling of the com-
plexities of flatworm structure and habit is fortu-
nately a very active field of modern research.

Soft-bodied animals that are several to many times
as long as they are wide are inevitably tagged as
worms, and this name has been applied to soft, elon-
gated members of practically every large grouping of
animals. Of all the kinds of worm-shaped creatures,
the members of the phylum Platyhelminthes (“flat
worms’) are on the whole the most flattened and the
most primitive. The digestive cavity, when present at
all, has only one opening, as in the coelenterates. In
place of the jelly that provides much of the coelen-
terate bulk, however, flatworms have a solidly cellu-
lar middle layer, which includes several sets of mus-
cles and a variety of organs, especially of reproduc-
tive organs, a specialty of these animals.

With few exceptions, the flatworms are hermaph-
roditic—that is, each individual produces both eggs
and sperms. This does not mean that self-fertilization
is the rule. On the contrary, most flatworms are en-
dowed with an amazingly complex set of organs for
exchanging sperms with their neighbors or chance
acquaintances and for storing the sperms toward the
time when their eggs are to be fertilized. The ferti-
lized eggs, enclosed in delicate capsules or in hard-
ened shells, are shed to the exterior, and by means
of adhesive secretions may be strung together in egg
ribbons or masses or attached singly to stones or other
objects. Some of the fresh-water flatworms are espe-
cially noted for their ability to multiply asexually by
fragmentation or by crosswise rupture of the body.
This has led to detailed studies of their ability to re-
generate when experimentally cut into small pieces.

Beginning with the flatworms, all the groups of
animals are two-sided or bilaterally symmetrical. Or
they have some secondary modification of that kind
of symmetry. Bilateral animals have a front end that
goes first when the animal moves, and a rear or tail
end that follows along. They also have differing up-
per and lower surfaces, and right and left sides that
mirror each other. Organs that occur singly are usu-
ally in the mid-line, and paired organs occur on each
side of the mid-line as in ourselves. This means that
the flatworms are the first animals with a head. The
major sense organs are concentrated on the head or
front end, and most of the animal’s wits are gathered
into a brain, a concentration of nerve cells in the
head. Speedier, more coordinated behavior is the re-
sult, with more rapid responses to prey or enemies
than in the radial coelenterates.

The free-living flatworms have a highly developed

120]

talent for clinging to surfaces, and some fresh-water
planarians even have well-developed muscular suck-
ers for holding on. So it is not surprising that flat-
worms eventually took up parasitic habits and pro-
duced the formidable array of suckers and hooks by
which the various flukes and tapeworms maintain
their tenacious hold on the hosts that nurture them.

The Free-living

Flatworms

The free-living flatworms are at least partially
clothed with cilia that propel the smaller forms and
the young stages of larger members. In water these
cilia create the turbulence that suggested the name
of the group. The larger turbellarians, whether
aquatic or terrestrial, glide along primarily by mus-
cular waves, though these may be invisible to the
naked eye. To ease their way, land turbellarians
must lay down a thick carpet of secreted mucus, over
which they glide smoothly or sometimes hurry by a
more energetic series of muscular contractions. Even
the aquatic forms use a mucous bed, especially over
rough surfaces.

Shapes vary from elongated cylindrical worms
to extremely thin and flattened leaflike marine forms
that are almost circular. Though a few have tail lobes,
or little sensory lobes or tentacles on the head, these
are for the most part streamlined little animals with
no projections.

A very few turbellarians are parasitic, and some
are internal or external commensals that share the
food of their hosts while doing no serious harm. Most,
however, are carnivorous, eating tiny animals of suit-
able size or working away, bit by bit, at large pieces
of dead flesh or at living sessile animals, such as oys-
ters or barnacles, that cannot flee. Land planarians
can subdue insect larvae, snails, or even earthworms.

Turbellarians are divided into five orders based
primarily on differences in the form of the digestive
cavity; this internal distinction can often be readily
seen through the transparent body wall.

THE ACOELS

The name “acoel” means “without a cavity,” and
these minute and delicate worms have no digestive
cavity. The mouth, usually in the center of the under
surface, directs the food into the inner mass of cells,
where it is digested. Acoels are exclusively marine,
and most of them are elongate or broadly oval and
measure from 1%; to 14 of an inch in length. They
live so inconspicuously under stones, among algae,
on muddy bottoms, and sometimes on sandy shores,
that they are seldom seen by anyone not actively

(Class Turbellaria)

searching them out. Perhaps this is why almost all
the known species of acoels have been described
from temperate or arctic Atlantic waters close to the
haunts of most biologists, or in the Mediterranean or
other seas that connect with the Atlantic. That part
of the Atlantic known as the Sargasso Sea is the home
of Amphiscolops sargassi, which lives on the floating
sargassum seaweed. Tropical or Pacific species are
usually drifting forms picked up in nets towed from
boats. Two shore species are known from Monterey
Bay, California; but again, this is a base for sharp-
eyed biologists.

Most acoels are white or drab in color, but one of
the most celebrated species, Convoluta roscoffensis,
is a beautiful rich green from the green algal cells
that pack the elongated body (Plate 36). This spe-
cies of Convoluta is named for Roscoff, France, the
little lobster-fishing port where the University of
Paris maintains the largest of its several marine sta-
tions. It occurs also on certain sandy beaches in Brit-
tany and Normandy, always in dense concentrations
of many thousands or millions of tiny worms. The
patches look like splashes or streaks of fresh dark
green paint on the wet sand laid bare by a receding
tide. Concentrated only where they can be continu-
ously wetted by rivulets of draining water throughout
the low-tide period, the worms lie moist and glisten-
ing, displaying their green cells to the sun. Then as
the tide returns and the first waves roll in, the green
patches erase themselves in an instant. The worms
sense the distant wave shock and dig rapidly below
the surface. Twice in twenty-four hours, in rhythm
with the tides, the worms rise to the surface and later
sink below, keeping beyond the reach of pounding
waves yet providing exposure to light for the green
cells.

The young convolutas are white, like most acoels,
but soon they become infected with green cells, which
appear to be derived from little green flagellates that
may also be found living free in the sand. At first the
convolutas continue to feed voraciously on small or-
ganisms, and the plant-animal bond seems no differ-
ent from what we saw earlier in protozoans and coel-
enterates. The photosynthetic cells utilize gaseous
and especially nitrogenous animal wastes, and this
benefits the animal also by speeding its chemical
turnover. As the convolutas mature something hap-
pens that suggests the relationship has become un-
balanced. The worms stop feeding and begin to di-
gest the green cells, eventually dooming both part-
ners, though not before the convolutas have laid
eggs in the sand and ensured a new generation.

Many acoels have no eyes and depend on general
sensitivity of the body to light; some have on the
head two pigmented spots that overlie nervous tissue
sensitive to light. Convoluta roscoffensis has two such
orange-pigmented eyes, and between them lies an

otocyst, a tiny balancing organ like those seen in
many coelenterates. It shows as a golden dot in the
center of the head on several of the worms in
Plate 36.

THE RHABDOCOELS

A straight and unbranched digestive cavity distin-
guishes the little rhabdocoels (“rodlike cavity”), and
it can be readily discerned through the transparent
and usually colorless body wall. These are very small
worms, microscopic or in most cases measuring less
than % of an inch. Of elongate shape, they may be
plump or slender, and usually are clothed with short
cilia. Most have a pair of pigmented eyes at the head
end. Rhabdocoels are common in all fresh waters and
on marine shores, especially on sandy or muddy bot-
toms. A few are restricted to caves or hot springs or
manage to live in moist places on land. Microstomum
occurs in both fresh and salt waters. A fresh-water
species common in the eastern United States and in
Europe is known for its armory of stinging cells, ob-
tained from the hydras on which it feeds. When
Microstomum undergoes asexual division of the body
the parts do not separate at once, so that after several
successive divisions there results a chain of connected
subindividuals, each with its own mouth.

Formerly lumped with the rhabdocoels are the
similar, though generally a little larger, alleocoels.
These are now placed in a separate order.

THE TRICLADS OR PLANARIANS

Called triclads from their “three-branched” diges-
tive cavity, or planarians because they are usually
“level” or flattened, this group of flatworms is the
most familiar because of the extensive use to which
certain fresh-water species have been put in teaching
and in research, as was mentioned earlier. Especially
when the thin body wall is unpigmented, one may be
able to see the three main branches of the digestive
cavity, each with numerous side branches. From a
point not far from the middle of the body, one main
trunk extends forward into the head, and the other
two extend backward on either side of the elongated
body, which tapers to the rear. The mouth is on the
under surface, near the middle of the body, and
through the mouth triclads can protrude a long, mus-
cular feeding tube or pharynx.

The fresh-water planarians, the marine ones, and
those that live in moist places on land, belong to dif-
ferent suborders. Such correspondence between hab-
itat and classification, were it more general, would
greatly simplify the text of a book such as this one.
Unfortunately it is very unusual among animals, as is
pointed out by Libbie Hyman, the American author-
ity on flatworms, in that volume of her Treatise on
Invertebrates that deals exhaustively with the group.

Fresh-water planarians favor temperate waters

[121

The head of the fresh-water planarian, Dugesia ti-
grina, shows two pigment-cup eyes and a pair of sen-
sory lobes. (P. S. Tice)

everywhere, and may also be found in cold mountain
streams. In the warm waters of the tropics or sub-
tropics they appear to be scarce. Though the usual
size range of these worms is from ¥% of an inch to 1
inch or so long, there are 4-inch planarian giants in
Lake Baikal in East Siberia. Common colors are
white, gray, brown, or black, sometimes spotted,
streaked, or striped. In the most familiar genus, Du-
gesia, the head is triangular with two prominent little
sensory lobes that detect chemicals, food, touch, and
water currents. Most fresh-water planarians, how-
ever, have blunt heads which lack conspicuous lobes,
though the sides of the head serve the same sensory
functions. Dugesia and others have two eyes, each
consisting of a pigment cup that shields light-sensitive
cells in all directions but one, enabling the animal to
respond to the direction of the light that strikes the

122]

eye. A few planarians have two clusters of tiny eyes;
and many are wanting in specialized eyes, though
the bodies may be generally sensitive to light.

Planarians can be amusing and undemanding ani-
mals to keep and to watch. Dugesia (formerly Eu-
planaria), which has many species in Europe, Asia,
and the Americas, can be collected in ponds or
springs. Almost any spring or spring-fed marsh that
supports watercress will have a lively population of
worms moving about the vegetation or clinging to the
underside of almost any stone one may overturn. A
piece of raw meat, beef liver, or fish, strategically
placed in such a spring, will bring worms from their
hiding places by the hundreds, and they can be seen
gliding smoothly upstream to the bait, guided by the
meat juices in the current. A few worms can be easily
maintained in a small bowl filled with bottled spring
water or clear pond water. Tap water in most places
is too toxic; and the worms will not flourish in an
overheated room. They move about on the bottom
and sides of the bowl in a slow glide, with the head
bending from side to side as though testing what lies
ahead. They will be seen to move toward the dark
side of the bowl and to remain whenever possible in
contact with some solid surface or film. Planarians
do not swim freely through the water, but if they
have been moving along the underside of the surface
film they will leave the surface by gliding down at-
tached to a strand of mucus. When the worms are not
being observed the dish should be kept loosely cov-
ered to reduce evaporation and to protect the worms
from strong light.

Bits of beef liver are most convenient for feeding
many kinds of planarians; the food may be left with
the worms for several hours, but then it must be re-
moved, the bowl rinsed, and the water changed.
When actively feeding, Dugesia extends its agile, tu-
bular pharynx through the mouth opening, near the
middle of the under surface. Sucking movements of
this feeding tube break up the food into microscopic
bits which can be swallowed along with the oozing
juices. If unfed for weeks or even months the worms
will not die but will use up their reserves and become
smaller and smaller.

Dugesia, and several other common genera as
well, are noted for multiplying by asexual rupture of
the body, usually just behind the region which houses
the feeding tube. Dugesia tigrina, the commonest
species of the United States, breeds sexually only in
early spring and summer, fastening its stalked egg
capsules under stones. The rest of the year the worms
reproduce only by asexual rupture; and in some
places Dugesia seems to be permanently asexual.
Those planarians that multiply by natural rupture
have extraordinary powers of regeneration. Almost
any piece of moderate size cut from a Dugesia will
reorganize itself into a complete worm. If the worm

is cut down the middle of the head and the gash re-
newed for several days so that the wound is not re-
paired, there will after a time be two complete heads
on the single body.

The familiar white fresh-water planarian of the
northeastern United States is Procotyla fluviatilis,
which has a blunt head; also an adhesive organ, in
the center of the front edge, which is used to capture
prey. Procotyla belongs to the dendrocoelids, most
of them white planarians, which are much more
abundantly represented in the fresh waters of Europe
and Asia.

The marine triclads are found mostly on gravelly
or rocky shores in temperate or cold seas, and are
known especially from the Mediterranean and Black
Seas, though they occur also on other protected
shores of the North Atlantic and of Japan. None is
yet described from the Pacific coasts of the Ameri-
cas or from Africa. A well-known marine triclad of
the American Atlantic coast is Bdelloura candida,
shaped something like a spearhead. It clings to the
leg bases and gills of the horseshoe crab, feeding on
small organisms brought in by the movements of the
host. On English shores the commonest triclad is
Procerodes ulvae, a tiny gray-banded or streaked
worm with two eyes on the blunt head, and a broad
rear end. It abounds under stones in places where
fresh water trickles down a cliff or beach and is
known for its ability to endure great changes in the
salinity of water.

The land planarians have thoroughly exploited the
use of slime as a means of overcoming the hazards
of terrestrial life. Their invasion of the land is limited
mostly to damp forest floors, where they hide during
the heat of day under stones, fallen logs, or leaf mold,
coming out only at night to find their prey. They
seize, mount upon, and subdue small animals, often
even snails or earthworms. Occasionally they turn up
in well-watered gardens, where they hide in the day-
time under boards or pots. Land triclads are often
more brightly colored than their fresh-water relatives.
When not uniformly gray, green, brown, or black,
they may have black stripes on a yellow or orange
ground, or light stripes on a dark ground. A few are
blue or violet. Though there are hundreds of tropical
and subtropical species, some of these a foot or two
long, only a few species live in moist temperate woods
or in temperate gardens. Those seen most often in
the United States are not native planarians, but tropi-
cal ones shipped in with ornamental plants. Trans-
planted tropical planarians survive briefly in green-
houses or gardens, but usually die out, even in the
kindest temperate climates, because they do not be-
come sexually mature. The most successful tropical
transplant, perhaps originally from the Indo-Ma-
layan region, is Bipalium kewense, named for Kew
Gardens near London, where it was first discovered.

Since it reproduces readily by asexual fragmentation,
it has become permanently established in gardens in
California, Louisiana, Florida, the West Indies, and
other subtropical places. Large size (up to 14 inches
long), striped pattern, and an expanded half-moon-
shaped head edged with numerous minute eyes,
make it easy to recognize.

THE POLYCEADS

The polyclads grace marine shores in every part
of the world, most of them gliding about on the ocean
bottom to seek their prey, or hiding under stones and
in damp rocky grottoes when the tide is out. Some
tolerate brackishness, but only one species, living in
Borneo, is known from fresh water. Though they are
named for the multiple branchings of the digestive
cavity, most polyclads are instantly recognizable by
their broadly oval, extremely flattened, leaflike bod-
ies. Few follow the elongate fashion of triclads. On
the whole these are turbellarians of fairly large size,

A planarian flatworm, Sorocelis americana, from a
Missouri cave. This white dendrocoelid flatworm,
with two rows of eyes, has many close relatives in
Eurasia. (Ralph Buchsbaum )

A striped polyclad flatworm, Prostheceraeus vittatus,
about 1% inches long, glides over weeds or under
stones on marine shores. The head, at top, bears sen-
sory projections. (England. D. P. Wilson)

often 1 or 2 inches long. Many have a pair of sensory
tentacles on the head, and two or more clusters of
minute eyes. Numerous eyes may also be scattered
over the front end or all or part of the body margin.

Warm-water polyclads, especially those of coral
reefs, may be richly colored (Plate 35). Others are
striped in strongly contrasting colors. Even many of
the white, gray, or brown ones of temperate waters
delight the eye with their translucency, their ele-
gantly ruffled edges, and their graceful undulations
when they take off on a brief swim through the water.
Pelagic species, which drift or swim, are usually
transparent or translucent and are found down to
three thousand feet, as well as at the surface. Some

124]

live in the open sea only by clinging to floating sar-
gassum seaweed. None of the polyclads is a parasite,
though a number are supposedly harmless commen-
sals, like Hoploplana inquilina, which lives in the
mantle chamber of the big marine snail Busycon, on
the American Atlantic coast. The oyster leech, Sty-
lochus frontalis, does serious damage to oyster beds
in Florida, and it has close relatives that prey on
oysters of both American coasts. Some members of its
family are the largest American polyclads, broad
worms over 2 inches long.

The Flukes

The flukes take their Anglo-Saxon common name
from their flat shape, and the technical name of the
group comes from the Greek word trema, “a hole,”
which refers to the cavity of the suckers by which
these small, often leaflike, exclusively parasitic
worms attach to their human or other vertebrate
hosts. Some have sharp hooks to supplement their
suckers or other adhesive organs. The adults have
lost the ciliated epidermis, the outer layer of cells
that covers their turbellarian relatives. In its place is
a thin cuticle secreted by underlying cells. Flukes,
also called trematodes, are structurally simple in most
respects, but the reproductive system, which occu-
pies most of the animal’s interior, is something else
again. In complexity it equals any to be found in the
higher animals, and its efficiency makes these lowly
parasites truly formidable contenders for man’s blood
and other living tissues.

(Class Trematoda)

THE MONOGENETIC FLUKES

The monogenetic flukes are so labeled because
they have a simple life history, with only one host.
Of about seven hundred species described up to now,
most are external parasites that live on the gills, or
sometimes on the skin, of both fresh-water and ma-
rine fishes, feeding on the external covering layer or
on oozing blood. In nature they seldom do much
harm. But when man steps into the picture, provid-
ing special fish hatcheries where young fishes are
raised in dense concentrations, these external flukes
can cause serious losses of fish.

Hanging onto the outside of a fast-moving fish is
not accomplished without a really tenacious hold,
and Gyrodactylus fastens onto the gills of its hosts
with a well-developed adhesive disk at the rear end.
The center of the disk has two or four large hooks,
and its periphery is bordered with small hooks. As
they loop about on the surface of the host, external
flukes inevitably stray occasionally into the cavities
which connect with the exterior: the mouth, the nasal
cavities, and the urinary bladder. In the course of
much time, some of the monogenetic flukes have be-

come adapted to living in the shelter of these cavities
in fishes, amphibians, and aquatic reptiles. Polystoma
hangs on with a rear disk equipped with six large
suckers. The different species live, as larvae, on the
gills of frog tadpoles; the adults of Polystoma are
found in the urinary bladder of amphibians and also
in the bladder, nose, and mouth of turtles.

DHE DIGENETIC FLUKES

The digenetic flukes, as their name implies, have
complex life histories involving two or more hosts.
Typically they have four larval stages and live suc-
cessively in three or even four hosts. As adults they
are internal parasites of practically every kind of
vertebrate—fresh-water, marine, and terrestrial. The
larval worms live in snails, fishes, and other small
animals. So large is this group of parasites, and so
varied in structure and habit, that it can barely be
touched on here. The five thousand or so known spe-
cies are added to constantly. Details must be sought
in zoological textbooks or in specialized books on
parasitology suggested in the bibliography.

Adults of the digenetic flukes live mostly in the
vertebrate intestine or in organs that connect with it,
such as the liver. The Chinese liver fluke, Opisthor-
chis (Clonorchis) sinensis, occupies the bile passages
of the human liver, causing serious anemia and liver
disease from Japan and Korea through China to In-
dochina and India. The adult fluke is about 34 of an
inch long, and has two suckers, one at the front end
surrounding the mouth, one a short distance back
from the first. As in many flukes, the digestive tube
rather promptly forks into two long digestive sacs
with blind ends. The flattened baglike body is stuffed
mostly with reproductive organs, and covered on the
outside with a cuticle that resists digestion by the
host. Hundreds or even thousands may obstruct the
ducts of one host, shedding fertilized eggs that pass
from the liver into the intestine and out with the
feces. If it reaches fresh water, as is commonly the
case, the egg may be eaten by an aquatic snail of a
species favorable to the growth of the parasite.
Within such a snail the egg hatches and the parasite
develops through three larval stages, two of which
multiply asexually. Finally a fourth stage, the cer-
caria, which has the two suckers and the forked in-
testine of the adult but has also a long tail, escapes
from the snail in large numbers and swims about ac-
tively. On encountering fishes of certain species, the
cercarias penetrate into the flesh and encyst there.

The Chinese human liver fluke, Opisthorchis (Clo-
norchis) sinensis, is about ¥ inch long. The front
sucker, the muscular sucking pharynx, the two-
branched digestive tract, and both male and female
sex organs show in this stained preparation. (General
Biological Supply House)

Since fish are commonly eaten raw in the countries
where Opisthorchis occurs, the young flukes emerge
unharmed into the human intestine, make their way
up the bile duct to the smaller bile passages, there at-
tach by their suckers, and feed on blood.

Another well-known liver fluke is Fasciola hepat-
ica, whose cercarias leave the snail host and encyst
on grasses and other vegetation in nearly all parts of
the world. It thrives best in the dense concentra-
tions of hosts provided by man’s herding of cattle,
sheep, and goats, and it may also be found in pigs,
horses, and many wild animals. In some countries it
finds its way into man by means of cercarias that
cling to wild watercress.

Far more serious as a human problem is the blood
fluke, Schistosoma, referred to in the introductory
part of this chapter. A member of one of the several
families of elongated flukes that live in the blood ves-
sels of fishes, turtles, birds, and mammals, Schisto-
soma differs from the liver flukes not only in shape
but in some other ways. For one thing, this fluke oc-
curs as separate males and females, and the sides of
the male fold over to form a groove in which the even
longer and more slender female is held. Three wide-
spread species debilitate an estimated 114,000,000
people. Schistosoma haematobium infects primarily
the small veins of the urinary system and is found in
much of Africa, the Middle East, and part of Portugal.
Schistosoma mansoni, which occupies small intestinal
veins, spreads misery in most of Africa, in South
America from Brazil to Venezuela, and in some of
the West Indies. Schistosoma japonicum, also a para-
site of intestinal veins, accounts for an estimated
46,000,000 cases in Japan, China, the Celebes, and
some of the Philippine islands.

For each of the three species of flukes there are
particular species of fresh-water snails that serve as
hosts to the larval stages. The fork-tailed cercarias
that emerge from the snail burrow through human
skin or are taken in with drinking water. Wherever
schistosomes that infect man are prevalent it is haz-
ardous to drink untreated water, or to bathe, wade
in, or dip the arms in fresh waters. Millions of Chi-
nese and Japanese become infected during the plant-
ing of rice as they stand bare-legged in flooded rice
fields. In recent years the extension of irrigation sys-
tems in Africa and in the Near East has steadily mul-
tiplied the habitats for fresh-water snails, speeding
the increase of this serious disease despite many con-
trol measures.

The temperate and more sanitary parts of the
world are not free of blood flukes, for wherever suit-
able snail hosts occur, there may be swimming cer-
carias of some kind of schistosome. The adults often
live in wild birds, especially ducks. Though the cer-
carias of bird schistosomes do not reach the human
liver, their penetration of the skin causes a skin irri-

126 |

tation known as “swimmer’s itch.” Repeated expo-
sures may so sensitize an individual that he becomes
prostrate and develops a severe rash. Swimmer’s itch
is especially serious in certain lakes in the north-
central United States, but many other fresh-water
and marine shores are affected. Chandler’s /ntro-
duction to Parasitology lists as victims of swimmer’s
itch: vacationers in Quebec and New England west
to Manitoba and Oregon, carp-breeders in Ger-
many, rice-growers in Japan and Malaya, lake bath-
ers in Australia and New Zealand—also sea bathers
and clam-diggers on the American North Atlantic
and Florida coasts, fishermen in San Salvador, and
naturalists on the rocky shores of southern California
and Mexico. Wherever bathers are aware of this an-
noyance they should wipe the skin dry immediately
after leaving the water, and should avoid getting al-
ternately wet and dry by playing in shallow water.

The ‘Papeworms (Class RD

The cestodes, named from the Greek word for
“girdle” or “ribbon,” are mostly long, flattened,
Opaque white or yellowish ribbon-like parasites. The
adults live inside vertebrates, almost always in the
intestine, but the larval stages develop in either ver-
tebrate or invertebrate hosts. The life cycle is com-
plex, involving one or two intermediate hosts in ad-
dition to the vertebrate “final host” that nurtures the
adult.

Aside from the enormous length, 50 feet or more,
attained by some tapeworms, their most notable fea-
ture is a complete lack of a mouth or any digestive
apparatus. The body is covered with a protective
cuticle, as in flukes, and the worms absorb much of
their nutrition directly through the body wall from
the intestinal contents of the host.

The scolex is a very small knob at the narrow or
front end of the long body, and it bears the only or-
gans of attachment. These may be suckers, hooks, or
sometimes glandular adhesive areas. Behind the sco-
lex there is usually a short, narrow, undivided neck
region or growing region, and from this there is a
constant budding off of body segments. Those closest
to the neck are smallest and youngest, those farthest
away the largest and most mature. Thus the chain of
segments represents every stage of development, and
widens gradually along the body’s length.

Tapeworms have no specialized sense organs, not
even the poor ones seen in turbellarians and in some
flukes, though the body wall, especially that of the
scolex, is well supplied with sensory cells. These
worms are all business, and their energies are chan-
neled into a prodigious reproductive effort which in-
sures that a sufficient number of the young will find
new hosts and keep the species going.

Not all tapeworms are divided into segments like
the typical forms. There are undivided ones, which
look more like flukes, but the distinction is not as
fundamental as was once thought, and the two sub-
classes are based on other characters. The subclass
Cestodaria includes forms with an undivided body
and a ten-hooked larva, that live in the body cavity
and intestine of lower fishes. The subclass Eucestoda,
in which the larva has six hooks, comprises a few
undivided forms and all the typical segmented tape-
worms, including those few described here.

The beef tapeworm, Taenia saginata, maintains
its place in the human intestine, despite the constant
movement of materials in that active organ, by means
of four suckers on the scolex. As in many other tape-
worms, the male sex organs start to grow first and
appear most prominent in the younger segments;
both sets of organs are well developed in middle seg-
ments; and toward the most mature region the seg-
ments are nothing but little bags stuffed with eggs
that have already begun to develop into embryos.
The fully ripe segments, loaded with embryos, de-
tach from the worm and pass out with the feces onto
the ground or onto vegetation. As cattle graze they
may ingest shelled embryos, and in the bovine intes-
tine the eggshell is digested off and the six-hooked
embryo is released to burrow its way through the in-
testinal wall and into a blood vessel. Carried by the
blood to the muscles, the embryo remains there and
grows into a sac or bladder which sprouts from its in-
ner wall the inverted future head of the tapeworm.
When man eats raw or undercooked beef the enclos-
ing bladder is digested off, and the head everts and
attaches to the human intestinal wall by means of
the suckers.

Meat inspection has greatly reduced the incidence
of beef tapeworms in Western countries; but though
the bladders of this tapeworm are almost 2 of an
inch long, they can easily be overlooked in the rou-
tine inspection of the jaw muscles and the heart, the
parts of the cow usually examined by official meat
inspectors. It is best to avoid raw or seriously under-
done beef. Where sanitation is poor, as in Africa, or
in countries where meat is broiled in large chunks,
much of the population is infected. Among the Hin-
dus of India, who have religious restrictions against
eating beef, a diagnosis of beef tapeworm may be
embarrassing to the patient; or when due to mistaken
diagnosis through confusion with other tapeworm
eggs that show six hooks, it can be deeply insulting to
the patient as well as rather embarrassing to the
physician.

The pork tapeworm, Taenia solium, which has a
crown of hooks on the scolex in addition to the suck-
ers, is likewise rare among Jews and Moslems.
Though the bladderworms are common in pigs, the
adult in humans is rare in the United States, more

common in parts of Europe where pork is eaten with-
out thorough cooking.

The largest and most injurious tapeworm that par-
asitizes man is the broad fish tapeworm, Dibothrio-
cephalus latus (formerly Diphyllobothrium latum),
a monster up to 55 feet long, with three to four thou-
sand segments. In man it usually averages from 15 to
20 feet long. For centuries it has infected central Eu-
rope, and now occurs in 20 per cent of Finns and al-
most 100 per cent of the population of certain Baltic

The circlet of hooks on the scolex of the dog tape-
worm, Taenia pisiformis, as seen by darkfield photo-
micrography. (Montana. W. C. Marquardt)

areas. It may be found also in such places as Ireland,
Palestine, Uganda in Africa, Siberia, Japan, and
Chile. In North America it is known from Michigan,
Minnesota, Wyoming, Manitoba, Alaska, and even
Florida. Long thought to have been brought to the
Great Lakes region by lumbermen from northern
Europe, this tapeworm may also have come with
Asians over the Bering Straits; or it may have been
well established in fish-eating wild carnivores, like
the brown bear, before man’s arrival. In addition to
man and the bear, it has been reported also in the
dog, cat, fox, and others. The life history involves

[127

two intermediate hosts. The eggs must reach water
and must be eaten by copepods (tiny crustaceans),
which in turn must be eaten by one of a variety of
fishes. In the Great Lakes region northern pike and
pickerel are most commonly infected, as are also the
sauger and yellow perch. Since this region ships great
quantities of fish to other localities, the tapeworm has
been widely spread. One should therefore not taste
raw lake fish during food preparations, or eat smoked
fish from infected regions unless it is known to be
adequately treated.

Common in the great cattle- and sheep-raising re-
gions of the world, especially in Africa, the Middle
East, Australia, and South America, is Echinococcus
granulosus, which passes its adult life in dogs and
doglike animals but usually develops as a larva in
herbivorous animals. The eggs may be passed by the
lickings of a friendly dog to the hands and face of
man, from where they can reach his mouth. Though
the adult is minute in this case, the larva (developing

128 |

into what is called a hydatid cyst) can grow, in the
human liver, to the size of a grapefruit or larger.
When one or more of these cysts develops in the hu-
man brain, the results can be very serious or fatal.

The dwarf mouse tapeworm, Hymenolepis nana,
is the smallest adult tapeworm found in man, but it
makes up for its small size by large numbers, perhaps
hundreds or thousands in one person. The greater the
number present, however, the smaller they grow, so
that in heavy infestations they are only about 1 inch
long. World-wide in distribution, this is the common-
est tapeworm of the southern United States, where it
infects from 1 to 2 per cent of the population, espe-
cially children. Though different from almost all
other tapeworms in being able to complete its life
cycle in a single host, such as man, the rat, or the
mouse, it can revert to ancestral habits and use fleas
or flour beetles as intermediate hosts. Usually people
ingest the eggs by contamination with human feces
or in food containing mouse droppings.

CHAPTER VI

The Ribbon Worms

l HE smallest of these soft, elongated, mostly ma-
rine worms may be threadlike and only a fraction of
an inch long. The giants of the group, however, are
the longest, though certainly not among the largest,
of invertebrates. Exactly how long it is difficult to say,
for all the ribbon worms are highly elastic, and the
really long ones stretch out, threadlike, for yards
and yards—some say much more than 30 yards in
Lineus longissimus, the blackish brown worm of the
North Sea. The English call it the “bootlace worm.”
Modest length, not more than about 8 inches, is more
usual. The body may be cylindrical, as in Lineus,
though more often flattened on both sides or flattened
below and convex above.

Bright colorings of orange, red, purple, or green,
these mostly on the upper surfaces, may betray the
worms to the eyes of naturalists scanning rocky crey-
ices or overturned stones at low tide. More often the
colors blend with red or green algae or other colorful
growths among which the worms live. To find small
nemerteans, collectors place masses of seaweed or of
bryozoan colonies that resemble delicate seaweed in
dishes of sea water and let the small worms creep
out on the walls of the dishes, where they can easily
be seen. Some worms are white or yellowish, others
somber grays or browns, but many are handsomely
patterned with strongly contrasting rings or longitu-
dinal stripes or both. The front end is not set off as

(Phylum Nemertea)

a distinct head, though the tip may be expanded and
have colored markings, several or numerous eyes,
and sensory grooves, which make it look superfi-
cially like a head. The rear end is more or less
pointed.

Another common name, proboscis worm, less
widely used, calls attention to the most distinctive
feature of nemerteans. This is a long, extensible, tu-
bular proboscis that can be shot out the front end
with explosive force to grasp prey or discourage ene-
mies. The proboscis coils about the prey, holding it
firmly and entangling it in sticky mucus which may
be irritating or even poisonous. The proboscis is also
everted as a device for burrowing in sand or mud or
for attaching to objects as an aid in creeping about.
It can be made to evert by irritating the animal, by
plunging it into fresh water, or by placing it in a small
dish of sea water and cautiously adding alcohol, drop
by drop. The accurate aim of the proboscis receives
recognition in the technical name of the phylum,
Nemertea, from a Greek word that means “unerr-
ing.” In some of the commonest worms the tip of the
proboscis is armed with a sharp spike or stylet, which
pierces the prey, sometimes several times, before a
toxic secretion is poured on. Worms may have two
or more pouches with a reserve supply of stylets, so
that replacement can be made quickly if the main
one is damaged. When not in use the proboscis is

[129

The bootlace worm, Lineus longissimus, a fragile nemertean that is often many yards long. At
low tide it hides under rocks or in the holdfasts of kelps. (England. M. A. Wilson)

sheathed in a muscular tube that lies above the diges-
tive tract.

As it goes on mostly at night, feeding is not often
observed. The favored food seems to be annelids,
and these have been seen to be swallowed whole,
making a prominent bulge in the thin, elastic body
of the nemertean. Mollusks, crustaceans, and fishes
are also eaten, though bigger prey may be sucked at,
not downed in one piece. Undigested residues do not
have to be cast out the mouth, for the nemerteans are
the lowest animals that have an anus, a second open-
ing to the digestive tract, which voids materials from
the rear end of the animal. The ribbon worms are
built much like flatworms, but aside from the anus
they can boast another important improvement. They

130]

have contractile blood vessels. Waves of contraction
in the strong muscles of the body wall also help to
push blood and food along their respective tubes,
and in a worm at rest it is these powerful muscular
waves that are seen to pass along the body.

A few ribbon worms swim by undulations of the
long body. The young and the smaller forms glide
along, by means of beating cilia on the body surface,
over a lubricating bed of secreted slime. In larger
worms more use is made of muscular contractions for
creeping. Some even spiral ahead at times by agile
body contortions.

One may grasp several inches of a delicate, slimy
nemertean and pull cautiously lest it break, yet have
it slip from one’s fingers and disappear down a crack

in the rock. Worms that do break in escaping from
would-be captors, human or animal, almost always
replace a missing rear end; and certain species can
regenerate a whole worm from any fragment that
contains a portion of one of the lateral nerve cords.
As in flatworms, the capacity for regeneration goes
with the natural capacity of certain species for repro-
ducing asexually by fragmentation of the body, es-
pecially during warm months. A large specimen of
Lineus socialis, which lives gregariously under stones
on the American Atlantic coast (or of Lineus vegetus
on the west coast), may fragment into six to twenty
or more pieces. After transforming into complete
worms of smaller size, these grow again and later re-
produce sexually. Most though not all ribbon worms
are of separate sexes. The eggs are usually laid in
gelatinous strings or masses, and the young hatch as
juvenile worms. In some species of Linews, in Cere-
bratulus, and in some of their relatives, the egg
hatches as a gelatinous, helmet-shaped, free-swim-
ming little larva, called a pilidium. It must feed on
microscopic organisms and develop further before it
takes on the structure of the adult.

For the most part, ribbon worms are bottom dwell-
ers on temperate marine shores, where they burrow
in mud or sand or creep about among rocks and sea-
weeds between tide marks or in shallow waters. Only
a few burrow into the deep-sea bottom, sometimes at
depths of forty-five hundred feet or more. Of some
570 described species, nearly 200 are found along
the Atlantic or Mediterranean shores of Europe.
About 100 live on the Pacific coast of North Amer-
ica, at least 18 of them identical or very similar to
European species. The Atlantic coast of North
America has few more than 50 known species, and
W. R. Coe, the American authority on nemerteans,
thought this was due to the cold arctic current that
comes close to the coast as far south as Cape Hat-
teras, for many of the missing genera are warm-tem-
perate forms. Almost 30 species are described from
Japanese shores. In the open seas, chiefly the south-
ern parts of the North Atlantic, there are nearly 60
gelatinous species that drift or swim slowly far below
the surface. They have been brought up from depths
ranging from six hundred to nine thousand feet, most
from below three thousand feet. Nemerteans are less
common in tropical or subtropical seas, but well rep-
resented in arctic and antarctic waters, often by the
familiar temperate genera: Lineus, Amphiporus,
Cerebratulus, and Tetrastemma.

Perhaps the most cosmopolitan species is Lineus
ruber, found from Siberia to South Africa. The slen-
der, rounded body is 3 to 9 inches long; and different
varieties are colored red, green, or brown, any of
them difficult to see in natural surroundings, even
when one has lifted the stone under which the worm
lives.

Fresh waters, especially in northern latitudes,
harbor species of the genus Prostoma. What seems
to be a single species, Prostoma rubrum, a slender
reddish worm less than | inch long, can be found
in pools and quiet streams in nearly all parts of the
United States. It clings to the leaves of aquatic plants
and feeds on minute crustaceans, nematodes, and
turbellarians. In Europe this genus has also an eye-
less variant that lives in caves.

Land nemerteans are all of the genus Geonemer-
tes. The two best-known species are slender, pale in
color, and not more than 2 inches long. By exploit-
ing the nemertean talent for copious secretion of
slime, land nemerteans manage to live along marine
shores, in moist earth, or under foliage and fallen
logs, in such places as Bermuda, Australia, New Zea-
land, and many South Pacific islands. In the Sey-
chelles, Geonemertes arboricola occupies the leaf
bases of a screw pine (Pandanus) tree, often living
high in the tree.

A common nemertean of the American Pacific coast,
Amphiporus bimaculatus, that has many relatives on
other shores. It is short (up to 6 inches) and broad
for a ribbon worm. (Ralph Buchsbaum )

Only Carcinonemertes has been classed as a para-
site. It lives on the gills of various crabs when it is
young, and then moves to the egg masses, both feed-
ing on the eggs and living as a commensal by eating
any small animals it can find as it clings to its host.
Adults of Carcinonemertes carcinophila are about 1
inch long and orange- or brick-red.

Commensal nemerteans live mostly in tunicates,
sponges, or bivalves, sharing the food in the host's
feeding currents. Common in the mantle cavity of
various clams on European and both American
coasts is Malacobdella grossa, a short, white, thick
worm, with an adhesive disk at the rear. It creeps in
leechlike fashion. The genus to which it belongs con-
stitutes a separate order of nemerteans.

The other three orders contain all the more typical
elongated worms; they are distinguished from each
other mostly by internal characters, such as the ar-
rangement of the muscle layers. The paleonemer-
teans, with an unarmed proboscis, include such forms
as Tubulanus, species of which are shown in Plate 37
and below. Also with unarmed proboscis are the
heteronemerteans, among them Lineus and Cere-
bratulus. The latter is a very large, firm, and flat-
tened worm which lives in burrows in sand or mud
and swims actively through the water. The hoplone-
merteans, with an armed proboscis, are divided into
two suborders. In one the members have at the tip
of the proboscis a single stylet, a straight or curved
thorn which pierces and holds prey. These include
many quite common shore forms such as Amphi-
porus; the very slender Emplectonema, found
among mussels and barnacles on pilings; and Para-
nemertes peregrina of the American west coast, of-
ten a rich purple on the upper surface. The parasitic
or commensal Carcinonemertes belongs here, as do
various commensal species, the fresh-water forms,
and also the land nemerteans. In the second subor-
der, members have on the tip of the proboscis not one
large stylet but a large number of minute ones. These
worms include some shore species, but most float or
swim in the open sea far below the surface. Many are
broad, flattened worms, of yellow, orange, pink, or
red hues. The drifting types are quite gelatinous, the
swimming ones equipped with tail and sometimes
also with side fins.

Tubulanus annulatus, a long, slender ribbon worm
common on European shores, may be several feet long.
It lives in a mucous tube under stones or in crevices
at low shore levels. (Rupert Riedl and Encyclopae-
dia Britannica Films)

CHARTERS VAL

A Variety of Animal Groups

is the animal kingdom are a number of small
groups whose members have charms for people with
the most observant eyes or a special curiosity and per-
sistence for seeking out animals of small size, few
species, or unobtrusive habits.

All of these descriptions apply to members of the
phylum Mesozoa. They are minute ciliated worms
found living as parasites in the kidneys of squids and
octopuses, clinging to the walls of tubes while their
elongate bodies float freely in the urine. Mesozoans
parasitize many other invertebrates, finding homes
in the tissues and body cavities. Their habits remind
us of protozoans, but their bodies are multicellular
more like the two-layered little planula larvae of
coelenterates. It is tempting to think of mesozoans as
being transitional between these groups, and this
temptation has led to the phylum name. Probably
they are degenerate in their simplicity, degraded by
parasitism, but they still appear to be the simplest of
multicellular animals—simpler than any flatworm
or coelenterate.

Quite another kind of group is the Phylum Nema-
toda, enormously abundant, and with great numbers
of species, and boasting among its members some of
man’s most loyal companions, though they can
hardly be called friends. Nematodes are included
here only because they are thought to be related to
five of the small groups that follow them immediately
in this chapter. The six groups are often lumped to-
gether as six classes of a superphylum, Aschelmin-
thes, but the evidences for doing this, or for separat-
ing the six from certain other phyla in this chapter,
are too technical to be given here. Instead, each
group is awarded separate status as a phylum with
a distinct body plan.

The Roundworms
(Phylum Nematoda)

The cost of minimizing one’s enemies always runs
high, and we are now paying dearly for having so
long underestimated the prevalence and powers of

roundworms. The big ascarids that live in the human
intestine were well known to the ancient Egyptians,
as one can hardly ignore a foot-long worm that slips
out with excrement when it dies, or one that may go
astray and suddenly emerge from a nostril. In our
own day ascarids are widespread in the world, in-
cluding Europe and the Americas, especially in
warm, moist areas. In the mountainous parts of the
southeastern United States, clay soil, a mild, rainy
climate, dense shade, and the habits of small chil-
dren, dogs, and pigs combine to spread and protect
Ascaris eggs in the dooryards where children play,
and from where they carry the eggs into their homes.
In hot, dry climates, especially from Arabia to India,
the 4-foot guinea worms that lie coiled under the
surface of the skin are even harder to overlook. Very
likely these are the same as the “fiery serpents” that
plagued the Israelites in biblical times.

Every species of vertebrate that is examined turns
out to harbor nematode parasites, and there are two
billion estimated cases of human infection, not much
less than the total number of people in the world.
Roundworms as huge as ascarids and guinea worms
are very exceptional, but parasitic forms are gener-
ally larger than the free-living ones. These last are
much more numerous and barely visible to the naked
eye. Magnified, they look like animated bits of fine
sewing thread, hence the phylum name, Nematoda,
which means “threadlike.” Free-living roundworms
are inconceivably abundant in moist soils, present
even in deserts and on mountain tops, common in all
fresh waters, found in hot springs and arctic ice pools,
living in every sea from pole to pole. Yet small size
and transparency kept them unseen until after the
discovery of the microscope. They find their own
food, steadily devouring bacteria or small animals
and plants of soil and water. Their teeming numbers
and their versatility were noted by nineteenth-cen-
tury zoologists.

In 1881 a German investigator, seeking to find
out why sugar beets, a mainstay of German agricul-
ture, seemed suddenly “to tire” of any soil in which
they had grown for many successive years, traced the
trouble to parasitic “eelworms.” At first the study of

[133

soil nematodes parasitic in plants grew very slowly.
Beginning in the 1940’s, however, Western countries
have been greatly stepping up their efforts at nema-
tode research, having suddenly begun to appreciate
the ways in which modern farming methods have in-
tensified the competition between man and the nem-
atodes for large agricultural crops. Parasites are usu-
ally highly specialized, able to live on only one or a
few closely related species of host, so that originally
soil nematodes found their wild plant host sparse and
widely scattered. Then man discovered agriculture
—how to grow edible plants in such dense concen-
trations as to make it worth while for the big human
animal to feed on even the smallest grains.

Nematode head with hooks (top)
and whole worm

The nematode threat must have grown slowly
through the centuries, until recent methods for plant-
ing vast acreages to the same crop, and the explosive
expansion of the human species, created unlimited
horizons for nematode hangers-on. Though round-
worms parasitic in man share only a small part of his
food after he digests it, the soil nematodes parasitic
in plants take more than a tenth of the crops grown
by American farmers, for example, even before the
harvest. The damage in the United States is estimated
at $500,000,000 each year; in Great Britain the an-
nual loss of potatoes alone is judged to cost about
£ 2,000,000. Since the worms increase with the years
and with crop size, the best remedy is crop rotation
to deny the nematodes access to their host. Much of
what was in the past attributed to soil exhaustion, to
be cured by crop rotation, was in reality nematode
damage, especially by those nematodes that pierce
plant roots and suck the juices. The plant symptoms
are wilting, stunted growth, leaf discoloration, and
root swellings or galls—none of these specific to nem-
atode infestation or always easy to tell from losses
due to drought or a lack of soil nutrients. Our con-
centration on methods for treating these last prob-

134 ]

lems has delayed appreciation of the role of parasitic
worms.

Lists of animal numbers usually credit the nema-
todes with about ten thousand known species. The
true number of existing species is estimated to be
about five hundred thousand—second only to the in-
sects. The discrepancy is easily explained. The larger
number takes into account all the as yet unexamined
but highly specialized parasites of many thousands
of vertebrates, invertebrates, and plants, plus all the
free-living forms, judged to outnumber the parasites.
Nematodes are typically minute, cylindrical, tapered
at both ends, covered with a tough cuticle that is
transparent or translucent; they usually thrash about
in a way that immediately identifies them to the eye,
and they look so much alike, even under the micro-
scope, that the job of distinguishing and naming so
many superficially similar species makes even the
experts stand back.

Nematodes used to be studied either as parasites
or as free-living worms, and students of one group
often paid scant attention to the other. Since the hab-
its of nematodes, like those of most animals, do not
necessarily correspond to the evolutionary relation-
ships on which classification must rest, the grouping
of these worms has had recently to undergo exten-
sive repairs in order to combine the two kinds of
worms. For details one may refer to Volume III of
the treatise by Hyman, to the specialized volumes
on nematodes by the Chitwoods, or to Chandler’s
very readable text on parasitology. Here we shall
merely present some points about roundworms in
general and then go on to discuss a few kinds of
worms of special interest.

Nematodes occur in two general forms. The really
long, threadlike ones, that have hardly any taper,
are greatly outnumbered by the shorter spindle-
shaped forms, which taper markedly to blunt or slen-
der tips, the rear end often the more tapering and
pointed. Especially in the minute forms, the animal
is colorless and the cuticle is transparent, putting the
internal organs on full display. Or the cuticle is trans-
lucent and lends a whitish or yellowish cast. There
are no cilia, outside or in, and in parasitic forms the
cuticle is often very smooth; but it may be finely
striated, or bear bristles, spines, ridges, or other
markings and expansions. The mouth is at the front
tip, surrounded by little sensory lips, which may also
be muscular and used in sucking. Just inside the
mouth there may be cutting ridges, teeth, or piercing
stylets for puncturing plant or animal prey. Beyond
these there is usually a short muscular pharynx that
sucks food into the intestine. The sexes are almost al-
ways separate; and the smaller male bears special
equipment at his slightly curved rear end. The stiff
cuticle and the lack of any but lengthwise muscles
permit only serpentine undulations for swimming or

gliding, crawling when assisted by body bristles or
other devices, and in microscopic worms a kind of
thrashing about, which in open water leads nowhere.
Among aquatic plant debris, in sand or mud, in soil,
or in the fluids or tissues of a host, friction against
solid particles may help the whiplike contortions to
move minute worms along or enable them to explore
their surroundings.

Marine nematodes are on the whole the largest of
the free-living forms; some are nearly 2 inches long.
They turn up in any sample of shore sand or mud,
but especially in soft muds full of the microscopic
plants and organic debris on which they feed. On
such bottoms they are the most numerous of all mul-
ticellular animals. A handful of muck could easily
contain many thousands of individuals of fifty or
more species. Even in antarctic waters a thimbleful
of bottom material will teem with hundreds of nema-
todes of species common almost anywhere. The rec-
ord depth for bottom-living nematodes is more than
21,000 feet.

Fresh-water forms are also widely distributed,
being carried about by currents, by wading birds and
other animals, or by drifting plants. They occur in
still or running water, but are most abundant on the
shores of lakes, where they favor stony or muddy or
plant-invaded bottoms. Some have hollow stylets and
suck plant juices; others are feeders on decaying par-
ticles; many are voracious feeders on protozoans, on
other nematodes, or on their little relatives, the
rotifers and gastrotrichs, discussed later in this chap-
ter. Nematodes able to survive in hot and sulphur
springs in Germany are of the same or closely related
genera as those found in Yellowstone Park in the
United States or in hot springs in China. Those of
swift or tumbling mountain streams are able to fas-
ten by sticky secretions from glands at the tail tip,
and such adhesive glands occur in most free-living
nematodes, though not in the parasitic ones.

Land nematodes are spread about by winds and
plants and other animals, almost like protozoans, and
indeed they are similarly suited for wide dispersal of
the same common species by their small size and
habit of resisting drying when in an inert state. Some
species, however, have very specific niches, and the
one most often pointed out is Turbatrix silusiae, de-
scribed from the felt mats on which beer-drinkers set
their mugs in Silesia, in Germany. A relative, Turba-
trix aceti, long called the vinegar eel, feeds on the or-
ganisms that form the “mother” of naturally ferment-
ing vinegar.

The mermithid nematodes, such as Mermis above,
are long, threadlike worms that taper less than
typical members and are often mistaken for the hair-
worms described later in this chapter. They do, how-
ever, taper more than the hairworms. The adults are
from a few to 20 inches long, and are found in soil,

sometimes in water, but do not feed. The juvenile
stages are parasitic in insects, often in grasshoppers
or crickets, feeding on all the organs as they grow to
adult worms and then emerge. Mermithid damage to
insects should be of some consolation to farmers, be-
set as they are with nematodes harmful to crops.
The free-living soil nematodes have been carefully
estimated in Danish soils, where grassland may
teem with almost 2,000,000 worms per square foot,
and cultivated soils with up to 200,000 worms in the
same area. For most species 90 per cent of them can

Mermis, a mermithid nematode worm. (Pennsylvania.
Ralph Buchsbaum)

be found in the top two inches of soil, and none be-
low four inches. Some soil nematodes have been re-
ported, however, down to a depth of twenty-five feet.
The smaller ones, perhaps only 14, of an inch in
length, feed on bacteria and small algae. The larger
ones with teeth or grinding devices feed on proto-
zoans, rotifers, and other nematodes. To gather
them for microscopic examination one needs to put
fresh garden soil in a piece of cheesecloth and set it
in a funnel stopped by rubber tubing and a clamp.
When the funnel is filled with water, the nematodes
wriggle downward into the stem and collect there.
After some hours the water in the stem can be run
into a glass dish.

The parasitic soil nematodes, referred to near the
beginning of this chapter, spend the active part of
their lives in plant hosts, but many have inert cysts
that have been known to survive in soil for many
years, one as long as thirty-nine years. Attempts to
control their depredations range from crop rotation
to chemical fumigation, flooding of the soil, or en-
couraging the growth of fungi that trap nematodes.
None of these methods is completely successful. The
sugar beet eelworm, Heterodera schachtii, reterred
to earlier as the first nematode known to infest crops,
is restricted to the roots of a few plant species. The
potato-root eelworm, Heterodera rostochiensis, also
attacks tomatoes, and it causes great losses from Ire-
land and Great Britain to Germany and most of west-
ern Europe except Norway. The root-knot nema-
todes, said to be a number of distinct species of the
genus Meloidogyne, infect nearly a thousand varie-
ties of plants, at least seventy-five of them garden
and field crops, fruit and shade trees. These are
mostly warm-climate nematodes, but under glass
they flourish anywhere. In England they do great
damage to tomatoes and cucumbers in commercial
greenhouses unless controlled by steam sterilization,
an effective method where the soil used is limited in
quantity.

Man’s struggle with parasitic roundworms was re-
corded about 1550 B.c. in the Ebers Papyrus, named
for the archaeologist who made the first translation.
Found in 1872 in a tomb in the Nile valley near
Thebes, the papyrus is a collection of remedies
against the various diseases that harassed the ancient
Egyptians. To “expel the roundworm in his belly,” it
advises the physician to try thirty-two different reci-
pes, with ingredients ranging from pomegranate roots
and red ochre to turpentine and goose fat. Old Chi-
nese writings, one from 217 A.D., speak of “the long
worm,” 5 to 6 inches or up to | foot in length. The
size and symptoms are those of Ascaris lumbricoides,
which may even reach 14 inches. It is thought that
man picked up this long-time companion when he
started to domesticate pigs, and in the process also
domesticated his own human strain of worms. The
ones that attack man and pig look identical, but they
do not readily exchange hosts. Nevertheless, both
pigs and dogs ingest the eggs of the human parasite
and help to spread them about to small children play-
ing outdoors. Prevention of infection with Ascaris
eggs must begin with sanitary disposal of human fe-
ces and with teaching young children to wash their
hands before eating. Even in parts of the world
where human feces are used as fertilizer to grow
leafy vegetables, the most important source of in-
fection is direct contamination through the hands.
Though a female Ascaris may lay 200,000 eggs daily,
many hazards beset the eggs: drying, too high or too
low temperatures, and the sanitary plumbing or

136 |

sometimes cleanly habits of men. When the shelled
eggs do find their way back to the mouth, they al-
ready contain young larvae, and these hatch in the
intestine, burrow into blood vessels, and are carried
to liver, heart, and lungs. In the lungs they take hold,
make their way back to the trachea and throat, and
down to the intestine again, this time arriving with
size and health improved by travel. They bite the
intestinal wall, sucking in tissue juices, and also tak-
ing the digested food of the host. Most of the really
serious damage is done by the young worms as they
travel, but even the adult is a very unreliable para-
site. It may puncture the intestinal wall or wander
up the bile duct, with fatal results.

The trichina worm, Trichinella spiralis, is much
less widespread in the world, and almost entirely ab-
sent from the tropical regions that have more than
their share of other parasitic worms. In arctic regions
it is common among Eskimos, and it does occur to
some extent in Mexico and temperate South Amer-
ica. But chiefly it is a parasite of Europe and the
United States, where it is encouraged in its efforts to
keep going by the habit of feeding garbage, which
usually contains pork scraps, to pigs. Wherever gar-
bage is fed to pigs as a method of disposal in larger
American cities, the incidence of trichinosis is high.
In the United States this applies chiefly to the North
Atlantic seaboard and to California. Many of the
most serious cases are concentrated among people
who enjoy various kinds of raw sausage and who
make it themselves from a single but highly infected
hog. Most infections are due to eating raw or under-
done pork, occasionally bear or walrus meat. In the
United States fewer than six hundred clinical cases a
year are clearly diagnosed, and of these less than 5 per
cent are fatal. But many serious infections are mis-
takenly said to be intestinal flu, food poisoning, or
typhoid fever. Since the estimated incidence in the
United States, as determined from examination of
the diaphragm at autopsy, ranges from 5 per cent in
New Orleans to more than 27 per cent of the people
in some northern and western cities, the vast major-
ity of cases must go undetected or end in medical
statistics as “psychosomatic” or other illness. Perhaps
the milder symptoms of trichina worm infection are
simply less severe than the weakness, diarrhea, ab-
dominal pains, nausea, fever, puffy eyes, and ex-
treme muscular pains that characterize fatal attacks.
The adult trichina worm is a tiny intestinal parasite,
but serious or fatal results are attributable to the
even smaller larval worms as they burrow through
the intestinal wall and enter lymph or blood ves-
sels, become distributed about the body, then bur-
row through every tissue or organ to settle down in
striated muscle tissue. There they grow to be '4; of
an inch long, ten times their larval burrowing size.
They become sexually differentiated, roll into a spi-

ral, and become enclosed in a walled cyst developed
by the host. They do not develop further unless host
muscle is eaten by another susceptible host and the
cyst wall is digested away in the host’s stomach or
intestine. An ounce of infected sausage may contain
more than 100,000 encysted little worms; and the
person who eats it may become the sole support of
1500 offspring from each female that hatches in the
stomach or intestine, so that the body tissues become
riddled by more than 100,000,000 larval worms.
Since the cysts are microscopic, gross meat inspec-
tion does not reveal trichina worm infection. Preven-
tion could be greatly aided by careful inspection of
pork, as in Chile, or by prohibiting the feeding of
garbage to hogs, as in Canada or England. Until bet-
ter measures are adopted in the United States, each
individual should take care never to eat pork that is
not thoroughly cooked.

Hookworms are tiny worms, only about 2 of an
inch long, that live in the human intestine, holding on
by clamping the mouth on a bit of intestinal wall,
and feeding by sucking in blood and tissue juices.
Only recently have these worms been brought under
enough control to cede first place to the schistosomes
(discussed in the chapter on flatworms) as the most
damaging wormlike parasites of man. Necator amer-
icanus, whose name means “the American killer,”
probably came to the United States from Africa and
is primarily a tropical worm, abundant in middle lat-
itudes around the world wherever moderately warm
temperatures, moisture, and soil conditions are fa-
vorable. Its dependence on warmth and moisture
keeps it confined in the United States to the south-
eastern states—from Virginia west and southwest to
Arkansas and Texas.

Somewhat more injurious to its hosts is Ancylos-
toma duodenale, chiefly a northern species and the
dominant one in Europe, North Africa, western Asia,
northern China, and Japan. In most countries farm-
ing and mining are the main occupations of hook-
worm victims; and in western Europe the worms first
attracted attention during the building of the Saint
Gotthard tunnel through the Swiss Alps. Afterwards
the worms were spread to many European mines.
Other species of hookworms occur in cats and dogs
and occasionally also in man. The life history has
some similarities to that of Ascaris, but the eggs hatch
in the soil and it is the active larval worms that enter
the human body, usually burrowing through the skin
of bare feet, but also sometimes taking advantage of
any other means to penetrate the human skin or en-
ter the mouth. Once inside the skin, they enter lymph
or blood vessels, are carried to the lungs, coughed up
and swallowed, arriving finally in the intestine. There
they sap vitality, chiefly through blood loss, of indi-
viduals who are malnourished to begin with. The ef-
fects of hookworms are not dramatic, but they under-

>

Aa
4 wes Ae f
ae, in Ths

eof?

Trichina cyst in hog muscle. The dormant curled-up
larva of Trichinella spiralis is about %; inch long

and is enclosed in a wall formed by the host. Stained
preparation. (P. S. Tice)

mine whole communities, generation after genera-
tion. The wearing of shoes is an important means of
protection against ground polluted with hookworms;
even light sandals help.

The guinea worm, Dracunculis medinensis, was
referred to earlier. In central Africa, Egypt, the East
Indies, and especially from Arabia to India, it is one
of the really serious penalties for a way of life in
which the same sources of water serve for drinking,
bathing, and laundering. The large female worm,
only 14, of an inch wide but up to 4 feet long, lives
in the deeper skin layers but comes close to the sur-
face to produce a skin ulcer and discharge larval
worms whenever an infected arm or leg is suddenly

[137

plunged into cold water, as in laundering or in dip-
ping up water from wells or village ponds. The tiny
worms swim about until they perish or are swallowed
by a second host, a species of Cyclops, a tiny crus-
tacean. When drinking water is dipped up (often by
the same individuals who infect the water by stand-
ing in it as they lower their buckets) it contains in-
fected crustaceans that harbor larval worms. Rede-
signing wells and filtering water could eliminate this
disease, but in India religious traditions that surround
the ways of obtaining and using water have made
change slow.

More than fifty species of roundworms parasitize
man occasionally, but only about a dozen are impor-
tant human parasites. Five have already been men-
tioned. Some others are the subtropical and tropical
filarial worms that cause elephantiasis; the African
eye worm, Loa loa; and the world-wide whipworm,
Trichuris trichiura, which usually lives in the large
intestine, causing symptoms ranging from abdom-
inal pain to severe emaciation and prolapse of the
rectum.

The one roundworm most likely to have parasit-
ized readers of this book is the pinworm (seatworm
or threadworm) Enterobius vermicularis, found all
over the world, but rare in the tropics. It flourishes
in Europe, where even the cleanly Dutch children
are said to be 100 per cent infected, and in North
America, where sample surveys show that 30 to 60
per cent of white children in Canadian and Ameri-
can cities have pinworms. Negroes are less suscep-
tible, and in Washington, D.C., Negro children have
an incidence of only 16 per cent, compared with 40
per cent for white children. These are little white
worms, the females up to 2 of an inch long, that
live in the cecum, appendix, and adjacent parts of
the large intestine. When the females are full of eggs
they migrate to the rectum and lay their eggs around
the anal opening. Their movements cause intense
itching, often sleeplessness and nervousness. Scratch-
ing of the anus, and liberation of the eggs into the
air and onto sheets and clothing, spreads the eggs
about so effectively that in some households and in-
stitutions eggs can be taken from almost any surface
or object. It is easy to imagine how the eggs reach the
mouths of adults, but more especially of children, in
such places. For this worm, treatment is easier than
prevention.

The Rotifers

One of the most fascinating, and busiest, of sights
is a drop of pond water magnified to reveal a field of
feeding, crawling, and swimming rotifers. These in-
tensely animated microscopic creatures occur in a

(Phylum Rotifera)

138 |

great variety of fantastic shapes and handsome sur-
face sculpturings. Their greatest attractions, how-
ever, are their incessant external activity and a trans-
parency that displays the lively inside workings as
might a glass model.

After the bewilderment induced by a first glimpse
of a vivacious rotifer, attention centers on an eye-
catching piece of gadgetry at the front end, the co-
rona or “crown,” used for both feeding and swim-
ming. It includes the mouth and the more or less ex-
panded area of delicate ciliated skin surrounding or
close to the mouth. In the hunting rotifers, which go
forth in search of food, swimming or gliding through
food-laden water, the corona is external and often
convex. In many species which live permanently
fixed by a long stalk, or in those which attach tem-
porarily while feeding, the coronal lobes may be
protruded from the mouth during feeding, then re-
tracted. Some of the large and beautiful stationary
rotifers have a lobed and funnel-shaped corona with
long bristles that prevent escape of the prey when
the lobes of the funnel close down on some small ani-
mal that happens to enter.

The most familiar rotifers of fresh waters are the
bdelloid (“leechlike”) rotifers, elongate little ani-
mals that creep in leechlike or inch-worm fashion on
the bottom or on plants. Bdelloids typically have a
corona consisting of two elevated disks, and these
propel the animals on brief excursions through the
water. The large fused cilia that fringe the two coro-
nal disks beat in such a way as to create the illusion
of two rotating cogged wheels. These were the first
rotifers discovered by the early microscopists, so that
long before the illusory matter was finally cleared
up, all the microscopic creatures with expanded
crowns of cilia at the front end had been named
“wheel animalcules.” The formal name of the phy-
lum, Rotifera, means “wheel-bearers.”

Rotifer shapes may be wormlike, as in bdelloid
rotifers; flower-like, as in the sessile forms that have
great expanded coronas; or rotund, as in the rotifers
that float freely in open water. The common fresh-
water bdelloid rotifer, Philodina, has an elongate
body distinguishable into a corona-bearing head, a
central region or trunk, and a tapering foot region.
At the end of the foot are two pointed projections
called “toes,” and from each of these open cement
glands that secrete a sticky substance by which the
animal anchors temporarily while feeding. The toes
are also of use in creeping about, as the flexible body
alternately lengthens and takes hold by the front end,
then contracts and fastens by the toes. The whole
body is enclosed in a flexible cuticle which is folded
into sections that telescope into each other when the
animal contracts. In some rotifers the cuticle of the
trunk region is hardened into an armored case or
lorica, either smooth or ornamented with grooves or

spines. One or more eyes may be seen on the front
end as red flecks.

From the mouth the digestive tube leads promptly
to a gizzard-like swelling, the mastax, which has
powerfully muscled hard jaws. Through the trans-
parent wall the toothed jaws of the mastax can be
seen grinding away at the food that is swept down
the mouth. In some species the jaws are long and
slender, forming a kind of forceps that can be ex-
tended through the mouth to grasp prey.

The tiniest rotifers are not nearly as small as the
smallest protozoans, but members of both groups are
generally of comparable size, and the largest rotifers
are only about 15, of an inch long, not as long as the
giant fresh-water protozoan, Spirostomum. Little
wonder, then, that the early microscopists confused
the many-celled rotifers with ciliated protozoans, for
the two groups are similar in many superficial ways
and resemble each other even more in habits. Like
ciliated protozoans, the rotifers swim in spiral fash-
ion, attach to vegetation and feed by ciliary currents,
often live in cases attached to water plants, and have
a cosmopolitan distribution. Geography means noth-
ing to animals so small that they can be swept along
in the feeblest movements of water—and so resistant
to drying, either as dormant eggs or as desiccated
adults, that they can be carried about by winds and
on the feet of birds. After months or even years in
the inert state, some rotifers can again spring into
activity at the first wetting. If conditions are the
same, a lake in Germany, or for that matter one in
China or in South Africa, will have the same species
of rotifers as one in the United States. Relatively few
species are restricted to special conditions, as are
those found only in highly alkaline lakes in the west-
ern United States, or those that live attached to par-
ticular species of aquatic plants.

Basically, however, protozoans and rotifers are
very different, for the latter are composed of the
equivalent of a large number of extremely small
cells. The cell membranes present in the embryo
mostly disappear in the adult, leaving tissues that
are protoplasmic masses with numbers of nuclei.
Each of the nuclei occupies a definite position, and
through the transparent body wall they can be seen
and counted. The number of cells of a late embryo,
or the number of nuclei of an adult, is constant for
any species—usually between nine hundred and one
thousand. In their cell or nuclear constancy rotifers
are almost unique among multicellular animals,
though this phenomenon does occur to a lesser ex-
tent in a few other phyla. The rotifer body is of a
structural grade that includes several complete sys-
tems of organs, some of them more complex than
those of the flatworms, some less so.

No large grouping of animals is more partial to
fresh waters than are the rotifers. Of some seventeen

hundred described species, only about fifty are said
to occur solely or mostly in the sea, though common
fresh-water species are often carried into brackish
or salt waters and manage to survive there. Of the
marine forms nearly all live on shore bottoms. Only
two species have been seen afloat in mid-Atlantic.
The fresh-water rotifers also stay close to shore,
about 75 per cent of them living on the bottom or on
plants at the edges of lakes and ponds. Not more
than about a hundred species are freely floating
types, completely independent of any firm substrate.

A few rotifers live on the external surfaces of other
animals, as on the gills of crustaceans. Among the
parasitic species are Proales parasita and Asco-
morpha volvocicola, which enter colonies of the co-
lonial protozoan Volvox, living and breeding within
the spherical colonies and feeding on the members.
Drilophaga parasitizes fresh-water annelids, and
there are rotifers parasitic on protozoans, hydroids,
pond snails, and plants.

Two rotifers (at top),
a gastrotrich and a kinorhynch

Though many bdelloid rotifers are fully aquatic,
this group is the one most characteristic of lichens
and mosses. Their almost incredible capacity to sur-
vive when seemingly as dry as dust particles enables
them to live even in such intermittently wet places
as rain gutters and cemetery urns, moss-covered walls
or roofs, glaciers, rocks, and the bark of trees. Dry-
ing must occur gradually, as it does in the crevices
of moss, and the rotifer withdraws into the central
trunk region, puckering the two ends shut. The body
shrinks by loss of water and becomes more and more

[139

wrinkled. In the desiccated state rotifers in moss usu-
ally survive three or four years, in one presumably
reliable case as long as twenty-seven years. When
wet again they return to normal activity in from ten
minutes to a day.

Reproduction in rotifers can be sexual, and the
sexes are separate. But much of the time the females
are fully in charge, producing young without having
to bother with males. In one small group of primitive
marine rotifers, so far known only from European
waters, males and females are nearly similar in struc-
ture, though the males are slightly smaller and less
abundant. The eggs must be fertilized, and they
hatch into animals of either sex. Among bdelloid
rotifers no males have ever been seen, and the eggs
laid by the females always develop, without fertiliza-
tion, into more females. About 90 per cent of all roti-
fers are members of a third group, the Monogononta,
in which males are produced only during a few weeks
of the year, at which time they are fairly abundant
but live for only a few hours to a few days. They usu-
ally impregnate the females by hypodermic injec-
tion through the body wall, rarely by copulation.
These males are often about one-third the length of
the female, sometimes much smaller. They are also
degenerate, lacking mouth and mastax, or other or-
gans as well. There are two kinds of females, indis-
tinguishable externally. During most of the year one
type prevails, laying eggs that develop without ferti-
lization into females of the same type. At critical
times in the year, when the environment is under-
going some marked change, another kind of female
hatches from the eggs. These are capable of being
impregnated by males, but if they are not, their eggs
hatch into males. When males do impregnate this
second type of female, the eggs that are laid have
thick, hard, and often ornamented shells and can
withstand drying, freezing, or other hazards. Such
“resting eggs” or “winter eggs” can tide the species
over unfavorable seasons or events; they later hatch
into the type of female that carries on without males.

The Gastrotrichs

(Phylum Gastrotricha)

Anyone who examines old protozoan cultures or
pond debris under the microscope, looking for proto-
zoans or rotifers, will sooner or later see gastrotrichs,
elongate transparent creatures usually less than 155
of an inch long, and colorless except for any colored
food they have ingested. Most observers pass them
by as just another kind of ciliated protozoan, but the
cilia by which they swim or glide are restricted to the
under surface, and there are some on the head.

140 |

The upper surface of the cuticle of the trunk is usu-
ally clothed with overlapping scales, with bristles or
spines, or with spined scales. Those most often seen
in fresh waters are bristly, have a slightly constricted
neck that sets off head from trunk, and end in a
forked tail that has at each tip a cement gland serv-
ing the same function as in rotifers. They browse on
the bottom or on vegetation, and swim only briefly.
About the size of rotifers, the gastrotrichs also re-
semble them in many details and feed on the same
small organisms or organic debris. They have no
spreading feeding disk, and food particles are sucked
in by a muscular throat (pharynx) like that of nema-
todes, the group to which they seem to show most
affinity.

About 60 per cent of known gastrotrichs live in
fresh waters, but one group is exclusively marine.
So far it is known only from European shores, where
the most devoted observers have worked. The ani-
mals glide, crawl in leech fashion, or remain attached
for long periods. They are hermaphroditic, produc-
ing both eggs and sperms.

The group which includes most of the common
gastrotrichs of fresh waters has many marine mem-
bers also. The fresh-water forms are seldom found
in running water, for they favor habitats with much
decay, such as vegetation-choked shores of ponds
and lakes, mossy pools, and bogs. Surprisingly, they
also occur in large numbers in the damp sand near
the water’s edge on sandy beaches. In all these gas-
trotrichs the male organs seem to have degenerated;
all individuals are females and lay eggs that develop
without fertilization.

The Kinorhynchs

(Phylum Kinorhyncha)

A little more than a century ago, the ardent French
microscopist Felix Dujardin turned his attention to
some seaweeds collected along the coast of the Eng-
lish Channel. Upon these marine plants he discov-
ered a strange creeping animal less than 4, of an
inch long. It resembled nothing he had ever seen
before, and it had spines around the region he re-
garded as its neck. For this reason he named it an
“echinodere.” Thirty years later, a German zoologist
concluded that the echinodere and several similar
creatures that had been discovered should be re-
garded as belonging to a special group, the Kino-
rhyncha, using this term to show that all of them pull
themselves along by a sort of snout. Some people
would have preferred the group to be called the
Echinodera.

These are exclusively marine and microscopic,
with elongate bodies covered by a jointed cuticle that

suggests segmentation. Most of what is known about
kinorhynchs has been learned from those along Eu-
ropean shores. Yet these animals have been found
on northern American coasts, Japan, Zanzibar, and
the Antarctic. They must be widely distributed.

Kinorhynchs have no cilia and cannot swim, but
crawl about on muddy or slimy bottoms, swallowing
fine debris. Some live on seaweeds, browsing on mi-
croscopic algae. To feed, the animal extends the
spiny, retractile head and protrudes a mouth cone
with a circlet of spines. Then it sucks in the food by
means of a muscular throat. Externally the males
and females cannot usually be told apart, but sex-
ual reproduction occurs at all seasons. The eggs hatch
into a larval stage.

The Priapulids

(Phylum Priapulida)

This small phylum has, so far, only six species of
marine wormlike animals of dull color and moder-
ate size, the largest about 3 inches long. The cylindri-
cal and superficially ringed body, so warty that the
animal was once classed with the sea-cucumbers, has
a shorter front region which can be inverted and
withdrawn into the longer trunk region. The front is
well armed with rows of spiny teeth, for capturing

prey as the worm plows through muddy bottoms.
Three species have long been known from northern
seas around the globe, down to 1500 feet (S00 m.),
and as far south as Massachusetts and Belgium. One
of these, Priapulus caudatus, or a form almost like it,
is found also in antarctic seas, as is another species
of the same genus. Until 1959 no priapulids were
known from middle latitudes; then a new species
was brought up from the cold bottom of the mid-
American trench, at a depth of nearly 17,000 feet,
off the western coast of Costa Rica.

The Horsehair Worms

(Phylum Nematomorpha)

The horsehair worms have been known for many
centuries, and almost from the beginning have been
associated with the myth that they were animated
horse hairs, transformed after being dropped from
horses into bodies of fresh water or into drinking
troughs. The resemblance is not too far-fetched, for
these long, fine worms are often about 6 inches long
and black or brown in color, though the color may
be yellow or gray and the length may approach 3
feet. The diameter of the body (145 of an inch at
most) is almost the same throughout, though it ta-
pers very slightly at the rear and a little more at the
front end. Males are shorter than females and usu-
ally slightly curved at the rear.

We no longer need a fanciful explanation for why
horsehair worms suddenly turn up, full-grown, in a
body of water that had none the day before. The lar-
val worms develop within the bodies of insects, usu-
ally land beetles, crickets, and grasshoppers. The
adults emerge full grown and make their way to wa-
ter. They have a degenerate digestive tract and never
feed. Though the males can swim slowly, the females
do little more than writhe about.

In the springtime one may find writhing masses of
as many as twenty tangled worms, and this has given
rise to another common name, gordian worms, refer-
ring to the Gordian knot of the ancient Greek myth.
Only one pair of worms is involved in a copulation,
however, and the fertilized eggs are laid in long,
gelatinous strings. After hatching, the larva swims
about for a short time, then presumably encysts on

[141

vegetation at or near the water’s edge. Thus larval
cysts can be ingested by water beetles, and perhaps
a falling water level exposes some of the vegetation,
making the cysts available to crickets and grasshop-
pers feeding near the water’s edge. The genus Gor-
dius is known from ponds and ditches all over the
world. Other genera are less cosmopolitan, but horse-
hair worms occur from the tropics to cold-temperate
regions, even above timber line on mountains. There
are about eighty species, only one of them marine.

The Spiny-headed

Worms

Only when they are tucked away in someone else’s
intestine can these worms be looked on as animals
of unobtrusive habits, though it is true that few peo-
ple ever see any of the four hundred known species
or are even aware of their existence. The spiny head
referred to in both common and technical names is a
burrlike and retractile proboscis by which the worm
clings to the intestine of fresh-water, marine, or land

(Phylum Acanthocephala)

vertebrates. Fishes and birds are favored hosts, but
many mammals receive their share of attention, and
occasionally also man. Like the tapeworms, which
they resemble in many respects, these spiny-headed
parasites have no mouth or digestive tract at any
time in life, risking all on finding hosts to support
them. They have few internal organs that are not di-
rected toward a prodigious production of offspring,
and the success of the species rests on enough of these
surviving all hazards and eventually making their

142]

way back to the vertebrate host to reproduce again.

The adult lives a life of ease, absorbing food
through the body wall and resisting digestion by
means of the thin cuticle that covers the body. The
chief damage to the host is local injury at the point
where the proboscis is attached, but if the proboscis
perforates the wall, it may cause a fatal peritonitis.
In really heavy infestation the worms may interfere
with digestion and cause loss of appetite.

The spiny proboscis, armed with rows of stout re-
curved hooks, can be turned inside out on retraction.
And the knoblike or slender forepart of the body,
made up of the proboscis and an unarmed neck at
the base of the proboscis, can be withdrawn into the
much larger trunk region. The trunk may be short
and plumpish or long and cylindrical, but only in
certain worms is it curved or coiled or beset with
spines.

Most acanthocephalids are under 1 inch long,
some only a small fraction of an inch, but the com-
mon species that lives in pigs all over the world
reaches a length of more than 2 feet and looks as
formidable as its name, Macracanthorhynchus hirudi-
naceus. This giant parasite has, in the past at least,
been reported in people of the Volga valley in south-
ern Russia. The knoblike proboscis is armed with
five or six rows of very stout thorns, and the long,
pinkish, wrinkled trunk tapers from front to rear. As
in nearly all spiny-headed worms, the male is much
smaller than the female. The eggs develop, within
the mother, into a young larval stage that is enclosed
in a hard spiny embryonic shell. Shed with the host’s
feces, the shelled embryos can survive in soil for up
to three and a half years. When swallowed by grubs
of June beetles or similar insects, they develop within
the insect body. Pigs become infected when they eat
either grubs or beetles as they root about in pastures.

The only other species that has been found at
times in man is Moniliformis dubius, a common par-
asite of house rats. In the United States and in South
America it spends its larval life in cockroaches, and
these infect rats that feed on them. In Europe a bee-
tle (Blaps) has been implicated as a larval host. The
adult worm may reach 1 foot in length and has a
really wicked-looking proboscis, cylindrical and coy-
ered with twelve to fifteen rows of thornlike hooks.

People sometimes unwittingly eat cockroaches or
beetles, and there are other possibilities for getting
infected with these resourceful parasites, but fortu-
nately human infections are quite rare. The habits
of dogs provide more opportunities for such worms,
and dogs or coyotes in North America sometimes
harbor Oncicola canis and may display rabies-like
symptoms. In Texas, where most of the known cases
occur, the armadillo may act as a transport host be-
tween the dog and the arthropod that first harbors
the larva.

The Entoprocts
(Phylum Entoprocta)

These are tiny (less than %4 of an inch high)
aquatic animals that live as solitary individuals or
little colonies, superficially resembling hydroids be-
cause the round or bell-shaped, flower-like body sup-
ported on a stalk is crowned by an oval circlet of
tentacles.

Under the microscope, an entoproct’s tentacles are
seen to be ciliated on their inner surfaces and to cre-
ate ciliary feeding currents that gather microscopic
organisms and particles. The intestine is U-shaped;
and this, together with the tentacular crown and the
habit of growing attached to various objects or on
other animals, reminds us of the familiar moss ani-

mals (bryozoans). For many years, in fact, the en-
toprocts were included within the phylum Bryozoa.
But the body of an entoproct differs from that of a
moss animal in so many ways that a separate phylum
became necessary for them. It is named for the posi-
tion of the anus—within the circlet of tentacles. In
moss animals the anus opens outside the tentacular
crown. In hydroids, of course, there is no anus.

Entoprocts are almost entirely a marine group. So
far the only fresh-water genus (Urnatella) has been
found in India and the eastern part of the United
States. The remainder of the sixty-odd known species
of entoprocts have been collected widely on marine
shores or in shallow waters around the world. Find-
ing these inconspicuous animals is an exciting chal-
lenge to anyone who likes to see at first hand a small
group known to most people only from books.

[143

CHAPTER VIII

The Arrow Worms

(Phylum Chactognatha)

Ae. any bucketful of sea water, whether
from the surface close to shore or from the depths, is
likely to contain a few pencil-slender arrow worms,
so transparent as to be overlooked. Even hundreds
of them may draw no attention to themselves unless
the water in which they swim is poured into a shallow
dish with a black bottom. Then the arrow worms
show as ghostly, darting creatures from %4 to 4 inches
in length.

All of the thirty-odd species of arrow worms are
free-living. Most of them are pelagic and cosmo-
politan. Sometimes they become extremely abun-
dant, swimming in great masses that can cloud the
water with a grayish tint, particularly at certain times
of the day and year. Usually this matches occasions
when the sea is locally rich in the favorite foods of
arrow worms: microscopic diatoms and other algae,
protozoans, copepod crustaceans, and larvae of
many other animals, including fish. Toward all of
these an arrow worm is a formidable predator, but
to jellyfishes, ctenophores, small fish, whale sharks,
and whalebone whales, it is merely part of the nour-
ishing plankton.

As an arrow worm rests quietly in the water, its
body ordinarily is straight and horizontal. Folded
compactly under a thin rounded hood at the anterior
end is a pair of sickle-shaped hooks set with movable
spines. These serve as jaws when the hood is turned
back and the arrow worm darts for about its own
length after prey. Between the hooks and surround-
ing the slitlike mouth are dozens of short bristles.

144]

The chaetae from which the phylum Chaetognatha
takes its name (“bristle-jaws”) are the spines on the
prehensile hooks which, when spread and held out
stiffly, form the most conspicuous feature of an
arrow worms head. Closer inspection, however, soon
leads to discovery of two widely spaced clusters of
simple eyes (ocelli), each cluster roofed by a three-
part, light-collecting lens. The largest part faces
somewhat to the side. A diminutive brain may be visi-
ble, connected by very fine nerves to the eye clusters,
to the muscles controlling the grasping hooks, and to
a narrow organ on the midline believed to apprise
the animal of chemical substances in the water—the
aquatic equivalent of the senses of taste and smell.

Fully half of an arrow worm’s body is trunk, set
off from the head by a slightly narrowed neck and
from the tail by another change in body diameter.
The sides of trunk and tail bear thin, streamlined fins
suggesting the feather vanes on an arrow. From these
the principal genus gains its name (Sagitta) and
chaetognaths receive the familiar term arrow worms.
The tip of the tail also bears a transverse fin.

Each of the fins is supported firmly by hair-thin
rays, but no special muscles permit separate move-
ments of these extensions of the body. Instead, they
serve in maintaining balance and in making more
effective any movements of the body as a whole in the
water.

Except for the fin rays, no structure resembling a
skeleton ever develops in an arrow worm. The mus-
cles are chiefly longitudinal ones, used in bending

the body in locomotion. They are supplemented in
the head by other muscles serving to move the grasp-
ing hooks.

An arrow worm’s digestive tract is a straight tube
from mouth to anus. Often it is the most conspicuous
part of the animal simply because the small crea-
tures being digested in it have not yet achieved the
degree of transparency of the predator surrounding
them.

Arrow worms resemble chordates in having a skin
that is several cells thick in some areas and in pos-
sessing a tail posterior to the anus. The body cavity,
moreover, arises during embryonic development in
the manner characteristic of echinoderms and chor-
dates but no other phyla. Yet the chaetognaths have
no separate circulatory system nor respiratory or
excretory mechanisms. Instead, the fluid in the body
cavity is propelled by cilia and by movements of the
body as a whole, and serves to transport food and
wastes from the digestive tract to the body wall, and
oxygen absorbed from the sea in the other direction.

Actually, the body cavity is cut into a head portion,
a trunk portion, and a tail portion by transverse par-
titions, and is separated incompletely into a right side
and a left by a perforated longitudinal sheet of tissue
(mesentery ) holding the digestive tube in place.

The tail cavity contains a pair of testes, from
which the sperm cells escape through ruptures after
being coated with mucus to form spermatophores.
The trunk cavity, on the other hand, contains a pair
of slender ovaries, with ciliated oviducts opening to
the outside of the body. Hence an arrow worm is a
hermaphrodite, with a male tail and a female trunk.
The fertilized eggs are discharged and develop while
floating in the water. In many features the embryos
resemble those of echinoderms and chordates.

Probably the planktonic genera Sagitta, Eukroh-
nia, and Pterosagitta include only species depending
upon self-fertilization. Sagitta is easy to recognize
from the two pairs of lateral fins, Eukrohnia by the
long, slender neck region and single elongated pair
of lateral fins, and Pterosagitta from the thick-
necked appearance given by a massive collarette
extending back to the single pair of small lateral fins.

Spadella is a very different arrow worm, asso-
ciating with the bottom and clinging to objects there
by means of adhesive papillae. In S$. cephaloptera
these are located on the ventral surface of the tail;
other species wear the miniature suckers on finger-
like projections situated just in front of the tail fin.

In all members of Spadella, the body is more
stocky, and the animal spends much of its time hold-
ing to a rock or an alga, waiting for food to come
within darting distance. Often it seizes victims with-
out even letting go of its support. Cross-fertilization
is the rule in Spadella, and the eggs are cemented to
the bottom.

Temperature of surrounding water seems impor-
tant to many arrow worms at the time of reproduction.
The pelagic kinds that migrate vertically in the trop-
ics are exposed to a large range of temperature every
day, since at one thousand feet below the surface
the water is close to the normal freezing point
whereas surface layers may be quite warm. Appar-
ently they become dependent upon access to tem-
peratures higher than those in the depths, for, if
currents carry them into colder water, they fail to
reproduce even though they may grow to twice their
normal size.

The arrow worm, Sagitta setosa, occurs in surface wa-
ters in incredible numbers at certain seasons. At such
times it is an important food for fishes. (England.

D. P. Wilson)

[145

CHAPTER 1X

‘The Acorn Worms

and ‘Their Kin

(Phylum Hemichordata)

An

acorn

burrow in the sea bottom

Aa the treasures to be found in sand and
sandy mud along the world’s seashores are fragile,
pinkish tan animals called acorn worms. At first
glance each might be thought to be a pale, soft-bod-
ied earthworm. The 5- to 6-inch body even wears a
swelling near the anterior end, suggesting the clitel-
lum of an earthworm. But the body of an acorn
worm is not segmented, and the enlarged region is a
collar that extends completely around it.

Sometimes an acorn worm is exposed when a
stone, half-sunken in the bottom, is lifted. One wall
of the worm’s burrow is taken away. These creatures
build branching U-shaped or Y-shaped tunnels in
the bottom sediments, lining them with mucus. At
night an acorn worm may emerge from its burrow
and creep over the bottom among eelgrass or other
plant tangles, but by day it is almost sure to be out of
sight.

In spite of the wormlike body, acorn worms pos-
sess a feature that, until recently, was regarded as
earning them a place in phylum Chordata, as de-
generate relatives of the vertebrates. Between the
pharynx region of the digestive tract and the outside
of the body, acorn worms and some of their close kin
show a series of paired openings. Clefts of this kind
are known otherwise only among the chordates
and, possibly, one extinct genus of echinoderms.

Today the phylum name Hemichordata is re-
garded as suggesting a sort of halfway station, not
really eligible for inclusion among primitive chor-
dates but rather worthy of a phylum by itself. Similar-
ities between embryonic stages of hemichordates and

146]

worm

in its

echinoderms may indicate a closer link with sea stars
and their kin.

The first part of an acorn worm, anterior to the
collar region, contains a contractile chamber serving
as a heart. It draws blood from a dorsal longitudinal
vessel, pumps it through an organ assumed to serve in
excretion, thence around the digestive tract on each
side, to join into a ventral longitudinal vessel. This
first part of the body is used also in burrow-making
and in pulling the body along when the animal is ex-
posed on the surface. Cilia, which cover the body,
help in a slower, gliding kind of locomotion.

The mouth opens below the forward end of the
collar and leads into a long, straight digestive tract.
The anus is at the posterior end of the body, and
there is no postanal tail as in chordates. Just behind
the collar, the gill openings from the pharynx dis-
charge water taken in through the mouth. This copi-
ous flow is directed from the dorsal surface into the
worm’s tunnel or the surrounding sea.

In some species of the genus Balanoglossus, the
first part of the body and the collar together might
suggest an acorn in its cup; from this the most familiar
of the hemichordates receives a common name. In
Saccoglossus the first part of the body is greatly ex-
tended. The twenty-odd species of Balanoglossus in-
clude B. clavigerus from the Mediterranean and B.
aurantiacus from the coast of the Carolinas. Sacco-
glossus kowalevskii is found on both sides of the
North Atlantic and is probably the acorn worm most
frequently encountered.

Members of the genus Ptychodera resemble Ba-

lanoglossus but have large, conspicuous gill pores.
P. flava is a denizen of the Indian and Pacific oceans,
and P. bahamensis of the Bahamas and West Indies.

In addition to nearly one hundred different kinds
of acorn worms, the phylum Hemichordata includes
a few diminutive colonial members which bear
tentacle-studded arms on the second region of the
body but lack gill slits. These animals secrete a cover-
ing for themselves and live within deep cupshaped
cavities in a manner reminiscent of moss animals
(bryozoans). Related to this life in a blind tube,
each has the anus far forward, just posterior to the
arm-bearing collar region, and hence over the edge
of the tube opening while the animal is feeding, its
ciliated tentacles exposed, creating a current in the
water that brings food particles and oxygen.

Each individual of Cephalodiscus may be 4 of an
inch long, not counting the slender stalk extending
down into the depths of the community shelter, there
making contact with other neighboring individuals.
From the dorsal surface of the second region of the
body, Cephalodiscus has two rows of from five to
nine arms each, every arm fringed with from twenty-
five to fifty tentacles.

Individuals of Rhabdopleura are less than 1 ¢ of
an inch long, not counting the stalk. Each bears two
comparatively huge, gracefully curved arms with cil-
iated tentacles, again on the middle region of the body.

Both of these colonial hemichordates reproduce by
budding and also sexually. Ordinarily a colony con-
sists of the matured buds from a single individual.
The buds are formed low on the stalk and begin as
an extension of the previous animal. The first body
division of the new individual proceeds to secrete a

new addition to the community shelter, and later
matures in it—still with the possibility of producing
further buds either in the same line or as branches of
the colony.

Rhabdopleura normani has been collected from
west Greenland to the Azores, usually attached to
old dead parts of corals. Cephalodiscus is a larger
genus, with representatives from the Arctic to the
Antarctic, most of them obtained by dredging. They
grow on rocks, clamshells, and other firm surfaces.
Often, in turn, they are overgrown by hydroids and
moss animals, adding to the complexity encountered
among the living things on a shell or a stone.

The acorn worm Ptychodera bahamensis of the Ba-
hamas and West Indies uses its acorn-shaped probos-
cis as a burrowing organ and makes branching U- or
Y-shaped tunnels in bottom sediments. (Bermuda.
Ralph Buchsbaum )

CHAP TEREX

The Beard Worms

53 ee the most astonishing discoveries made
with deep-sea dredges in the twentieth century was
the finding of this assemblage of tube-building,
wormlike creatures, for they live their solitary lives
and reach a length of as much as 13 inches, a diame-
ter to 14, of an inch, with no trace whatever of a
digestive system—a condition unique among free-
living many-celled animals.

The body of one of these long and exceedingly
slender worms shows a subdivision into three regions:
a proboscis bearing from one to more than two hun-
dred tentacles on its underside; a collar-like enlarge-
ment; and a long posterior body whose final third
may be marked off into a large number of successive
rings by rows of raised adhesive areas. With these a
beard worm clings to the slender, close-fitting tube it
has secreted in the bottom mud. The tube consists
of a series of rings or slightly funnel-shaped pieces

148 ]

(Phylum Pogonophora)

composed of animal cellulose—the material found in
the tunic of a sea squirt.

Enough is known about the embryos of beard
worms to show that they too lack a digestive tract
and consequently cannot be assumed to store enough
food to last for the lifetime of the worm. Instead, a
beard worm seemingly must depend upon decompo-
sition products diffusing to it from bacterial action in
the surrounding abyssal water, or must be able to
control digestion outside its body in an enclosed space
of some kind.

In searching for an enclosed space of this descrip-
tion, scientists have looked suspiciously at the slen-
der cavity within the spiral of the single tentacle in
species of Siboglinum, or between the outstretched
parallel tentacles of worms in other genera.

In Galathealinum somewhat more than one hun-
dred tentacles lie side by side, anterior to the worm
in its tube. In Spirobrachia the number may be more
than two hundred. In Lamellisabella the tentacles
form a watertight cylinder for most of their length,
and only the tips are free. Into this cylinder extend
short lateral projections comparable to those found
on one or both sides of the tentacles in all other
beard worms.

The tentacles do have thin walls and an extension
of the closed circulatory system. But so far, no gland
cells have been discovered that could secrete diges-
tive ferments, and the secret of the beard worms’
nourishment remains an intriguing enigma.

Of the twenty-four known species of beard worms,
thirteen have been found only at great depths be-
tween Kamchatka and the islands just north of Ja-
pan. Four more appear to be limited to somewhat
shallower waters in the same general region. Sibogli-
num has been dredged from the Skagerak off the
Norwegian coast at depths from 500 to 2000 feet,
from British waters, and from tropical western parts
of the Pacific. The last is the only known home of
Galathealinum. Lamellisabella has been recovered
from close to ten thousand feet below the surface in
both the Okhotsk Sea and the Gulf of Panama.

CHAPTER XI

‘The Phoronids

(Phylum Phoronida)

Rane the level of low tide, pier pilings in the
Bay of Naples wear a feltwork of interlacing mem-
branous tubes two or three inches thick. Each tube
is the individual home of a wormlike animal, Pho-
ronis kowalevskii. Like the fourteen other species
comprising this phylum, these tube-dwellers wear
a horseshoe-shaped crown of ciliated tentacles with
which they entrap food particles in a mucous film
carried to the mouth at the bottom of the horseshoe.

Most phoronids are less than 8 inches long, some
as short as 14, of an inch. A giant is Phoronopsis
californica, which lives singly in the estuaries along
the California coast in blind tubes as much as 18
inches long and °4, of an inch in diameter. The en-
tire 12-inch body of this phoronid is orange, its tenta-
cles an even brighter shade of the same color. Some-

times it leaves the *4-inch plume of orange tentacles
exposed at the end of its sand-impregnated tube, and
draws attention in this way.

On the Atlantic coast of North America, 5-inch
Phoronis architecta is common in the sand flats of
North Carolina and as far north as Chesapeake Bay.
It also builds isolated tubes.

In Australia, a different reddish-colored phoronid
as much as 6 inches long builds a home for itself in
the wall of another tubedweller, the tube anemone
Cerianthus.

Phoronids have red blood in a closed system of
vessels. Most are hermaphroditic, and the fertilized
eggs develop into swimming larvae. Eventually the
young settle down to build a tube and grow by meta-
morphosis into adult form.

[149

CHAPTER XII

Ait curious about animal life in water is
almost sure to meet moss animals (bryozoans) in
many guises. A piece of seaweed is cast upon the
beach: over some of the floats and leaflike areas is
a limy coating with a pattern of minute pores. This
encrustation is a “lace coral,” the work of one type
of bryozoan (Plate 33). Or the spire of a whelk shell
is rough with a different limy coating: the colony of
another moss animal.

The nautically minded often meet bryozoans. A
skiff, pulled ashore after a summer at its mooring in
salt water, must be examined underneath for bar-
nacles and other fouling organisms. Some of the
shrubby and fuzzy growths are almost certain to be
bryozoans. Even in fresh water toward autumn, the
piers of a boat dock may develop enormous masses
of gelatinous material patterned in a mosaic of
brown markings over the surface. This too is a co-
lonial moss animal, not the egg mass of a giant frog.

Moss animals are all colony builders, and never
live alone. Each individual is of microscopic dimen-
sions, seldom more than 1, inch in length. It lives
a few weeks attached to the walls of a chamber
formed of its own secretion while capturing still
more minute particles of food in a current of water
created by cilia on its many tentacles. The presence
of cilia on the tentacles distinguishes a moss animal
from any coelenterate hydroid.

Bryozoans have a U-shaped digestive tract in which
the mouth is centrally placed in a ring or horseshoe-

150]

The Moss Animals

(Phylum Bryozoa or Ectoprocta)

shaped group of tentacles and the anus lies near the
mouth but is not encircled by the tentacles. The anus
is exposed when the tentacles are fully extended from
the chamber housing the animal. Otherwise the body
of each individual is astonishingly simple. It contains
no respiratory, circulatory, or excretory system. Nor
do the reproductive organs open to the outside by
organized passageways.

The brevity of life span for individual moss ani-
mals could be suspected from examining a healthy
colony with a hand lens. Each community begins as
a sexually produced single individual maturing from
a newly attached juvenile which has just gone through
marked changes from the embryonic swimming stage.
The first individual produces asexual buds, each of
which adds another chamber and another zooid—
and more buds. Consequently the periphery of a
growing incrusted colony or the tips of the branches
of a feathery clump of bryozoans is always the
youngest part.

Back from the edge or the tips, the hand lens usu-
ally reveals chambers empty except for minute brown
lumps, the “brown bodies” which remain from a de-
generated individual zooid. Still older parts of the
colony are likely to be inhabited again by feeding in-
dividuals, for into the chamber of a dead zooid the
colonial cross-connecting strands send a new bud to
provide a replacement. Often the first meal of the new
zooid is the brown body representing its predecessor.

No one is sure why each zooid dies so young. Pos-

sibly it is poisoned by nitrogenous wastes, with no
excretory system to discharge them to the outside
world. This seems improbable, since oxygen is ex-
changed for carbon dioxide with no respiratory sys-
tem, merely by absorption and release through thin
areas of the body wall, including the crown of tenta-
cles. Perhaps the zooid dies by rupture in freeing its
sexually produced offspring. The timing would cor-
respond well. And a habit of this kind would not be
without precedent, whether in the clamworms or the
sea lamprey or Pacific salmon.

Each active zooid is a sort of jack-in-a-box, often
concealed by a little trap door. Contraction of certain
body muscles causes an increase in the hydraulic
pressure inside the body cavity. This pressure is re-
lieved when the crown of tentacles moves through the
doorway into the surrounding water. Additional mus-
cles may even widen the opening, as though to speed
the tentacle crown on its way. Yet the first disturb-
ance is enough to cause still other muscles to drag
the everted crown back into the safety of the cham-
ber. If it has a lid, the door snaps shut.

In order to use this hydraulic method in extending
the crown of tentacles, each zooid must fill its cham-
ber. It must also retain space to accommodate the
tentacle crown whenever this feeding organ is en-
dangered. These conflicting requirements leave no
space for growth. Nor does the organization of the
colony provide for the general expansion of individu-
als. The colony grows by addition of new chambers
and new zooids.

The permanence of a bryozoan colony is improved
if the chambers have thickened walls. The zooids are
also better supported, and can reach more success-
fully into the water for particles of food. Yet allow-
ance must still be made for the out-and-in movements
of the tentacle crown. Several solutions to this prob-
lem are possible, and different bryozoans have be-
come adapted in one way or another.

Some moss animals with armored chambers leave
one wall—usually an end one, overhung by protective
spines—thin and membranous, flexible enough to be
pulled in while extending the tentacles, and to bulge
out again when the feeding organ is retracted. Other
bryozoans possess a second, special “compensation
cavity” within the chamber, with its own small open-
ing to the outside world. Muscles that dilate the com-
pensation cavity squeeze the zooid and cause the ten-
tacle crown to pop out. Retraction of the crown forces
water from the compensation cavity, giving the zooid
space within its box.

A third method seems still simpler: the contraction
of muscles dilating the opening of the chamber com-
presses the fluid in the zooid’s body cavity and ejects
the tentacle crown. Retraction is at the expense of
space in the chamber opening through which the feed-
ing organ is withdrawn.

So many different forms of life compete for space
on rocks and shells, pilings and boat bottoms, that
bryozoans are ever in danger of being overgrown. In
many places, suffocation under inedible sediments is
another hazard for all attached animals. Seemingly to
deal with this dual jeopardy, most colonies of bryo-
zoans in the larger of the two marine orders support
non-feeding zooids serving to police the immediate
world of the feeding individuals. That this should also
be the order in which hinged doors is usual is no co-
incidence. The defending zooids are merely ones
whose trap doors are modified as tools.

One type of policing zooid is the avicularium, in
which the movable door has become the jaw of a
snapping individual resembling a beaked bird’s head,
and named from the Latin avicula, a little bird. The
other type has the door modified into a long, whip-
like organ that can be swept over the surface of the
colony. Avicularia seize and hold small invaders of

A large colony of a fresh-water bryozoan, Pectinatella
magnifica, found growing on submerged wood in
quiet water. This massive species is common east of
the Mississippi valley. (Pennsylvania. Ralph Buchs-
baum )

all kinds, preventing them from settling among the
feeding zooids. Usually the little jaws continue to
clamp on victims until they die and decompose. Bac-
teria and other microorganisms from the decay proc-
esses may well augment the diet of the feeding mem-
bers of the bryozoan colony.

Under the microscope the gelatinous matrix of a Pec-
tinatella colony is seen to be studded with delicate
flower-like individuals, each with a crown of ciliated
tentacles that gather food. (Pennsylvania. Ralph
Buchsbaum )

About 6000 different species of living moss ani-
mals have been discovered, distinguished primarily
upon differences in the chambers they construct. One
small class is confined to fresh water. With rare ex-
ceptions, all members of the other, larger class live
where the sea has its full salinity. Most are shore or
shallow-water forms. They occur in all latitudes. Some
are known from depths of 19,500 feet.

152]

Fresh-water Bryozoans
(Class Phylactolaemata)

A microscope is needed to see that in this class a
little flap of body wall projects over the mouth as
though guarding the gullet. Yet this detail has given
the name of the class, from the Greek phylacterion,
a guard, and /aimos, the gullet. Far more obvious is
the fact that the tentacle crown is horseshoe-shaped
or at least kidney-shaped, rather than circular. The
body wall of each zooid contains a layer of muscles
and the body cavity (coelom) is a colonial affair, con-
tinuous from one zooid to the next.

Fresh-water bryozoans are widely distributed, often
cosmopolitan. During warm weather they reproduce
sexually, but when winter comes they bridge it in the
form of asexually produced armored balls of cells
called statoblasts. These latter tolerate freezing in the
ice, and can be carried from pond to pond on the
muddy feet of birds and muskrats. The statoblasts
are released in autumn when the parent colony dies
and disintegrates.

On the undersides of stones and sticks in ponds and
streams, particularly in shady places, fine-branching,
vinelike growths or bushy clumps with a zooid in
each end chamber are usually either Fredericella or
Plumatella. The former has oval or kidney-shaped
crowns of tentacles, the latter strictly horseshoe-
shaped food-capturing organs.

Another type of moss animal in fresh waters pro-
duces masses of gelatinous material as a base. Pec-
tinatella individuals form a thin crust over the com-
mon jelly secretion, organized into a mosaic of brown-
streaked areas each half an inch across, on a mass
reaching two feet or more in diameter. The brown
streaks radiate from a center, yet each streak is itself
a complex colony—a radial line of zooids. Each
area in the mosaic may include twelve to eighteen
zooids, all reaching out their feeding tentacles, yet
able to snap back into the protection of the jelly.

Pectinatella’s central jelly becomes the repository
for the innumerable statoblasts. These are armed with
a belt of hooks around an encircling air-filled cushion
suggesting a life preserver. Empty shells of germi-
nated statoblasts and dead ones sometimes drift to
shore in windrows, speckling a beach to a width of
one to four feet from the water.

Pectinatella forms fixed masses on underwater ob-
jects. Cristatella remains oval or elongate, as a creep-
ing ruglike colony often encountered on the under-
side of a water-lily leaf. These colonies glide very
slowly over plant stems, apparently through con-
certed movement of the muscles in the body walls
of the zooids that secrete the underlying jelly. Half
an inch to an inch a day are respectable speeds for
this bryozoan. At intervals a colony of Cristatella

pinches itself into two or more pieces, and each goes
off on its own, elongating as new zooids are added.
By late autumn, a lily pad floating on a pond particu-
larly rich in food for bryozoans may wear a whole
mesh of Cristatella, where separate colonies have
fused together.

Marine Bryozoans

(Class Gymnolaemata)

The zooids of marine moss animals have no little
flap of body wall projecting over the mouth, and
hence the gullet is exposed, as is indicated by the
name of the class (from Greek gymno, naked, and
laimos, the gullet). In these bryozoans the tentacle
crown is circular. The body wall contains no muscle
layer, and each zooid has a separate body cavity
(coelom).

A great many marine moss animals are cosmopoli-
tan, apparently having been carried throughout the
world on floating seaweeds, drifting wood, and the
bottoms of ships. Consequently a remarkable variety
can be found on almost any rock covered by water
at low tide, on any wharf piling that has stood for a
season, or among the fouling organisms on a boat
bottom.

Each of the three methods by which moss animals
provide for hydraulic extrusion of the tentacle crown
is characteristic of an order. Those retaining at least
one wall of the chamber as a thin, flexible membrane
may thicken the other walls but not impregnate them
with lime. These bryozoans wear around the extruded
feeding organ a pleated collar with stiffening rods,
suggesting a circular comb. They use this device to
close the opening of the chamber after the tentacles
have been withdrawn, and are the “comb-mouths” of
order Ctenostomata. One of the strangest of them
is Victorella pavida, whose long, slender, vaselike
chambers arise from a branched, vinelike growth at-
tached to underwater objects. It was discovered first
on docks in the Thames River at London, and not
only tolerates brackish water to a degree unusual
among bryozoans but seemingly lives also in the fresh
waters of Lake Tanganyika in Africa, on stones and
shells and in cavities of fresh-water sponges there.

Members of several ctenostome families specialize
in dissolving their way into the limy shells of conchs

and other heavy marine mollusks, replacing the mate-
rial removed by thin-walled chambers of their own.

Bryozoans whose chamber walls are all calcified
have circular openings, and exchange space in the
narrow vestibule opening to the sea for space in
the body cavity when the tentacle-bearing crown is
pushed out or pulled in. These are the “narrow-
mouths” of order Stenostomata. None of them pos-
sesses avicularia or the whip-wielding vibracula, but
reproduction may include a technique found nowhere
else among bryozoans: they produce a number of em-
bryos from each fertilized egg—like identical quintu-
plets, except still more numerous. The largest genus
(Tubulipora) includes many kinds forming prone or
erect colonies, often expanded into fanlike clusters
from which the reproductive zooids project as clearly
specialized members of the population.

The remaining marine bryozoans either retain one
membranous wall in the calcified chamber or produce
a compensation cavity. The opening of the chamber
is usually protected by a movable door, as the “lip”
referred to in the name of the order Cheilostomata,
the “lip-mouths.” This order is the only one in which
some zooids are modified into avicularia or vibracula,
serving to keep the colony immaculate and unin-
vaded. Most marine bryozoans are cheilostomes.

One of the most striking and largest of the cheilo-
stomes is the barely calcified Bugula turrita, colonies
of which are treelike, with branches each a spiral tuft
of flat, fan-shaped groups of branchlets. Double rows
of zooids on each branchlet have the openings facing
in a single direction, the surface over which the avicu-
laria patrol. These guardians swing on slender, flexi-
ble necks, back and forth with beaks wide open.

Fully developed Bugula colonies may protrude
from wharf pilings and sea walls to a distance of 12
inches, the bright yellow or orange tentacles con-
trasting with the dark water anywhere from Maine
to Brazil. Other species of Bugula are widely distrib-
uted in the northern and eastern Atlantic (Plate 34).

A very different type of cheilostome is the sea mat
Flustra foliacea, so abundant on the shores of western
Europe. Often it is mistaken for a seaweed, for it
forms erect, leafy colonies. Each surface of the broad,
bladelike branches is densely fitted with zooid-con-
taining chambers, each with two little horns. Among
the zooids are scattered, smaller, rounded avicularia
with broad lips suggesting the distorted mouths of
Ubangi women in the Belgian Congo.

[ 153

CHAPTER XIlIl

The Lamp Shells

(Phylum Brachiopoda)

A variety of lamp shells: (center) a
lingula with its stalk in mud; (top
right) hinged lamp shells clinging to

a rock

ie two parts of a brachiopod shell fit together
like saucers facing one another. But instead of these
being a right valve and a left, as in clams, one bra-
chiopod valve is dorsal, the other ventral.

In most brachiopods, the ventral valve is somewhat
larger and more convex, and extends beyond the
dorsal valve around a definite opening. This gives the
shell a general form like that of the oil lamps of Greek
and Roman times, so often represented symbolically
as the “lamp of wisdom.” The classic lamp was lit
through a hole corresponding in position to the one
through which a living brachiopod has a short stalk
serving to anchor the animal to some support. Usu-
ally the stalk holds the larger valve uppermost.

The 260 or so existing species of lamp shells are
all marine. They represent today a slowly dwindling
line whose ancestors can be traced clearly in the fossil
record for 500 million years. During four-fifths of
that time, they have been in slow decline. About
3000 different extinct species of brachiopods are
known.

Two genera of brachiopods hold the record for
surviving longer than any other group of animals.
Lingula, found first in the early strata of Ordovician

154]

age, goes back at least 350 million years, although
none of its existing species is particularly ancient. The
other genus, Crania, dates from late Ordovician to
the present, and is still millions of years older than
the next competitor. During Ordovician times, lamp
shells were more abundant than any other fossil-
producing type of animal.

Inside its shell, each brachiopod shows a relation-
ship to bryozoans and phoronids in possessing a pair
of curled, tentacle-bearing arms, one on each side of
the mouth. Cilia on the tentacle surfaces create water
currents which enter at the sides of the shell, bringing
minute food particles and oxygen. Glands on the ten-
tacles secrete a mucus film in which food becomes
trapped. The loaded mucus is then swallowed. The
water leaves on the animal’s midline, where the shell
valves gape most broadly when the muscles control-
ling them relax.

Modern brachiopods include a few with shell valves
as much as 3 inches in greatest dimension. Some fos-
sil forms exceeded | foot across. Existing lamp shells
inhabit all seas at all latitudes, and find places at all
depths, from the intertidal sand flats to the great
abysses. Many of them are abundant locally. Some

are widespread, either geographically or in the depths
they tolerate.

The shells of brachiopods provide easy cues for
identification. Those of Lingula are elongate, oval,
suggesting a finger nail, and the two valves of a pair
have almost identical dimensions and shape. The stalk
emerges between them instead of through a hole in
one valve. Lingula and Crania both represent the
smaller class Inarticulata, in which the shells lack an
interlocking hinge mechanism. Both valves are mov-
able, and sometimes they are twisted in relation to
one another while the animal is feeding.

Crania lacks a stalk, and is found cemented by the
ventral valve of its almost circular shell to rocks along
north European coasts and in the West Indies. By
contrast, Lingula and the similar animals of genus
Glottidia have a long, slender, flexible stalk, and use
it to anchor themselves temporarily at the bottom of
vertical, mucus-lined burrows in sand flats below low-
tide mark. If the waves wash the sand away, these
brachiopods can dig in again. Lingula has many spe-
cies in the Indian and Pacific Oceans. It is one of the
commonest lamp shells around Japan. There, and
around islands in the South Pacific, they are some-
times gathered as shellfish for human consumption.

Glottidia is found on both coasts of America, from
the Carolinas to the Gulf of Mexico and from Cali-
fornia to Peru. The shell valves may be 1 inch in
length, 25 inch across, with a stalk extending about
¥% inch.

Most modern brachiopods have limy teeth on each
shell valve, serving to lock them in alignment at the
hinge on the posterior edge. As such they are mem-
bers of class Articulata. They differ also from the in-
articulates in that the intestine ends blindly, with no
anus, and residual wastes must be discharged as pel-
lets through the mouth. The supporting stalk extends
through a hole in the ventral shell valve, and custom-
arily is used to hold the animal in a horizontal posi-
tion like a little bracket from some vertical rock sur-
face.

The hinged lamp shells are identified according to
the form of the shell and the degree of development
of a symmetrical pair of limy loops inside the smaller
valve, serving to support the food-collecting, tentacle-
bearing arms (lophophores). The one common bra-
chiopod along the New England coast (Terebratulina
septentrionalis ) , for example, has a pear-shaped shell
about 2 inch long, % inch wide, within which the
skeletal loops have fused into a single ring resembling
a small stirrup with a hole the shape of an inverted
heart. This same species is found also on coasts of
Norway and Scotland. Others of the same large genus
occur from the Antarctic to the Arctic in essentially
all oceans.

In Neothyris lenticularia of New Zealand waters,
the support for the tentacle-bearing lophophore has

become a tremendous loop suggesting the newspaper
holder below a metal letterbox, except that the center
of the delicate skeleton is fixed by a median, blade-
like extension from the region of the shell’s hinge
teeth. Even more crossbars bolster the lophophore
skeleton in Laqueus californianus, whose barely
ridged and highly convex shells reach a length of
2 inches on animals affixed to rocks along the Pa-
cific coast of North America.

Lamp shells of the genus Argyrotheca, from the
West Indies and western South Atlantic, are her-
maphroditic. Otherwise brachiopods are either male
or female. Their eggs and sperms are released into
the body cavity and discharged from the excretory
tubules (nephridia).

Most brachiopods retain their eggs within the shell
valves until fertilization has been followed by some
embryonic development. A few possess special brood
pouches, either in the vicinity of the tentacle-bearing
lophophore or, as in Argyrotheca, as enlargements of
the excretory tubules.

When the swimming larvae are released, they move
slowly through the water, propelled by cilia over at
least the anterior lobe of the three-lobed body. A few
days later, the larva metamorphoses, sinking to the
bottom. Its posterior lobe elongates as the supporting
stalk. The middle lobe enlarges to envelop the rest
of the body and becomes modified into the two layers
of tissue (mantle) secreting the shell valves and the
food-gathering lophophore.

Irregularities in the rate of shell secretion usually
provide eccentric rings comparable to those that have
been used in estimating the age of clams. Apparently
four years is a common life span for a lamp shell.

Three brachiopods attached to a piece of rock and to
each other. Preserved. (P. S. Tice)

CHAPTER XIV

The Peanut Worms

(Phylum Sipunculoidea)

| O a group of about 250 different species of sed-
entary marine worms the name “peanut worm” has
been applied, although the extended animal resem-
bles more a baseball bat with a crown of food-collect-
ing tentacles at the small head end. Yet, if disturbed,
the worm suddenly shortens, pulling in the anterior

half or third of its body, and rounding out to an ap-
pearance remarkably like that of the edible part
(seed) of a peanut.

The most striking feature of these worms is the
slender anterior part of the body (the introvert),
which rapidly and smoothly runs in and out of the
larger, cylindrical, posterior part. Actually the intro-
vert turns in like the finger of a glove or the wall of a
slender balloon pressed at the end by a lead pencil.

An undisturbed peanut worm extends its introvert
from the opening of the burrow and sweeps the mu-
cus-covered tentacles over the sea bottom, collect-
ing microscopic plants and other bits of nourishment.
These are digested in a long intestine which is both
looped upon itself to open at an anus well forward on
the animal’s ventral surface and also spirally twisted
within the body cavity.

Most sipunculoids live in shallow water, but some
have been found in depths greater than fifteen thou-
sand feet. Many peanut worms live in holes in sub-
merged rocks. Sipunculus nudus reaches a length of
about 8 inches and a diameter of 2 of an inch along
sandy coasts of southern California, Japan, Europe,
and Florida. Golfingia (Phascolosoma) margarit-
acea of more northern shores in both the Atlantic
and the Pacific is more slender but may be 14 to 18
inches long. All peanut worms develop from an ac-
tive swimming larva (trochophore) and discharge
their eggs or sperms through their excretory tubules
(nephridia) from the body cavity into the sea, where
fertilization takes place.

The peanut worm Golfingia (Phascolosoma) loses its
similarity to a peanut as soon as it extends from the
contracted position. Here the smaller front end is
being everted into the sand, turning inside out like a
finger of a glove. (Oregon. Ralph Buchsbaum )

CHAPTER XV

The Echiuroids
(Phylum Echinroidea)

Nore the marine animals for which none of
the scientific pigeonholes seems adequate are some
sixty-odd whose general sausage shape as adults con-
ceals the fact that they originate, as do so many
mollusks and annelid worms, from a swimming troch-
ophore larva. The echiuroid proceeds, in fact, as
though to become an annelid, developing exactly
fifteen segments to the body. Then it loses almost all
evidence of these features, and takes up life either
buried in the mud or protected within the cavity of
some shell or coral rock.

Echiuroids ordinarily hold their mouths at the
doorway of the burrow or hiding place. Beyond it,
into the sea, the animal extends a long, troughlike or
spoon-shaped prostomium and moves this about
while cilia on the concave surface gather detritus
from the bottom and pass it to the mouth.

On both sides of the Atlantic Ocean and along the
Pacific coast of America from California northward,
Echiurus pallasii reaches a length of 12 inches plus
the 4-inch prostomium. Echiurus echiurus of Eu-
rope is found in the same mud flats but makes a
U-shaped burrow and enlarges this as it grows.

In Bonellia the prostomium is as much as 3 feet
long and forked toward the tip, but the living habits
and food-gathering procedure of the female are al-
most identical with those of Echiurus. Larval Bo-
nellia appear able to develop into either sex, but all of
those that settle on the bottom become females. A
larva that chances to settle on the extended prosto-
mium of a female Bonellia becomes, instead, a male.

The female echiuroid Bonellia viridis has a green-col-
ored oval body with a long, extensible proboscis,
forked at the tip. The minute male lives within her
body. (France. Ralph Buchsbaum)

He remains microscopic in size and lives as a parasite
upon his mate, in her mouth or excretory organs or
reproductive tract.

Urechis, an echiuroid of the intertidal zone, has a
different method of feeding. It uses its burrow as the
support for a finger-shaped tube of mucus cemented
to the rim of the burrow opening. Body movements of
the worm in the U-shaped burrow draw water through
the mucus filter, which strains out food particles.
After the mucus tube becomes loaded, pumping is
more difficult. Urechis then swallows the tube with
its enclosed meal, moves to the burrow opening, and
attaches the rim of a new mucus filter. When the wa-
ter is charged with microscopic particles, Urechis
may swallow and replace its filter every two or three
minutes. But if the water is clear, a whole hour may
be needed to load a single mucus tube.

[157

CHAPTER XVI

(Left) octopus; (below octopus) sea cradle or chiton;
(center top) scallop; (center bottom) tooth shell;
slug and clam.

ck many people the mollusks are “shellfish.”
Clams and oysters, perhaps snails and squids, are the
most familiar kinds. Yet squids have no obvious
shell, and no one seriously would consider a plate of
cooked snails as fish except on “fish day.” Nor did
those who gave the phylum Mollusca its name (from
the Latin mollis, soft) have in mind the giant squids
of the open oceans, creatures that wrestle—some-
times successfully—with the great sperm whales.

Better than forty thousand different kinds of living
mollusks are known, a total exceeded among inverte-
brate phyla only by the arthropods. These mollusks
include representatives above the snow line in the
Himalayas at an altitude of 16,400 feet, and deep
blue sea slugs creeping on the underside of the sur-
face film in the open ocean, and clams plowing the
sea bottom at a depth of at least 17,400 feet where
the hydrostatic pressure is almost four tons to the
square inch. Some snails manage to survive freezing
in the ice over ponds, and others tolerate thermal
springs at a temperature of 112 degrees Fahrenheit.
A few desert snails live where the air above them at
noon is in the same temperature range.

All of this versatility demonstrates the possibilities

158]

The Mollusks

(Phylum Mollusca)

in an unsegmented body whose dorsal and lateral
surfaces bear a fleshy tissue (the mantle) capable of
secreting an external limy shell. Ordinarily the ven-
tral surface is a flat, creeping foot. Features of the
foot, mantle, and shell are particularly helpful in
identifying each different kind of mollusk.

Some features of mollusk anatomy are peculiar to
this phylum. A rasping organ (radula) is found in the
mouth of most mollusks as a ribbon-shaped tool that
can be slid back and forth while its sharp teeth act
like those on a file, scraping free small particles of
food. All mollusks, even the largest and most active,
have a nervous system consisting of only three paired
ganglia. One lies above or beside the mouth, a sec-
ond below the gullet as a center for nerves to the foot
region, and a third still more ventrally with connec-
tions to mantle, gills, heart, and other visceral organs.

This way of life is very old. Clams appear early in
the fossil record, along with uncoiled snails and the
ancestors of today’s splendid pearly nautilus. Alto-
gether, more than forty thousand extinct kinds of
mollusks have been found, showing that modern
shelled types are but the living heirs to a spectacu-
larly diverse heritage.

The Mollusk Aborigines

(Class Monoplacophora)

Until 1957 no mollusk had been found giving
more than token support to the scientists’ hunch that,
in the remote past, a limpet and a clamworm had
shared a common ancestor. All known mollusks had
gone ahead with their evolution in ways that placed
no premium on a segmented body, whereas the anne-
lids had found special advantages in partitions isolat-
ing a series of chambers—each a part of the body
cavity.

Then, among a collection of bottom animals
brought aboard the Danish research ship Galathea
in 1956, from nearly twelve thousand feet below the
surface of the Pacific Ocean some three hundred
miles from the nearest shore (Nicaragua), biologists
found some “living fossils’—ten complete, preserved
specimens and three empty shells of a kind of crea-
ture no one had ever seen before. They named it
Neopilina galatheae, and recognized it from its shell
as representing a type of life believed extinct since
the Devonian period of geological time, four hundred
million years ago. No animal discovered in recent
years has meant so much in scientific understanding.

The deeps of the sea must hide many such treas-
ures. In December of 1958, four more specimens of
Neopilina were hauled up to daylight from more
than nineteen thousand feet below the surface. Until
the dredge of the American research vessel Vema ar-
rived, these mollusks had been living on the bottom
of an ocean valley known as the Peru-Chile Trench,
about one hundred miles from the coast of northern
Peru. This was more than thirteen hundred miles
from and seven thousand feet deeper than the earlier
find. The species collected aboard the Vema received
the name N. ewingi, to honor Dr. Maurice Ewing of
Columbia University, who had arranged the expedi-
tion as part of a long-term enthusiasm for deep-sea
biological exploration.

Both kinds of Neopilina could easily be mistaken
for some kind of limpet with a small flat foot. The
largest of the thin, almost circular shells is about 34
of an inch long and about 34, of an inch high, like a
short stocking cap with the extra material drawn to a
low point in the middle at the front.

Shells of this general style are known from the
early Paleozoic sedimentary rocks, and the only
strange thing about them is the pairs of little scars on
the inner surface, showing where muscles held the
animal to its armor. That these scars were (and are)
paired attracted no special attention until a pre-
served Neopilina became available for study. Then
the creature was seen to have a pair of gills on each
side of the foot under the mantle to correspond to
each pair of muscle attachments. And between the

gills, paired excretory tubules open—tubules (ne-
phridia) far more like those of marine annelid worms
than those of any mollusk known.

Neopilina cannot be said to be segmented, for its
body contains no crosswise partitions—but, in this
sense, neither can an adult leech. And no one has yet
seen the young of these mollusk aborigines. The du-
plication of parts, whether gills or excretory tubules
(nephridia) or shell-holding muscle bands, all show
a similarity to annelid worms. At the same time, a
pair of fleshy flaps on each side of the mouth suggest
the food-manipulating organs of a clam. A series of
short tentacles just posterior to the mouth, in front of
the foot, could well represent on a diminutive scale
the “arms” of an octopus or squid.

Whether Neopilina creeps over the oozy bottom on
a thin cushion of secreted mucus or lies on its back
and uses the mucus film as a trap for food may even-
tually be learned. Its one-piece shell provides the
basis for the name devised in 1957 for the new class
Monoplacophora (‘“one-plate-bearer”). No doubt
other “living fossils” will come to light as explorations
continue in the dark depths of the sea.

The Sea Cradles

(Class Amphineura)

If an animal clinging to a rock at the seashore
wears a shell consisting of eight transverse limy
plates, it is a sea cradle (chiton). The natives of the
West Indies call these exclusively marine animals
“sea beef,” and sometimes collect them to cook as
food. American Indians on the Pacific coast used
them in this way too, and had available the largest sea
cradle in the world—as much as 13 inches long.

The broadly oval foot of a sea cradle provides the
animal with a suction cup for clinging to rocks and a
means for slowly moving from place to place while
rasping algae from the rock face by repeated strokes
of the filelike radula. The edge of a sea cradle’s man-
tle comes down around the foot, and wears an en-
circling girdle of minute limy plates suggesting a
coat of mail.

Above the girdle, the mantle secretes the eight
valves of the shell proper, each fitted to its neighbor
in such a way that the animal can curl up into a ball
if detached from its support. While partly curled, the
inverted chiton may rock gently like a cradle.

Sometimes the hard, whitened valves from a dead
sea cradle wash ashore separately and are called “sea
butterflies” because of the limy wings that provide
the hinge action between one plate and the next. In
some localities the chiton itself is known as the “‘but-
terfly fish.” The series of shell valves might be as-
sumed to indicate segmentation. But it does not cor-
respond to the arrangement of bushy gills (six to

[159

eighty pairs) along the sides of the sea cradle’s foot,
or to the ladder-like cross connections between the
two separate but parallel nerve cords from which the
class Amphineura takes its name (Greek amphi, on
each side, and neura, a nerve). None of the other in-
ternal organs shows a pattern suggesting repetition.

Although they lack eyes, most chitons are sensitive
to light and feed only in hours of darkness. Many of
them return to the same site whenever not actually
foraging. Others apparently never leave the “home
spot.” The commonest sea cradle of exposed coral-
line- and mussel-covered rocks along the Pacific
coast of America (Nuttallina californica) remains
fixed in this voluntary way. Repeated pounding by
the waves and erosion aided by this 12-inch mollusk
produce depressions the size and shape of its spiny
girdle and create little eddies with the ebb and flow
of each wave. The eddies deposit seaweed debris in
the depressions, bringing food to the animals in this
way. Nuttallina is believed to survive for more than
twenty-five years in this sedentary life, and the de-
pressions are used by generation after generation of
this mollusk, probably for thousands of years.

The giant of all sea cradles is Cryptochiton stelleri,
whose brick-red girdle completely covers the shell
valves. It is called the sea boot or gumboot, and in-
habits rocks from Bering Strait to California and to
Japan. A 13-inch specimen may be 6 inches wide.

On the intertidal coasts of Alaska, the most abun-
dant sea cradle is the large, dead-black Katharina
tunicata (Plate 39), whose valves barely show
where the expanded girdle leaves little heart-shaped
gaps along the back. It is common on both sides of
the North Pacific, seeming to prefer rocks that form
ledges about halfway between mid-tide and low. It
tolerates full sunlight longer than most chitons.

Along Atlantic coasts the sea cradles are smaller
in high latitudes, and the 34-inch species of Lepido-
chiton tend to be the chief ones found with a clean-
appearing zone of girdle platelets. Chaetopleura
apiculata, of about the same size, is common below
low-tide mark from Cape Cod to Florida; it has a
hairy girdle and a keel down the middle of the shell
valves. In tropical waters, far larger chitons tolerate
intense sunlight for hours while exposed by the tide.

Each sea cradle is either a male or a female. Many
of them congregate in springtime, which is spawning
time, and the females may each lay two long, spiral
strings of eggs in jelly. The egg strings of /schno-
chiton magdalensis on the California coast average
31 inches in length, and have been found to contain
between them from 100,000 to 200,000 eggs. The
young emerge as swimming larvae, but within a cou-
ple of hours they settle and transform to the shell-
bearing adult.

In addition to the sea cradles or chitons with
plates (the “loricates” of order Polyplacophora), the

160]

class Amphineura includes some seemingly degener-
ate, shell-less animals (order Aplacophora). These
are the 1-inch, wormlike solenogasters, which live in
the sea at depths greater than ninety feet, creeping
over hydroids and corals upon which they feed.

Each solenogaster has a cylindrical body with a
mouth at one end and an anus between two project-
ing gills at the other. If a foot is present, it consists
only of a narrow ventral groove. Apparently all
solenogasters begin as a larva with seven transverse
limy plates on the back and a radula in the mouth.
But the plates, and in some cases the radula as well,
are lost at maturity. The body is then clothed in limy
spicules that project from the enveloping mantle.

The Snails and Slugs

(Class Gastropoda)

When a person describes something as being a flat
spiral, he usually compares it with a watch spring, a
butterfly’s tongue, or a snail shell. All snail shells to-
day do have a spiral origin, even when (as among
the limpets) no outward trace of this may remain.
Back at the beginning of the fossil record, however,
the earliest known snails had straight shells or long,
curved, conical ones suggesting today’s tusk shells,
except that they were closed at the small end.
Through adoption of a spiral shape, a snail can carry
within the armor of the shell a long, pointed mound
of body and manage it in a neatly portable form.

Most snails glide about on the large, flat, foot por-
tion of the body and show a definite head end, often
with eyes and sensitive projections (tentacles). Usu-
ally, when danger threatens, the snail can withdraw
into the safety of the shell, pulling in first the tenta-
cles and head, then the complete foot. A good many
snails even carry on the side of the foot a flat plate
which forms a hard door (operculum), closing the
shell completely after the animal is inside.

That snails and slugs appear to creep on their
belly surfaces is recognized in the class name (from
gaster, the belly, and pes, podos, a foot). The gastro-
pod combines a skidding action of the rim of the foot
along a sheet of mucus secreted at the anterior end,
with movement of the sole proper in a series of
waves. Transverse bands of the sole alternately sup-
port the weight of the animal and are moved back-
ward in a stretching action, and then are lifted clear
to shift forward again, ready to take part in the next
downward cycle.

The '%-inch chink shells (Lacuna), which super-
ficially resemble periwinkles, creep about on sea-
weeds and eelgrass with a different gait. The foot is
grooved lengthwise, and the snail waddles—advanc-
ing one side of the foot and then the other, swaying

[continued on page 177 ]

60. The spotted sea hare, Aplysia dactylomela, ejecting a cloud of purple secretion
on being disturbed. The two fleshy lobes that form the sides of the body cover a thin
homy shell that lies buried under the skin. From the southern half of Florida to the
West Indies it may be seen in shallow water during the breeding season. (West In-

dies. Fritz Goro: Life Magazine)

61. A sea slug, Okenia quadricornis,
with a tuft of gills near the rear end.
Like other sea slugs, it has a larval
shell, which later disappears. (Eng-
land. D. P. Wilson)

62. One of the commonest sea slugs
on the American Pacific coast is
Hermissenda crassicornis, with tufts
of gill-like extensions on the back.
It is usually colored as shown here,
but the color may vary. (Oregon.
Ralph Buchsbaum )

———>

64. Two members of the species shown in Plate 62 here
display their opalescence and their two pairs of tentacles
as they feed on a hydroid colony. Common on mud flats
but also on rocks or pilings. (California. Woody Williams)

63. Its coloring and the branching processes make Dendronotus frondosus, a
sea slug 2 to 3 inches long, hard to detect when it crawls among seaweeds. It
often feeds on Tubularia (Plate 5). Distributed on northern shores around the
world. (England. D. P. Wilson)

65. A tropical sea slug, Ceratosoma, with a retractile tuft of gill-like
plumes surrounding the anus. Except in coloring, it resembles many
white or yellow sea slugs that live in temperate waters. (New Caledonia.
René Catala)

66. A bizarre tropical sea slug, very firm in
texture and about 3 inches long, crawling
about on the branches of a gorgonian colony.
(Great Barrier Reef. Jerome M. and Dorothy
H. Schweitzer) ‘ ;

67. The clown sea slug, Triopha carpenteri, about 21 inches long, lives
on seaweeds and in tide pools but seems to be avoided by tide-pool
fishes. (California. Woody Williams)

68. Sargassum sea slugs, Scyllaea pelagica, live attached to floating sargassum sea-
weed. One of the sea slugs, freed from the seaweed, shows two pairs of leaflike ex-
tensions from the back that serve as gills. Two still cling to the seaweed, which is
covered with delicate little branching colonies of a hydroid. (Marineland, Florida)

69. The sea slug shown in Plates 62 and
64 is here shown laying a spiral ribbon
of eggs against the glass of an aquarium.
(California. Woody Williams)

70. A common garden slug, Limax, often
feeds on tomatoes. It seldom faces such
bright light, as it lives in gardens and
woods and comes out to feed only at
night. The mantle covers less than half
of the body and hides a rudimentary
shell. Native to Europe and introduced
into the United States. (Hal H. Harrison:
National Audubon)

71. The black slug, Arion ater, grows to 6 inches in length. It lives in coarse grass in
meadows or gardens. (England. John Markham)

72. A group of swimming European squids, Loligo vulgaris, seen head-on through
glass at the Naples Aquarium. Squids are greatly relished as food in Italy and in

many Asian coastal communities. (D. P. Wilson)

72

73. A group of American squids, Loligo pealii, about 8 inches long, seen in side
view. Living in great schools from Massachusetts Bay to Cape Hatteras, these squids
serve as food for fishes and as bait for fishermen. (N. J. Berrill)

—

74. \ pearly, or chambered, nautilus, Nautilus macromphalus, that lived for fifty-
nine a iys in the aquarium at Nouméa, New Caledonia. The many small arms can be

withdrawn into the shell’s last chamber, and the entrance closed by the hood seen
above the arms. (René Catala)

75. The common cuttlefish of Europe
Sepia officinalis, in a tank at the Den
Helder Zoological Station in Holland.
One of the two females is attaching black
egg capsules, one by one, to the stick
the foreground. (Ralph Buchsbaum)

76. A baby octopus just hatched from the egg.
(Banyuls, France. Ralph Buchsbaum)

77. The common octopus, Oc-
topus vulgaris, with a mass of
egg clusters fastened to a rock

in the aquarium at Marine-
land, Florida. Each egg is
inch long, and is attached to
vertical strands supporting
about 1000 eggs in each clus-
ter. A female may lay 180,000
ggs in two weeks. (Marine-

egg
land, Florida)

78-80. The lesser octopus of European waters,
Eledone cirrhosa, shown crawling on the bottom
of a tank, just taking off, and swimming. Like the
common octopus, it feeds on fishes and even more
on crabs. It ranges from the North Atlantic to the
Mediterranean, rarely has a span of more than 3
feet, and has only one row of suckers on each arm.
In contrast, the common octopus is mainly tropical
and subtropical, extending north only to the Eng-
lish Channel. It has two rows of suckers on each
arm, and in the Mediterranean may have a span
of 10 feet. (Plymouth, England. D. P. Wilson)

82. A serpulid tube worm, Serpula vermicularis, fastened
to a scallop shell. The red tentacles, or gills, are pro-
truded from a pink or greenish hard calcareous tube 3
to 4 inches long. The worm lives below low-tide mark,
and is widely distributed on Atlantic, Pacific, and other
shores. (England. D. P. Wilson)

81. A feather-duster worm, Eudistylia
vancouveri, a large sabellid annelid
that lives in sand and mud flats on the
American Pacific coast. The feathery
tentacles, used in feeding and respi-
ration, are protruded from a tough
parchment-like tube, which extends
deep into the substrate. (California.
Woody Williams)

83. Several sabellid fan worms, Spirographis, shown

——— here with the long tubes laid on sand in a tank of the
Station Biologique, Roscoff, France. It lives upright,
with the tube imbedded in sand and mud flats, from
the English Channel to the Mediterranean. (Ralph
Buchsbaum )

84. The largest fan worm in English waters, Bispira
tolutacornis, with an elegant double spiral of tentacles
protruding from the tube. (England. D. P. Wilson)

8,

its back to show the brist , Segmented appendages that line
both sides of the body. It is s wide and up to 6 inches long,
and the back is covered with matted bristles. Found on European
and American shores, in sandy mud, with only the hind end protrud-
ing. (Plymouth, England. Ralph Buchsbaum)

86 and 87. The honeycomb worm, Sabellaria alveolata,
forms honeycombs of tubes (below) on wave-washed
rocks near sandy bottoms that furnish the grains with
which the tube is strengthened. At low tide the worms
draw in their heads and stopper their tubes with two
front feet (see enlarged portion of colony at right).
(Widemouth Bay, England. D. P. Wilson)

wi

a a
ee)
3 ad

88. A peripatus, Macroperipatus geayi, about 5
inches long, from the forest floor of Panama. Although
of great interest as an animal transitional between
annelids and arthropods, it is seldom seen. It lives
mostly under leaf mold and logs in tropical forests
and comes out at night to feed on small animals.
(Ralph Buchsbaum)

89. A large pill bug, Ligia pallasii, which scurries
about roc cliffs, close to the water's edge, from
Alaska to California. When the tide is out it ventures
into the intertidal area to feed, but with the return-
ing tide hurries back. (Oregon. Ralph Buchsbaum)

[continued from page 160]

from side to side as it shifts its weight from the one
being moved.

The abundant little salt-marsh snails (Melampus),
which breathe by means of a lung, hitch themselves
along by clinging alternately with the forward half
and then the hinder portion of the foot. As they do so
they suggest a cautious child taking short, sliding
steps on glare ice. By contrast, the curious little tube
shell Caecum glides along on a ciliated foot, holding
steady its blunt-ended limy cone with its many en-
circling rings.

Gastropods show tremendous variation in the de-
gree of development of the shell. The horse conch
Pleuroploca gigantea of Atlantic shores from North
Carolina to Brazil, and an Australian marine snail
Megalotractus auruanus, each with a 24-inch shell,
share the distinction of being the world’s largest uni-
valves. On land the giant is Achatina achatina of
African jungles, especially in Liberia, with a shell 8
inches long and 4 in diameter. All of these animals
can pull well back into their shelters and remain hid-
den for days or even months if conditions are un-
favorable.

In other gastropods, the shell offers so little space
that it can serve only as a sort of badge, proving
snailhood. Among sea butterflies (pteropods) it
scarcely hinders progress as the animal swims freely
near the ocean’s surface far from land, waving a pair
of winglike expansions from the sides of the foot. Or
the shell may be lost altogether at a tender age, as in
another sea butterfly (Clione), found in great
schools, swimming in cold waters between the Arctic
and New York, Scandinavia, the northern parts of
the British Isles, northern California, and Japan.
Clione serves as a major food source for several
kinds of whalebone whales. The sea slugs (nudi-
branchs) and many land slugs also lose their embry-
onic shells and manage thereafter with almost none.

Some small snails lack a radula. Most of these are
parasites on and in echinoderms, or they browse on
the slime accumulating at the end of a clam’s ex-
posed siphon. Otherwise a radula seems important
in rasping off minute particles of food, whether this
is vegetable matter or flesh. Oyster drills and whelks
use the radula to cut neat circular holes through the
shells of clams and oysters, and then thrust the organ
into the victim’s shelter to remove the meat—killing
the shellfish in the process. In tropical seas, many
whelks and conchs with this habit are collected for
human food and as bait.

Auger snails (Terebra) and cone snails (Conus
marmoreus; Plate 59) have a barb at the end of the
radula, connected by a duct to a poison gland near
the gullet. These carnivorous snails use the radula as
a weapon, “stinging” victims to subdue them. Some
of the larger cone snails, whose shells are much
prized by collectors, have been known to sting a hu-

man hand and inject a fatal dose of poison. For this
reason they are quite honestly feared in the South
Pacific.

Quite apart from any coiling of the body in rela-
tion to the shell, all gastropods go through a strange
process found in no other group of mollusks. During
their embryonic development, the body mass atop
the head and foot undergoes a torsion through 180
degrees until the anus, mantle cavity, and any
respiratory organs (ctenidia) come to lie at the back
of the head instead of the rear of the body.

Among the majority of marine snails, from aba-
lones and limpets to whelks, this arrangement per-
sists. They are “prosobranchs,” with the respiratory
organs at the front. Other snails and all slugs undo
the twist in one way or another, placing the respira-
tory organ at the rear again or replacing it with some-
thing else. These are the “opisthobranchs,” such as
sea hares (with a very reduced shell) and nudi-
branchs (with no shell at all), or the “pulmonates”
in which the mantle cavity has become functional as
a lung—these last animals usually are found in fresh

The sea butterfly Clione is a shell-less, swimming
mollusk found in great schools in surface waters,
particularly of the colder oceans, where it becomes
an important food of whalebone whales. (Delaware
Bay. William H. Amos)

[177

178 |

When an abalone (Haliotis) is dislodged from its
rocky support, it tends to curl the edges of its broad
foot, here seen from below. (California. Ralph Buchs-
baum )

Until the heavy growth of hydroids, moss animals, and
seaweeds is cleaned from the red abalone ( Haliotis
rufescens), the attractive shell cannot be seen, al-
though its breathing holes remain unobstructed. (Cal-
ifornia. J. A. Aplin)

water or on land. Curiously enough, the prosobranch
snails are either male or female, whereas the opis-
thobranchs and pulmonates are hermaphroditic.

PROSOBRANCHS

Abalones (the word has four syllables, the final e
being sounded) are also called ear shells or ormers.
They are widespread vegetarians with definite pref-
erences in location and habits. Man enjoys the big
muscle attached to an abalone’s shell so much that
these animals are always in danger of extermination.
Those used for food on the island of Guernsey in the
English Channel (Haliotis tuberculatus) have virtu-
ally vanished. In California the large abalones of sev-
eral kinds were in similar danger until minimum size
limits were enforced on residents and shipment of
both abalone meat and the handsome, iridescent
shells from the state were forbidden.

Shells of the red abalone Haliotis rufescens are al-
most always encrusted heavily by hydroids, bryo-
zoans, and plants. Water passing the abalone’s gills
emerges through three or four open holes in the shell
as the animal browses on sea lettuce and kelps. The
red abalone reaches breeding age at six years and a
length of 4 inches. Minimum size for legal possession
is now 7 inches, which may correspond to about
twelve years of age since one thirteen-year-old speci-
men kept under observation was 8 inches long. Red
abalones with 10-inch shells are now rare except in
collections.

The green abalone H. fulgens has a flatter shell
with six open holes and very little growth of other
life on its shell. Yet it resembles H. rufescens in
clinging to rock ledges where the water is fifty to
seventy feet deep and consequently fairly free of
wave action. The black abalone H. cracherodii, by
contrast, is a surf-dweller, in the cracks of rocks
through which waves plunge. Its shell is regularly
clean and shining, with from five to eight perfora-
tions. Large numbers reach the legal minimum size
for harvesting—5 inches.

Apparently the black abalone feeds on micro-
scopic plants, whereas the others take larger fare.
The green abalone is particularly quick when a bit of
seaweed strikes the long tentacles projecting under
the mantle edge. It whirls and uses the anterior end
of its foot to clamp the seaweed against the rock until
the mouth can be brought to bear and the radula can
rasp the plant into pieces small enough to swallow.
This same whirling movement is a protection against
starfish, one that is successful unless the abalone is
too small or the sea star too large.

A limpet has the reputation of being able to cling
to a rock more tightly than an abalone—more tightly,
in fact, than any other animal. But an undisturbed
limpet holds just tightly enough to keep waves from
dislodging it. A sudden push from the side usually

separates it from its rock surface. The merest touch,
however, before the shove arrives is enough to in-
duce a limpet to exert its full abilities as an animated
suction cup. This suction has been measured as
seventy pounds to the square inch of foot surface.
That it is actually suction can be demonstrated by
sliding a thin knife blade between the foot and the
stone, letting air or water break the mucus seal; the
animal will then be found to have lost all hold upon
its support.

After growth is well under way, the shell of a
limpet shows little of its spiral origin. The shell is
tentlike as soon as a whorl or two have been pro-
duced, and thereafter additions are made evenly all
the way around, keeping the shelter bilaterally sym-
metrical. A keyhole limpet (Plates 47, 48) has a
hole at the peak like the crater of a volcano, and for
this reason is sometimes called a volcano shell. The
hole originates as a notch in the outer lip of the be-
ginning shell. Later growth closes the notch, and
the limpet goes on to make the shell symmetrical.
But it continues to use the opening for discharge of
wastes from the anus and for a current of water
drawn under the shell at the anterior end by cilia coy-
ering the mantle surface.

The dunce-cap limpet Acmaea mitra of North Pa-
cific coasts is the tallest of the true limpets. It reaches
a shell length close to 2 inches and a height of 1 inch,
and hence is probably the bulkiest of all limpets.
Some other lower-spired species cover a greater area
of rock. The largest of keyhole limpets is Lucapina
crenulata of southern California and Mexico. It
reaches a length of 7 inches and a width approach-
ing 3. On the Atlantic coast of America, the eastern
keyhole limpet Fissurella alternata ranges all the way
from New Jersey into the West Indies and the Gulf
of Mexico, but seldom attains a length of more than
an inch.

One of the sea’s strangest snails is the wearer of
the “purple shell,” Janthina fragilis. This eyeless,
violet-colored animal drifts near the surface of all
warm oceans, suspended from a raft of air cells in a
mat of mucus. Often these creatures advance in large
schools, yet the individual members appear able to
find enough of their favorite jellyfishes to eat. Each
Janthina is an expert at spearing small medusae on
along, prehensile proboscis.

Probably sea birds are Janthina’s chief enemies.
Against them it is camouflaged by its own color, and
in addition it is armed with a glandular bag full of
purple liquid. It expels this fluid into the surrounding
water in a cloud, against which it shows no contrast.
Janthina produces a floating egg raft too, and usually
stays with it until the young snails hatch. Often both
Janthina and its rafts are cast upon subtropical and
tropical beaches as prizes for the curious.

Another oddity encountered by the beachcomber

Limpets that live high on the shore, like Acmaea dig-
italis, common along most of the American Pacific
coast, must withstand extremes of temperature and
drying. (Oregon. Ralph Buchsbaum)

is the sea collar, a capelike thin swirl of sand grains
among which the eggs of the moon snail Polinices
(Plate 55) appear as transparent dots when the col-
lar is held up to bright sunlight. The moon snail it-
self has a tremendous foot, so large that the heavy,
globular shell can scarcely accommodate it. The ani-
mal uses the foot as a bulldozer blade while plowing
through the surface sediments of sandy beaches, feel-
ing for clams it can hold while drilling through the
shell to reach their flesh.

When Polinices is ready to lay eggs, she exudes a
film of mucus from the foot and spreads this over the
exposed part of her body, adding eggs at the same
time as the mucus covering becomes impregnated
with sand grains. When the mucus hardens to a
leathery jelly, the parent snail slips out of a gap in the
sea collar, leaving it on the sandy bottom. If the col-
lar washes ashore, it may remain intact in very humid
air. But if it dries out, the mucus becomes brittle and
the collar extremely fragile. Sand collars are some-
times 8 inches across and 2! to 3 inches high.

Polinices is so obyiously too large for its shell that

[179

The common European limpet, Patella vulgata, clamps down tightly when tide is out but
moves about to browse on seaweed when water returns. (England. D. P. Wilson)

it seems incredible for any other mollusk to occupy
space inside the doorway. Yet the boat shell Crepid-
ula often takes up residence there. Actually the boat
shell is not very selective about an attachment site,
for it will even cling to others of its own kind until
masses of as many as forty come to lie as a cluster
on the bottom. Crepidula holds to its oval, boat-
shaped shell by a horizontal shelf across the posterior
end inside—and because of this shelf, the shell is of-
ten called the “quarter-deck shell” or “slipper shell.”

Crepidula feeds on small plants and animals
trapped in a mucus film spread over the gills on each
side of its foot. About every four minutes, the mol-
lusk twists its head to one side or the other and gath-
ers the loaded mucus into its mouth. Small particles
are swallowed immediately, but large ones may be
stored in a pouch at the front of the mouth as emer-
gency rations. These are used when Crepidula must
clamp its shell down tight and hold on.

Freshly matured boat shells are males. Later they
become bisexual, and still later completely female.
At breeding season the mother snail produces about
fifty or sixty membranous bags, each loaded with
around 250 eggs, and guards these for the month un-
til they hatch. The young swim freely for about two
weeks, and then settle on some surface where they
can become more or less permanently attached.

The edible periwinkle Littorina littorea is collected

180]

by the ton along European shores and sold roasted on
the streets of London. About 1857 it was introduced
into Nova Scotia and gradually spread southward,
now well past Chesapeake Bay. The sexes are sep-
arate, the female being a little larger than the male,
about 34 of an inch in diameter and in height—a
squat, thick cone, usually olive-colored but often
banded with dark red or brown. Almost no one eats
winkles in America. Other species of Littorina
(Plate 56) are found on almost all of the world’s
coasts, rasping algae from the rocks or cleaning the
film of vegetation from the surface of mud flats.

The old-maid’s curl or worm shell Vermicularia
starts out as a tightly coiled high spire, but the
snail inside changes its construction habits after a few
turns have been completed. It progresses with its
building of new shell in a very straggling manner,
producing a winding tube with lengthwise keel and
grooves, often totaling 6 to 9 inches in length. In
tropical waters these shells are found entwined
among sponges and corals, where they suggest the
products of tube-building worms. Occasionally they
become grouped in tangled masses or attach them-
selves to oyster shells and other mollusks.

Conchs and whelks produce far more regular and
massive shells. These are aggressive, carnivorous
snails, whose large shells usually provide a “canal”
for the siphon through which water is discharged

after passing the gill, the excretory pore, and the
anus. The queen conch Cassis cameo and the king
conch Strombus gigas of warmer coasts in the Atlan-
tic, Caribbean, and Gulf of Mexico produce shells 10
to 12 inches long, covering animals weighing up to
five pounds. These shells are much sought for ship-
ment to Europe (particularly Italy) as the material
from which cameos are carved. The trumpet shell
Charonia tritonis is similar but more slender; it
reaches a length of 20 inches in the Gulf of Mexico
and also in the Indian Ocean.

Cowries (Cypraea and other genera—Plate 58)
produce massive shells too, with such strikingly hand-
some patterns that they are favorites with collectors.
Yet the shell of a live cowry rarely shows unless the
animal is disturbed, for the shell-secreting mantle
covers its product almost completely. Many cowries
have the habit of dissolving out the inner whorls
of the shell, making more room for their bodies and
salvaging the lime as material to be added in en-
larging the outer whorl. In the South Pacific certain
small cowries have served as money, and been car-
ried like perforated coins strung on cords.

In former times even greater value was attached

to the murex snail Murex trunculus of the Mediter-
ranean, one of a large genus with perhaps a thousand
species around the world. M. trunculus produces in
its anal glands a brownish fluid which, upon exposure
to air, oxidizes to a substance which man has used
for thousands of years as a dye—Tyrian or royal pur-
ple. The ancient Tyrians did not know how to re-
move the glands. They obtained the secretion
through the crude technique of crushing the whole
body of the snail in bowl-shaped cavities along the
rocky coast. They filtered the fluid and treated it in
various secret ways to purify it, making the material a
mysterious substance. It has proved to be one of the
most beautiful, colorful, and permanent dyes for
cloth. Yet the snail itself is almost equally striking, a
predator that creeps rapidly and can swim too, in
spite of a medium-weight shell with elongated siphon
canal and a large number of ornamental ribs and
spines.

A close relative of Murex is Urosalpinx, the oyster
drill, which causes thousands of dollars’ damage an-
nually by cutting through the shells of oysters and
clams and removing the commercially valuable meat,
killing one victim after another.

Under surface of a limpet, Acmaea, at left shows the head and large muscular foot, mantle
edge, and a feathery gill at left of head. Only sensory tentacles on the head protrude beyond
the upper surface of the shell, at right. (Maine. Ralph Buchsbaum)

A top shell usually confined to a narrow tidal zone on
European Atlantic shores is Osilinus lineatus. It lives
on fairly bare rock covered by water about half the
time. (England. Ralph Buchsbaum)

OPISTHOBRANCHS

Marine opisthobranch snails usually go through a
shell-producing stage and then stop, or even obliter-
ate the shell completely. Presumably these animals
have an extremely disagreeable flavor, for almost
nothing will eat them, with or without armor. Per-
haps this is why the sea hare Tethys californica,
which feeds on seaweeds, so often reaches a length
of 15 inches and a weight of fifteen pounds. It has
only a vestige of shell, completely hidden by large,
fleshy folds of the mantle. The similarity to a rabbit is

suggested by a pair of upright ear-shaped organs
(thinophores) on the back of the head; they are be-
lieved to be organs of taste. If a sea hare is dis-
turbed, it gives off a great flood of purple fluid, often
concealing its own yellowish to greenish color
(Plate 60).

Among the most bizarre of mollusks are the sea
slugs or nudibranchs, which lack a shell altogether
(Plates 61-69). They are fancifully colored and
wear a highly decorative tuft of plumes (ceratia)
upon the back as elaborations of the mantle. These
have a respiratory role; gills are lacking. Nudibranchs
creep over seaweeds and hydroids, browsing upon
coelenterates and bryozoans. Aeolids (Aeolis and
related genera) even digest away all of a coelenterate
except its stinging cells, and transfer these weapons
intact and undischarged into the surface tissues of the
plume filaments and sensory projections. In this way
the aeolid uses the hydroid’s weapons long after the
coelenterate itself has been absorbed as food.

In warmer seas far from land, the deep violet-
blue nudibranch Glaucus eucharis creeps along on
the underside of the surface film, scavenging for
minute plants and animals. Branched extensions of
its body make a strikingly symmetrical pattern as
seen from air, but its color provides Glaucus with
excellent camouflage over deep water.

Pond snails often travel in the same way along the
water film, and waves of movement in the exposed
foot can be watched as crosswise bands shifting
from front to back. At intervals a pond snail presses
its mantle against the surface film and opens a dark
pore through which it can exhale and inhale a lung-
ful of air. Land snails and slugs breathe with a sim-
ilar lung cavity in the mantle. While active they dis-
play the pore every few minutes, closing it between
one breath and the next.

The common snails include larger Lymnaea with
right-handed shells (coiling clockwise as viewed from
the open end), smaller Physa with a left-handed
shell, and the wheel snails (Planorbis) with a flat
spiral. Many of these creatures are a mixed blessing.
They serve as important food for fish in which man is
interested, but also as the intermediate hosts for
dangerous parasites among the flatworms and flukes.
Some fresh-water snails live as much as 120 feet be-
low the surface of lakes, where the oxygen supply is
very limited. Others thrive in marshes around Lake
Titicaca in the mountains of southern Peru, 12,550
feet above sea level.

Terrestrial snails and slugs are mostly scaven-
gers, feeding on decaying vegetation. A few are
strictly carnivorous, some burrowing in pursuit of
earthworms, others hunting for insects, other snails
and slugs, and carrion. Slugs have been known to
enter beehives, apparently raiding for honey.

Black turban snails, Tegula funebralis, form great
clusters in crevices and on rocky surfaces from Alaska
to Lower California. Their shells are afterward ap-
propriated by small hermit crabs. (Oregon. Ralph
Buchsbaum )

Scavenging slugs, such as Limax maximus (Plate
70) may reach a length of 8 inches. They can pro-
tect themselves by spurting out jets of milky mucus
quite unlike the colorless, transparent film they se-
crete over the body surface and beneath the foot
while traveling along. Until the mucus trail becomes
covered with dust, the path of a snail or slug on land
can usually be followed as a glistening ribbon. In
places it may remain as a vertical rope, showing
where the animal crept to the end of a leaf or twig,
then let itself down in slow motion on a strand of its
own secretion—like the Indian rope trick in reverse.

Land snails and slugs have a pair of eyes, each at
the tip of an upper, retractile tentacle. If touched, the
tentacle is inverted like a glove finger, pulling the
eye down into the safety of the head. Yet if some
animal nips off an eye-bearing tentacle, the mollusk
can regenerate a new one.

Pond snails, by contrast, wear their eyes at the
base of the single pair of tentacles on the sides of the
head. These tentacles cannot be withdrawn, al-
though they appear in position to correspond to the
lower, retractile pair on land snails and slugs.

The custom of eating land snails in Italy antedates
the Christian era. Snails became a delicacy in France
in the latter part of the eighteenth century. Now
Paris is the center for them, with more than two
hundred million snails consumed annually during
the season from September to April. Most of these
are Helix pomatia, raised on vegetables and bran
mash in snail gardens or snaileries fenced with wire
netting—about ten thousand snails to each pen
twenty-five or thirty feet square. No market of com-
parable size has been found for them in any other
part of the world.

Shell collectors everywhere are attracted to a tree
snail of Cuba and isolated bits of higher land in
swampy parts of Florida and the Florida keys. These
are the homes of Liguus, a tan-bodied animal with a
14-inch banded shell the shape of a tear drop.
Every isolated colony seems to have its own color
pattern, although the diet in each is essentially the
same: fungi and lichens growing on the bark of sub-
tropical and tropical trees. During winter or ex-
tended dry weather, Liguus cements the rim of its
shell to the bark and waits for a good rain that will
allow growth of its food plants.

Among the largest of land snails (Plate 49), the
most famous today is Achatina fulica, a native of
Mauritius and perhaps also eastern Africa from
Natal to Somaliland. These large snails weigh up to
a pound, part of this a sturdy brown shell marked
with streaks of purple, green, pink, or snow white.
Both very young and old Achatina snails feed on
decaying vegetation. But at intermediate ages they
are active at night, attacking living plants and scay-

The eggs of the moon snail Polinices are embedded
in a mixture of mucus and sand, forming the “sea
collar” which is flexible enough while wet that waves
can cast it unharmed upon the beach. When the col-
lar becomes dry in the curio cabinet of a beach-
comber, it is extremely fragile. Its form matches the
upper surface of the foot of Polinices [see color plate
55]. (Massachusetts. Lorus and Margery Milne)

enging only for dietary supplements. Within six weeks
each individual matures as a male, then changes to a
female and begins laying batches of as many as three
hundred pea-sized eggs month after month. A con-
servative estimate of over a billion offspring from
each gravid female in five years could be translated,
at a pound apiece, into more than half a million tons
of mollusks, representing a frightful toll of vegetation.

In its African homelands, quite a number of differ-
ent animals prey on Achatina fulica. Native people
prize the snails as food and their shells as utensils
and the raw material from which to carve spoons.

Common periwinkles, Littorina littorea, are gathered
in great numbers for use as food. The largest of Euro-
pean periwinkles, they live on the lower half of the
tidal shore. (North Wales. D. P. Wilson)

The handsome shell of the tiger cowrie, Cypraea
tigris, is concealed by the enveloping mantle as the
animal creeps along (left), but its spots show dis-
tinctly when the snail pulls back into its shelter
(tight). (Berlin Aquarium. Otto Croy)

Among the most wide-ranging land snails is the tiny
(shell %4 inch long) Lamellaxis (Opeas) gracilis,
carried by commerce over the whole tropical world
from a probable origin in America. In the United
States it is found from South Carolina to Louisiana
and in greenhouses. (Japan. Y. Fukuhara)

Together, these enemies of Achatina keep it in check.
In 1847 a shell collector who visited Mauritius
took a few live specimens of A. fulica to Calcutta and
released them in the Chouringhie Gardens just out-
side the city. There the snails had no obvious ene-
mies, and the people—although often starving—re-
fused to touch them as food. The snails multiplied
and spread. By 1900 A. fulica had reached Ceylon
and had become a serious agricultural pest. By 1911
it was common around Singapore and, with further
human help, it island-hopped to Borneo. There, two
decades later, a bounty was offered for the bodies
and eggs of the snails, with no effect on their num-
bers. By 1933 Achatina was attacking rubber trees
on Sumatra and Java. In that year too it reached
Formosa, and was welcomed by the Japanese peo-
ple on the island as an interesting food and potent
medicine, although on no scientific basis. Living
specimens were shipped promptly to Japan, and by
1936 some had been carried by Japanese people to
Hawaii, where Achatina was soon out of control.

The Japanese took A. fulica to most of the islands
of the South Pacific, either just before or during
World War II. There the snails are providing more
lasting devastation than all the bombs and artillery
shells. They are still threatening to establish a beach-
head on the North American continent, and they re-
main a potential pest perhaps as menacing as most
of the fungus diseases or insect immigrants to reach
the western hemisphere.

The Clams (Class Pelecypoda)

One has only to mention clams, mussels, oysters,
and scallops to realize how many bivalves man en-
joys as food. If pearls are thrown in for good measure,
the economic importance of the class Pelecypoda
soars still higher. All of these creatures have a way of
life geared to the ultimate in retirement—existence
between two half shells in the seas or fresh waters,
depending upon food particles that can be drawn in
between the valves.

The fact that clams and their kin cannot be active
on land and cannot fly is no reason to assume that
their habits are completely monotonous. Various
members of the class can leap or swim, tether them-
selves like captive balloons and then take off again,
cement one shell to the bottom and lie indolently ever
after, burrow many feet below the surface of the
ocean floor, cut cavities in rock and timber, plow a
furrow without getting stuck in the mud, creep up a
plant stem, or lie back in the tropical sun and raise
plants as food. Clams and their kin live in the great-
est depths of the ocean, and also in the shallow
waters at the source of every great river in the

t

Me

: oe
ae io i. ex

In sheltered places, such as under fallen logs, slugs (Limax) deposit their glistening eggs.
(Massachusetts. Lynwood M. Chace )

world. Some of these ways of life date back at least
six hundred million years.

The class Pelecypoda is named for those members
that can leap or tether themselves or burrow or plow
or creep, for these are the ones in which the ventral
portion of the body is extensible as a bladelike foot
(pelekys, a hatchet, pes, podos, a foot). No pelecy-
pod has a head—not even a radula to represent this
region of the digestive tract. Essentially everything
has been sacrificed to the various ways in which
the clams and their kin draw food particles from the
water into the mantle cavity, between the two great
fleshy mantle lobes that secrete the two-part hinged
shell.

The hinge of the shell introduces a special prob-
lem in growth, since nothing must interfere with the
ability of the two valves to gape or to close while the
animal is exposed to enemies. Consequently the
hinge lags behind the growth of the shell, and enlarge-
ments are added eccentrically.

As in all mollusks, the outer surface of the mantle
(particularly its edge) secretes the materials and
lays down the molecules in precise orientation. This
masterful accomplishment produces an outer horny
layer (periostracum) protecting the limy shell from
external erosion. Under this, calclum carbonate crys-
tals lie in tightly packed prisms, forming most of the
thickness of the shell. The innermost layer, to which

The large slug Ariolimax columbianus reaches a length of 8 inches in the humid coastal regions
around Puget Sound, Washington. (Ralph Buchsbaum)

Nine wee

Mating slugs (Limax) have lowered themselves from
a tree trunk by means of a mucus cord. While thus
suspended their bodies entwine. (Massachusetts. Lyn-
wood M. Chace)

additions are made discontinuously throughout the
life of the animal, is of “mother-of-pearl,” in which
extremely thin layers of limy material alternate with
equally thin films of horny material. These provide
the diffraction of light that produces the iridescence
for which these creatures are famous.

If a grain of sand or a small animal gets between
the mantle and the mother-of-pearl layer of the
shell, the soft tissues may become irritated enough to
wall off the foreign object and then continue to de-
posit mother-of-pearl over its surface. This creates a
pearl. It may be sperical, but more frequently it is ir-
regular. “Cultured pearls” are the products of pearl
oysters between whose shells a foreign object has
been placed deliberately.

From season to season the abundance of food par-
ticles in the water varies markedly. When food is
easily available, pelecypods usually grow rapidly;
whereas during adverse times the mantle adds little
to the rim and inner surface of the shell valves. Often
these changes in the rate of shell production show as
ridges on the outside of the shell. If growth is slow at
only one period in each year, the ridges may indicate
how many years the clam has been enlarging its
shell. Great care must be used in making these esti-
mates, however, for a storm can stir up the bottom
sediments and induce pelecypods to cease feeding,
simulating the malnutrition of a winter season and
adding “growth rings” several times a year.

SWIMMING CLAMS

Over much of the world, the word “Shell” has
come to be a familiar trademark, an emblem taken
for a big corporation from the valve of the scallop
Pecten. Scallops are swimming clams (Plates 41-43)
whose shells bear “ears” at each end of the hinge.
They are handsomely fluted in a radiating pattern as
well as regularly wavy (“scalloped”) along the outer
edge.

Scallops swim by a gobbling movement of the
shell valves, taking water in around the scalloped
margin and expelling it in little jets through the
“ears” at the hinge line. The edges of the mantle
serve as valves in controlling this flow of water.
They also bear many bright little eyes with which a
scallop can keep informed of moving objects nearby.

When scallops complete a bout of swimming and
settle to the bottom, they come to rest on the right
valve. If they fall on the left valve, they immediately
turn themselves over. Only a single large muscle con-
trols these shell movements. It is the short, cylindrical
morsel that is so delectable when fried in deep fat
or served in cream sauce.

The flavor of an approaching sea star in the water
or of an octopus is enough to start scallops into a dif-
ferent type of swimming—a flight reaction at much
higher speed, with the hinge in advance. In this emer-

gency reversal of the normal direction of swimming,
a scallop’s behavior suggests that of the octopus itself
or of lobsters and crayfish.

These same reactions and ability to swim are
found in the file shells (Lima—Plates 44-46), whose
obliquely oval valves commonly bear close-set and
overlapping edges across the ridges that radiate from
the narrow hinge. In some species these edges sug-
gest the teeth of a file. The two valves are of equal
size and are mirror images in shape, whereas a scal-
lop’s upper (left) valve bulges more than the lower
(right) valve. From Lima shells, a double fringe of
long, slender, pale tentacles extend, often hiding the
minute eyes between them at the mantle edge.

Lima has a diminutive foot from which the animal
can extrude fine threads of a plastic material, the
byssus. With these threads a file shell builds a crude
tubular nest somewhat resembling those created by
some of the wolf spiders. Usually the nest of Lima
is under the sheltering bulge of a rock, and is open
at both ends. This permits the 1-inch clam to create
a feeding current through the nest, entering at one
doorway and leaving at the other.

Scallops too, when quite young, can secrete byssus
threads. Most of them give up the habit. Pecten
latiauritus of America’s Pacific coast is an exception,
a small scallop that ties itself to kelp and other sea-
weeds by a single byssus strand. Sometimes it uses
the byssus gland at the tip of its mobile tongue-shaped
foot to hold temporarily to hard surfaces. By this
means it can hitch its shell along, even up the verti-
cal side of a glass aquarium.

TETHERED MUSSELS

Marine mussels (Mytilus—Plate 40—and Modi-
olus) are more expert at using byssus threads. They
not only creep along by secreting one short thread
after another from the extended foot, but can also
hold fast to several dozen strands fanning out like
guy ropes at a point of more permanent attachment.

Mussels the world over anchor themselves in this
way to rocks and to each other, sometimes producing
a “scalp” several inches thick over a sand bar and
retarding erosion by waves. In France and other
parts of Europe where Mytilus edulis is appreciated
as food, the deep blue iridescent shellfish are culti-
vated in shallow coastal waters by providing them
with tree branches driven into the bottom, or with
other surfaces upon which they can attach themselves
and feed. Cultivated mussels usually grow larger
than their unaided brethren, and shells over 2
inches long are regarded as salable. The horse mussel
Modiolus is a larger animal, often living partly buried
in mud flats; its flavor is less attractive.

Byssus threads anchor far larger and more fragile
shells in moderately deep and warm water. Pen
shells (Pinna) are triangular or wedge-shaped, as

Garden snails, such as the Helix aspersa introduced
into North America from Europe, glide out of damp
corners at night and browse on a wide variety of
plants, leaving glistening trails of mucus wherever
they go. (California. H. S$. Barsam)

much as a foot in length. In some species the byssus
is coarse and black, but in Pinna nobilis of the
Mediterranean it is silky, fine, and of a bright golden
color. From this material in ancient times artisans
wove “cloth of gold” (tarentine fabric), particularly
in the Greek city of Tarentum (now called Tarento)
under the heel of the Italian boot. Museums now dis-
play gold-cloth gloves made of this “marine silk,”
and point out how permanently flexible the material
remains. So fine is the texture of this cloth that a pair
of lady’s gloves made from it can be crushed without
harm into the space of a walnut shell. Pinna shells
are a source also of black pearls.

OYSTERS AND OTHER FIXED CLAMS

One of the scallops, Hinnites giganteus, from the
Pacific coast of America, shows how easy is the step
from a free-swimming life to a permanently attached
one. As a youngster it swims about, flapping its equal
shells as though it were a Lima with a smoother shell
and shorter tentacles. Then it slips into a crevice be-
tween rocks on the bottom and settles down. To the

[187

The tree snail Liguus fasciatus roseatus is but one of
many with strikingly colored shells in southernmost
Florida. During the rainy season it feeds on fungi,
but in dry seasons withdraws into the shell and at-
taches itself firmly to a tree. (Ralph Buchsbaum)

rock it cements its left valve, and begins to thicken
both halves of the shell until they become quite ir-
regular. There it reaches a diameter of more than 4
inches, still ready to snap its right valve closed and
to squirt water at any animal that disturbs it.

Oysters (Ostraea) settle after an even briefer
swimming experience. At an age of about two weeks
the ciliated larva sinks to the bottom, forms a minute
shell, and attaches itself to some solid object. This

188 ]

stage is known as a “spat.” Unless it finds a suitable
support it dies. But once “set,” it proceeds to de-
velop into a reasonable facsimile of its parent.

European and Pacific oysters begin their develop-
ment while the fertilized eggs are retained in the gills
of the female, whereas the Atlantic oysters of Amer-
ica shed both eggs and sperm, letting fertilization
occur in the sea. Since a Maryland oyster may release
sixteen million eggs at a time, and repeat the per-
formance several times a year, oysters seem unlikely
to die out unless the spats fail to find suitable sup-
ports upon which to set.

Oyster culture is largely a matter of providing an
attractive bottom and preventing overcrowding so
that each oyster will grow well formed and to a mar-
ketable size. Oystermen also try to reduce the num-
ber of sea stars preying upon growing oysters, and to
find ways to discourage Urosalpinx and other carniv-
orous snails that thrive in oyster beds at the expense
of the industry. Pearl oysters (Meleagrina) of warm
seas and Japanese waters are cultured too because
they appear to produce better pearls; the quality of
their meat is low.

Pelecypods include quite a number of other fixed
clams. Of these the hoof shells (Chama) of tropical
waters and the eastern Pacific take the other alterna-
tive, affixing themselves by their right valves. Jingle
shells (Anomia) hold the left valve down but in a
very strange way. The valve next to the rock has a
hole in it, and the closing muscle of the mollusk goes
through the hole to an attachment area on the sup-
port. Both valves of a jingle shell are extremely thin,
and they may be ridged or smooth and highly pol-
ished. If several left valves of Anomia are strung on
a cord and shaken gently, they give the jingling
sound for which the shells are named.

BURROWING CLAMS

Other pelecypods burrow into sandy and muddy
bottoms, remaining out of sight for most or all of their
lives. Among the most active of them are the bean
shells or coquinas (Donax), which live in the sur-
face sands between tide marks and just below low-
tide level along many of the world’s coasts.

A bird or a beachcomber can watch these 2- to
1-inch shellfish simply by standing quietly as waves
expend their energy on a gradually sloping beach.
As the water hurries in, it carries sand with it and ap-
parently buries the Donax clams more deeply than
they tolerate. By dozens or hundreds or thousands,
they shove themselves up into the water just about
the time the wave reaches its highest point. For a
moment they may lie on their sides on the sand in
the clearing, momentarily motionless water, feeding
in the liquid that covers them to a depth of a few
inches. Then the water rushes out again, rolling over
and over those little clams that have not dug them-

selves down again. With the next wave the process is
repeated.

In Florida, people collect Donax by the thousand,
separating them from the sand with coarse sieves,
as the distinctive ingredient for coquina soup. Oth-
ers pick through the beach drift for empty shells of
this kind and mount them on place cards as “‘butter-
fly shells.” They are marked with suffused colors or
with radiating bands in purple, pale blue, green, yel-
low, tan, and various shades of pink, but hardly any
two of them are identical. In some places the accumu-
lation of dead coquinas becomes consolidated into a
soft limy rock that hardens upon exposure to air.

The Pacific Ocean, despite its name, tends to be
violent on the coast of America. There the surf-
dwelling clam Tivela stultorum is known as the Pismo
clam. It is a far larger animal with a somewhat tri-
angular shell. These clams maintain their position
in the sand, always with the hinge toward the open
ocean. They appear to use a jet of water from the

mantle cavity beside the foot to aid themselves in
pulling the shell into the sand.

In spite of the difficulty of collecting Pismo clams
in the heavy surf, and the fact that man is their chief
enemy, the annual census of this shellfish in Cali-
fornia shows that its numbers are shrinking. Even a
limit of fifteen S5-inch clams per person per day, plus
a ban on all shipments and complete protection in
some areas, has not halted the decline.

On sandy coasts throughout the world, razor clams
live just below the surface, sometimes with the pos-
terior end of the shell projecting slightly above the
flooded beach. Siliqgua has a rather short oval shell
with a very sharp edge, Ensis an elongate and almost
rectangular shell, slightly curved and suggesting the
blade of a straight razor. The foot in each kind is
at one end and is extremely agile. With it the clam is
expert at digging in quickly if waves wash the sand
away.

At slightly greater depths in beaches where the

Queen scallops, Chlamys opercularis, swimming about as they escape from a starfish. (Eug-

land. D. P. Wilson)

PRR ee, 5
eager ee

[189

The common edible mussel, Mytilus, attached to rock
by fine but strong secreted threads. (England. Ralph
Buchsbaum )

sand is mixed with mud and provides a firmer cover-
ing, burrowing clams of many other kinds live in con-
stant readiness to jerk back into the buried shell.
Only when undisturbed do they extend above the
mud the siphon or “neck,” which is actually part of
the posterior end of the mantle, a part through which
water and food enter and then water and wastes are
discharged.

This is the way of life of the economically impor-
tant soft-shell clam Mya arenaria, whose brittle, thin,
oval shell averages less than 5 inches in length and
bears a large spoon-shaped projection on the left
valve at the hinge. The soft-shell is common on both
coasts of America, having been introduced acciden-
tally on Pacific shores along with Atlantic oysters.
Mya is a favorite for New England chowders and
clambakes. In the Arctic it is the principal diet of the
walrus, which uses its tusks as a clam rake to dig
the shellfish from the bottom.

An extremely popular clam with the same burrow-

190]

ing habits is the quahog Venus mercenaria, known
also as the hard-shell clam, the little-neck clam, and
the round clam. Immature ones, less than 3 inches
in length, are called cherrystone clams. This is the
shell from which New England Indians cut and
pierced small beads as shell money (wampum) that
could be carried as a necklace string.

West Coast Indians showed a preference for the
bent-nosed clam Macoma nasuta, which lies upon its
left side several inches below the beach surface
and extends to the water above a long, slender, in-
current siphon. The excurrent siphon is a separate
tube, equally slender but somewhat shorter, dis-
charging into the sand near the clam. The asym-
metrical bend in the incurrent siphon matches the up-
ward bend of the bent-nosed clam’s shell. Usually the
incurrent siphon extends as much as three-quarters of
an inch above the mud. It waves back and forth,
turned downward and sucking in food particles from
the surface sediments. At intervals of two to three
minutes the clam retracts its siphon slightly and
flushes out any inedible or coarse materials. At longer
intervals it pulls the siphon well down into the mud
and then extends it to the surface a few inches away,
to sample a new feeding area.

The largest burrowing clam in the world is the
edible geoduck [pronounced goo’ee-duck] of Puget
Sound and adjacent coasts of British Columbia,
Washington, Oregon, and northern California. Pa-
nope generosa may weigh as much as twelve pounds,
but the 8-inch shell accounts for only a minor part of
this. The shell is relatively thin and in a mature geo-
duck fails to cover the body. The siphons are almost
as large as the body proper and stretch far enough
to allow the clam to live three or four feet below the
surface of the muddy bottom.

Geoducks constitute a sports fishery in Washing-
ton, with a bag limit of three per day enforced by
wardens. Almost as strict protection comes from the
animals’ position in the beach. They are exposed only
by tides lower than mean low (minus tides), and
consequently are within reach of a man with a shovel
for only a few hours a month.

Apparently it is only a small step from maintain-
ing a vertical burrow in firm mud to boring into soft
rock. The arctic rock-borer Saxicava, with a 1- to
14-inch shell, holds tight with its foot while using
the anterior end of the shell as a scraping tool with
which to cut cylindrical cavities as much as six inches
deep into rock and concrete. A later inhabitant of the
same burrow in a breakwater or seawall may not be
satisfied with the cavity, and may enlarge it or intro-
duce a side branch. After a while the whole man-
made structure is weakened and may crumble. The
larger piddocks (Zirfaea and Martesia) show simi-
lar habits, using their 4-inch shells to bore into wharf
pilings with disastrous results.

One of the marine mussels (Lithophaga) is a tropi-
cal animal with a very different means for boring into
rock. It secretes an acid that attacks limy materials,
and uses this chemical means to excavate a place for
itself. Lithophaga (the “rock-eater”) protects its
own shell by a thick brown horny material whose
color, along with the shape of the shell, gives the ani-
mal the common name “date mussel.”

At Pozzuoli, near Naples, Italy, visitors are shown
the work of date mussels as conspicuous pits in the
upright limestone pillars of the temple of Serapis.
This edifice was built on dry land, and it now stands
on dry land, some little distance above the waters of
the Mediterranean. Yet in historic times, between
the days of Roman civilization when the temple was
constructed and the recent past, the land support-
ing the building must have subsided enough to let the
sea cover the pillars, permitting Lithophaga to pit the
surface. More recently the land has risen again, put-
ting an end to the erosive action of the mollusks.

The burrowing habits of pelecypods reach an ex-
treme in the wormlike borers that cause so much de-
struction to wharf timbers and hulls of wooden ships.
The shipworm Teredo navalis may be as much as 24
inches long when fully grown, yet its shell consists
only of two little 12-inch plates used as boring tools.

The minute swimming larva of the shipworm set-
tles on a submerged timber and there transforms into
the shell-bearing clam. It bores into the wood and
continues to do so for the rest of its life. It becomes,
in fact, a captive in its own burrow, for as the animal
grows it scarcely enlarges the original opening. In-
stead, the shipworm excavates a bigger and bigger
tube for itself deeper and deeper into the timber, and
maintains connection to the sea only by way of two
thread-sized siphon tubes. One of these brings in
food particles and oxygen. The other discharges
wastes (including powdered wood) and reproductive
products. Teredo usually follows the grain of the
wood, turning aside only to avoid a neighboring ship-
worm or a knot. Eventually the timber breaks apart,
letting a dock collapse or a ship founder.

THE AGILE-FOOTED CLAMS

It would be difficult to find a greater contrast
based upon a single body plan than between a ship-
worm grinding away, self-imprisoned in a timber
from which it gets no nourishment, and a scallop or a
cockleshell skipping through the water. The cockle
(Cardium) is famous for the brittleness of its shell,
which is obliquely spherical with rounded ribs. With
its long and agile foot the cockle kicks itself along the
bottom. Often it draws attention to itself, and a fish
swallows it whole or a beachcomber picks it up.
Cardium magnum of the Atlantic coast of America
reaches 5 inches in diameter on shores from Vir-
ginia to Brazil. C. corbis of Pacific coasts is only

slightly smaller. In both, the extended foot is about
as long as the greatest length of the shell.

A very different means of progression is found in
the little fingernail clams of fresh water. The stouter
ones (Sphaerium) and thinner kinds (Musculium)
both live in pools of small streams and produce light-
weight shells seldom more than % inch across. The
foot is very slender and adhesive. With it the animal
can glide up or down a plant stem as smoothly as
though it were a snail or a flatworm.

The larger clams of fresh water plow a furrow in
the bottom, leaving much of the shell exposed. The
bladelike foot is extended well ahead of the body,
diagonally downward into the mud. Into the tip of
the foot the clam pumps blood, producing a knoblike
swelling as an anchor. Then it shortens the foot by
muscular contraction. If the anchor holds, the clam
draws itself forward and downward a little. As the
foot is made slender again and extended for another
move, the clam’s shell may be raised slightly. In
consequence, the furrow of the fresh-water denizen
usually has an almost regular pattern of greater

Coquina shells are also called wedge shells or butter-
fly shells. This species of clam, Donax variabilis, is
only 1 inch or so long, occurs abundantly on sandy
beaches from North Carolina to Florida, and is used
to make soup. (North Carolina. Ralph Buchsbaum)

The commercially valuable razor clam of the Ameri-
can Pacific coast, Siliqua patula, lives on sandy
beaches and can completely bury itself within about
seven seconds. The one in the foreground has just
done so, leaving only the siphons protruding. (Ore-
gon. Ralph Buchsbaum )

and lesser width—greater where the foot pulled the
shell deeper into the bottom.

The two size ranges of fresh-water clams represent
two unlike families. The small ones (family Sphaeri-
dae) lack a mother-of-pearl lining to the shell and
are dull white inside. These clams retain the fertilized
eggs in a brood pouch formed of the inner gill on
each side of the foot, and release shelled clamlets. A
viviparous parent may produce from two to twenty
young at a time, but they breed repeatedly through-
out the year.

The larger fresh-water clams (family Unionidae)
are often called mussels. Their shells have been
much sought in tributaries of the Mississippi River as
material from which pearl buttons can be cut, for
the inner surface of the shell is coated with mother-
of-pearl. From fifteen to twenty buttons of different
sizes can be made from one 5-inch valve. In Ano-
donta the shell lacks hinge teeth and the two valves
are held in alignment only by the hinge ligament. In
Unio and related genera, hinge teeth inside the shell
give extra support.

Unionid clams have become strangely adapted to
life in flowing fresh water. Instead of retaining the
eggs in a viviparous habit, they discharge the young
as larvae, called glochidia. Each glochidium has a
pair of small, widely-spread valves, each terminat-
ing in a tonglike hook. It uses these to pinch into the
skin of a passing fish or to hold to its gills if taken
into the mouth. The glochidium thereupon becomes
a temporary parasite, absorbing nourishment from
the fish’s blood stream. After a few weeks the larval
stage ends with the glochidium freeing itself, drop-
ping to the bottom wherever the fish happens to be,
and changing to the adult form of clam. In this way

192]

the unionids make use of fish to distribute their off-
spring, and depend upon the ability of the fish in re-
sisting the current—staying in fresh water and not
being carried to the sea.

A still stranger way in which a pelecypod depends
for success upon the activities of another type of life
was revealed recently in the giant bear’s-paw clam
Tridacna of the South Pacific. These mollusks lie
hinge downward in coral reefs, usually in quite shal-
low water, and display a thick purple mantle over the
coarsely fluted, exposed edge of the heavy shell. If a

A European razor shell, Ensis siliqua, with the foot
extended. It is common on many sandy beaches, but
can be found only by digging for it at low tide. (Eng-
land. D. P. Wilson)

Pay

ee)

person examines the mantle surface closely, he sees
little bright spots suggesting eyes. These are actually
“skylights” admitting energy from the sun into
“greenhouses” within the mantle. In these spaces,
microscopic green algae grow and carry on photo-
synthesis. Tridacna uses its white blood cells to har-
vest the algae and, as an adult animal, seems not to
use its digestive tract. It depends instead upon the
plant food raised in the exposed parts of its body.

The bear’s-paw clam has become world famous
as a trap for unwary persons walking on a coral reef,
for the shell valves will surely close tightly on a leg
or arm accidentally thrust past the soft mantle folds
into the interior cavity. Native people actually fear
these clams very little, and often use a hammer to
break a portion of the shell edge so that a hand
wielding a knife can be slid into the interior to cut
free as food the big muscle that clamps the shells to-
gether. Tridacna shells of small size are often used
elsewhere in the world as bird baths and baptismal
fonts. Large ones, weighing half a ton or more, are
usually left in the reef, where the live animal con-
tinues to demonstrate how the giant of the clam
world succeeds in getting enough to eat.

The Elephant-Tusk
Shells

When white men first reached the west coast of
America, they found Indians there wearing necklaces
of almost cylindrical shells, each slightly curved and
open at both ends. The Indians esteemed the shells
according to their length, and used them for barter.
A 1-inch shell had only slight value, but a 2-inch
shell was equivalent in purchasing power to a shilling
(then twenty-five cents )—equal to a dollar at pres-
ent-day prices. Rare 3-inch shells were owned only by
the wealthy chiefs.

An elephant-tusk shell or tooth shell seems made
to order as a piece for a necklace, since it is open at
both the larger end and the smaller. While occupied
by the mollusk that secretes it, the large end is usu-
ally below the surface of the sandy sea bottom and
the shell slants upward, exposing the smaller end.
This latter is the place where water enters and leaves
the shell, attending to the respiratory needs of the
scaphopod merely through the walls of the mantle
cavity, for no gills of any kind are present.

From the larger end of the shell, the elongated and
bilaterally symmetrical animal extends a foot resem-
bling a horse’s hoof, using this as a digging organ.
Behind the foot, at the edge of the almost cylindrical
mantle, a cluster of ciliated tentacles arises around
the mouth. They bring food particles to the mouth,

(Class Scaphopoda)

The jackknife clam, Tagelus gibbus, sometimes erron-
eously called a razor clam, occurs from New England
to north Patagonia, and is often eaten where no
better clam is available. (North Carolina. Ralph
Buchsbaum )

the small ones to be swallowed whole, the larger
ones to be rasped into fragments by use of the radula.
The digestive tract bends in a U and opens at an
anus, exposed from the larger end of the shell when
the scaphopod is fully extended.

The sexes of elephant-tusk shells are separate, and
the eggs are laid singly, the sperm discharged as a
cloud into the sand through the pair of excretory
tubes opening beside the anus.

The most widespread genus of these exclusively
marine animals is Dentalium. The common tooth
shell D. entale reaches a length of 2 inches in quiet
sandy bays on both sides of the North Atlantic. The

[193

precious tusk shell of the North Pacific is D. pre-
tiosum. In New Guinea, heavy tusk shells as much
as 5 inches long are used by native people as decora-
tions thrust through holes in the septum of the nose,
in the lower lip, or in the ear lobes.

The Octopus and Its Kin
(Class Cephalopoda)

For almost everyone, the octopus holds a fearful
fascination. This had led man to call it the ‘“devil-
fish.” Actually, octopuses are extremely shy, retiring
creatures, eager to slither out of man’s way. The big-
gest of them has an arm spread of about 12 feet, but
the average octopus can barely stretch across a circle
1 foot in diameter. All of these animals seem com-
pletely unwilling to bite, even if provoked.

The same denial cannot include the octopus’ kin,
for some squids bite viciously if handled. Yet no
member of the class Cephalopoda has been reliably
recorded to have attacked a person without provoca-
tion. Admittedly, all of them possess a pair of ar-
mored jaws suggesting those of a parrot, except that
the lower half of the beak closes outside the upper
half. These jaws supplement a typical molluscan
radula and aid the animals in tearing apart the crabs
and other foods in their strictly carnivorous diet.

The distinctive feature of the octopus and its kin is
the eight or more arms that extend from the head and
are used in capturing food. They make the animal
“head-footed” and give class Cephalopoda its name.
Most cephalopods have also a pair of large eyes re-
sembling those of man and other vertebrate animals
to a degree that is uncanny, for the organs arise en-
tirely differently in the embryo.

Millions of years ago, all cephalopods supposedly
used the mantle to secrete an external shell, and
were able to take shelter inside the secretion. Today
this habit is continued only by two different “living
fossils,” the several species of Nautilus in the south-
west Pacific and the strange little Spirwla at the upper
edges of the abysses in the Atlantic and Indian
Oceans.

The common cuttlefish Sepia officinalis of the
Mediterranean and eastern Atlantic (Plate 75) pro-
duces an internal limy shell of degenerate form—the
“cuttlebone” sold to hang in cages with canaries and
other pet birds. Squids, such as Loligo, gain some
support from a concealed relic of the shell, the chi-
tinous “pen,” which may be shaped somewhat like
the feather of a quill pen, or narrow and slightly
curved like a sword blade. The octopus lacks all
traces of a hard shell. Yet all cephalopods retain the
U-shaped digestive tract which is helpful to an ani-
mal whose body is covered by a conical external
skeleton.

194]

X-rays disclose a dense population of shipworms,
both the larger Teredo and the smaller Bankia, as
they sabotage a timber exposed to the sea. These
degenerate mollusks use their small shell valves as
boring tools in making chambers for their bodies.
Apparently they use the wood only as a home, but
the damage done is comparable to that of wood-eating
termites on land. (Florida. Charles E. Lane)

Apparently the earliest cephalopods found diffi-
culty in combining the activities demanded by preda-
tory habits and a carnivorous diet with a slender
body concealed in a heavy shell. As an adaptation
helpful under these circumstances, they developed
the unique ability of secreting gas into the spire of
the pointed shell, giving it buoyancy and hence re-
ducing the weight to be pulled around. The animal
came to live in the enlarged open end of the limy
cone, with the gas bubble above it. Addition of lime
helped bring the shell into a horizontal position, but
at the same time seemingly encouraged elongation
of the animal in a direction truly dorsal in terms of
its own anatomy. Few animals in the world are so
high and so short and so narrow.

Shell-bearing cephalopods greatly improve their
control over the gas bubble by dividing it with trans-
verse shell partitions. The location of each of these is
evident on the outside of a Spirula shell as a slight
constriction, but the nautiluses show no external indi-
cations. The shell, in fact, is an object of outstanding
beauty, one that appeals especially to mathemati-
cians since its curvature (and the curvature of all in-
ternal partitions) follows the logarithmic spiral, with
each turn of the shell about thrice as broad as the
preceding turn.

Cephalopods are muscular animals, able to subdue
struggling prey. They are alert, too, with a far larger
and more complexly developed nervous system than
is to be found in any other mollusk. Around the en-
larged central ganglion above the mouth, they de-
velop a good substitute for a skull, formed of cartilage
tissue closely resembling that in vertebrate animals.
At other points in the body also, cephalopods have
cartilaginous rods and bars as stiffening supports.
These give the whole animal a firmness that is un-
expected from watching the fluid, graceful move-
ments of a swimming, darting squid, or the lithe,
sinuous flexibility of a live octopus.

The cynic who remarked that man is the only ani-
mal that blushes, or needs to, was not acquainted
with cephalopods. Their blushes can put any other
creature to shame, and may well be a means of
communication. In the thin epidermis over all ex-
posed parts of the body are small flexible bags of
pigment—blue, green, yellow, brown, or red chro-
matophores—each surrounded by a set of radiating
muscle fibers. When the fibers contract under the con-
trol of the nervous system, the little bag of pigment
is suddenly stretched into the form of a flat disk
parallel to the surface of the body. Its presence be-
comes noticeable as a spot perhaps 14, of an inch in
diameter, whereas when the fibers relax, the pig-
ment sac rounds out and becomes invisibly small.

An excited cephalopod twinkles all over as the
pigment sacs change dimensions. Waves of color
may sweep along the body, like blushes in a variety of

hues. At one moment the animal may be conspicu-
ously banded and at the next a uniform wine red, and
then may blanch uniformly to the ghastly bluish
white so characteristic of dead octopus and squid of-
fered for sale in fish markets.

The members of the genus Nautilus (Plate 74)
are unique among living cephalopods not only in
their handsome shells, often 10 inches across, but
also in having about ninety tentacular arms, and
twice as many gills (four), heart auricles, and
kidneys as any other in the class. The arms, more-
over, lack the firm-rimmed, muscular suction cups
with which all other cephalopods cling to prey. And
the eyes of nautiluses have no lens, making them
operate as pinhole cameras—a type of visual organ
unique in the animal kingdom.

All cephalopods except the nautiluses are armed
with a gland secreting an intensely dark liquid, used
by the animal as an emergency discharge becloud-
ing the water and confusing the flavor trail by
which an enemy might follow in pursuit. Long ago
man began collecting the contents of this gland from
cuttlefish in the Indian Ocean for use as a permanent
ink—old-style India ink.

The males of eight-armed octopuses and ten-
armed squids can be distinguished from the females
by a strange feature of one arm—the lowest on the
left side. It differs from the other arms in form and in
the shape of the suction cups. The animal uses it to
transfer into the mantle cavity of the female the trans-
parent bags of sperm cells she needs to fertilize her

eggs.

Fresh-water clams lie partly imbedded in sand or
mud, with the shells slightly agape and the openings
for water currents protruding. (Lynwood M. Chace:
National Audubon)

The male octopus goes to an extreme in this
final step of an elaborate courtship. He drops off the
tip of the arm with its load of sperm bags deep in his
mate’s mantle cavity. Early observers found the still-
living arm tips anchored securely there and con-
cluded that they were parasitic worms entirely dif-
ferent from all others known because of the scores
of sperm-filled cavities. To these “worms” the name
Hectocotylus was given (hecto, a hundred, kotyle, a
hollow vessel). When the true situation was discov-
ered, the word came to be used as an adjective de-
scribing the peculiar arm as being the “hectocoty-
lized” one.

The body of an octopus is rounded or saclike, usu-
ally with no fins (Plates 76-80). Ordinarily the ani-
mal crawls about on its flexible arms. But if fright-
ened, it ejects water from the capacious mantle cavity
through a narrow nozzle-like siphon. The water
spurts forward, and the animal darts backward by
jet propulsion.

The female octopus cements her eggs to a rock or
other firm support. Some species attach them like
punching bags, singly on short stalks. Others include
a whole series of eggs in a slender string of jelly and
affix the end of the string. For as much as three
months, the mother octopus may stand lonely vigil
over her developing offspring, not forsaking them
even to find food. With her sucker-studded arms she
polishes the outside surfaces of the egg coverings,
keeping them free of dirt and fungus growths. Some
kinds of octopus use their siphons as a sort of hose,
sending jets of water among the egg strings and flush-
ing out any minute particles that might contaminate
them.

Squids, by contrast, lay many smaller eggs in cigar-
shaped masses of jelly attached to the bottom and
then go off, leaving the “dead man’s fingers” to fate.
Very few animals actually attack squid eggs, which
suggests that they have an unpleasant flavor or toxic
nature. When octopus eggs are left unattended
through the death of the parent, fungi soon smother
them.

Squids get far more effective use of jet propulsion,
since their bodies are more cylindrical, tapering to
a point and hence affording better streamlining
(Plates 72 and 73). On each side the body bears a
pair of horizontal muscular fins under exquisite con-
trol. With their help alone, a squid can hover, swim
forward or back, or turn about sharply. Sometimes it
uses the flexible siphon tip to direct a jet of water to
rear or downward or to one side instead of forward,
and gains an extra lift in this way.

Squids tend to hunt in packs, darting by jet pro-
pulsion through a school of fish and seizing victims
by the head. Octopuses, on the other hand, are more
solitary and bottom-dwelling. They may stalk a crab
or wait for it to come within snatching distance. Al-

//

The sea butterfly (pteropod) Creseis is a delicate
little free-swimming snail of the open ocean. It ex-
tends a pair of wing-like expansions of the foot from
the larger end of the thin shell and flits through the
water in company with many others of its kind. The
specimens shown were dredged from Bikini lagoon
in the South Pacific. (Fritz Goro: Life Magazine )

ways, however, they seize it from behind and thus
avoid the crab’s claws.

The extra two arms of squids, beyond the eight
characteristic of octopuses, are considerably longer
than the rest and are used in grasping prey. In the
giant squid Architeuthis princeps of moderate depths
in colder oceans, these prehensile arms may be 30
feet long on a 15- to 18-foot body as much as 5 feet
in diameter.

Architeuthis is a real sea monster, the largest of all

- [197

Large clam, Tridacna, wedged among coral on Great Barrier Reef. The giant
species of Tridacna may be 4 feet long and weigh up to five hundred pounds.
(Fritz Goro: Life Magazine)

198 J

Four tooth shells (scaphopods), one with its three-
lobed foot extended and two with the foot showing
at the larger opening of the tapered shell. These are
Dentalium from the beach at Roscoff, France. (Ralph
Buchsbaum )

An X-ray photograph of a Nautilus showing the
curved partitions separating the gas-filled chambers
of the shell, and the living animal occupying the
largest, outermost chamber of the spiral. See color
plate 74 of this same Nautilus. (New Caledonia.
René Catala)

known invertebrate animals. It must be a formidable
adversary. Sperm whales, which feed almost exclu-
sively on squids, often bear circular scars near the
mouth, showing where the suction cups of a giant
squid’s arms grasped in the contest to avoid being
eaten. Some of these scars are 5 inches across. The
indigestible jaws of big squids found in the stomachs
of these whales often exceed any from Architeuthis
discovered dead, washed ashore. Consequently no
one is sure how large the giant squid really grows.

No one knows either how many squids live in the
sea. The number must be enormous, for seals dive to
catch them and the toothed whales eat little else.
Man’s nets are too slow-moving and too obvious to
fast-swimming squids for any reasonable sample to
be caught from large boats on the ocean’s surface.
Consequently one is amazed, as were the adventurous
scientists aboard the raft Kon-Tiki, when squids
pursuing fish at night break through the surface water
and tumble aboard a low craft. Or a person remains
unconvinced that the echoes of depth-measuring
equipment could be reflected back to the ship (indi-
cating a phantom bottom about six hundred feet
down at midday) largely because of squids congre-
gated there—waiting at the edge of twilight in the
water until the day above fades and lets them ap-
proach the surface to feed.

The slower squids in the deep sea (and perhaps
also the sick and decrepit of faster-moving kinds) do
get caught in the nets towed by oceanographic re-
search ships. Many of them prove to have curiously
gelatinous bodies and large numbers of light-pro-
ducing organs along their sides and underneath.
Very few of them are blind. Most have large eyes,
even with the organs on swiveling turrets that can be
aimed in many directions. Apparently they find food
and mates by recognizing luminous patterns passing
in the black water.

These depths are home to another “living fossil,”
one discovered toward the end of the nineteenth
century and given the imaginative name Vampyro-
teuthis infernalis, the “vampire squid of the infernal
regions.” This improbable creature reaches a length
of 8 inches and a diameter of 3 inches. Its blue-black
body is literally pint-sized and wears at one end a
group of eight tentacles linked together by a web.
Vampyroteuthis is not an octopus, for it has two more
arms, slender as feelers, kept curled up and tucked
away in pockets outside the ring of webbed, sucker-
studded arms. Yet the vampire squid is not a true
squid either.

Deep-sea Vampyroteuthis may well have the larg-
est eyes in proportion to body of any animal in the
world. A 6-inch specimen wears a pair of globular
visual organs each | inch across, more than a third
of the body diameter, and as large as those of many
full-grown dogs. Toward the other end of the body

the vampire squid can extend from a slit on each side
a blunt projection 1 inch long, ending in a brilliant
reflector suggesting those set along highways to
glow a warning as each car’s headlights approach.
How they are used in the intense blackness of the
abysses may eventually be learned.

The vampire squid itself is bedecked with light-
producing organs of many shapes and sizes. Only the
mouth and surrounding surfaces of the arms and
webs are devoid of luminous spots. Vampyroteuthis
may stalk its prey behind a black cloak of webbing
stretched by tentacles ready to seize and hold. Or it
may vanish from view by turning off its lights and
pulling the silvery reflectors into the pockets from
which they were extruded.

This strange little octopus-squid, linking two types
of cephalopods, has been caught in the depths of
most oceans, seemingly so far from the surface and
the bottom (as well as from shores of any kind) that
it is a truly pelagic creature. In its wandering life it is
merely a deeper counterpart of the paper nautilus,
Argonauta argo, a drifting denizen of the Atlantic
and Pacific. The paper nautilus takes its name from
the parchment-thin shell the 8-inch female secretes
from the expanded ends of her two upper arms.

For many years, people familiar with the sea be-
lieved that the argonaut sat in her shell and raised
her expanded arms as a sail, drifting before the
wind. Now her ways are better understood. The shell
is only a floating, boat-shaped egg case with a single
compartment. It is not a product of her mantle and
hence is not comparable to the true shell of a cham-
bered nautilus.

The argonaut’s shell may be as much as 8 inches
long, but it has no known role except as a place of
security for the young. The parent is free to leave it
or return to it, swimming smoothly along as a com-
pletely independent little octopus. Her mate is much
smaller (about 1 inch in length) and lacks the ex-
pansions on the upper arms. But he does contribute
his share to the family venture: the tip of his hecto-
cotylized arm, holding a supply of sperms for his
mate to use when her fragile bark is ready.

When swimming, the octopus (Octopus) holds its
eight arms close together and drives itself along by
jet propulsion. The suckers on its tentacles are at-
tached directly to the arms, not borne on short stalks
as in squids and cuttlefishes. (Fritz Goro: Life Maga-
zine )

[ 199

CHAPTER XVII

Feather-duster worms in tubes and a paddle-footed
worm creeping on bottom

The Segmented Worms

O F all the many kinds of worms, those with seg-
mented bodies are surely known to more people than
any others. Thus the inland angler seeks an earth-
worm as a lure, and the coastal fisherman realizes
that in salt water a sea worm will remain attractive
longer to fish, and therefore baits his hook with a
ragworm.

Just about everyone sooner or later wades bare-
foot in a pond or stream where bloodsucking leeches
live, and finds these parasites attracted to his own
skin. In many parts of the world, pharmacies main-
tain a supply of live medicinal leeches, whether to
take the color from a black eye or to extract “bad
blood” from a patient.

The earthworm, the ragworm, and the leech are all
segmented worms. The same phylum includes the
far smaller Enchytraeus and Tubifex, worms sold in
pet stores as food for aquarium denizens.

The rings that mark the body of an earthworm or
ragworm are the features giving the phylum Annelida
its name, from a French corruption of the Latin
anellis, a ring. Each of the encircling grooves corre-
sponds to the boundaries of an internal partition di-
viding the body into a series of almost identical seg-
ments. Many of these segments have not only a priv-
ate portion of the worm’s body cavity, but also a local
exchange station (ganglion) of its nervous system, a
pair of excretory tubules (nephridia), and access to
the products of digestion both directly from the walls

200 |

(Phylum Annelida)

of the digestive tract and from blood vessels which
extend through all segments from one end of the
worm to the other.

The anterior segments of an annelid worm show
specializations related to feeding. It is here that the
worm has a particularly important part of its nervous
system, even when no head is recognizable. Most
annelids can survive loss of the hinder end of the
body, and even regenerate new segments to take the
place of those lost. But even when a worm’s body is
severed very near the anterior end, both pieces are
likely to die.

Annelids are the most efficient animals of worm
body plan. They live in the bottom muds of the sea’s
deepest abysses and in the almost oxygen-free sedi-
ments below deep fresh-water lakes. Others inhabit
the open surfaces of glaciers high on mountain shoul-
ders, and the foliage along jungle paths where passers-
by may furnish food. They perform midnight ballets
at the dark of the moon in tropical waters, and till
the soil in lands where winter’s frost reaches far below
the surface.

Annelids form an important part of the diet for
many hydroids and anemones, corals and jellyfishes,
flatworms and nemerteans, other annelid worms,
crustaceans and insects, sea stars and serpent stars,
fish, and a host of terrestrial vertebrates. Of the six
thousand-odd kinds of living annelids, most swim or
build shelters for themselves in the sea.

The Paddle-footed
Annelids

When a coastal fisherman picks up a clamworm
to put it on his hook, he needs to look carefully and
seize the animal close behind its apparent head. Oth-
erwise he is almost certain to be bitten. The clam-
worm Nereis has a pair of horny jaws deep down in
its body. To defend itself or to take prey, the worm
everts its pharynx and exposes its two jaws, spreading
them widely. It can give quite a painful nip as it
presses the jaw teeth against a person’s skin and then
attempts to withdraw its pharynx.

A novice gives no thought to the fact that a more
delicate victim would have been torn apart, a piece
of it swallowed as the clamworm’s dinner. He is too
amazed as well as chagrined at having dropped his
bait as though it were a snake.

Some kinds of Nereis are as big as small snakes.
Nereis virens, found on both coasts of America in
cooler water and in northern European mud flats as
well, reaches a length of 18 inches in New England.
Its body is a handsome reddish brown, showing an
iridescent greenish sheen. From Long Island south-
ward, shelly bottoms are home to Nereis pelagica, a
more tapering animal rarely more than 8 inches in
length. Sandy shores seem more suited to Nereis suc-
cinea (limbata).

On European coasts the sea worm used for bait is
most frequently Nereis cultrifera, the chainworm or
ragworm, whose “rags” are its paddles, which droop
like wet cloth when it is removed from the sea.

In its native element, a sea worm’s paddles are ex-
tremely important. Without them the muscles of the
body wall could do little to promote locomotion while
the worm was lying on the bottom or surrounded by
water. But members of the class Polychaeta have the
body wall extended into one pair of paddles (para-
podia) on each of the many segments. Stiff bristles,
for which the class was named, support the paddles
and hold them almost at right angles to the body. The
paddles may be slightly fleshy or mere thin vanes, yet
they provide a hold on the water next to the worm
and make efficient the locomotory movements of
muscles in its body wall.

Among the largest of these paddle-footed swim-
mers is 3-foot Nereis brandti of America’s Pacific
coast. These worms, which are as broad-bodied as a
garter snake, swim to the ocean’s surface at night.
Scientists sometimes wonder how a “sea serpent” of
this kind would impress a slightly inebriated fisher-
man in a rowboat on a protected bay. He might need
to do no more than shine a flashlamp over the side
to see a few of the giants moving through the dark
water, their paddles glistening in the light.

(Class Polychaeta)

The Greek mythmakers peopled the Mediterra-
nean with between fifty and a hundred nereids, and
pictured them in human form, riding sea horses. To-
day’s annelid worms in salt water can be almost as
unbelievable when they ready themselves for repro-
duction. Even closely similar kinds show specific fea-
tures in the methods used in starting a new generation
on its way.

Nereis and its nearest relatives introduce altera-
tions even in parts of the body not intimately con-
nected with production of eggs or sperms. The eyes
enlarge; the paddles change form; and for many
years the sexual stages were believed to be members
of a different genus (Heteronereis). They are still
referred to as heteronereid individuals.

The male heteronereid is regularly much smaller
than the female, and often almost white with sperm
cells showing through the body wall. The female het-
eronereid is usually heavy with reddish eggs, and
swims much more stiffly and sedately. The males
spiral in dizzy paths.

On the Pacific coast of America, Nereis vexillosa

Clamworms such as Nereis virens are the fish-
worms of the sea. At night they swim or creep over
the bottom, feeding on dead clams and other bits of
food. By day they often reach food through the mud,
burrowing up to it from underneath. (Long Island,
New York. Ralph Buchsbaum )

The paddles of Hesione, the bristle worm, are sup-
ported by stiff bristles and trail a long filament,
giving a fringelike effect as the animal undulates
from side to side. The head (top) bears eyes and
several pairs of sensory tentacles. (Wimmer )

reaches sexual maturity during the spring and sum-
mer months when the extreme high tides at new
moon come near midnight. One after the other the
male heteronereids appear at the surface, each a
mere 42-inch animal but swimming furiously. Fe-
males with red after-segments rise slantwise from the
depths and join the crazed ballet. The males redou-
ble their pace and commence shedding sperm cells
as though they were stunt planes skywriting a mes-
sage of welcome. This change in the water excites
the female heteronereids, and they release their eggs
through rents in the body walls of the loaded seg-
ments. By dawn, the survivors are spent.

On the New England coast, Platynereis megalops
swarms for about two hours every night during the
dark of the moon in summer months. In this species
the male heteronereids appear to be in two parts: an
anterior portion swimming violently with the maddest
capers, and a posterior portion tagging along like a
trailer, loaded with sperm cells. The females attack
the males and bite off the segments containing the
sperms. This mass the female heteronereid swallows
in one long gulp. The sperms emerge into her phar-
ynx, penetrate the segments where her eggs are wait-
ing, and accomplish fertilization internally. Only af-
ter the event is complete will her body wall rupture
and spill out the sexual products. Eggs of P. megalops
cannot be fertilized artificially in sea water; some es-
sential ingredient is missing.

Most famous of these nocturnal annelid ballets is
the swarming of the palolo worm Eunice viridis in
the South Pacific. There the big polychaetes live in
holes among the coral reefs, hunting for food in the
same general way as any Nereis. But at the third
quarter of the moon in October and November come
the “little rising” and the “great rising” for which the
native peoples wait—ready to feast on the swarming
worms.

202 |

At this season the palolo is mature, with eggs or
sperm concentrated in a hinder part of the body.
This posterior portion develops an eyespot and, at the
appointed time, separates from the parent to swim
to the surface and there mate like a heteronereid
with other similarly dissociated individuals. This is
actually mating by proxy, for the parent palolos re-
main in the rock crannies and develop new reproduc-
tive regions for the following year.

A very different polychaete worm swarms in the
darkness near Bermuda. Odontosyllis partners find
one another in the black water by bright lumines-
cence. The little males flash like fireflies as they swirl
near the surface. Each female glows steadily until a
male reaches her and mating begins. Then her light
goes out permanently, and so does his.

Nereids are inconspicuous as they prowl the bot-
tom and tunnel through its surface sediments. Re-
lated worms, with added protection from enemies,
can be more conspicuous in their foraging.

Among coral reefs of the Bahamas and West In-
dies, Hermodice carunculata moves about in appar-
ent unconcern over the nearness of hungry fish. Its
8-inch body offers an attractive meal, yet few crea-
tures molest Hermodice the fire worm. The soft-ap-
pearing white bristles on the rose-pink sides may sug-
gest the texture of a Persian cat, but they are fine,
stiff, brittle lengths of glasslike material that pene-
trate skin or the lining of mouth and stomach, pro-
ducing agonizing pain. Brushing against Hermodice
is like brushing against a hot poker. The burning sen-
sation lasts for about an equal length of time, and is
only aggravated by rubbing, since this drives the
broken bristles even deeper.

Scale worms carry on their backs shields—over-
lapping plates in pairs—as armor. Lepidonotus has
twelve such pairs, Eunoa fifteen, and Halosydna
eighteen. These flattened worms, from 1 to 4 inches
in length, are found on both sides of the North At-
lantic where a beachcomber can discover them.

An even more astonishing polychaete of these
same regions is the sea mouse Aphrodite aculeata
(Plate 85), whose fifteen pairs of scales are com-
pletely hidden by a dense felt of long hairs, grayish
down the middle of the rounded back, brilliant iri-
descent green and gold along the oval sides. Sea mice
reach a length of 7 inches and a width of almost 3,
far exceeding in size the mammals for which they
were named.

The polychaetes that move about so freely are of-
ten grouped for convenience as “Errantia,” the wan-
derers. Their counterparts are the more settled
worms, the “Sedentaria.” The latter build regular
tubes and maintain a fixed address. Actually no
sharp distinction can be drawn, for many of the
wanderers are like Nereis in building mucus-lined
tunnels in the bottom. Cistenides, among the sup-

posedly sedentary types, fashions a beautiful slender
tube of sand grains cemented together, and drags it
over the sea floor like a trailer motorist in his mobile
home.

One of the chronic burrowers, Arenicola marina,
is known as the lugworm by fishermen on both sides
of the North Atlantic. Other species of the same ge-
nus dig homes in the mud flats of the Pacific. These
stout animals reach a length of more than 15 inches,
with extra encircling wrinkles concealing the fact that
the bristle-bearing trunk part of the body has only
about twenty-one segments. Tufts of bright red gills
mark the sides of each of these segments, but are
lacking on the more slender, tail-like, posterior ex-
tension of the animal.

Arenicola lacks teeth in its eversible pharynx, but
uses the organ as a burrowing tool in the sandy mud.
While feeding, the worm engulfs the bottom material
almost indiscriminately, swallowing a lump about
every five seconds. It continues at this pace for from
half a minute to a minute, then rests about twice to
three times as long. From a quarter to a third of each
day is spent in feeding, with occasional trips to the
surface of the mud flat to expel a coil of sand from
which the food materials have been digested.

The presence of Arenicola in a beach can often
be suspected from the circular holes at the ends of
the tunnels and the neat coils of castings which ac-
cumulate and erode into miniature volcanoes around
some of the openings. In reproductive season, these
worms enclose their fertilized eggs in great tongue-
shaped masses of jelly as much as eight inches long,
three inches wide and an inch thick, anchored at the
small end in the sea bottom while the larger portion
flops back and forth with each wave. After the en-
closed eggs hatch, the developing worms use the jelly
as food and continue to live in the enlarging cavity.
Eventually they have more than a dozen segments
and are beginning to resemble their parents; at this
stage the small worms escape and the jelly disinte-
grates.

The parchment worm Chaetopterus builds a U-
shaped tube lined with a tough secretion suggesting
sheepskin. At the bend of the U the creature rests,
waving its fan-shaped paddles (parapodia) to propel
water past its body. The current brings both oxygen
and particles of food; the latter are captured in a re-
markable bag of mucus secreted by a pair of wing-
like parapodia extending to the tube wall near the
anterior end of the body. At intervals of about eight-
een minutes, Chaetopterus stops pumping water, rolls
its mucus net into a ball, and swallows it. Then it be-
gins fanning again. Each ball of food contains virtu-
ally every microorganism in approximately a cupful
of water pumped through the tube.

Although Chaetopterus rarely leaves the seclusion
of its tube, it is a luminous animal. At night the pro-

The polychete worm Eunice is an active animal,
hunting for bits of food among rock crannies and
swimming or creeping by means of bristle-bearing
paddles on each body segment. (Wimmer)

truding tips of its parchment tube may glow from the
reflected light. No one is sure whether this attracts
minute animals useful as food or has some other
significance in the life of the worm.

On mud flats from New England to Georgia, the
presence of another tube-builder, Diopatra cuprea,
can be inferred from the conspicuous “‘chimneys” it
constructs. These extensions of the vertical, three-
foot tube project several inches above the bottom
and are reinforced externally with bits of shell, plant
debris, and seaweed fragments. The worm itself may
be 1 foot in length, 2 of an inch in diameter. While
covered by quiet water it extends from its tube a
strikingly handsome pair of scarlet gill plumes, each
treelike, with whorl after whorl of branches arising
from a pulsating spiral central stem.

Tide pools and wharf pilings are home to some of
the most spectacularly beautiful polychaetes, the
feather-duster worms (Plate 81). Many of them are
known more correctly as sabellids. They build tubes
as much as eighteen inches long, and from the open
end extend a pair of stubby, armlike organs (palps),
each bearing a spray of gaily banded, feathery gill
plumes which serve also in trapping food. In many
cases the worm detects the merest shadow falling on
the plumes, and snaps back out of sight into its tube.

[203

The parchment worm Chaetopterus lives in a U-shaped
tube in muddy bottoms. Its bizarre paired paddles
pump through the tube a current bringing oxygen and
food, and help manipulate the mucus bag with which
food particles are trapped. (Massachusetts. George G.
Lower )

After a few minutes the whole headgear emerges
slowly, mushrooming to a diameter of perhaps 3
inches like the cloud from an erupting volcano. Cilia
covering the surfaces of the gill plumes then begin
driving water against them. Any food particles are
trapped in a mucus film carried down channels to the
mouth.

Serpulids (Plate 82) are mostly smaller worms,
with gill plumes seldom over 1% of an inch across.
They have gone one step further than the feather-
duster worms in that one part of the gill plumes has
become a “stopper,” pulled into place in the tube
opening like a cork in a bottle as the worm jerks back
into the security of its shelter.

Serpulids build limy tubes that coil or spiral. Spi-
orbis attaches to seaweeds a white, snail-like shell,
often no more than 4% of an inch across. Hydroides
and Serpula range widely, often to moderate depths,

204]

usually attaching their larger and irregularly coiled
tubes to the shells of large mollusks.

A few exceptional polychaetes live in fresh water.
Largest of these is Nereis limnicola, found in lakes
and streams of California, close to the Pacific Ocean.
Others inhabit remote Lake Baikal in Siberia. Even
better known is the tiny, gill-bearing Manayunkia
discovered in a Philadelphia suburb but now known
also in the Great Lakes, where it builds tubes attached
to stones. Its blood contains a green pigment (chloro-
cruorin) rather than the red hemoglobin found in
most other annelid worms.

Some minute worms, all of them less than % of an
inch in length, as adults resemble juvenile stages of
polychaete worms. For years they were suspected of
being “missing links” and received the name “archi-
annelids.” Now it appears that they are merely de-
generate types. Each of them has but five or six seg-
ments and develops neither parapodia nor bristles.
On the dorsal surface, bands of cilia mark the bound-
aries of the segments; the ventral surface is rather
uniformly ciliated. Some species are transparent,
others bright orange or translucent white. Polygor-
dius is almost as slender as a hair, and is a salmon-
pink; it lives under stones on both sides of the North
Atlantic and in the Mediterranean. Dinophilus is
more oval in outline, and occupies similar sites
around the world.

The Bristle-footed
Annelids

An earthworm maintains its grip upon the soil with
the bristles that give the class Oligochaeta its name
(from the Greek oligos, small, and chaeta, a bristle).
Each segment of the animal has four pairs of glassy
bristles which can be detected as roughnesses when a
finger is rubbed along its sides or undersurface.

The worm has muscles with which to tilt the bris-
tles forward or back, and it uses this simple control
to determine whether the alternate contractions and
extensions of its body will shift it ahead or toward the
rear. If an earthworm tilts the bristles to slant back-
ward and extends them to catch upon the soil, it is
ready to move forward. The bristles then permit any
portion of the worm to slide ahead, but prevent it
from slipping backward. If the worm tightens its lon-
gitudinal muscles and shortens itself, the anterior end
of the body holds to the creeping surface while the
posterior end skids forward. When the worm con-
tracts its encircling muscles and relaxes the longitu-
dinal set, its body lengthens. The bristles in the pos-
terior segments hold fast while those in the anterior
region slip easily, and the worm moves ahead.

(Class Oligochaeta)

Fan worms (sabellids) are annelids that extend from their parchment-like
tubes a lovely crown of feathery tentacles with which suspended food particles
are gathered and oxygen obtained. (Bimini. Fritz Goro: Life Magazine)

The large burrowing terebellid worm at left, Amphi-
trite johnstoni, shares its burrow, and probably a
little of its food, with a smaller guest (commensal),
the scaleworm Gattyana cirrosa. (England. D. P.
Wilson )

To retreat, the worm simply tilts its bristles in the
opposite direction and repeats the cycles of changes
in body length, time after time.

This method of locomotion is adequate for oligo-
chaetes wherever they live. A very few, such as the
very slender, 22-inch Clitellio worms found under
stones in the intertidal zone, and the white, 1-inch
Enchytraeus worms among living and dead plant de-
bris in the same regions, can tolerate salt water. A
few creep over glaciers, apparently feeding on micro-
scopic plants in the film of water that melts when sun
reaches the ice surface. These are “glacier worms.”
But most oligochaetes live in fresh water or in soil,
on all continents and major islands with the exception
of Antarctica and Madagascar.

Oligochaetes in fresh water inhabit their realm
from top to bottom, and tend to be world-wide in dis-
tribution, perhaps carried from place to place in the

206]

mud on the feet of migrant wading birds. Little Dero,
scarcely 4 of an inch in length, secretes a slender
tube below a duckweed leaf, and slips in and out (or
reverses itself) at astonishing speed. Dero captures
small crustaceans (chiefly water fleas) that come to
rest against the undersurface of the miniature floating
plant.

Bright red or brownish members of the genus Tu-
bifex thrive where the bottom mud is rich in organic
matter, and can manage with almost no oxygen. Of-
ten they become conspicuous as an assemblage form-
ing a carpet in polluted water. If undisturbed, each
worm clings to the upper end of its individual slime
tube, a tunnel extending downward into the bottom.
Its inch-long slender body waves in the water, creat-
ing a feeding current. Yet the merest commotion is
enough to send every 7ubifex instantly into its refuge.

Many fresh-water oligochaetes reproduce asexu-
ally, simply by dividing the body transversely into
two, each half regenerating the missing region. Often
the regeneration is essentially complete before the in-
dividuals separate. Sometimes several offspring of
this kind are being formed at the same time, one af-
ter the next in a chain.

Otherwise the bristle-footed worms mate in the
manner that has become familiar from observations
of earthworms. Each oligochaete is both male and fe-
male. At mating time a pair of equal size lie with an-
terior ends overlapping, facing in opposite direc-
tions. Sperm cells are passed from each worm to the
other, and collected in special flask-shaped chambers
opening to the outside by small openings. Then the
worms separate, each to use the store of sperms in
fertilizing a batch of eggs.

When the eggs are ready, the worm secretes a
slime tube around its body, heaviest and charged
with a special protein in the region of the clitellum
(the saddle-shaped thickening so conspicuous a short
distance back from the head end). Slowly the worm
moves in reverse, sliding the slime tube like a girdle
over the anterior end. As the thick part of the tube
passes the sperm cavities, these discharge their load
into the space between the worm and the slime tube.
Opposite the ovaries, the eggs are extruded into the
same space and fertilization occurs. Gradually the
worm works out of the slime tube, and the latter
purses up to form a lemon-shaped cocoon enclosing
the developing young. By the time they escape from
the cocoon, they are miniatures of the parent.

Quite recently, scientists have discovered that the
common earthworms emerge from the cocoon with
the full adult number of segments. In Lumbricus ter-
restris, the flat-tailed night crawler, this is about 150.
In the barnyard earthworm Eisenia foetida, which
Izaak Walton called the “brandling,” the total is only
about 95 segments.

The clitellum, too, has a definite position. That of

Lumbricus extends from the thirty-second to the
thirty-seventh segment as counted from the anterior
end. In Eisenia the glandular enlargement lies in seg-
ments twenty-five through thirty-two. The cocoons
produced are similar, about the size of a grain of
wheat in Lumbricus, slightly smaller in Eisenia.
Those of the giant 11-foot earthworm Megascolides
australis of Australia are almost three inches long
and half an inch in diameter—about two-thirds as
thick as the slender worm itself.

Some kinds of South Asian earthworms appear
able to regenerate new individuals from both parts
if they are cut in two. Earthworms in the northern
parts of Europe and Asia, Australia, Africa, and the
Western Hemisphere cannot do this. They will re-
place four or five segments at the anterior end, and
this may be the most they will do even if the loss
there is as great as ten segments. On the other hand,
a cut between segments eleven and thirty-six is al-
most sure to kill the worm.

If its first thirty-five segments remain intact, a well-
nourished worm may regenerate a new posterior
end and add segments closely matching the number
amputated. Somehow the worm is able to install re-
placements bringing the total almost exactly to the
tally at hatching age.

In most soils, earthworms constitute about half of
the entire weight of animal life. Half a ton of earth-
worms to the acre is an average figure. In rich soil
it may reach twelve tons to the acre, which could be
regarded as a fair indicator of fertility. Appreciation
of the earthworm’s role in the soil is far younger than
a knowledge of its use in angling. Juliana Berners, a
nun in an English Benedictine convent, gave clear in-
structions for finding and using worms as bait in the
fifteenth century. Aristotle referred to earthworms
inelegantly as “‘earth’s guts,” but he recorded no
knowledge of where they came from or any value
they might have.

Not until 1777 was the value of earthworms to
plant economy guessed at by the English naturalist
Gilbert White, who wrote:

Earthworms, though in appearance a small and des-
picable link in the chain of nature, yet, if lost, would
make a lamentable chasm. For to say nothing of half
the birds, and some quadrupeds which are almost
entirely supported by them, worms appear to be great
promoters of vegetation . . . the earth without them
would soon become cold, hard-bound, and void of
fermentation, and consequently sterile.

Less than a century ago, Charles Darwin published
a fuller account, The Formation of Vegetable Mould
through the Action of Worms, a book drawing to-
gether extensive observations which showed how
much of the humus matter in the soil came from
leaves and other plant debris pulled by earthworms
into their subterranean tunnels. The passageways

also serve vegetation by admitting oxygen and rain.

Darwin summarized his discoveries with the state-

ment:
The whole of the superficial mould [topsoil] over any
such expanse has passed, and will again pass, every
few years through the bodies of worms. The plough
is one of the most ancient and most valuable of man’s
inventions; but long before it existed the land was in
fact regularly ploughed and still continues to be thus
ploughed by earthworms.

Darwin collected the castings over sample areas of
ground, and dried and weighed the material col-
lected. He estimated that between seven and one-half
and eighteen tons of material were annually brought
to the surface by worms in each acre of ground.
Later scientists found that the amount of earth-movy-
ing actually ranges from two or three tons per acre per
year in light soils to more than a hundred tons in
some tropical parts of the world.

The conspicuous saddle-shaped clitellum of earth-
worms secretes the cylindrical sheath which becomes
the “cocoon” for developing eggs. (Bavaria. Otto Croy)

few

Earthworms use their soft sucking mouths to seize
plant debris on the surface of the ground while they
are extended from burrow openings at night. Al-
though these worms have no eyes, their skins are
sensitive to light (except red light), and each indi-
vidual will draw back into its tunnel if illuminated.
Anglers often hunt them with a ruby lens on a flash-
lamp, taking advantage of the animal’s blindness to
this part of the spectrum useful to man.

All over the world, earthworms have many natural
enemies. The national bird of Australia, the kooka-
burra or “laughing jackass,” is actually a kingfisher
whose remote ancestors gave up diving for fish and
took to earthworms instead. Elsewhere moles tunnel
after earthworms. Skunks dig them out or pounce on

The European medicinal leech Hirudo medicinalis
has its larger sucker at the rear end (below). This
leech is still being imported for sale in the United
States, although it thrives in many ponds in Amer-
ica as an introduced animal. (P. S. Tice)

them at the surface. Owls eat amazing numbers and
feed them to their young. Robins and other birds use
earthworms as an important part of their diet.

Recent experience in Ann Arbor, Michigan, has
emphasized the extent to which earthworms bury
leaves and robins eat earthworms. In that city, prized
elm trees were sprayed heavily with insecticide to
check the spread of bark beetles carrying the Dutch
elm disease. Poison-coated leaves fell to the ground
in autumn, and were pulled by earthworms into their
burrows for winter meals. The worms digested the
plant matter without noticeable harm from the in-
secticide. But when the robins arrived the following
spring, at the end of northward migration, the fliers
encountered poison-charged earthworms. The robins
ate so many worms that they succumbed to the in-
secticide. Soon Ann Arbor’s formerly abundant rob-
ins were no more.

The Leeches

Most leeches will take a blood meal from a verte-
brate animal if they have an opportunity. Only a
few, however, require this food, having become truly
parasitic. The rest get along quite well on a mixed
diet of snails, insect larvae, crustaceans, and small
bristle-footed worms, swallowing these victims whole
into the capacious crop portion of the digestive tract.

Leeches swim gracefully by undulating the body.
Those that are flattened make especially rapid prog-
ress. At the end of the journey, however, all leeches
settle down and hold to something solid by use of a
muscular suction disk just ventral to the anus at the
posterior end of the body. Most leeches have a sec-
ond suction disk surrounding the mouth, and often
stitch themselves along from place to place like an
inch worm, holding to the bottom with one sucker
and then the other alternately.

The saliva of blood-sucking leeches contains a
powerful anticoagulant (hirudin), which prevents
formation of a clot. It may also serve to preserve a
blood meal, since, if permitted, a leech will usually
swallow enough to last for several months. Almost as
rapidly as the blood is taken in, the leech’s excretory
organs (nephridia) dispose of the water, concentrat-
ing the meal for maximum nourishment. A half-
ounce leech has been known to gorge itself with two
and one-half ounces of concentrated blood and then
survive with no more to eat for fifteen months.

The leeches include a number of exceptional ani-
mals radically unlike other members of their class.
One (Acanthobdella) has bristles and retains a true
body cavity in adult life; otherwise leeches lack bris-
tles, and the body cavity of the embryo is obliterated
by a meshwork of connective tissue, muscles, and
expanded portions of the blood system.

(Class Hirudinea)

[continued on page 225 ]

90. The barber-shop shrimp, Stenopus hispidus, trails its tremendously long white
antennae and large banded front pincers when it uses its tail fin as a water scoop and
darts backward out of danger. It scavenges for food on coral reefs and wharf pilings
throughout the West Indies. (Marineland, Florida)

91. The Californian mantis shrimp, Pseudosquilla bigelowi, burrows in ocean

bottom mud, digging in at an angle of 45 degrees to a depth of as much as
s for small fish to come within

snatching distance. (Scripps Institution of Oceanography. ilson)

92. The prawn, Palaemonetes, hides among eelgrass and floating seaweeds
& g g

in northern, cooler waters of the North Atlantic. (Delaware. William Amos)

93. The pond crayfish, Procam-
barus blandingii acutus, often mi-
grates in considerable numbers at
night, traveling from one pond
to another. (Illinois. John Gerard:
National Audubon) —

94. The burrowing crayfish, Cambarus diogenes, digs its home close to a
stream, avating a chamber three or four feet below the soil surface where
water will seep into it. A mud chimney several inches high is built around
the burrow opening. (Illinois. John Gerard: National Audubon)

. The common green crab, Carcinides maenas, of
rica’s North Atlantic coast, dines on a variety of
young clams and marine worms, such as this beak-
thrower (Glycera). (New Jersey. David C. Stager)

96. The most familiar edible crab in American Pacific
coast markets is Cancer magister, often 7 inches across
the body. It lives mostly on deeper sandy bottoms,
feeding on fishes. In summer, breeding pairs come

to the shore. These, and also young crabs, can be dug
up at low tide from rockbound sandy pools. (Oregon.
Ralph Buchsbaum )

97. A cornered crab will back, if possible, into a pile of seaweed and prepare to defend
itself with pincers ready. (Maine. Eliot Porter)

99. The ghost crab, Ocypoda arenaria, haunts sandy beaches from Long Island to
Rio de Janeiro, roaming freely at night but spending most of each day in a U-shaped
or Y-shaped burrow in the sand. (Florida. William J]. Jahoda: National Audubon)

~~ . =e

98. The land crab, Cardisoma
carnifex, with a body about 8
inches wide, is found around
the shores of the Indian Ocean
and on islands of the East In-
dies as far as Samoa and Tahiti.
It eats fruit and dead animals,
including fish, but seems to
prefer fresh water for an oc-
casional bath. (London Zoo.
Ralph Buchsbaum)

100. From Boston southward on America’s Atlantic coast, the fiddler crab, Uca pugi-
lator, occurs in small armies that run as groups over the sandy shores. The male
(left) has an enormous “fiddle” claw, used in courting the female (right) and in de-
fense. (Florida west coast. Charles Lane) |

» is able to climb coconut trees

and knock down the husk, which it then opens

with its
(Bora Bora.

to g the meat inside.
ind Dorothy Schweitzer)

101. The land hermit crab, Coenobita
rugosa, of East African coasts, is known
as a “soldier crab” because it hunts in
large numbers, climbing trees and
bushes, eating fruits, carrion, and ani-
mals slow enough for it to capture. Thi
specimen in the London zoo carried a
borrowed marine snail shell 34 inches
in length. As the crabs grow they ap-
propriate larger snail shells (Ralph
Buchsbaum)

103. The sponge crab, Dromia vulgaris,
carries on its back, like a beret, a con-
cealing piece of sponge, held securely
by the highly modified last two pairs of
legs. (France. Ralph Buchsbaum)

104. The large hermit crab of the American Atlantic

ast is Pagurus pollicaris, com-

caer ee ee Florida. This one has its soft abdomen securely protected by the
heavy shell of a whelk, Busycon, a carnivorous marine snail. (Marineland, Florida)

—_—_>

107. Large hairy-legged tarantulas from
Central and South America often reach
countries far from the tropics in bunches
of bananas where they have hidden dur-
ing a nighttime hunt for insects, small
lizards, and mice. (Roy Pinney)

105 and 106. (Above) The giant whip scorpi s, is a fearsome-
looking but harmless denizen of the Sonoran desert in Arizona. (Eliot Porter) (Below) Only two of
North America’s scorpions have a deadly sting, and even they are reluctant to use the venom-bearing

tail tip except in defense or to subdue a struggling insect se ‘ed in the pincer-tipped legs. (Roy Pinney)

108. On yellowing green foliage this spider is
well camouflaged, but on the bark of a pine
tree in a sandy woodland it is a good target
for wasps and birds. (Berlin. Otto Croy)

109. The wolf spider, Dolomedes, runs lightly
over the ground and also ventures out upon
the surface of ponds and streams in search of
insect prey. (New Mexico. Eliot Porter)

110. Wolf spiders, such as the members of genus Lycosa, drag with them wher vy go the
silk-covered ball of eggs from which spiderlets will emerge. (Delaware. William H. Amos)

———-

113. The female black widow spider,
Latrodectus mactans, wears a bright red
hourglass mark on the underside of her
spherical black abdomen. She defends
her nest with a bite that is dangerous to
man. (Texas. Andreas Feininger)

111 and 112. Some spiders make a specialty of hunting for prey below the surface of ponds. Dolome-
des carries a film of air caught in hairs over the body as it dives (above), but sheds the water quickly
upon returning to air with a victim ( below). (William H. Amos; and John Gerard: National Audubon )

114. The banded garden spider, Metargiope
trifasciata, builds an orb web but spends many
hours repairing holes made in it by heavy in-
sects that break through and escape. (New
Mexico. Eliot Porter)

115. Immature stages of the velvet water mite,
Limnochares, have six legs and live as parasites
on water insects. The adult (left) swims read-
ily and clambers over the shore while scaveng-
ing for prey. (Delaware. William H. Amos)

[continued from page 208 ]

One leech in southern Chile (Macrobdella valdi-
viana) reaches a length of 30 inches as a burrower
in soil, probably depending for food on earthworms
and insects; otherwise the 12-inch horse leeches
(Haemopis) acting as predators in ponds and lakes
over much of the world hold the record for size.

One leech (Haemodipsa) in the moist jungles of
southern Asia is terrestrial, and stays on foliage or
tree trunks beside animal trails as much as 11,000
feet above sea level in the Himalayas. Holding firmly
by its posterior sucker, it reaches out its slender 1-inch
body, ready to catch a victim and be carried while
collecting a blood meal. The bite is painless but is
often followed by an ulcer due to infection of the
wound. And a few dozen of these leeches can with-
draw substantial amounts of blood, since each is un-
willing to drop off before its dimensions resemble
those of a small cigar. Other leeches live in ponds and
streams, the sea, and wet soil.

Marine leeches are encountered on sharks and
rays, although smaller kinds attack a variety of bony
fishes. Branchellion is a very active leech which is as
much as 9 inches long, highly distinctive because the
sides of its dark-colored body bear lobed, fleshy,
overlapping gills. Pontobdella has only little tuber-
cles over the surface of its 3-inch cylindrical body.
Both of these attack skates, but Pontobdella appears
to favor sharks, especially the hammerhead shark.
Smaller leeches, 1 inch or less in length, are some-
times found among the gills of bony fishes. Smooth-
bodied Piscicola is commonest on flounders, attach-
ing itself to the upper side. Trachelobdella, with con-
spicuous transverse wrinkles, seems less selective.

Even the method by which a leech’s sperm cells
reach the eggs seems bizarre. Each leech is a her-
maphrodite, with both ovaries and testes. At mating
season, one leech deposits on the back of another a
small mass of mucus loaded with sperm cells. The
mass remains cemented in place until the body wall
becomes irritated and develops an open sore. Through
this gap in the body defenses the sperms penetrate
and work their way through the blood spaces to the
ovaries, fertilizing the eggs there. Meanwhile the mu-
cus mass drops off and the skin heals over.

In fresh waters the turtle leech Placobdella is often
found clinging to the skin at the base of the hind legs
of pond turtles, including snapping turtles. While un-
molested, its body remains broad, flat, and hand-
somely patterned in yellow on a green background.
But if disturbed, Placobdella drops off and curls into
a ball that sinks quickly to the bottom.

Glossiphonia, the common flattened leech of run-
’ ning water, has a similar shape and color pattern.
Both of these leeches are interesting because they
lay their eggs in large gelatinous capsules, and each
parent carries a capsule attached to the undersurface

of the body until the young hatch out. Sometimes the
young leeches cling for a week or more to the par-
ent’s back, and drop off one at a time. This may help
get them distributed more widely as the parent swims
about.

Other leeches ordinarily deposit their eggs in a flat
cocoon, attaching this to a stone or other firm sup-
port in the water. In a few kinds the parent remains
close to the eggs and protects them from disturbance
for as much as three consecutive months.

The common bloodsucker Macrobdella is dark
olive-green, with a thin body as much as 6 inches
long and 2 of an inch in width. It frequents ditches
and pond margins hunting for food of many kinds:
frog’s eggs, tadpoles, worms, and insect larvae. It is
particularly sensitive to any vibrations in the water,
however, and comes swimming to get a blood meal
from fish, frog, turtle, cow, or man.

Picnickers should know that it is far easier to get
an attached leech to drop off by sprinkling a little
salt on its body than by pulling at the slippery, elastic
animal itself. The same recipe is effective with the
jet-black or chocolate-brown Herpobdella, which
manages to get a blood meal occasionally despite the
fact that its mouth has neither jaws (as have Haemo-
pis and Macrobdella) or a stabbing muscular pro-
boscis (as is found in Placobdella and Glossiphonia).

The medicinal leech Hirudo medicinalis has gone
somewhat out of fashion, although it may still be
purchased over the counter of pharmacies in big cities
of America, and more readily on the European con-
tinent and throughout Asia. It is cultured deliberately
in fish ponds, especially carp ponds, in Europe and
the Orient, and has become a relatively docile ani-
mal. Medicinal leeches released in New World lakes
and streams have often succeeded in colonizing
American waters.

Hirudo medicinalis is so easy to handle that it will
attach itself where guided. With its clot-liquefying en-
zyme hirudin it can remove the color-producing evi-
dence of a bruise or a black eye. Or, in the hands of
primitive medicine men, it will draw off load after
load of “bad blood” in the practice of blood-letting.
Application of a little salt to the engorged leech in-
duces it to disgorge; the freshly washed leech is then
ready for another meal.

So common was this use of leeches in the Middle
Ages that physicians became known as “leeches.” In
1846 the French physician Moquin-Tandon calcu-
lated that between twenty and thirty million leeches
were used annually in his country. By 1863 the hos-
pitals in Paris were requisitioning close to six million
leeches a year, those in London another seven mil-
lion. The requisitions usually specified full-grown 5-
to 6-inch adult leeches because these have the largest
capacity for blood.

Loon]
N
i)
n

CHAPTER XVIII

(Upper left) Orb-weaving spider and horseshoe crab; (upper right)

The Arthropods

(Phylum Arthropoda)

velvet worm and lobster; (lower left) centipede; (lower right) bear

animalcule and water flea

QO, all the invertebrates, it is only members of
the phylum Arthropoda that have mastered flight. In-
deed, no other phylum of animals is so widely dis-
tributed, from pole to pole, from the greatest abysses
to the highest peaks, from glacier to boiling spring,
as well as from the driest desert and saturated salt
lake to the felt of moss kept perpetually wet by the
misty spray from a waterfall.

It is tempting to refer to the arthropods simply as
“the insects and their kin,” for the insects, which be-
long to this phylum, constitute three-quarters of the
known kinds of animals. With other arthropods, in-
sects share the possession of an external skeleton
composed of hard cuticle, and jointed legs—the fea-
ture from which the entire phylum derives its name.
Typically, the hard cuticle is molted at intervals, al-
lowing the animal to grow by a succession of steps
during the few hours while the body wall is flexible.
Typically, too, each segment of the body bears a pair
of jointed limbs. Commonly each leg ends in a pair
of claws.

By interpreting these features liberally and watch-
ing for others that are found in arthropods about
which no argument can be raised, it is possible to
gather into this huge phylum two minor groups—
the tardigrades and the onychophorans—which show
affinities to other phyla as well. The remaining ar-

226]

thropods can be subdivided easily into those with
true jaws and those without.

The “mandibulate” arthropods have as append-
ages a pair of mandibles that do not end in claws. In-
stead, they work from side to side as chewing or
crushing organs, or are modified in ways making
them useful in piercing or sucking. The mandibulates
also have antennae, either two pairs as in crusta-
ceans Or one pair as in centipedes, millipedes, and
insects. Moreover, their body appendages tend at
the base to show a forked character.

Arthropods without true jaws are spoken of as
“chelicerate” because they all have associated with
the mouth a pair of pincer-tipped appendages, the
chelicerae. Chelicerate arthropods all lack antennae.
Their body appendages are never forked at the base,
and the first pair behind the chelicerae are usually
modified into fingering organs, the pedipalps. Chelic-
erate arthropods include the marine horseshoe
“crabs,” the arachnids (the terrestrial spiders, scor-
pions, ticks, and mites), and the sea spiders.

The Bear Animalcules
(Class Tardigrada)

An almost infallible method for collecting live
bear animalcules can be applied after a day or two

of rainy warm weather. Put a fist-sized clump of
damp moss into a pint bottle half full of water, shake
vigorously for five minutes, remove the moss, strain
the water through a pocket handkerchief, and exam-
ine the residue on the cloth with a strong lens or a
low-power microscope. Nearly every clump of moss
in the world is home to a few bear animalcules. But
they are minute creatures—rarely more than 14;
of an inch in length.

The name “tardigrade” refers to the slow steps
taken by the bear animalcule as it lifts its stout body
along on four pairs of stubby legs. Three legs arise
on each side, and a fourth is at the posterior end. All
legs end in a little cluster of four or five claws or
hooks that are movable and help the animal cling to
a moss plant, a lichen, a bit of bark, or a shingle on
the roof. A tiny eyespot adorns each side of the body
just forward of and higher than the first pair of legs.

Bear animalcules are scavengers, feeding on both
animal and plant matter sucked into the small mouth
or cut free through use of a pair of sharp teeth. Each
individual combines the organs of both sexes, but the
feature most effective in insuring the continuation of
bear animalcules in the world is their ability to lose a
little water, become dormant, and be blown in the in-
active state as dust particles. As a result, most tardi-
grades are cosmopolitan and can be collected as eas-
ily in the arctic as in the tropics, in Africa, America,
Eurasia, or Australia.

Tardigrades can remain dormant for years, and
then become active again in a few minutes when
wet or exposed to very humid air. It is after rains that
they climb about and can be shaken free from a sup-
port. Some bear animalcules inhabit ponds, particu-
larly temporary pools. A few are marine, and creep
in the capillary water film between sand grains on
the beach, or cling to the surface of sea cucumbers,
sea fans, and other slow-moving or attached animals.

Bear animalcules are so uncomplicated anatomi-
cally that biologists have often been uncertain of
their proper place in the animal kingdom. Sometimes
the tardigrades have been simply left in a little phy-
lum of their own, sometimes grouped with nematode
worms in the phylum Aschelminthes.

The Velvet Worms

(Class Onychophora)

Almost 150 years ago, the Reverend Landsdowne
Guilding was poking about, searching for snail shells
on the hilly slopes of the island of St. Vincent in the
West Indies. Under a rotting log he found an inch-
long brown animal. It moved slowly, and he mistook
it for a slug. Since it did not have a shell he popped it
into a vial of preservative solution, and did not ex-
amine it carefully until many months later. In 1825
he described the strange animal for science as a mol-

The head end of a peripatus, shown in color plate
88, here greatly enlarged. Thousands of minute papil-
lae give the skin of a peripatus its unique velvety tex-
ture. (Panama. Ralph Buchsbaum)

lusk, Limax juliformis, curiously equipped with a
series of lumps along each side of the almost cylin-
drical body as though it were a centipede. That the
“lumps” were really legs never occurred to him.

Not until many years later did anyone examine a
living velvet worm and realize how neatly it handles
its more than two dozen pairs of stubby legs. Each
leg ends in a flexible knob armed with a pair of claws.
From these the name of the class Onychophora
(“claw-bearing”) is derived. On its unusual legs the
creature (Plate 88) glides over the ground, latching
each leg temporarily to some support by expert move-
ment of the claw-bearing knob.

A pair of projections at the head end, which the
Reverend Mr. Guilding mistook for the tentacles of
a slug, are actually flexible antennae. They bear no
eyes and curl out of harm’s way, whereas the tenta-
cles of a land snail or slug carry eyes and draw back
inside the head like an inverted glove finger. Velvet
worms do have a pair of simple eyes, one on each
side of the head. But these organs are more like those
of some polychaete worms than of any mollusk.

The West Indian velvet worm was eventually rec-
ognized as a creature that superficially resembled a
caterpillar but was not an insect. It was neither a
centipede nor a millipede. It had many features in
common with annelid worms, yet was no annelid. It
was a “walking worm,” and so it received the generic
name Peripatus.

[227

Other animals of the same general type have now
been found living on every continent except Europe.
Each one may be referred to as a peripatus (spelled
without a capital), although the eighty-odd different
kinds are now placed in a dozen genera and two dif-
ferent families.

Wet forests conceal these animals, from within a
few feet of sea level to high in the Andes of South
America. Various kinds of peripatuses are found as
far north as Mexico and as far south as the Cape of
Good Hope. One kind in Panama and adjacent coun-
tries reaches a length of 5 inches and the diameter of
a lead pencil; it is Macroperipatus geayi. Best known
of the velvet worms, however, are Peripatopsis ca-
pensis from South Africa and Peripatoides novae-
zealandiae from New Zealand.

Creatures of this body form have been walking
the earth for at least five hundred million years. They
may well have been among the earliest animals to
creep out upon the land. Today’s velvet worms are
all terrestrial, extremely retiring in habit, and seldom
seen except by naturalists who hunt them out. Per-
haps this is because the peripatus avoids air contain-
ing less than 90 per cent of full saturation with water
vapor. In so limiting themselves, the velvet worms
parade in the open only at night or during rains,
while the relative humidity is close to 100 per cent.
By day they take shelter in the ground, or under
stones and rotting logs, or between the leaf base of a
palm tree and the trunk.

Every velvet worm has an amazing means of de-
fense. On each side of the thick-lipped sucking mouth
a small papilla marks the opening of a duct from
large salivary glands. From these glands the animal
can spit a blob of sticky secretion resembling clear
rubber cement. Within seconds the liquid becomes
opaque white and fairly firm. If a peripatus ejects its
special slime at an annoying ant or other small at-
tacker, the aim is usually excellent and the insect is
effectively restrained.

Whether velvet worms use their salivary cement

Fairy shrimps (Eubranchipus vernalis) appear sud-
denly in meltwater ponds in springtime. They swim
about catching microscopic green plants as food, and
reproduce before migrant birds arrive or other poten-
tial enemies awake from hibernation. (Pennsylvania.

Ralph Buchsbaum )

to subdue insects as prey is still questioned. Most
peripatuses appear to eat dead insects and worms
which they find as they explore among the leaf litter
and bark crevices. But in the southern hemisphere
some velvet worms live in termite nests, devouring
dead termites. Whether they occasionally take a live
termite has not been determined.

In captivity, some individual velvet worms will ac-
cept bits of liver. Some will seize live termites, other
small insects, and woodlice. Most will feed readily
upon freshly-killed flies and grasshoppers, cock-
roaches, and crickets. Others refuse food of all kinds,
and within a few weeks die as a result of their hunger
strike.

Occasionally a peripatus makes the mistake of
spitting on its own back. The slime hardens, affixed
firmly to the wrinkled, pebbled, water-repellent skin.
In a few days, however, the velvet worm frees itself
from the inflexible encumbrance by shedding the
outer layer of the skin. This ability to molt is one of
the ways in which a peripatus earns a place for itself
among the arthropods. Another feature assumed to
have similar meaning is the pair of bladelike jaws in
the mouth. And a velvet worm breathes in a manner
most like some of the centipedes, millipedes, and in-
sects—using branched air tubes (tracheae) admit-
ting air through openings on the surface of the body
to inner organs.

Unlike that of typical arthropods, however, the
skin of a velvet worm never develops a rigid cuticle.
Molting tends to be by patches, rather than of a com-
plete body covering at a time. In this respect a peri-
patus seems more akin to some of the annelid worms.
Such resemblance extends to the excretory organs as
well, for each leg base of a velvet worm carries the
opening of a nephridium—the kind of organ serving
annelid worms in much the same way that the kidney
does a vertebrate animal. No other arthropod has
nephridia.

Each peripatus is either a male or a female. Often
the sexes can be distinguished in that the males have
two or three fewer pairs of legs than the females.
Male velvet worms sometimes seem unaware of sex-
ual differences, for they may deposit a package of
sperm cells upon the back of another male almost as
readily as upon the body of a female. Only in the
latter instance, however, does the skin develop an
ulcer below the sperm packet and white cells from
the blood open a passage through the skin. In this
way the sperms are admitted into the body cavity,
where they can migrate directly to the ovaries. For as
much as a year, the arriving sperms may all be ab-
sorbed and used as nourishment for the developing
eggs. Then, with the eggs finally ready for fertiliza-
tion, another swarm of sperm cells can initiate the
steps whereby a fertilized egg grows into an embryo
and then a new individual.

One Australian kind (Ooperipatus) lays large
yolk-filled eggs. Most other velvet worms retain the
embryos inside the mother’s body until the young are
ready to be born as 12-inch facsimiles of the parents.
Some South American peripatuses develop a connec-
tion between mother and unborn offspring that is
analogous to the placenta of mammals. Across this
bridge the parent furnishes her young with food and
oxygen and attends to the disposal of wastes, includ-
ing carbon dioxide.

Pregnancy in peripatuses may last for more than a
year, and a female may even be carrying two differ-
ent generations of young at a time. Often the mild
excitement of being caught and placed in captivity is
enough stimulus to cause a pregnant mother peripa-
tus to expel her babies. For several weeks they may
remain with her, and then wander off on their own—
quite capable of feeding themselves.

The Crustaceans

(Class Crustacea)

People who enjoy seafood are likely to think of
crustaceans as lobsters and crabs and shrimps. A
whaler is prone to regard the class Crustacea as
chiefly krill—the shrimplike denizens of the open
oceans upon which whales feed so extensively. In-
landers may be more familiar with the crayfishes or
crawfishes that resemble lobsters in body plan but
thrive in fresh waters. The twenty-five thousand dif-
ferent members of class Crustacea include not only
these animals—obviously “crusty” ones—but also an
astonishing array of others, from water fleas to bar-
nacles and fish parasites. Many are delicate micro-
scopic creatures that drift in the waters of ocean and
lake as plankton.

When the lobster and its many relatives are viewed
as a group, the chief feature in common beyond their
arthropod nature seems to be possession of two pairs
of antennae. Other generalizations are subject to
many exceptions. Most crustaceans are marine ani-
mals, but some live in rivers and lakes. A few inhabit
the land, their gills modified in ways that require no
wetting to be useful in respiration. The majority of
crustaceans walk or creep or swim with their feet
downward; a few regularly swim inverted. Most crus-
taceans live out their lives in waters illuminated by
the sun. Yet others burrow in the bottom, and a sur-
prising number inhabit the lightless abysses of the
oceans.

PHY LLOPODS

Those crustaceans that regularly swim inverted
are best known from the fairy shrimp Eubranchipus
and the brine shrimp Artemia. Both are members of

Brine shrimps (Artemia salina) swim inverted in brine
so concentrated that crystals form on their undersides.
These phyllopods are found only in salty lakes, where
they reach a length of a little under ¥% inch. (Great
Salt Lake. Fritz Goro: Life Magazine)

the order Phyllopoda. They drive themselves along
in shallow water by successive waves of motion in the
leaflike gill-feet, which are combined respiratory and
swimming organs. They manipulate food with their
leg bases, chewing it a little before swallowing it. Yet
phyllopods have a clearly defined head with a pair
of compound eyes, and a slender abdominal tail pro-
jecting behind the thorax with its paired gill-feet.

Fairy shrimps appear and disappear so suddenly
that magic seems the only explanation. They occupy
very temporary pools, such as meltwater from snow
banks, and go through their growth stages so rapidly
by feeding on microscopic algae that suddenly a clear
new pond is occupied with inch-long swimming ani-
mals of iridescent colors—red, flesh-colored, green-
ish, bronze, or bluish.

Male phyllopods pursue the females, reaching for
them with relatively huge claspers that extend from
one pair of antennae. Mated pairs swim in tandem,
the female often with dark spherical eggs filling a
pair of large brood pouches at the base of her ab-

[229

The water flea Daphnia pulex, less than % inch long,
swims by jerking the large, branched antennae. (Ja-
pan. Y. Fukuhara)

dominal tail. The eggs drop out, sink to the bottom,
and either develop promptly into a new generation
of young or remain dormant until the pond dries up.
Then the eggs can stay for years if necessary, until
conditions are right again for hatching. They may
blow as dust and fall into other temporary pools,
starting other sudden swarms of fairy shrimps.

Brine shrimps 2 of an inch long are almost as un-
believable as they disport in salt-saturated bays of
Great Salt Lake, Utah, and other bodies of concen-
trated sea water. Often they swarm in astonishing
numbers in the artificial pans where man evaporates
brine to get salt. In these places Artemia finds abun-
dant microscopic plants of salt-tolerant types, and

230 ]

few enemies, since most fish cannot endure the salt.
Flamingoes may compete in filtering out the algae,
and take small brine shrimp as well.

CLADOCERANS

Both salt water and fresh have their water fleas,
members of order Cladocera. These creatures ex-
tend their antennae, legs, and abdominal tip through
the gap in a bivalved carapace saddling them like the
blanket on a pet dog. A water flea’s second pair of
antennae are remarkably long and bear a fringe of
bristles or hairs that make the organs effective as
swimming oars. A single compound eye occupies a
central position in the head, but it can be shifted by
muscles.

The most familiar of the water fleas in ponds and
lakes is Daphnia, adults of which reach a total length

just over ¥s of an inch. In surface waters these pink-

ish or flesh-colored motes dance all day, while sweep-
ing into their mouths microscopic algae.

Small fish eat enormous numbers of Daphnia and
other cladocerans. Yet the rapid reproduction of
these little crustaceans makes good all losses. For
much of the year only female Daphnia can be found,
and each releases another brood of fifty young ones
every eleven or twelve days entirely by virgin birth
(parthenogenesis). When living conditions deterio-
rate or autumn approaches, however, some of the
young released mature as males and fertilize a final
crop of eggs for the year. These “winter eggs” are re-
sistant to freezing and to desiccation. The parent
coats them in an extra shell (an ephippium) which
may have air cells providing buoyancy. As the pond
dries up, wading birds often become loaded with
these armored eggs in the mud on their feet, and then
wash off the living load in another pond where con-
ditions are more suitable for water fleas.

Some of the larger cladocerans are carnivorous.
Leptodora is an especially fierce one, sometimes
reaching a length of 1% of an inch. It rows rapidly
with winglike antennae in pursuit of smaller water
fleas, insect young, and water mites. Like so many
of its crustacean victims, Leptodora tends to swim at
somewhat greater depths at midday, but comes to the
surface in the late afternoon and feeds there until the
sun brightens the sky in the morning.

COPEPODS

Members of another order of small crustaceans,
the order Copepoda, swim by jerky, oarlike move-
ments of the antennae. The name “copepod” comes,
in fact, from the Greek kope, an oar. But the swim-
ming antennae of a copepod are its second pair, not
the first. And the body is usually a streamlined pear
shape, with segmentation clearly visible through a
microscope.

The largest of the free-swimming copepods is less

than 12 of an inch long. Those of average size are so
small that they are easily overlooked, even when a
cupful of pond water or sea water contains several
hundreds of them.

The copepod encountered most frequently in fresh
water is Cyclops, named for the one-eyed giant of
Greek mythology. Cyclops seldom reaches a length
of '4, of an inch and appears to the unaided eye as
a translucent milky white mote jerking along slowly
through the water. It does have a single eye in the
middle of the front of the head. If the individual is a
female with eggs, her two egg masses may be almost
as large as she is and suggest saddle bags. If a male is
attending his mate, he holds to her with his second
pair of antennae and they swim in tandem hour after
hour while he transfers enough sperm cells to ferti-
lize several batches of eggs.

Copepods in the drifting plankton near the surface,
whether in fresh water or the ocean, tend to be highly
transparent and colorless. Those associating with the
bottom in shallow water may be pink or green or
blue, whereas those in the black abysses of the ocean
are more often black or blood red. All of them use
fans of bristles on their feet to gather in microscopic
plants or other nourishing particles as food. Often di-
gestion is rapid enough that the digestive tract re-
mains inconspicuous even when the body itself is
glass-clear.

Most copepods hatch as six-legged, one-eyed crea-
tures and undergo a number of molts before this
“nauplius” stage is succeeded by the adult body form.
An adult usually has many pairs of legs and no eyes,
or one, or several. Yet the role of eyes is not easy to
demonstrate, for even eyeless copepods tend to make
long vertical migrations every day, swimming down-
ward around daybreak and up again in late after-
noon.

Some of these daily journeys are spectacular. The
abundant marine copepod Calanus finmarchicus,
about the size of a big grain of rice, travels from its
daytime hideaway 1100 to 1500 feet below the sur-
face to the topmost 150 feet of water at a speed of
about 150 feet per hour. Before dawn it heads down
again, diving about three times as fast.

These movements are not dependent upon light or
the availability of food, for they are shown by cap-
tive animals in an endless ring-shaped tube at the
same times of day in complete darkness. For a 14-
inch crustacean to travel up a thousand feet and
down again each day at half an inch each second is
equivalent to a man’s dog-trotting for the same length
of time at four miles an hour—covering forty-six
miles daily to reach a vegetable plate!

The number of animals performing these vertical
migrations daily in the sea is unimaginable. With the
copepods go slightly larger crustaceans and the small
fish that prey upon them. With the small fish go larger

fish and squids in fantastic abundance. So dense is
this migratory population during the day that the
most modern sonar depth-measuring devices on ship-
board sometimes cannot distinguish between the DSL
(deep scattering layer) and the true bottom. The
“phantom bottom” reflects the sound waves but of-
fers no discernible resistance to the line and lead
weight with which depth was formerly tested.

Directly or indirectly, the copepods provide a tre-
mendously important link between the microscopic
green algae that create foodstuffs in the sea with the
energy of sunlight, and the multitude of larger ani-
mals that live far from shore. Vitamins elaborated
by the algae and transferred into the copepods and
then into the carnivorous crustaceans of the krill
turn up in the oil of whale livers and then in the
bottled concentrates for human dietary supplements.
Proteins of plant cells, transformed into copepod
proteins, are reorganized into the flesh of herring
and salmon, cod and tuna.

Some copepods turn the tables on the fish, attack-
ing these larger denizens of the ocean and sucking
their blood or lymph as food. Many a marine fish,

The one-eyed Cyclops is a fresh-water copepod. This
is a male, about 49 inch long; the female usually car-
ries a cluster of eggs attached to each side of her

body. (P. S. Tice)

The marine copepod Calanus finmarchicus is only the size of a large grain of rice. This abun-
dant crustacean makes amazing daily migrations between depths of 1500 feet and the topmost
150 feet of water. Also shown are a few, smaller cladoceran Evadne. (England. D. P. Wilson)

when freshly caught, is found to have small, flattened
crustaceans scurrying over its surface. Others may
be discovered clinging to the gills or the lining of the
mouth, taking nourishment through the thinner, softer
parts of the fish’s skin. These are likely to be Ar-
gulus, the fish louse, a copepod with two prominent
suckers on the under surface. Still other copepods go
through an ordinary nauplius stage and then attack a
fish, embedding themselves and growing larger as al-
most formless parasites. Yet when the female para-
sitic copepod produces eggs, she extrudes them in
two egg pouches suggesting those of tiny, independ-
ent Cyclops.

OSTRACODS

The nauplius stage found in copepods appears to
be an important first step in the life history of many
crustaceans, both small and large. It is the first free-
swimming stage for members of order Ostracoda,
creatures a microscopist is likely to encounter while
examining a bit of oozy mud from the bottom of a
pond or a fragment of the floating algal mat at the
surface. Ostracods have an almost egg-shaped, bi-
valved shell rarely more than '4, of an inch in
length, hinged at the back and capable of being closed
entirely by contraction of a special muscle. These
crustaceans are omnivorous scavengers which climb

or cling on duckweed or other submerged vegeta-
tion by use of the same slender swimming legs that
can be extended through the gap in the shell. Cypris
is one of the common genera.

BARNACLES

Barnacles, which are crustaceans too (order
Cirripedia) go through first a nauplius stage and
then a bivalved form called a “cyprid” stage because
of its resemblance to an ostracod. It is the cyprid
stage that attaches itself to some solid object by
means of the first pair of head appendages. There-
after for a short time the young barnacle ceases to
feed. It transforms itself into the degenerate adult
form, secreting around its body a hard limy shell
composed of several separate movable pieces. Inside
this shell the barnacle is a prisoner, unable to move
from place to place. It is attached to its covering by
the region corresponding to the back of its neck, a
fact that led an eminent biologist to describe a bar-
nacle as an animal lying on its back, kicking food
into its mouth with its feet. Much of what is known
about barnacles comes from the monumental re-
search work of Charles Darwin—work that estab-
lished his reputation as a professional scientist fully
a decade before the appearance of The Origin of
Species in 1859.

Wharves and pilings, as well as ship bottoms and
floating timbers, often bear a lively covering of
gooseneck barnacles (Lepas), each holding to the
support by means of a flexible leathery stalk that
holds the shell-covered portion of the animal out into
the surrounding water. Gooseneck barnacles usually
have a shell composed of five limy plates, and pre-
sent a somewhat flattened appearance suggesting a
strange kind of clam attached by its siphon.

Barnacles attached to rocks are more often of the
acorn type (Balanus), in which a conical ring of four
closely fitted plates is closed at the top by two addi-
tional movable plates. When the latter are spread
apart, the animal reaches out feather-like feet and
combs the adjacent water for microscopic food parti-
cles. These are pulled into the cavity of the shell and
there transferred to mouthparts that consolidate the
catch and pass it to the mouth proper.

Both plankton organisms and the detritus from
partial decomposition of living matter are acceptable
food to barnacles. Upon a diet of this kind the acorn
barnacle Balanus nubilus of Puget Sound on North
America’s west coast reaches a diameter of nearly a
foot, and becomes an attractive item of food for hu-
man beings.

Man usually regards barnacles as “fouling” organ-
isms that fasten themselves to ship bottoms and
greatly increase the frictional drag of the hull upon
the water. Barnacles also find a place on or in the
skin of whales. Coronula, the commonest barnacle of

This fresh-water ostracod, whose head end is at the
left, is less than 14; inch across its enclosing bivalved
shell. Antennae and legs, which can be extended be-
tween the valves, beat and kick the animal along.
(Illinois. P. S. Tice)

whale skin, may reach a diameter of 3 inches. Often
this acorn barnacle, in turn, supports a few of the
gooseneck barnacle Conchoderma, which is unusual
in that it has only minimal shell covering and its feed-
ing organs are enclosed in little hoods opening in the
direction toward which the whale swims. From the
appearance of its paired hoods, Conchoderma is
called the rabbit-eared barnacle.

The step from being an embedded barnacle to one
living a parasitic life may not be very big. It has been
taken by a number of cirripedes, which thereby be-
came “root-headed barnacles.” The best known of
them is Sacculina, since it attacks a variety of crabs,
including the widespread green crab Carcinides mae-
nas of the North Atlantic’s shores and several differ-
ent common kinds on the Pacific coast of America.

Sacculina reaches its victim while still in the free-
swimming cyprid stage, but thereafter follows a truly
amazing course. The Sacculina larva pierces a hollow
bristle on the crab’s body and through it frees into
the crab’s blood stream a few cells that float about
inside the victim until they come to rest at the junc-
tion between the crab’s stomach and intestine. There
the cells attach themselves and grow on nourish-
ment from the crab’s blood while extending a mass of
rootlike processes throughout the body of the host.

The growing Sacculina parasite invades and de-
stroys the crab’s reproductive organs. This not only
terminates the host’s ability to reproduce but alters
its sex hormones until, at the next molt, it assumes
female body form regardless of its inherited sex. Fe-
male body form includes an apron-shaped abdomen,
which effectively protects Sacculina when the latter
creates an opening in the crab’s body wall on the
under side at the base of the abdomen and extrudes a

[233

|
Gooseneck barnacles, Lepas anatifera, on a floating
bottle. (England. D. P. Wilson)

The rose-colored acorn barnacle Balanus tintinnabulum
is one of the largest barnacles of the southern Cali-
fornia coast. It reaches a width of 234 inches and is
common on boat bottoms, wharf pilings, and rocks.
(California. Woody Williams )

large shapeless mass. This bulbous extension be-
comes filled with eggs, which develop parthenoge-
netically to the nauplius stage and then escape to in-
fect more crabs.

ISOPODS

A number of other crustaceans, ranging from %2-
inch to larger sizes, become familiar to many people
because they can be found alive or washed up on sea
beaches. Still other crustaceans thrive in damp places
on land far from any body of water. Under fallen
logs, stones, and even human possessions in many a
cellar, little oval flattened crustaceans known as sow-
bugs or slaters are often common. They are members
of the order Isopoda, a name that indicates the var-
ious pairs of legs to be about equal in length.

Many isopods take advantage of their flexibility to
curl up into a ball when disturbed. From this habit
they have acquired the name “pill bugs,” and been
likened to miniature armadillos. Members of the
common genus Armadillidium are particularly ready
to exhibit this method of self-protection.

A pill bug of the seacoast is Ligia (Plate 89). Like
the more inland members of Oniscus and Porcellio,
it is more flattened and shows less tendency to curl
up. Sowbugs are all scavengers, a few reaching %4 of
an inch in length. Their gills are greatly reduced
but still serve in air for respiration. The females carry
a batch of eggs with them in a brood sac formed by
flat projections from the legs.

In fresh waters, whether stationary or slowly flow-
ing, the isopods are represented by a 1-inch aquatic
sowbug, Asellus. It tolerates stagnation better than
many other creatures, and creeps over muddy bot-
toms eating refuse of all kinds. Females seem always
to be carrying eggs or a brood of recently hatched
young, with one generation succeeding another every
five to eight weeks from very early spring throughout
the summer.

Around wharves in salt water, the cosmopolitan
wharf louse /dotea baltica is an isopod reaching a
length of 1 inch or more. It shows surprising agility
as well as awareness of its surroundings by expertly
dodging the fingers of small boys who try to capture a
specimen. It takes full advantage of its flattened body
by scuttling into crevices.

The %-inch gribble Limnoria lignorum goes even
farther by burrowing into submerged timbers, often
to a depth of half an inch or more, weakening docks
and other wooden shore installations. Often pilings
become eroded to an hourglass shape at low-tide
mark primarily from the activities of this isopod.

AMPHIPODS

Whereas isopods tend to be flattened and broadly
oval, members of the order Amphipoda are more
usually compressed from side to side, and hence more

flea-shaped or shrimplike. Fresh-water scuds with
this form include the %2-inch Gammarus and Hya-
lella, both acrobats of no mean ability. Their reper-
toire includes swimming or climbing submerged vege-
tation by using the legs on the thorax, and leaps
produced with the aid of longer appendages on the
abdomen. Most of the world’s seacoasts have species
of Gammarus, which feed on both living and dead
vegetation. All scuds provide fish with important
food.

The conspicuous amphipods on sandy beaches are
the '2-inch beach fleas, such as Orchestia agilis and
Talorchestia longicornis. These creatures hide in
vertical burrows in the wet sand or among piles of
seaweed, where they can remain in humid surround-
ings or explore for food. If the seaweed is disturbed
the beach fleas display the bouncing leaps for which
they have been named.

The order Amphipoda includes some astonishing
animals as well. One of them is Caprella, the 12-inch
skeleton shrimp, whose body is a series of elongated
cylindrical segments bearing two pairs of slender,
hook-ended legs near the head and three more pairs
at the rear. With these appendages the skeleton
shrimp clings to seaweeds, hydroids, corals, and
wharf pilings. It moves in slow motion with the gait
of a measuring worm while stalking animals it can
snatch with its anterior appendages. Some skeleton
shrimps are grayish and translucent, others cream-
colored or reddish.

Another strange amphipod is Paracyamus, the
whale louse, which resembles the skeleton shrimp in
size and body parts, but which is broader, more flat-
tened, and constricted between segments. Its legs are
more powerful grasping organs than those of Cap-
rella. Whale lice creep in large numbers over the sur-
face of huge whales, hooking their legs into the skin.
They grasp a firm hold while gnawing out pits in
which the body of the amphipod is protected from
water rushing past the swimming whale. The entire
nourishment of a whale louse is taken at the whale’s
expense.

Still another member of order Amphipoda is the
glassily transparent Phronima_ sedentaria, whose
head is so elongate as to suggest that of a horse. It is
occupied almost entirely by the compound eyes.
Inch-long Phronima captures one of the equally
transparent colonies of the tunicate Salpa (p. 288)
and takes up residence in the hollow, barrel-shaped
tunic. It is carried along by the salp colony, and feeds
on the larger animal particles entering the colony’s
central cavity. Phronima even uses this adopted
home as a brood chamber for her own young.

Crustaceans more than an inch long tend to be
more familiar to us, and to be valued either as human
food or as nourishment important to large fish in

om Ae

Rocks are often almost coated by the shells of acorn
barnacles (Balanus). The two pieces of the shell that
close the cavity can be drawn apart to let the bar-
nacle use its feet to kick food into the mouth. (Eng-
land. Ralph Buchsbaum )

which man is interested. A majority of these crus-
taceans have at least a superficial similarity to
shrimps and lobsters. Their paired compound eyes
are on movable stalks, and at least the first few seg-
ments of the leg-bearing thorax are fused together
with the head to form a cephalothorax with shield-
like top and sides (a carapace). This lends some
rigidity to the fore part of the body, and often corre-
sponds to use of the tail fin as a scoop in swimming
backward, as is so characteristic of lobsters and cray-
fishes.

OPOSSUM SHRIMPS

Among members of the order Mysidacea the
carapace does not extend far enough backward to
cover all of the leg-bearing segments. Mysids are al-
most entirely pelagic, and their legs are all forked
paddles suited for swimming but not for walking.
These creatures are called “opossum shrimps” be-
cause the female carries her eggs beneath her thorax
in a pouch formed of special plates. The young
usually hatch in the nauplius stage and transform into
the shrimplike adult form.

Mysis stenolepis is one of the most important
mysids to man, for it is a major item of diet for such
commercial fishes as shad and flounder. They find
the mysid in abundance near shore, often among
tangles of eelgrass. Sometimes a person can detect

[235

The sowbug Oniscus is about 34 inch long. Like other
sowbugs it is a terrestrial isopod common under bark
of fallen trees, or logs, or stones. (Hugh Spencer )

The pill bug Armadillidium is one of the terrestrial
isopods that are ready at a moment's notice to roll up
into a compact ball. (Switzerland. Otto Croy )

F5%

mysids there at night, seeing them from a skiff as little
darting constellations of bright lights. Marine mysids
carry their light-producing organs with them, but the
few representatives of this order in the Caspian Sea
and in large lakes of Europe and North America
follow a different rule applying to all crustaceans in
fresh water: they lack luminous organs.

EUPHAUSIDS

Krill, the principal food of whalebone whales, are
pelagic crustaceans of the order Euphausiacea. Their
appearance is even more shrimplike than that of
mysids, for the euphausid carapace is fully developed,
shielding the bases of all of the swimming legs. Eu-
phausids carry their eggs below the slender abdomen.
Most members of this order are a brilliant red, and
when numerous they color the ocean’s surface until
whalers refer to it as “tomato soup.” Wherever this
color is widespread, whalebone whales can be ex-
pected.

At night euphausids may be equally noticeable be-
cause of their bright luminescence. When a ship
disturbs them, they glow for minutes at a time, mak-
ing the waves visible far astern. The underside of the
first four abdominal segments bear light-producing
organs. Usually another pair are located on the outer
surface of the eyestalks, where they shine like electric
torches into the water close to the mouth. The com-
pound eyes have components facing in this direction
too, and it seems likely that the animal actually jack-
lights its food (copepods) at night. In many euphau-
sids the compound eyes are strongly bilobed, one
portion seemingly directed upward and perhaps used
to identify the abdominal lights of other krill. The
other portion faces forward and downward, appar-
ently for use in feeding.

LONG-TAILED DECAPODS

True shrimps, along with lobsters, crayfishes, and
crabs, all belong to the order Decapoda. As the name
suggests, all of them have ten thoracic legs. These
include the large pincer-tipped appendages of North
Atlantic lobsters as well as the smaller legs used in
walking over the bottom. A number of pairs of ap-
pendages are associated with the mouth as food-
handling organs, and still additional pairs below the
abdomen serve in holding the eggs until they hatch.

Shrimps and prawns are free-swimming decapods,
usually with a compressed body (Plates 90, 92).
Peneus setiferus is the most important commercial
shrimp of American Gulf Coast waters, with about
100,000 tons taken annually. In Europe its place is
taken by Crago septemspinosus (also known as
Crangon vulgaris), a denizen of sand flats and tide
pools on both sides of the North Atlantic. On the
American west coast the commercial shrimp is Crago
franciscorum.

Commercial fishermen often refer to larger indi-
viduals as prawns and smaller ones as shrimps, but
some of these men have learned to distinguish be-
tween the true prawn Palaemonetes vulgaris (Plate
92), in which the second pair of legs bear the largest
pincers, and Crago, whose first pair of legs are the
biggest and have a transversely closing finger, and
Peneus, in which the third pair of legs bear the
prominent grasping organs.

Tide pools and coral reefs are home to pistol
shrimps, the “gunmen” of coastal waters. In these
burrowing members of the genus Crangon (= AIl-
pheus), the pincer on one of the front pair of legs is
enormously enlarged, although borne on a slender
limb. The movable claw near the end of the large
handlike part is the hammer of the “pistol,” cocked
by the animal to jut out at an angle of about 90 de-
grees. The shrimp fires its pistol by snapping the
hammer joint against the palm portion with amaz-
ing force, producing a sound audible all over a large
room if one of these animals is in an aquarium.

The pistol shrimps use their weapons both to de-
fend themselves and to obtain prey. The shock pro-
duced in the water is enough to stun a passing fish of
usable size. In the South Pacific, returning fishermen
are said to be able to learn the direction to the fring-
ing reef around a coral island by hanging over the
side of the boat and thrusting the head into the water.
The crackling sound of pistol shrimps can then be
heard all the way from the reef crevices.

The lobsters of North Atlantic coasts are members
of Homarus, a genus whose name is derived from
the old Scandinavian word for the animals. Epicures
delight in the delicate flavor of the muscles in the
large pincers and abdomen (“tail”). In conse-
quence, more research work has been done on Ho-
marus (and the similarly delectable oyster) than on
any other invertebrate food harvested from the sea.

South of the Bay of Biscay in Europe, the lobster
of Atlantic and Mediterranean waters is the spiny
Palinurus, named for Aeneas’ helmsman who fell
asleep at the wheel and tumbled overboard. Panu-
luris is the spiny lobster of the Pacific and of Atlantic
waters extending from North Carolina to Brazil.
Spiny lobsters lack pincers altogether, and use their
long and extremely strong antennae as whips to ward
off enemies and to discourage competitors while
feeding. As in Homarus and the various kinds of
crayfishes, the tail meat of spiny lobsters is mostly
muscles used to flex the abdomen, to drive the body
backward through the water at each flick of the
spread tail fan.

Throughout the spiny lobsters’ range—as far south
as the Cape of Good Hope—this tail meat is sought
by native peoples and commercial fishermen alike.
At the docks in Capetown, South Africa, the abdo-
mens of millions of living spiny lobsters are ripped

From curled-under tail to the tip of antennae, the
giant beachhopper Orchestoidea californiana may be
2% inches long. It lives in a burrow beyond reach of
the highest waves, and emerges at night to feed.
(Oregon. Ralph Buchsbaum )

off annually by hand to be quick-frozen and shipped
to markets in the United States. The still-struggling
bodies are pushed into the sea as waste. Those who
regard this practice as cruel have been met with a
ruling by the local Society for the Prevention of
Cruelty to Animals: by definition, only a vertebrate
animal can feel pain.

All true lobsters, whether with pincers or spines,
are scavengers. Yet they often engage in cannibal-
ism. Apparently this is due to a chronic need for
more lime than the environment provides, since the
habit disappears when broken shells of mollusks or
sand dollars are distributed on the bottom. Most of
the weight of a lobster’s exoskeleton is the lime that
impregnates it and gives it rigidity. Yet at intervals
each lobster sacrifices its hoard by molting the old
covering, growing about 15 per cent in weight inside
each new covering before it too must be shed. A
thirty-four-pound, 2334-inch Homarus is a record
catch. Palinurus sometimes grows almost as large.

Crayfishes (Plates 93, 94) have much the same

[237

The skeleton shrimp, Caprella aequilibra, is an elon-
gated amphipod about 1 inch long. Caprellids crawl
about on seaweed, as shown here, or on eelgrass or

hydroids. (England. D. P. Wilson)

body plan as North Atlantic lobsters, but they live in
fresh waters. Curiously enough, they are almost en-
tirely absent from the tropics, which divide the asta-
cids (such as Astacus and Cambarus) of Eurasia and
North America from the parastacids of South Amer-
ica, New Zealand, Tasmania, Australia, New Guinea,
and Madagascar. Africa itself has no crayfishes at all.

The largest crayfishes are the Tasmanian Asta-
copsis franklinii of surprisingly small streams. These
creatures reach nine pounds in weight. American
crayfishes are considerably smaller. Yet in the lower
Mississippi Valley they are hunted at night for food,
either for the tail meat itself or to give flavor and
protein to the thick soup known as crawfish bisque.
In the same regions, crayfishes often are a pest to rice
farmers, for they graze at night on the rice and then
retire to the concealment of shallowly subterranean
burrows in which water stands for most of the year.

Lobsters, crayfishes, shrimps, and prawns are of-
ten grouped as the long-tailed decapods, the Ma-
crura. With them should be included the hermit

238 |

crabs, which adopt empty snail shells as covering for
their unarmored abdomens. Hermits (Plates 101,
104) are very common on every coast. They become
familiar to beachcombers because they run about in
daylight where the water is quite shallow, or come
out on land in search of food.

The appendages which in a lobster form the sides
of the water-scooping tail fan have become modified
in hermit crabs and serve in holding to the inside of
the snail shell. When disturbed a hermit draws back
quickly into its shelter, often leaving only the tips of
its two big pincer claws exposed, simulating protec-
tive doors. When left to their own devices, however,
hermit crabs investigate every empty snail shell they
encounter, often trying out an alternate for size. In
this way they trade shells at frequent intervals and
keep up with their own growth. To human collectors
of shells, this habit can be most aggravating. A col-
lector who leaves a fine specimen beside an ant nest
for the ants to finish cleaning may find that a hermit
crab has come along, carried off the collector’s shell,
and left an old, dirty, worn one of a common kind.

Largest of the hermit crabs is Birgus latro, the
robber crab of South Pacific islands. After the cus-
tomary juvenile period in the sea, the robber crab
becomes progressively more terrestrial. Young ones
may use a large snail shell or a small coconut as a
cover for the abdomen. But gradually a robber crab’s
armor becomes heavier and the crab ceases to burden
itself with shells. At the same time its abdomen twists
toward a symmetrical position, although on its under-
surface the crab has abdominal appendages devel-
oped on only the left side.

With its great pincers, the robber crab can open a
variety of containers; it has earned its name by feed-
ing from human utensils. It can also hammer and
pick at a coconut husk until it reaches the contents of
the seed within. If necessary, the crab climbs coconut
trees and cuts the nuts from their attachments. Is-
landers who enjoy Birgus as food are said to take
advantage of this habit by winding a thick layer of
cloth around coconut palms well above the ground.
The crabs will pass the cloth in climbing the palm,
but on the downward return to the beach, they re-
spond to the cloth as though it were the ground and
let go of the trunk. Birgus is heavy enough that a
fully-grown one, more than 1 foot in length, is likely
to cripple itself by the fall and be unable to run away
—letting the islanders capture it.

TRUE CRABS

True crabs are the short-tailed decapods, the
Brachyura. Their bodies seem to be entirely cephalo-
thorax because the abdomen is held curled under-
neath, usually fitting between the bases of the legs.
In female crabs the abdomen forms a broad flat
apron, whereas in males it is narrower and com-

paratively inconspicuous. When a female crab is
carrying her eggs attached to abdominal appendages,
she lowers the apron at intervals and uses it as a
scoop to drive water among the developing young.

True crabs tend to run sidewise, “crab-wise,”
rather than forward or back, although they can pro-
gress fairly rapidly in any direction. Often the body
is elongated transversely too. For crabs with this
body form, the name Cancer has come down from
ancient times. This is the type of crab for which the
zodiacal constellation is named, and the sign astrolo-
gers apply to those born in the month following June
22, when the sun enters this portion of the sky.

Cancer crabs (Plate 96) are rock crabs, whose
hindmost pair of legs is fitted for running. In this re-
spect they differ markedly from the commercial blue
crab of America, Callinectes sapidus, whose last pair
of legs end in flat, oval paddles. Callinectes is easy to
recognize because its body extends to each side into
a long, sharp spine. It is sold as the “hard-shell crab”
or held in a pen until it molts and is then put on the
market promptly as the “soft-shell crab.” Actually,
any freshly molted arthropod has a soft shell.

The blue crab is an active swimmer. So is its near
relative the green crab, Carcinides maenas, although
Carcinides’ hindmost legs are merely flattened into
oars without losing their use in running (Plate 95).
Green crabs cause serious losses to shellfishermen by
eating young clams, oysters, and scallops.

Far stranger in appearance is the common spider
crab Libinia, found on muddy bottoms along the
Atlantic coast of America. The spiny sac-shaped
body and long-segmented cylindrical legs suggest
either a spider or, because of the pale ivory color, a
creature composed of bare bones attached to a sort
of skull. The giant of all crustaceans is a Japanese
spider crab, Macrocheira kaempferi, found in deeper
waters well offshore, where it achieves a reach of 11
feet from claw to claw.

On many beaches, particularly in the tropics,
ghost crabs (Ocypoda, Plate 99) make their homes
well away from the water. Ocypoda, the “sharp-
footed one,” has been described as the “rabbit of
the crustaceans,” for it races over the beach away
from enemies. Its compact body may measure 2
inches across and 112 from front to back, and the
legs straddle as much as 8 inches.

When a ghost crab is ready to disappear down its
U-shaped or Y-shaped burrow in the sand, it lowers
its prominent eyestalks from their normal vertical
position into protective grooves along the front edge
of the carapace. In less temperate latitudes, toward
the extremes of their range, ghosts even hibernate in
the dunes back of the beach and show clearly how
independent of water they have become as adults.
Their gills, so necessary at younger stages, have prac-
tically disappeared, leaving empty chambers under

Cave crayfishes are usually white, blind, and depend-
ent upon their especially long antennae. The body is
small and unpigmented, and the pincers as well as the
legs are unusually slender. (Missouri. Ralph Buchs-
baum )

The spiny lobster Palinurus, lacking pincer-tipped
legs, depends on the whip action of its heavy anten-
nae for protection when it ventures from crevices
among rocks. (France. Ralph Buchsbaum)

The mole crab Emerita (Hippa) talpoida, more than
1 inch long, burrows in sandy beaches and sand bot-
toms on both coasts of America. Its feathery antennae
serve to strain food particles from the water. (Dela-
ware Bay. William H. Amos)

the edges of the carapace where the body wall is thin
and blood comes close enough to the surface to be
aerated.

Beaches patrolled by ghost crabs at night are of-
ten the marshaling grounds by day of fiddler crabs
(Uca, Plate 100). Most fiddlers are less than 1 inch
from side to side and considerably shorter from front
to rear. Yet each male carries an absurdly big claw
(the “‘fiddle”’) on one side or the other. The “bow” is
the corresponding pincer-tipped foot on the opposite
side, used in feeding.

Female fiddlers have two “bows” and no “fiddle.”
They eat ambidextrously. Males use the oversize claw
in courtship gestures and in defense. Often, when the
big claw has been clamped firmly on an attacker,
the crab sheds the whole arm and scampers off. At

The house centipede Scutigera forceps frequents damp
places in houses, where it preys on undesirable house-
hold insects. It rarely bites and should be welcomed.
(Vienna. Eric Sochurek )

the next molt the loss is made good. On the damaged
side a new claw of “bow” size appears; and where
the crab had an undamaged “bow” it now has a new
“fiddle.” In this way the fiddler crab changes its
handedness for feeding and courtship. And for this
same reason almost exactly half of the males in any
army of fiddlers is right-handed, the rest left-handed.

MANTIS SHRIMPS

Of all the crustaceans, the most intelligent may
well be the mantis shrimps (order Stomatopoda,
Plate 91). The bodies of these animals range from 2
inches long to somewhat more than | foot in the giant
Squilla mantis. A few kinds are magnificently col-
ored. All of them suggest a lobster that has lost its
prominent antennae, its big claws, and the rear
portion of the carapace. The tail fan is not quite so
well developed. Yet when a mantis shrimp curls
its powerful abdomen under, it darts backward just
about as suddenly as any lobster or crayfish. In some
places, stomatopod tails are sufficiently easy to take
to be used as human food.

Mantis shrimps are predators that creep about or
wait in a burrow mouth or an opening in a big
sponge, watching for a fish to come within reach.
Then the largest and most posterior of the mouth-
parts is suddenly opened like a jackknife, the blade
being the outermost segment. It fits into a groove in
the portion of the appendage against which it is
folded.

In some mantis shrimps the blade is sharp and
smooth. In others it bears strong sharp spines. But
the snatching action with the blade is so fast as to
put to shame the praying mantis, the insect for which
these crustaceans were named. With its weapons a
mantis shrimp can slash a small fish in two or, es-
pecially if the stomatopod is large, inflict a very
severe wound.

The stalked eyes of a mantis shrimp are freely
movable, not only in swinging motions that might
compensate for change in position of a mate or
some potential victim, but also through rotations.
This allows the animal to use different parts of its
compound eyes for examining objects nearby. To
everything in its surroundings a stomatopod is alertly
responsive. Quite quickly it accepts food and forms
associations in an aquarium, achieving these con-
ditioned reactions much more rapidly than the ghost
crabs which seem so eminently trainable on land.

The Centipedes

(Class Chilopoda)

Every child learns to recognize a centipede as a
“hundred-legged worm.” But not many people take

the time to count a centipede’s legs. Most of the
common ones have 15 pairs (Plate 117), and mem-
bers of two different families hatch from the egg with
even fewer, then gain another body segment and an-
other pair of legs at each molt—just in front of the
last segment. The extremely long and slender Ge-
ophilus found in rotting logs may possess 173 pairs of
legs. It hatches with the full quota, as do other mem-
bers of its family.

The fifteen hundred different kinds of centipedes
are all carnivorous. The giant is Scolopendra gigas,
of Boca Grande Island off the coast of Trinidad in
the West Indies, which reaches a length of 12 inches
and a width of 1 inch. It is fond of mice and oc-
casionally catches a lizard, but feeds mostly on the
larger tropical insects on rocky hillsides.

The smaller centipedes of temperate climates move
quickly, their long antennae reaching out ahead in
search of earthworms, insects, and other prey. The
flattened body of the centipede and the fact that its
legs are attached at the sides permit the animal to slip
easily in and out of crevices while hunting. Victims
are killed with venom from glands opening in the
highly modified first pair of legs, which serve as jaws.

Despite the usual aversion shown by man to any
animal that can defend itself with poison, large centi-
pedes are esteemed as human food in some parts of
Polynesia. The islanders hold the centipede by its
two ends and roast it over a small fire, then chew the
toasted middle portions as a delicacy.

A comparatively harmless member of many
households throughout the world is the cosmo-
politan house centipede Scutigera forceps, whose
fifteen pairs of banded legs are so very long and
slender that the creature holds them in a bent po-
sition, suggesting a multilegged spider. The body it-
self may be 2 inches long, light brown with three
dark lengthwise stripes. Although Scutigera rarely
bites a human being, it can do so if roughly handled.
Its venom causes a reaction comparable to a wasp
sting.

A few centipedes can be seen at night by their own
light, but the significance of the light is still unknown.
Geophilus electricus, one of this luminescent kind,
with a very long, threadlike body, is found in many
parts of Europe.

The Millipedes (Cl Diseoes

The common name _ millipede (“thousand-
legged”) is a far less accurate description of these
animals than is the class name, which indicates that
each segment of the creature’s body bears a double
pair of legs (Plate 116). A millipede with fifty seg-
ments to the body, hence two hundred legs, is an

Many of the common cylindrical millipedes curl up
like a watch spring if disturbed. The head is at the
center of the spiral, and the animal lies on its side—
a position in which the armored back protects the
many legs. (Pennsylvania. Lorus and Margery Milne)

especially long one. Most possess between thirty and
forty segments and bear the jointed legs along the
underside of the cylindrical body. When disturbed, a
millipede may curl up on its side like a watch spring,
with the head at the center of the spiral and the legs
protected by the armored body.

No one need fear to handle a millipede and to
watch the waves of movement sweep along its legs.
These animals are mostly harmless scavengers, eating
decaying plant material. They have no venom, al-
though some millipedes include hydrocyanic acid in
their scent glands and might poison a mouse that ate
too many of them. The scent glands appear to pro-
duce an odor unpleasant to some potential enemies.

In wet weather millipedes sometimes attack living
vegetation and damage crops, particularly subter-
ranean roots and tubers. Julus terrestris, a burrowing
kind, is often called a “wireworm” and regarded as a
mild pest. Occasionally it causes serious losses by eat-
ing the sprouts from seed grain as the crop emerges
through the ground. This species shows some par-
ental care for its eggs. The female constructs a dome-
shaped nest from earth mixed with salivary secretion,
and lays her eggs through the hole at the top of the
dome. The nest is then sealed with another bit of the

[241

same cement-like material, and the parent goes off,
perhaps to repeat the process elsewhere. The young
hatch with only three pairs of legs, but at each molt
they add new pairs on new segments, acquiring four
more legs at each molt.

About 6500 different kinds of millipedes are
known. In the tropics, some reach a length of 8
inches and include dead insects and other bits of ani-
mal matter in their diet. In California, the millipede
Luminodesmus sequoiae is luminous; its eggs are not.

The Horseshoe “Crabs”

(Class Merostomata)

When Sir Walter Raleigh led his expedition to the
New World in 1584-1585, he fully expected to
encounter strange kinds of animal life. To help peo-
ple in the Old World become informed about any
unusual creatures, Sir Walter brought with him two
naturalists: Thomas Hariot, who would write accu-
rate accounts of whatever was encountered, and
John White, who would prepare watercolor draw-
ings. The reports of these men, published in Eng-
land in 1588 and 1590, made known for the first
time a very ancient type of life now familiar to many
people as horseshoe “crabs.”

Actually, the modern name is a corruption of a
very good description given in 1870 under the name
of the “horse-foot crab,” for the main part of the
animal’s body does have the form of a horse’s foot—
not a horseshoe. Thomas Hariot used the Indian

The horseshoe “crab” Limulus polyphemus, a living
fossil whose nearest kin today are scorpions and spi-
ders, breeds each spring in shallow waters. Females
deposit eggs in a beach near high-tide mark, and ac-
companying males deposit sperm on the eggs. (Flor-
ida. Allan Cruickshank: National Audubon)

name “seékanauk,” and remarked that “it is about a
foot wide, has a crusty tail, many legs, like a crab,
and its eyes are set in its back. It can be found in salt
water shallows or on the shore.”

John White added, in the caption to his drawing
showing these animals, that as the Indians “have
neither steel nor iron, they fasten the sharp, hollow
tail of a certain fish (something like a sea crab) to
reeds or to the end of a long rod, and with this point
they spear fish, both by day and by night.”

Horseshoe crabs run along the bottom with a
curious bobbing gait, or burrow shallowly in search
of a variety of food: seaweeds, young clams, dead
fish, marine worms. Or they swim inverted, some-
times to the surface of the sea. At the end of a swim-
ming bout, they may sink to the bottom and alight
upon their backs. The stiff, pointed tail is then used
as a lever in righting themselves.

Seen from above, the horseshoe crab’s body is
clearly armored but divided at a transverse hinge
into a larger forward part and a smaller hinder part.
The first bears the two large compound eyes and a
pair of smaller simple eyes, and the second ends in
the highly movable tail. The front portion of the
body is a shield covering the four pairs of walking
legs and two additional pairs of appendages asso-
ciated with the mouth. The mouth itself is an oval,
lengthwise opening between the leg bases. It gives
the class Merostomata its name from the fact that
the mouth extends over several segmental regions of
this portion of the body.

Most members of class Merostomata are known
only from fossils. The class includes both the horse-
shoe crabs (order Xiphosura—‘“sword-tailed”) and
the extinct eurypterids (order Eurypterida) or sea
scorpions. All of these animals seem strange in using
the spiny bases of the walking legs for chewing the
food, as though the animal’s shoulders took the place
of jaws.

Horseshoe crabs represent a style of life that has
existed in similar situations essentially unchanged for
at least 175 million years. All of the near relatives of
these creatures have been extinct for even longer, for
horseshoe crabs are not crabs at all. They are most
similar to modern land scorpions and spiders, and
quite unlike any of the crustaceans.

From below it is easy to distinguish the sexes
among horseshoe crabs. In place of a pincer-tipped
chelicerae on each side in front of the mouth (as in
the female), the male has sturdy leglike appendages
ending in grotesque hooks. With this armament he
can cling to the rear of a female’s shell for days or
weeks at a time and be towed along by her until she
is ready to deposit eggs. In both sexes the next pair
of appendages are the pedipalps, used in feeding.

The hinder portion of the body has a triangular
outline and bears below it a series of overlapping

transverse plates attached at their forward edges.
Each of these plates protects a pair of gill books, of
which the individual “leaves” are the respiratory
organs. When a horseshoe crab swims, it flaps the
plates with the gills and jerks the legs in a rhythm
that propels the body along like an animated wash
basin.

In springtime the horseshoe crabs migrate to shal-
low water, and the males hunt out the larger females.
Sometimes a “cow” crab is seen pulling a chain of
four or five males, each clipped to the rear of the one
ahead. When her eggs are ready, the cow crab drags
her escort on shore at some sandy spot while the tide
is at its peak, and there burrows into the beach to
lay. Weeks later, and long after the parents have sep-
arated and returned to deeper water, the young crabs
emerge from the sand. They have virtually no tail
and bear a superficial resemblance to the extinct tri-
lobites; so the larva has come to be known as the
“trilobite stage” of development. Soon it transforms
into a diminutive horseshoe crab.

At intervals each growing animal gets too cramped
in its shell and sheds it, molting to a larger size. Un-
like other arthropods, however, the line of weakness
which breaks and liberates the horseshoe crab does
not run down the midline of its back. Instead, a
horseshoe crab splits along the forward rim of its car-
apace and creeps out, as though escaping from its
own mouth. The cast shell is left seemingly intact,
and waves often cast it ashore where a beachcomber
can pick it up.

Young and comparatively soft-bodied horseshoe
crabs fall prey to true crabs, fish, and many birds,
including particularly gulls. Those that survive be-
come comparatively immune to attack. Eels often
follow horseshoe crabs into the breeding shallows
and gulp in the eggs as fast as they are extruded.
Coastal Indians used to eat horseshoe crabs, and ac-
cording to Thomas Hariot they were “good food.” In
more recent times, coastal fishermen have built traps
to capture horseshoe crabs for use either as cheap
nourishment for pigs and chickens or to be dried and
ground as fertilizer.

The horseshoe crab encountered by Sir Walter Ra-
leigh’s expedition was Limulus polyphemus. Today
it is known from the Bay of Fundy all along the At-
lantic coast to Key West, and at a scattering of places
in the Gulf of Mexico as far as Yucatan. Formerly it
may have been present in the West Indies, for old
books on the natural history of Jamaica include il-
lustrations of this animal.

Counterparts of Limulus occur in the Orient: Car-
cinoscorpius and Tachypleus along the coasts of
China, Japan, the East Indies, and one species as far
as India in one direction, the Philippines in the other.
Carcinoscorpius readily invades brackish shallows,
and has been found in the Hugli River at Calcutta,

ninety miles from the open sea, in water that is prac-
tically fresh.

The Spiders and
Their Kin

In Greek mythology, Arachne was a Lydian girl
who grew so proud of her ability as a weaver that
she challenged the goddess Athena to a contest. For
this impertinence Athena changed Arachne into a
spider and condemned her to weave forever with silk
from her own body.

Most members of the class Arachnida are indeed
skilled weavers, and the silk they produce is one of
the most marvelously versatile materials in all nature.
But with some 29,000 different kinds of arachnids
known, wide variation is to be expected. This is the
second most varied class of animals, exceeded only
by the insects.

(Class Arachnida)

SPIDERS

Spiders (order Araneae) are constricted conspic-
uously between a cephalothorax and an unsegmented
abdomen. Their webs can be found almost anywhere
on land. Charles Darwin reported them near the
Equator in mid-Atlantic on the remote, isolated,
guano-covered cluster of rocks known as St. Paul’s
Island—halfway between the bulge of Africa and the
bulge of South America. The British expert on spi-
ders, Dr. Thomas H. Savory, recorded jumping spi-
ders trailing silken threads at 22,000 feet above sea
level on Mount Everest, a good 4000 feet above the
highest plant and with no other animal life for com-
pany. He concluded that cannibalism was their only
way of existence, and in this they had to depend upon
a continuous immigration of more spiderlets, riding
the mountain winds on balloons and parachutes of
self-made silk.

Wherever a spider travels, whether by running or
leaping, it ordinarily spins out a fine strand of silk on
which it can go back in an emergency. In addition,
most spiders produce webs of some kind.

Early in the 1800's, the French entomologist P. A.
Latreille classified the webs of spiders into four main
groups: those of circular form suspended in a verti-
cal plane, such as the familiar orb web of the garden
spider; those with supporting strands in all directions,
such as the house spider weaves in window corners,
or with a horizontal sheet of web among bushes or on
the ground, such as the work of the doily spiders;
those of funnel shape, expanding from some crevice
or natural hole in which the spider waits for prey to
pass; and tubular webs spun in a hole dug by the

[243

The giant orb-weaving spider Nephila clavipes stands
guard over her eggs, which are fastened to a leaf.
Until the spiderlets hatch, she lets her 8-foot web go
untended. (Florida Everglades. Lorus and Margery
Milne )

The orange-and-black garden spider Argiope aurantia
weaves a platform with zigzag runways at the center
of her spiral insect trap, and waits there until vibra-
tions tell her that a victim has blundered into the
tanglefoot. (Connecticut. Andreas Feininger )

spider, often closed by a fitted lid, such as the trap-
door spiders produce.

In and near the tropics of both the Old World and
the New, spiders of the genus Nephila weave orb
webs between tall trees. Some of these webs are eight
feet in diameter, and so sturdily constructed that they
sometimes catch small birds and bats as well as quite
large insects. When a victim blunders into the net,
Nephila behaves in much the same way as the smaller
but heavier garden spiders, such as Argiope (Plate
114). The orb-weaver runs to the side of the prey
and expertly rotates the captive in the net while
spraying over it multiple strands of silk that reduce
struggling and prevent escape.

A spider has exquisite control over the spinnerets
from which the silk emerges. Every spider has three
or four different kinds available, each reaching the
outside world through a different shape of tube. One
product is the firm dry cord with which the orb-
weaver constructs the radial strands of her web—
lines that can be walked on without a foot adhering
to the silk. Quite different is the sticky and elastic
thread which is used for the spiral of the orb web—
the tanglefoot to which victims will adhere. Far
finer strands are those by which a spider lets itself
down or which it pays out behind. These fibers are so
uniform in diameter and so unaffected by changes in
temperature and humidity that they have been in
considerable demand as material for the cross hairs
in telescopic sights. Still another kind of silk is the
material in which the eggs are encased. Often it is a
warm brown, or pink, or saffron yellow.

The common house spider, Theridion, hangs her
silken spherical cases full of eggs in the irregular nest
she constructs in some corner. She watches the egg
cases, for if one of them falls, she hurries down and
rescues it. Wolf spiders (Plates 109-112), such as the
common small Lycosa of beach and woodland and
the large Dolomedes of fresh-water margins, usually
affix the ball full of eggs to the spinnerets and drag it
after them wherever they go. Their eyes are useful in
finding insect prey which can be run down or pounced
upon, but a wolf spider seems to recognize her egg
ball only by touch. If she becomes separated from it
she pays no attention unless it chances to come into
contact with her hindmost legs or abdominal tip. Only
then will she fasten it in place and run off with it.

Dolomedes not only runs dry-shod over the sur-
face of ponds after insects but occasionally creeps
down a plant stem or wharf piling into the water and
catches fish. During these underwater expeditions,
the spider’s hairy body seems silvered by an air film
held among the bristles. The European water spider
Argyronecta takes additional advantage of this load
of air. The creature spins a dome-shaped nest in the
water of a pond, anchoring the dome to bottom vege-
tation with strong lines. Then, on trip after trip to the

The mother wolf spider carries a silk-covered mass of eggs with her, held by her spinnerets,
until the young emerge. (Florida. Andreas Feininger )

surface, the spider brings loads of air below the dome,
combs them off as a series of bubbles, and goes above
the water again for a fresh cargo of gas. The air re-
leased under the dome accumulates as one big bub-
ble, and in this anchored diving bell the spider can
live well below the surface of the pond, sallying forth
at intervals to capture aquatic prey.

The largest spiders, such as the bird spider A vic-
ularia of South America and the false tarantula
Eurypelma of the southwestern United States and
Central America, hunt chiefly at night by touch and
perhaps by hearing. They overwhelm their prey by
sheer strength, and often capture earthworms, mice,
and small lizards. Occasionally these spiders are car-
ried to big northern cities in bunches of bananas and
create a panic among fruit-handlers, who fear them
without real cause (Plate 107).

Poison from the cheliceral fangs is the chief
weapon of smaller spiders. The venom is secreted by
large glands opening at the tips of the chelicerae,
making these appendages into efficient hypodermic
needles. The spider seizes a captive in the fang por-
tion of the chelicerae as though in a pair of ice tongs,
and injects a small amount of poison from each side.
The venom acts both as an anesthetic and as a di-
gestive juice of high potency. In a short time it lique-
fies the body contents of an insect. Then the spider
carefully inserts the fangs again and uses them as
drinking straws through which to suck out the liquid.

These differences in habit related to size explain
why large spiders, like large scorpions, make interest-
ing pets and rarely use their venom. Their poison is
actually less virulent and cannot hurt more than a
bee sting. Smaller spiders and scorpions have a more

potent poison, and a medium-sized individual may be
really dangerous. Actually man needs to fear only a
very few kinds.

A spider whose venom has been fatal to fully
grown men on many occasions ts the black widow,
Latrodectus mactans (Plate 113), which occurs
from Canada to Tierra del Fuego. Its abdomen is al-
most spherical, glossy black, and as much as /2 of an
inch in diameter. Below the abdomen is a red spot
that may be hourglass-shaped or rectangular. Prob-
ably most bites from the black widow are suffered by
people who accidentally disturb a mother Latrodec-
tus in a privy or cellar corner where she is defending
her eggs in an irregular nest similar to that of the
house spider. The male Latrodectus is much smaller
than his mate, as is usual among spiders, with a body
less than 14 of an inch long. He is harmless to man.

The diminutive males of Nephila and other orb-
weavers often make little webs of their own at the
periphery of the big web of their mutual mate. At in-
tervals they twitch the strands of the main web as a
courtship gesture. If the relatively huge female is well
fed, it is fairly safe for a male to approach her. Oth-
erwise she is likely to seize him as though he were a
fly, and digest the would-be suitor.

Most spiders have eight simple eyes like bright
jewels around the forward portion of the cephalo-
thorax—the leg-bearing subdivision of the body. The
arrangement of the eyes and their relative size differ
from one genus to another. Jumping spiders, such as
the little pepper-and-salt-colored Salticus, have one
pair of eyes enlarged enormously. With their help the
spider can gauge distance and identify prey, abilities
demonstrated by frequent leaps to a small branch as

[245

Young wolf spiders often ride on their mother’s back for several days after they emerge from
the egg, and then venture off one by one. (Florida. Andreas Feininger )

much as fourteen inches away, or atop a fly that set-
tles within a comparable distance. Jumping spiders
use their eyes also in following a complicated code of
semaphore-like signals through which the males seek
to excite a female into permitting an approach.

Other arachnids probably depend far less upon
vision, although elaborate claims have been made.
For a while it was believed that the white crab spi-
ders found on white daisies in midsummer would
change color to a butter yellow within a few days if
transferred to a yellow flower. But this camouflage
seems fortuitous. Crab spiders are white in midsum-
mer and yellow in autumn, whether on white flowers
or on yellow ones. They change hue gradually, and
happen to match a common sequence in flower col-
ors. That they often match the flower upon which
they crouch while waiting for an insect to visit and be
caught may be helpful in concealing them from spi-
der-eating birds. But insect victims are unlikely to
detect the waiting spider in a flower so long as the
spider remains motionless until its prey is within
snatching distance.

SOLPUGIDS

A constriction between the cephalothorax and the
abdomen is obvious also in the spider-like solpugids
r “false spiders” (order Solpugida) of tropical and
subtropical countries. The solpugid abdomen, how-
ever, is clearly segmented.

Solpugids are harmless, for they lack venom, de-
pending upon crushing insect prey between the for-
midable-appearing fangless chelicerae. For the most
part, solpugids are denizens of arid lands, venturing
out at night. They range in size from barely more
than /% of an inch in length to nearly 3 inches. They
run nimbly and will defend themselves if disturbed.
At such times the solpugid is seen to be using three
pairs of legs in locomotion and holding free of the
ground the front pair, as well as the cere but pin-
cer-tipped pedipalps.

SCORPIONS

A true scorpion (order Scorpionida) is obviously
segmented, the head bearing chelicerae suggesting
lobster claws, the thorax of four segments each with a
pair of walking legs on the undersurface, and the
segmented abdomen broad in front but tapering to a
more cylindrical portion that ends in a curved, poison-
injecting sting. Scorpions are largely nocturnal, hiding
under rubbish during the day or remaining in little
holes dug with the pincer-tipped chelicerae.

In ancient times, a scorpion was feared almost as
much as a lion. Both are among the animals repre-
sented in the zodiac—constellations of stars in the
band of sky through which the sun, moon, and plan-
ets seem to move. Scorpio, one genus of scorpions, is
thus the astrologic birth sign for people born in the

Some larger, thinner huntsman spiders are welcomed
in tropical and subtropical homes as the answer to
flies, roaches, and other household insects. This one,
Heteropoda venatoria, on the wallpaper of a Florida
home, has a 3-inch span. (Lorus and Margery Milne)

A wolf spider, its feet clothed in water-repellent hairs,
can run dryshod over the surface of ponds and streams.
(Herman Eisenbeiss )

A safety line is spun by the jumping spider Phidippus
audax even during a leap to a finger tip. (Colorado.
Walker Van Riper)

month following October 24, when the sun is between
the earth and that constellation.

Scorpions feed principally upon insects and spi-
ders, grasping them in the chelicerae and tearing
them to pieces or crushing them for their juices. Only
if a victim offers real resistance, or if the scorpion is
threatened by some enemy, is the sting brought into
use. Then the abdomen is arched forward over the
body (Plate 106) and the poison-bearing tip thrust
in vigorously.

Medium-sized scorpions, such as the 2- to 3-inch
Centruroides sculpturatus and C. gertschi of the
American Southwest, have enough poison to be dan-
gerous, and it may be virulent enough to cause occa-

The male jumping spider (Phidippus audax) uses
similar postures in courtship display and when threat-
ening a rival. This one is stimulated by his own image
in the mirror. (Colorado. Walker Van Riper)

sional human deaths. In Egypt and other tropical and
subtropical countries, scorpion-stung people are fre-
quent enough so that an antitoxin has become a med-
ical necessity.

Truly large scorpions, such as the 10-inch kinds in
equatorial Africa and tropical America, are compar-
atively inoffensive. Only toward other scorpions are
they hostile, and this habit is so characteristic of
scorpions of all kinds that they lead solitary lives.
Even well-fed females usually resort to cannibalism,
devouring the mate who has just fathered the next
generation of young.

Scorpions bring forth their young as diminutive in-
dividuals, active and ready to fend for themselves.
Yet the offspring often cling to the mother’s back for
many days after birth, riding with her wherever she
goes. From careful inspection of a mother scorpion
with her brood, it is easy to see that many sizes of
young are present. Ordinarily they are born one or
two at a time over a period of many weeks, rather
than the whole litter within a day or so. In some scor-
pions, a placenta-like tissue is formed within the par-
ent, permitting readier transfer of food and wastes
between the mother and her unborn young.

WHIPSCORPIONS

Arachnids include a variety of creatures suggesting
scorpions but entirely harmless to any animal larger
than an insect. The tailed whipscorpion Mastigoproc-
tus (Plate 105) is a formidable-appearing denizen
of dark corners in tropical and subtropical lands. Its
abdomen suggests the broader basal part of the cor-
responding region of a true scorpion, but ends in a
long, flexible extension, the tail, with no venom.

Tailless whipscorpions are equally retiring mem-
bers of the order Pedipalpi. In all whipscorpions the
pedipalpi are powerful and are used in grasping and
crushing spiders and insects as food. The first pair of
legs usually suggest whips—long, slender append-
ages ending in a flexible lash, used in the dark as the
animal feels its way about. In a large whipscorpion,
these legs may stretch 6 inches from side to side.

PSEUDOSCORPIONS

Diminutive pseudoscorpions (order Pseudoscor-
pionida) are encountered prowling for still smaller
insects among the stones along a sea beach. The larg-
est of them reach a length of about % of an inch, but
most are less than half this size. One of them invades
libraries, where it is known as the book scorpion,
Chelifer cancroides. Its flattened body, somewhat
suggesting that of a bedbug, is admirably fitted to
gliding between the pages. The creature runs about
on its four pairs of legs while holding up and forward
a greatly enlarged pair of pedipalps ending in pincers.
These are used in seizing tiny insects, such as the
young of silverfish and book lice (psocids), found

If the hinged door of a trapdoor spider's burrow is
raised carefully, the spider may remain with her feet
clinging to the silken covering of the door; otherwise
she drops quickly down into her vertical burrow.

among old papers. The abdomen of a pseudoscorpion
is broader than its cephalothorax, and it is clearly
segmented.

Pseudoscorpions are amazingly systematic about
building nests, using these as places in which to molt,
hibernate, and raise young. The chelicerae secrete
silk needed to cement together sand grains and bits of
vegetable matter into stationary or movable pouches.
A bag of this sort carried about affixed to the moth-
er’s body forms a brood pouch into which the eggs
are laid. They hatch there and the young remain in
the pouch, getting nourishment from glands upon the
mother’s body, exposed to them through the opening
at the top of the pouch.

HARVESTMEN

An arachnid familiar to most people is the daddy
longlegs (see illustration on page 252) or harvest-
man spider (order Phalangida). Its body is small
and very compact, its bristle-slender legs tremen-
dously long. No one need fear to handle a harvest-
man, but a naturalist should be very gentle to save
the animal from losing a fragile leg or two. Only at
the next molt can it make good such a loss.

The trapdoor fits the doorway perfectly, but the spider
usually builds its hideout where runoff rain water will
not flood over the doorway and soften it. (Florida.
Photographs by Andreas Feininger )

If left to their own devices, harvestmen use the
second and longest pair of legs to explore the sur-
rounding territory before moving on. Apparently vi-
sion with the two eyes in a little tubercle on the back
is inadequate, and touch takes its place. Often a har-
vestman can be found standing quietly, waving these
sensitive legs in the air. Probably this habit has led
to the old bit of folklore which claims that a dairy
farmer can tell where to find his cows by watching
the direction in which a harvestman points.

Phalangids have no venom and no silk glands.
They depend for food on mites, small spiders, tiny in-
sects, and other harvestmen. They deposit their eggs
in crevices or under stones, and ordinarily remain
solitary throughout the active months. During winter,
however, harvestmen often congregate by the dozens
or the hundreds. In the spring they can be found still
standing with their slender legs interlaced, even sway-
ing in unison as though dancing to music undiscerned
by human ears.

TICKS AND MITES

In man’s economy, few arachnids rank higher in
importance than the mites and ticks. These members

[249

The crab spider Misumena spins a safety line as she lets herself down (left). At any time she
can climb back up again (right). (Colorado. Walker Van Riper)

of the order Acarina have the whole body fused into
a single piece, and are peculiar too in going through
a very different, six-legged larval stage followed by
transformation into the eight-legged adult.

Ticks are mostly larger than mites, and live as par-
asites on land-dwelling vertebrate animals. Mites in-
clude many that are helpful to man through their
predatory habits, eating the eggs of plant lice
(aphids), attacking insects and nematode worms in
the soil, prowling over the surface of plants and of
the ground, and hunting even in shallow ponds. Most
mites are external parasites, particularly in larval
stages. Water striders and damsel flies are often
found carrying on their bodies little red lumps that
are the blood-sucking immature individuals of the
big predatory red mites found swimming in ponds or
along the shore (Plate 115).

When a parasitic mite or tick feeds, it thrusts its
whole head into the skin of the victim. There the
parasite is held in place through use of a dartlike an-
chor located just below its mouth. In ticks the outer
surface of the anchor bears recurved teeth, and these
hold so firmly that a pull on the body of a tick is
likely to break off its head in the wound rather than
remove it. In mites the anchor is smooth on the out-
side, allowing the parasite to be brushed off quite
easily.

The mite affecting most people directly is the chig-
ger, usually a member of the genus Trombicula. In
the Old World these unpleasant creatures are called
harvest mites. They lie in wait upon vegetation un-
til a vertebrate animal brushes against the plant.
Then anywhere from one to a hundred may be
“painted on,” and promptly begin spreading over the
skin. At a chosen site, each mite bites and discharges
into the wound a drop of digestive agent which opens
a tubular path far enough into the skin to enable nu-
tritious lymph to well up and provide the mite with a
meal. Soon the chigger drops off of its own accord,
seldom remaining on the skin for more than from
one to seven days. On the ground it completes its de-
velopment and, if a female, eventually mates and lays
a batch of eggs from which a new generation of young
ascend a grass stalk and wait for a host to pass.

The action of a chigger is intensely irritating, lead-
ing the host (whether man or rat or quail or snake)
to scratch vigorously, often breaking the skin and ad-
mitting serious infections. The extent of distraction
from mite bites can be evaluated on domestic fowl
in a hen house infested with the chicken mite Der-
manyssus gallinae. The hens spend so much time
scratching that they feed less frequently, become
malnourished, and cease to lay reliably.

Mite pests seem to be found on every hand. The
“seven-year-itch” is caused by the itch mite Sarcop-
tes scabiei of man and hogs. This creature burrows
under the skin and reproduces there. Related mites,

A mother scorpion Tityus serrulatus, with newborn
young clinging to her back, stands safely under the
arch of her sting-tipped abdomen. (Switzerland. Oth-
mar Danesch)

The whip scorpion Stegophrynus has a body about
142 inches long. It is harmless to any creature too
large to be crushed between the first pair of append-
ages. (Singapore. M. W. F. Tweedie)

living in the hair follicles, cause mange in many
kinds of mammals.

Beekeepers are familiar with Isle of Wight dis-
ease, a fatal epidemic in hives of cultivated bees that
become infected with a mite that invades their
tracheae and suffocates the insects.

The pest known as “red spider” in gardens and
orchards is actually a vegetarian mite. Severe infes-
tations can be recognized from the loose webs cover-
ing leaves upon which the female mites have laid
their eggs. Other mites attacking plants cause cancer-
like growths of characteristic forms, each known as a
plant gall.

Ticks have an equally bad reputation for transfer-
ring diseases from one animal to another. Texas cat-
tle fever is an infection of the sporozoan (a proto-
zoan) Babesia bigemina, transmitted by the tick
Margaropus annulatus. The larvae, called “seed
ticks,” are about 14. of an inch in length. After gorg-
ing themselves on blood, they drop off the steer and
transform into slightly larger, eight-legged nymphs.
Soon they again climb a grass blade and catch a pass-
ing animal. After gorging again, the nymphal tick
drops off and matures to the adult, either a 14 y-inch
male with an oval brown body, or a 14-inch female

Harvestmen are seen most often at harvest time. Their widespread legs well earn them the
name “daddy-long-legs.” (Colorado. Walker Van Riper)

of rectangular outline, whose color may be yellowish
to slate gray. These adults again seek a steer and
mate upon its back after another blood meal. The fe-
male then drops off and layers her five thousand eggs
on the ground, where they hatch, starting another
generation of seed ticks on its way.

Rocky Mountain spotted fever is a rickettsia dis-
ease transmitted by the widespread tick Dermacen-
tor, a parasite found commonly on dogs. It attacks
coyotes and many other wild animals in the western
United States. Some of these are reservoirs of infec-
tion for spotted fever. If an infected tick bites a hu-
man being, the person is almost certain to contract
the disease. If proper medical care is not given, the
outcome can be serious or even fatal.

The Sea Spiders

(Class Pycnogonida)

A skin diver who sits quietly watching a clump of
kelp, a sea fan, or a coral head may well discover a
spider-like creature moving with the utmost deliber-
ation among these. Sea spiders mostly possess four
pairs of very long legs, each pair arising from a sepa-

A wood tick, shown here with its beak inserted into
human skin, can transmit serious diseases. This one
became attached in a Panama rain forest. Related
kinds are common in temperate woods. (Panama.
Ralph Buchsbaum )

rate segment of the body. But the skin diver will
scarcely be able to detect the animal’s unsegmented
abdomen, and may wonder whether it has been lost.
Actually it is extremely minute, so small that it can
provide space for almost no part of the digestive tract.
As though in compensation, the legs are somewhat
broader toward the base and accommodate lobes of
the alimentary canal.

If the sea spider is a female, she will have a slen-
der head ending in a minute sucking mouth—al-
most a beak. If a male, he will possess additional ap-
pendages on the head, including a pair of small
jointed legs held downward and backward. These
little legs are the “ovigerous” pair, used by the male
to carry ball-shaped masses of eggs laid by his mate.

At the junction of the head and the first segment
of the body bearing walking legs, a sea spider has a
small eminence with two to four simple eyes—a
turret of visual organs that may keep the animal in-
formed of movements of fish and seals in the sur-
rounding water. To none of these does the pycno-
gonid react in an obvious way. It merely clings, sway-

The eight legs of a sea spider (pyenogonid) seem
joined to one another rather than to a body, for the
latter is so very small. The legs accommodate lobes
from the digestive tract, perhaps because there is no
room for them in the body. (France. Ralph Buchs-
baum )

ing gently with water movements, or progresses at a
sloth’s pace from one point to another.

In coastal waters, sea spiders are mostly small,
seldom spanning more than | inch in diameter. The
abysses are home to far larger kinds, including the
giant Colossendeis, whose legs span as much as 24
inches. Pycnogonids have been collected from as
deep as twelve thousand feet below the surface, and
the five hundred different kinds known include rep-
resentatives from all of the world’s oceans. They
seem particularly common in the frigid waters of the
Arctic and Antarctic.

Sea spiders seem to subsist as adults on micro-
scopic algae, but a number of kinds go through juve-
nile stages parasitic upon or within coral animals,
jellyfishes, nudibranch mollusks, clams, and sea cu-
cumbers. The young hatch from the egg equipped
with only three pairs of legs. Additional body seg-
ments and leg pairs are acquired at metamorphosis.
Some pycnogonids do not stop when four pairs have
been acquired but continue with the same body plan
until they have five or even six pairs of legs.

CHAPTER XIX

The Echinoderms

(Phylum Echinodermata)

O NE of the delights in visiting the seashore is to
find sea stars (starfishes) and sea urchins, brittle
stars, and sand dollars. Or perhaps a sea cucumber.
Their symmetries, their strange movements, are fas-
cinatingly different from those of any creature found
on land. Even after a naturalist has enjoyed years of
acquaintance with echinoderms, they remain a great
enigma. Almost none of their actions resembles the
activities of other kinds of animals. Yet in their em-
bryonic development and some features of the adult
animal, they show remarkable similarities to chor-
dates such as ourselves.

The name echinoderm comes from the Greek
echinos, a hedgehog, and derma, the skin. The word
is most suited to sea urchins, whose bodies are armed
with movable spines.

A sea urchin or sand dollar differs from a sea star
or brittle star in that its skeleton is composed of inter-
locking plates that cannot be moved. The stars, by
contrast, can be real contortionists if given time to
change position. When first picked up a star may
seem stiff. But its skeleton, just inside the skin, con-
sists of separate pieces, each hinged movably to
neighboring ones. Muscles keep the star from feeling
flexible in human hands. Sea cucumbers may have
granules of lime embedded in the skin, but the body
wall is comparatively soft.

A century and a half ago, the great French zoolo-
gist Baron Georges Cuvier grouped the echinoderms

254]

(Left) sea star, serpent star and sea cucumber;
(right) sea lilies and (below) sea urchin

with the jellyfishes as “radiate” animals. But when the
development of echinoderm eggs is followed, each
embryo is found to develop into a bilaterally sym-
metrical larva. Later it takes on a modified radial
symmetry with five similar sectors. Since the animal
develops no head end, it comes to show distinctly only
an oral surface bearing the mouth and an aboral
surface opposite this.

Sea cucumbers are unique among echinoderms in
giving up the radial pattern after acquiring it. They
lie over on one side, and thereby gain anew a distinc-
tion between right and left, between upper and lower
surfaces.

Sea lilies are found almost exclusively at depths
that neither a beachcomber nor a skin diver can ex-
plore. They live permanently attached by long, slen-
der stalks to the bottom, and are so fragile that their
remains are unrecognizable when washed ashore.
Their more modern relatives, the feather stars, in-
habit also waters nearer land. They begin a sedentary
life, but become detached and can swim gently by
convulsive flapping of the arms.

In all of these animals the body cavity is sub-
divided, one portion forming a water-vascular system
peculiar to echinoderms. This system consists of a
ring-shaped tube encircling the gullet, and five radial
tubes (“canals”) extending into the five sectors of
the body. This hydraulic system receives its fluid
either from the body cavity (in sea lilies, feather

stars, and sea cucumbers) or the outside world of
sea water. In the latter case it enters through a pore
connected to the ring canal by a slender tube (the
“stone canal”) whose walls are stiffened by deposits
of lime.

In sea cucumbers, sea urchins, and sea stars the
water-vascular system serves in locomotion. Its radial
canals communicate with an extensive series of short,
paired tubes, each with a muscular bulb and an elon-
gated, hollow tube-foot that projects from the body
surface. A tube-foot combines muscular and hydrau-
lic mechanisms. It is extended by contraction of the
bulb, forcing liquid into the cavity of the tube-foot;
muscles in the walls of the tube-foot control the di-
rection of extension.

The tip of a tube-foot is a small, glandular suction
disk by means of which the echinoderm can attach
the sticky tube-foot to solid objects. Contraction of
longitudinal muscles of the tube-foot shortens it and
forces water back into the bulb, pulling the echino-
derm along or shifting the movable object to which
it holds. Teams of tube-feet also cooperate in carry-
ing the body, in policing its surface, or in supporting
bits of seaweed, rock, or coral as a shade against
strong sun in shallow water.

Echinoderms maintain an important fluid in the
body cavity, taking the place of blood. It is shifted
from place to place by patches of cilia. In this fluid,
ameba-like cells move around freely, serving much
as white blood cells do in vertebrate animals. Some sea
cucumbers have red blood cells too, but with a hemo-
globin differing chemically from that of vertebrates.

In their response to the environment, echinoderms
manage with a minimum of complexity in the nervous
system. It consists primarily of a ring around the
gullet, parallel to the ring canal of the water-vascular
system. From the nerve ring extend radial nerves
that branch profusely. In most echinoderms they end
blindly, yet appear able not only to coordinate the
movements of the animal but also to report on chemi-
cal substances in the surrounding sea, on conditions
of light and shade, on vibrations of many kinds. Free
nerve endings thus take the place of specialized sense
organs.

Echinoderms generally are very casual about re-
production. In most instances, parents never meet.
They merely cast their eggs and sperms into the sea,
each to find the other by sorting themselves out in
the surface water from among a thin soup of repro-
ductive products of many species. Retention of the
eggs and some degree of maternal care are found in
each class, however; often they are correlated with
life in polar waters.

Members of this phylum use many of the same
basic body features found in the vertebrates, but
emphasize each in a very different way. As in the
chordates and no other phylum of animals, they de-

velop an internal skeleton. But instead of coordinating
that skeleton with muscles as a device important in
locomotion, they hide inside it as a shelter. Radial
symmetry seems to imply a readiness to withdraw,
moving away from molestation in any direction. Yet
with this different approach to life, often paralleling
ways found among coelenterates, the echinoderms oc-
cupy every habitat available in the seas, from oozy
muds at the greatest depths to the sandy beach and
the most wave-pounded rocky coasts.

The Crinoids

These delicate and often colorful creatures are
unique among echinoderms in that they live with the
oral surface uppermost. For food they depend upon
capturing small animals and plants drifting past them
in the sea, reaching out for this nourishment with
arms that may be more conspicuous than the body
to which they are attached. Usually each arm is
fringed along both sides with a row of short, tapering
branches, and suggests the fronds of a fern or the
petals of a lily.

Most crinoids have five arms, each forked near the
base—producing ten flexible appendages. In many
species the arms continue to branch and rebranch
with increasing size of the animal. Sea lilies rarely
have more than 40 arms; some possess only 5. Feather
stars may produce up to 200 arms. Most of the many-
armed forms are from tropical and subtropical seas.
Cold-water or deep-sea forms usually bear 10 arms.

Modern crinoids gather food by means of a method
believed to have been used by all primitive echino-
derms. Along a ciliated groove in the upper, oral
surface of each arm and its side branches, delicate
finger-like tube-feet respond to the arrival of each
food particle by bending quickly inward. This action
throws the food into the mucus-filled groove, where
it becomes entangled and is swept to the mouth.

Sea lilies remain for long periods, and possibly for
life, anchored to the bottom, mostly in water from
600 to 15,000 feet deep. Feather stars seldom venture
below 4500 feet. Sometimes they swim languidly to
the surface, or can be found near shore in shallow
water. Feather stars living where sunlight reaches
them often have beautiful colors, perhaps exceeded
by no other marine animals. Some are bright red,
others purple, green, orange, golden, white, black, or
even variegated.

All living crinoids belong to the same order. All go
through a swimming embryonic stage that is slightly
gourd-shaped, encircled by several rings of cilia, and
bearing a little tuft of sensory hairs at one end. As
skeletal plates begin to form, the embryo comes to
rest on the bottom, becoming attached there.

(Class Crinoidea)

[255

SEA LILIES

Until 1873, sea lilies were believed to be extinct,
represented only by fossils in ancient rocks. Then,
at the dawn of oceanography, scientists aboard the
famous British research ship H.M.S. Challenger be-
gan peering at animals from the sea bottom, brought
to light in special sampling dredges. Among the col-
lections, they found sea lilies still alive. About eighty
species are now known to live in the oceans, each
animal with an upright, flower-like body supported
from the bottom mud by a slender stalk. For them the
name of the class Crinoidea is particularly appropri-
ate. It comes from the Greek krinos, a lily, and the
ending -oid, similar to.

A dredge dragging along the sea bottom on the
end of a mile of steel cable is not particularly gentle.
It gathers indiscriminately, often breaking off forms
of life attached in the ooze. In consequence, no one
was certain for many years just how modern sea lilies
were anchored. Then, as oceanic telephone cables
were raised for repairs, a few stalked crinoids were
found attached to them. In most cases they ended in
a set of remarkably rootlike extensions, wrapped
around the covering of the communication wires.
Other sea lilies have a stalk tapering to a curled end,
capable of wrapping around solid objects. Or they
wear a set of grappling hooks, or a bulblike swelling,
or a flat circular disk. All of these are able to resist
most pulls that would tend to dislodge the animal
from the bottom sediments.

The stalk itself is supported by a long series of
skeletal pieces, giving it a jointed appearance. In
living crinoids the stalk may be as much as 20 inches
long. In members of one suborder it is ornamented
at intervals by short tendril-like extensions (cirri).
Apparently these sea lilies sometimes break away
from the bottom and thereafter move from place to
place, propelling themselves by awkward movements
of the branching arms or holding temporarily to firm
objects with the cirri. Members of another suborder
have no cirri or only rudimentary ones, or cirri only
at the attached end of the stem.

Often the skeletal pieces of the stalk have made
highly resistant fossils. The flower-like crown, which
is the main body of the animal, is less sturdy. Yet
intact fossils have been found with stalks over 70
feet long and as many as 200 branches of the five
arms. Altogether more than 5000 kinds of extinct sea
lilies have been discovered, some of them dating back
nearly 700 million years. Probably modern seas are
less hospitable to sea lilies and they can be regarded
as “living fossils,” and perhaps as candidates for ex-
tinction.

Recent work by oceanographers in arctic waters
has led to the discovery of a few kinds of stalked
crinoids in large numbers at a depth of barely fifty
feet. Apparently they take advantage there of the

256]

wealth of microscopic food that thrives, in turn, be-
cause upwelling currents bring dissolved nutriment
from the bottom.

FEATHER STARS

Feather stars (Plate 135) are the best-known of
crinoids, with about 550 different species. They begin
life much as do the sea lilies. But after establishing
themselves on the bottom with a slender stem, they
break away from its upper end and thereafter lead a
free existence. Around the area where the stem was
attached, each feather star wears a cluster of cirri
and uses these for holding to submerged objects. It
then spreads its arms gracefully to the sides, usually
curling their tips upward, and waits while small parti-
cles of food drift within range of its cilia-driven feed-
ing currents.

Along the Atlantic coast from the Arctic to Long
Island, New York, a grayish feather star with brown
bands is found at depths from 90 to nearly 6000
feet. It is one of the many species of Antedon found
on both sides of the Atlantic, and uses its ten long
arms in the characteristic swimming movements.
With mouth upward, the arms spread as much as 8
inches across. Five of them move down with delicate
side branches (pinnules) spread while the alternating
five arms rise with pinnules drawn together. If the
animal becomes inverted by swimming into a current,
it may settle to the bottom and there right itself. The
arms on one side are used as levers to raise the body
from the surface while the opposite arms reach around
and catch hold.

On the eastern side of the Atlantic, another Ante-
don clings to seaweeds in comparatively shallow
water, and British trappers of seafoods find it tem-
porarily attaching itself to the wicker traps set for
crabs and lobsters. In Jamaica and Barbados, British
West Indies, a Tropiometra with brownish golden
arms clips its cirri to coral rock in water as little as
six feet below low tide. These tropical animals are
more suitable for a skin diver to examine, for they
do not break to pieces (as Antedon does) when
touched. If freed from the bottom by chiseling loose
the piece of coral, they will let go of their own accord
and seize the diver’s fingers tenaciously in their cirri
as the next best support.

Feather stars are most abundant in the waters of
the Sulu, Celebes, and Banda Seas, in a triangle
pointed at New Guinea, Borneo, and the north island
of the Philippines. They are fewest in the Atlantic
and eastern Pacific, and clearly favor rocky bottoms
or coral reefs in preference to sand or mud. The
smallest adult feather stars, 1 inch across, live in
the West Indies and in abysses of the Pacific Ocean.
The largest is Heliometra glacialis, reaching 3 feet
in diameter in ice-cold water at the west side of the
Okhotsk Sea north of Japan.

[continued on page 273 ]

116. This giant millipede from Tanganyika,
about 8 inches long, is still not fully grown.
Such millipedes attain a length of 11 inches
and are often seen parading after a rain in
equatorial Africa. They are harmless scay-
engers, living on decaying vegetation. (Lon-
don Zoo. Ralph Buchsbaum)

117. A large centipede, Scolopendra heros, usually 4 or more inches long. Found in
Mexico and in the southern United States. (Arizona. Eliot Porter)

118-121. A starfish, Pisaster ochraceous, turned
on its back, rights itself by twisting its arms and
pulling with hundreds of vacuum-cupped feet.
This is the common starfish of surf-beaten rocks
on the American Pacific coast. Specimens range
from 6 to 14 inches across and occur in several
color phases. (Oregon. Ralph Buchsbaum )

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122. Despite its name, Pisaster giganteus capitatus is usually smaller than its relative
in Plates 118 to 121. This variety of a more delicate and more colorful species of
Pisaster, with relatively few but large spines, is found from Southern to Lower Cali-
fornia. (Cy La Tour)

124. The common European
starfish, Asterias rubens, feeds
mainly on bivalves, and is abun-
dant on beds of mussels. Two
American relatives, the more
northerly Asterias vulgaris and
the more southerly Asterias for-
besi, do great damage to east-
coast oyster beds. Roscoff,
France. Ralph Buchsbaum)

123. The long-armed starfish of
European waters, Luidia ciliaris,
has close relatives on the Amer-
ican side of the Atlantic. Like
most specimens from well-fished
waters, it shows evidence of
having regenerated parts of sey-
eral arms, probably after muti-
lation by fishermen’s trawls. It
feeds on starfishes, sea urchins,
and sea cucumbers. (Roscoff,
France. Ralph Buchsbaum)

125. The blood-red starfish, Henricia sanguinolenta, is found near shore but
ranges down to more than three thousand feet in the North Atlantic. A similai

species lives on the American Pacific coast. (Roscoff, France. R Uph Buchsbaum

126. The sea bat. Patiria miniata, about 5 inches across, and red, yellow, or purple in
color, occurs on protected rocks and on sandy bottoms from Alaska to Lower California.
The short spines are arranged in small concentric clusters. (S. H. Rosenthal, Jr.: Rapho
Guillumette )

127. The many-rayed sunflower star, Pycnopodia helianthoides, with up to twenty-
four arms, ranges from Alaska to southern California. Perhaps the largest of star-
fishes, it often measures 2 feet across. It becomes limp when exposed, and even if
handled gingerly may shed an arm or two. (Washington. Ralph Buchsbaum )

128. The spiny sun star, Crossaster
papposus, with up to fifteen arms,
feeds on other starfishes. It is found
around the world in northern waters
and as far southward as the English
Channel, New Jersey, and Vancouver.
(Roscoff, France. Ralph Buchsbaum)

129. The cobalt-blue starfish, Linckia, up to 12 inches across, is the most common and
conspicuous starfish on the Great Barrier Reef flats. Unlike other starfishes, Linckia
lies exposed in bright daylight. Members of this genus are the only starfishes that
can, and often do, regenerate a whole starfish from a piece of one arm. (Allen Keast)

130. A little starfish, Ceramaster placenta, brought up from a depth of 480 feet near
the Bay of Biscay, and photographed in a tank at the Plymouth Aquarium, where
it lived for at least a year. (D. P. Wilson)

———__

131. The common European
brittle star, Ophiothrix fragilis,
shown at about the size of the
largest specimens, are more of-
ten half this size. Especially
fragile, when handled they may
throw off all the arms in pieces.
Underwater cameras reveal that
in favorable spots the floor of
the English Channel is carpeted
with dense masses of this spe-

cies. (D. P. Wilson)

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132. Underside of the central disk
of Ophiocoma, revealing the star-
shaped mouth of this beautifully
patterned brittle star of the South
Pacific. (Great Barrier Reef. Je-
rome and Dorothy Schweitzer )

133. Brittle stars near shores are
usually insinuated under stones or
in the holdfasts of seaweeds.

These two (same species as in

Plate 131) were clinging to a
dead sea fan (Plate 12) in a tank
at the Station Biologique, Roscoff,
France. (Ralph Buchsbaum )

134. A common basket star of the American Pacific coast is shown here in a tank at the
laboratory of the University of Oregon. Seen from the underside, the animal displays the
star-shaped mouth and five arms. Each arm branches repeatedly, and the tiny end

branches curl and uncurl ceaselessly. (Ralph Buchsbaum)

135. A feather star, or stalkless crinoid, has
branched arms with short side branches
that make the arms look feathery. The ani-
mal lies with mouth and arms turned up-
ward. (New Caledonia. René Catala)

136. The European edible sea urchin, Echi-
nus esculentus, up to 6 inches across, with a
red shell and movable white spines, is found
from Norway to Portugal, usually below low-
tide mark. Only the ripe ovaries are eaten,
either raw, like caviar, or cooked. (Plymouth,
England. D. P. Wilson) ;

137. The giant red urchin, Strongylocentrotus
franciscanus, which may also be purple, is
more than 7 inches across. From Alaska to
Mexico it frequents the deeper tide pools and
rocky channels. (Ralph Buchsbaum)

138. The purple sea urchin, Strongylocen-
trotus purpuratus, has almost the same
range as its larger relative in Plate 137, but
is seldom more than 3 inches across and oc-
curs in great beds, especially in surf-swept

areas. In soft rock each urchin sits in its own
pothole. (California. Woody Williams)

139. A close-up of the mouth of a sea urchin
reveals the five white teeth that grind the
seaweeds and animals on which it feeds.
(West Indies. Fritz Goro: Life Magazine)

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140. A reddish sea cucumber, Cucumaria miniata. It lives under rocks in
temperate or cold waters around the world. In the quiet of an aquarium it
spreads the branched tentacles that surround the mouth and shows three of
the five rows of tube-feet by which it clings. Behind it is a white sea cucum-
ber, Eupentacta quinquesemita, with two double rows of longer tube-feet.
(University of Oregon Marine Laboratory. Ralph Buchsbaum)

doles i.

141. A sea cucumber found around the world in tropical waters is Holothuria
impatiens, here shown ejecting long, bluish white, opalescent, and very sticky
threads. Shot out from the rear of the aroused animal, these threads can con-
fuse or immobilize an enemy. (Great Barrier Reef. Allen Keast)

———

142. Patches of the colonial
golden-stars sea squirt, Botryl-
lus schlosseri, encrust rocks,
wharf pilings, boat bottoms,
and seaweeds on protected At
lantic shores. The yellow-ac-
cented individuals have sepa-
rate mouths but are arranged
in starlike or oval clusters that
share a vent. (Brittany, France.
Ralph Buchsbaum)

Sa Ri

143. The sea peach, Tethyum pyriforme,
is a sea squirt whose size, shape, and color
suggest a peach. The feeding and respira-
tory current goes in one opening and out
the other. (Passamaquoddy Bay, Canada.

N. J. Berrill)

144. Clusters of stalked tunicates are common on stones and wharf pilings on many
shores. In Clavellina lepadiformis, 1 to 2 inches high, the individuals are separate but
rise from a common base. The two body openings are close together. (Plymouth, Eng-

land. D. P. Wilson)

[continued from page 256 }

Sea Cucumbers
(Class Holothuroidea)

A person need wade out only knee-deep around
many of the Florida keys to encounter, lying con-
spicuously exposed on the muddy bottom, large sau-
sage-shaped creatures | foot or more in length and
better than 2 inches in diameter. Against the pale
gray surface on which they lie, the contrast may be
striking: dark brown with light spots, or brick red
with raised lumps of black or dark brown. They are
sea cucumbers (Plates 140, 141), with a name given
them (Cucumis marinus) in the first century A.D. by
Pliny, the Roman elder and encyclopedist.

Upon closer examination, none of the usual clues
is evident to show which is the head end of the ani-
mal. As it lies there quietly, both ends of the cucum-
ber appear to be doing something. At one end, an
opening appears, sometimes as much as | inch in
diameter. If the water is shallow, a current may be
noted pouring out of the opening. Or the sea cucum-
ber may be taking in water just as rapidly. The move-
ments of the opening and the slow enlargements and
contractions of the whole body suggest a sort of
underwater whistling. Actually, they are breathing
movements and, in this unusual animal, occur at its
rear end.

As though further to astonish the beachcomber on
tropical and subtropical shores, a sea cucumber may
be found from which a fish’s head projects. The fish
is very much alive, and the cucumber’s breathing
movements simply take in water or expel it around
the fish. If nudged, the fish may swim out, exposing
a slender tapering body as much as six inches long.

Usually a minor drama follows at once. The
blenny-like fish turns back immediately to the side
of the sea cucumber and moves about along the sur-
face, evidently searching for the respiratory opening
again. Often the sea cucumber closes the aperture
tightly, as though to keep the fish from returning to
its refuge. But eventually the need for oxygen be-
comes too great. The cucumber opens again, the fish
slips in either tail first or head first (and turns around
immediately ).

The cavity into which the fish goes is the cloaca of
the sea cucumber, a chamber serving not only respira-
tion but also as a common exit for wastes from the
digestive tract and sex cells from the reproductive
system. Sea cucumbers are unique in having a pair
of generously branched “respiratory trees” extending
blindly from the cloaca far forward in the body cavity.
Through their walls oxygen and water pass, keeping
the other internal organs aerated and maintaining the
plumpness of the cucumber’s body.

At the opposite end of the animal a set of tentacles
moves slowly, obtaining food. In most sea cucum-

bers, including the large kinds found near shore in
tropical and subtropical waters, these soft organs
around the mouth shovel the surface mud into the
digestive tract, letting the animal get the nourish-
ment from a great assortment of microscopic life,
especially diatoms. The gritty residue is expelled from
the cloaca, and sometimes accumulates into conspicu-
ous heaps. The late Professor W. J. Crozier estimated
from measurements of the cones of debris that the
sea cucumbers on each acre of bottom in one region
off Bermuda would pass between 100 and 200
pounds of sand through their bodies annually.

Substantial amounts of the nourishment obtained
by a sea cucumber are stored in its body wall. There
the food reserve usually gains protection from a
slimy, leathery skin in which are embedded little
limy secretions of remarkable variety. Some are mi-
croscopic plates perforated by many holes. Others are
knobby rods, or anchor-shaped, or resembling a con-
crete bird bath or a wheel with spokes but no rim.
Each species has its own distinctive limy granules.
Only a few kinds lack them altogether.

Many of the larger sea cucumbers that live close
to shore supposedly discourage attack by fish and
crabs through the presence of a poison (holothurin)
in their skins. If extracts of it are injected into mice,
they die quickly. The presence of certain sea cucum-
bers in an aquarium tank may be enough to poison
any fish present. With some of the large subtropical
and tropical cucumbers, the effect sometimes persists
in a tank for weeks after the echinoderm has been
removed and the water changed repeatedly.

Large cucumbers belonging to the genera Holo-
thuria (Plate 141) and Actinopyga have ready a truly
astonishing defense against animals that molest them.
Associated with the region where their respiratory
trees open into the cloaca they have short tubules of
red, pink, or white color. If the echinoderm is dis-
turbed seriously or repeatedly, it slowly turns its body
until the cloacal opening faces the molester, then
performs a general contraction and proceeds to send
out the slender tubules in great numbers. The blind
ends of the tubules may be enlarged; almost always
they are very sticky. And as they emerge from the
cloacal opening, they become darting, adhesive
threads that, in a minute or less, can so enmesh a
crab or lobster that it is immobilized. The cucumber
frees itself from the tubules and moves slowly away
as though nothing had happened.

With provocation these and many related sea cu-
cumbers will perform a far more amazing trick. With
a single powerful contraction they turn themselves
partly inside out—throwing out the respiratory trees,
the reproductive organs, and sometimes some of the
intestine as well. All of these emerge suddenly through
the cloacal opening as a tangled mass over and around
acrab or fish. From these too the cucumber separates

[273

itself, as one of the most spectacular instances of self-
mutilation and evisceration in the animal kingdom.
Until new organs are regenerated, the sea cucumber
continues its breathing movements, drawing sea water
directly into its body cavity. In six weeks or so, the
animal recovers completely and is ready to repeat
the performance if irritated sufficiently.

In many parts of the South Pacific and along Ori-
ental coasts, people deliberately annoy these large sea
cucumbers and gather up the extruded organs (par-
ticularly the ovaries of a female) as meat for the soup
pot or delicacies to be eaten raw. More widespread
is the custom of preparing holothurians as “trepang”
or “béche-de-mer.” Usually the animal is eviscerated,
its body wall boiled, then dried or smoked. In the
Indo-Pacific region the product is very popular as an
ingredient for soups or as gelatinous tidbits. Great
quantities of trepang are sold commercially to the
Chinese.

Trepang from the Mediterranean is almost two-

thirds protein, whereas that from the Indo-Pacific
averages between one-third and one-half protein. Ap-
parently the protein constituents are completely di-
gestible, and the method of preparation removes all
toxic materials.

Since the sea cucumbers in which the little pearl
fish Carapus seems an unwelcome guest are exactly
the ones producing fish poison and sticky threads
and eviscerating themselves when irritated, a person
can only marvel that the pearl fish is able to use the
cucumber’s cloaca as a refuge. Actually, Carapus
gets enough space for its body by sliding its tapered
tail well up into one of the cucumber’s respiratory
trees. Yet the fish seems never to trigger the common
responses and is completely immune to the poison.

The potency of the poison to fish in general is well
known among natives on many South Sea islands.
On Guam, for example, people cut the common black
sea cucumber in two and wring the contents of its
body cavity into tidal pools to drive the fish to the

The feather star Antedon bifida, found on European Atlantic shores and in the Mediterranean,
may be red, orange, yellow, or purple. It attaches itself temporarily to rocks by use of a circlet
of appendages (cirri) on its back, and holds the mouth up to receive food collected by the
feathery arms. (France. Ralph Buchsbaum)

surface. In the Marshall Islands, similar sea cucum-
bers are pounded and the mangled remains dropped
into pools at low tide, stupefying the fish enough that
they can be caught easily. Yet the poison is not feared
by the natives. It is harmless to human skin, and fish
caught through its use are often eaten raw with no ill
effects.

About 500 different kinds of sea cucumbers have
been found, living almost exclusively on or in the
bottom sediments. Most of them are dull colored,
and only a few have contrasting spots or stripes. Yet
they pursue their lethargic way of life on minute food
in so many different levels of the sea that a surprising
variety of form and body build is represented.

Something in common can be seen between a child
solemnly licking its fingers to clean them of jam, and
a big sea cucumber in its normal method of feeding
with ten or more profusely branched tentacles, each
like a shrubby tree. The cucumber spreads its tenta-
cles over the sea bottom and rubs them around, gath-
ering food particles in the mucus coating. Then, one
at a time, the animal thrusts a loaded tentacle into
its mouth, closes fleshy lips around it, and pulls out
the tentacle all clean and ready for reloading.

Sea cucumbers acting in this way can be found in
cooler waters between low-tide mark and 1200 feet
below the surface. Cucumaria frondosa, found in tide
pools along rocky coasts on both sides of the North
Atlantic, is one that presents a particularly magnifi-
cent set of bushy tentacles when fully expanded. Along
the body of a Cucumaria, five lengthwise tracts of
short tube-feet show the five-parted symmetry so ob-
vious in most echinoderms.

In Thyone, the whole body is studded with tube-
feet and curved into a broad U. Ordinarily these ani-
mals bury themselves in the bottom with only the
cloacal opening and the bushy tentacles exposed. If a
Thyone is dug out and then placed on the sea floor,
it usually needs three to four hours to work itself into
the hidden position again.

Some other sea cucumbers with bushy tentacles
have a scale covering. Usually these animals rest on
a solelike area of the lower surface, and give the
general appearance of an armored slug with tentacles
instead of gills. They creep from place to place, and
can climb the vertical walls of a glass aquarium at
fair speed. Psolus has tube-feet only around and un-
der the creeping sole, whereas Psolidium extends
degenerate tube-feet that lack sucker tips through
holes in the body scales.

Psolus antarcticus carries as many as 22 young
along with it, holding to smooth areas of the creeping
sole. Cucumaria parva has been seen holding plant
material against its body, helping keep young in
place. Other species of these two genera have pockets
in the body wall, usually around the anterior end, in
which the eggs develop.

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These large sea cucumbers in a coral reef of the South
Pacific face the danger of being collected and pre-
pared for human food as “béche-de-mer” or “trepang.”
(Great Barrier Reef. Fritz Goro: Life Magazine)

Large tropical and subtropical sea cucumbers usu-
ally have twenty tentacles, but each of these feeding
organs has an expanded tip and cannot be withdrawn
into the body as is done by cucumbers with bushy ten-
tacles. Holothuria is one genus of particularly inert
and sausage-like sea cucumbers, with no obvious
flattened surface to indicate a ventral side. Actinopyga
has a creeping sole, as has Stichopus. Both of these
live in exposed positions on mudflats, reaching rec-
ord lengths of 40 inches and a diameter of 8 inches.
Actinopyga differs from Stichopus in that the anus
opens into the cloaca through an armament of five
limy teeth. Stichopus lacks these teeth, but has the
ability to raise its body in waves of movement, like a
giant caterpillar walking, and shift the animal far
more rapidly than use of its tube-feet would permit.

Close relatives of these cucumbers live in the great
depths of the ocean. There Bathyplotes appears to
drift well above the bottom for most of its life, sup-
ported by a float extending around the rim of its
creeping sole. Mesothuria intestinalis, a grayish white
animal often tinged with pink or violet, is sometimes
found also near the surface. It covers its body with
debris, as though to hide from enemies, and has been
found to begin adult life as a male, later transforming
into an egg-laying female.

Molpadonias are sea cucumbers with a conspicu-
ous tail, often found buried in the bottom mud with
only the tail tip and cloacal opening exposed. These
animals lack tube-feet, or have them only around the
anus, perhaps used there in keeping the cloaca free

[275

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of sediments. The feeding tentacles are fleshy, some-
times with a few finger-like extensions at the ends.

According to Japanese scientists, molpadonias
feed particularly rapidly. An individual may move
from 125 to 150 pounds of bottom sediments through
its 7-inch body annually in extracting nourishment.
One of this type of cucumber is Caudina arenata,
found from Rhode Island to the Gulf of St. Lawrence
between 100 feet below the surface and low-tide
mark. Its tail tip can be found exposed from the sandy
mud, and used to capture the buried cylindrical ani-
mal. The body may be | inch in diameter and 7 in
length, in hues ranging from deep purple to flesh-
color.

Some sea cucumbers are wormlike, lacking tube-
feet and respiratory trees. Usually the body wall is
very thin, often translucent, and the animal itself is
more active than most other holothurians. Several
kinds with this shape of body burrow in the mud and
can bury themselves in five to six minutes. Others,
while only partly grown, swim to the surface at night
by a curious twitching movement of the body, sug-
gesting a scissors kick.

Synaptula is one of the commoner wormlike sea
cucumbers. It can be found clambering among sea-
weeds and through coral reefs. When fully extended
a Synaptula may reach a length of 3 feet, yet be
no more than 12 of an inch in diameter. Some mem-
bers of this genus have openings through the wall of
the intestine in the female, through which sperms
from sea water reach the eggs in the body cavity.
Thus fertilization is internal, and the embryos develop
for some time in the body cavity before being cast
out into the sea. The young of Chiridota rotifera, a
wormlike sea cucumber of shallow water in the West
Indies, reach the same body form as the parent be-
fore they emerge, and this sea cucumber is truly
viviparous.

Sea Stars (Class A steroidea)

For many people, a starfish, better called a sea star,
is a clear symbol of marine life (Plates 118-130).
They are aware that animals of this type are never
found in fresh water or on land. Sea stars are strictly
bottom animals, chiefly of the margins of the sea.
They range in size from less than 2 of an inch in
diameter to more than 3 feet across, and in shape
from regular stars with five or more arms to pentago-
nal and almost circular. Yellow, orange, pink, or red
are the commonest colors, but gray, green, blue, and
purple ones can be found.

Most sea stars take mollusks as their favorite food,
but some eat sea urchins, sea cucumbers, and other
sea stars. A few catch small fish and shrimps. Perhaps
a majority will devour carrion on the bottom. Sea

276]

stars of certain kinds swallow soft mud and digest
the organic matter, as do so many other echinoderms.

A sea star’s arms are actually part of its body
rather than appendages. If one of these animals is
turned upside down to expose its mouth surface, each
arm is seen to have a lengthwise groove filled with
moving tube-feet. Within each arm the star has also
one or two branches of its reproductive organs, and
often extensions from the digestive tract as well.

If the inverted sea star is balanced for a few sec-
onds on the back of a person’s wrist, it may take hold
firmly enough to hang from the human hairs after the
wrist is turned over. Its grip is not strong enough to
pull out the hairs, but once attached in this way, it sel-
dom will let go.

This trick is not due to tube-feet, for stars have
none of these organs on the aboral surface. Instead, it
is a demonstration of strange little modified spines
(pedicellariae) by means of which the animal ordi-
narily polices its body. Each pedicellaria commonly
has the form of a pair of pincers, or of a little clam
shell lying in a minute pocket of the surface. The
parts open or close under muscular control. Sea ur-
chins are the only other animals in the world with
pedicellariae.

Between the pedicellariae over much of the star’s
aboral surface, small domes of soft skin show where
the body cavity is separated from the sea by only a
thin layer of tissue. Here the blood can exchange car-
bon dioxide for oxygen. Elsewhere the outer surface
of the star, like the lining of its digestive tract and the
corresponding parts of sea urchins, crinoids, and brit-
tle stars, is covered by cells with cilia. These propel a
thin film of mucus from glands and, on the outside of
the body, efficiently keep it clean by sweeping away
any debris that falls on it.

One or more madreporites, flat plates perforated
by many holes, can be found on the aboral surface of
a sea star. Through these the water-vascular system is
connected to the ocean. Most sea stars have only one
madreporite, and naturalists have often used this land-
mark as a guide in trying to learn whether a sea star is
actually so versatile that it will travel with equal readi-
ness in all directions, letting any arm lead the way.
Some few kinds and occasional individuals seem to
show a distinct preference. For the rest, the radial
plan extends to habits, and all arms are equivalent.

When a star rights itself after falling on the bottom
with mouth up, it shows little partiality for one way or
another. Yet for a patient observer, the star's move-
ments provide a wonderful demonstration of its re-
markable flexibility and muscular control. The crea-
ture may take anywhere from two to ninety minutes
to get back on its tube-feet.

Some stars turn over by use of the “tulip method.”
Slowly they bend all of their arms in the same direc-
tion, perhaps raising them around the mouth like the

petals of a tulip. The disk of the body becomes
rounded and the animal is no longer in balance. It
topples to one side, and then proceeds to curl the un-
der arms and take hold of the bottom with its tube-
feet. Eventually it reaches the ordinary outspread po-
sition, mouth downward.

Other stars use the tulip method in reverse, bend-
ing the arms away from the mouth, rising up like an
inverted flower until they topple or can grasp the bot-
tom with extended tube-feet on some one or two
arms.

A great many stars, when righting themselves, ac-
complish the same end with far less obvious move-
ment. Just the tips of one or two arms (usually two)
curl under, away from the mouth side of the animal.
Their tube-feet gain a hold on the bottom and, with
this beginning, the star proceeds to walk under itself,
the region of bend shifting nearer and nearer the disk
of the body. Finally the remaining arms may be raised
free of the bottom, and the slow somersault is com-
plete. Or the folding may continue all the way to the
tips of the opposite arms, none of them ever being el-
evated into the water.

The tube-feet of sea stars are stout organs. Yet, un-
less the star is climbing a vertical surface, they appear
to push rather than to pull. Muscles in their walls
serve to aim the tube-foot as it is extended by hydrau-
lic pressure from the water-vascular system. Contrac-
tion of longitudinal muscles shortens the tube-foot
and expels the water.

It is on tube-feet slanting away from the animal in
a backward direction that real force is applied. As
these tube-feet are inflated with water, they push the
body along very much as a man’s feet push against the
ground in walking. A sea star strides very slowly ona
multitude of tube-feet all out of step with one another.
But in this way it can walk on soft mud as well as on
hard surfaces to which it clings.

At the end of each arm, a star has one or more
tube-feet of a different sort. They lack suckers and ap-
pear to be feelers, especially sensitive to vibrations
and chemical substances in the water. With them a
sea star can be repelled by a salt crystal or attracted
to a piece of clam.

In all but certain deep-sea starfishes, each arm has
at its tip a small cushion-like area that bears a cluster
of simple eyes. In most species this light-sensitive area
appears as a red spot. Often a creeping star curls the
tips of its arms upward, as though to peer vaguely in
the direction of movement by aiming the eyespot at
the surrounding bottom.

Nearly 2000 different species of sea stars have been
discovered, the greatest number from northern parts
of the North Pacific Ocean. Living sea stars all belong
to three great orders, separated upon inconspicuous
details of the pedicellariae and skeleton. Familiar and
remarkable sea stars are included in each of the three.

THE EDGED SEA STARS

A majority of deep-sea stars belong to the order of
“edged sea stars” (Phanerozonia), the record for
depth being held by Albatrossaster richardi, dredged
from 19,700 feet below the surface near the Cape
Verde Islands. This order has many members too in
waters a beachcomber or skin diver can reach.

Edged sea stars usually have a sharp boundary be-
tween the upper and lower surfaces. Along the mar-
gin of the often broadly joined disk and the arms, es-
pecially large skeletal plates commonly form two rows
(Ceramaster, Plate 130). These marginal plates, to-
gether with the ones that cover the upper surface with
a kind of mosaic pavement, give rigidity to the sea star.

Many edged sea stars have pointed tube-feet with
no suction tip, and live normal lives with neither ped-
icellariae nor an anus. These are all features of the
common, sluggish mud star Ctenodiscus crispatus,
and of the various kinds of Psilaster, Astropecten,
and Leptychaster encountered along muddy coasts of
the northern hemisphere.

Ctenodiscus crispatus itself is a short-armed, blunt-
tipped creature with a broad yellow disk. It sinks it-
self just below the surface of mud flats from shore to
depths of at least 6000 feet along coasts of both the
North Pacific and North Atlantic. Full size—3 to 4
inches across—is probably reached by the time it is
three years old, showing that the mud star is really
efficient at extracting food from the sediments car-
ried to its mouth by a veil of mucus propelled by
the ciliated cells of the skin.

The arms of Psilaster, Astropecten, and Luidia
(Plate 123) are pointed and far longer than those of
Ctenodiscus. Psilaster andromeda needs about four
years to reach the full 4-inch spread of its slender
arms, feeding on small urchins, little clams, mussels,
and microscopic life in surface sediments. Recently-
dead Psilaster are often washed ashore, for they live
in waters as shallow as 60 feet and from there to more
than 2500 feet below the surface on both sides of the
North Atlantic—from Delaware Bay to Greenland
and down the eastern shores to the Cape Verde Is-
lands off the westward bulge of Africa. A gelatinous
secretion on the aboral surface of this star makes it
slimy to the touch.

The -pecten of Astropecten is the comblike fringe
of spines attached to the marginal plates. Many of
these stars are large ones. A. articulatus and A. cin-
gulatus both reach 10 inches in span. The former
lives in comparatively shallow water from New Jersey
to the Gulf of Mexico, and can be bright orange or
purple above and yellow below with orange-red mar-
ginal plates and purple spines. A. cingulatus inhabits
deeper water and usually is colored more drably.

Still other species of Astropecten are the common-
est shallow-water sea stars in the Mediterranean.
They compensate for lack of suction cups on the

[277

tube-feet by having particularly large mouths, and
engulf astonishing numbers of small animals. One in-
dividual of A. auranciacus from the Mediterranean
was found to have swallowed ten scallops, six Tellina
clams, five tusk shells (scaphopods), and several
snails. Another species in the same region dines reg-
ularly on young sea stars, brittle stars, bivalves, snails,
segmented worms, and assorted crustaceans. Snail
shells regurgitated by Astropecten stars along the Pa-
cific coast of America are so intact and empty that
hermit crabs adopt them while house-hunting.

Leptychaster arcticus has a larger body disk than
members of Psilaster or Astropecten and differs from
them in lacking spines on the marginal plates. Fully
grown individuals seldom exceed 14 inches in diam-
eter, but they are well worth examining closely since
this is a sea star that may brood its young. It is found
in cooler coastal waters of both the North Atlantic
and North Pacific.

Brooding in these stars seems related to low tem-
peratures and, as among sea cucumbers, to echino-
derms that produce larger eggs than is usual, hence
with plenty of yolk as stored food. In Leptychaster
uber of the northwest Pacific and L. kerguelenensis
from close to Antarctica, up to thirty young are car-
ried in depressions of the greatly stretched aboral sur-
face of the parent.

Edged sea stars whose tube-feet have suction tips
are better able to hold a shellfish while attacking it as
food. The largest group with this characteristic (fam-
ily Goniasteridae) includes perhaps the most bril-
liantly colored sea stars of Australian waters, and
has representatives in many other parts of the world
as well. Thick, massive plates border the broad-based
arms, and the whole aboral surface is commonly
roofed by a mosaic of skeletal pieces under a smooth
or granular skin. Mediaster aequalis is studded above
and below with compact little paxillae, giving the ap-
pearance of everlasting flowers in a honeycomb pat-
tern. It is found in shore waters along the Pacific
coast from Alaska to California.

The largest sea star of the Atlantic coast of Amer-
ica is Oreaster reticulatus of Florida, the Bahamas,
and the West Indies. The name reticulatus refers to
the network pattern evident on the upper surface,
where the parchment-thin skin sags a little between
the mesh of the bar-shaped skeletal plates. Like oth-
ers of its family, it is a massive animal, quite thick in
the middle. Specimens measuring 16 to 20 inches
across are often displayed as trophies of the sea. They
may be almost any color from deep purple through
maroon, Orange, green, or bluish, with bright yellow
points where the skeletal plates join one another at
prominent rounded spines. O. nodosus, brilliant in
red and blue, is equally admired in the Indo-Pacific.

The marginal plates in Linckia (Plate 129) are
much less evident on the more-or-less cylindrical

278 |

arms. The whole body is clothed in rounded or squar-
ish plates, often with a pebbled surface. L. guildingi
inhabits tropical waters of all oceans. L. colombiae,
which grows to as much as 4 inches across, can be
found on rocky shores from Los Angeles, California,
to the Galapagos Islands off Ecuador. All of these
animals show spectacular powers of regeneration, for
even a piece of an arm less than 12 of an inch long
can reorganize itself into a whole new sea star. At
least part of the body disk must accompany a whole
arm for such a fragment of any other kind of sea star
to regenerate the missing parts.

THE SPINY SEA STARS

A connoiseur of sea stars recognizes those with
conspicuous spines over much of the upper and lower
surfaces as being very different from any of the edged
sea stars. These features are marks of a spiny sea star
(order Spinulosa), the skeleton of which usually
consists of a network of limy bars or of plates over-
lapping one another. The boundary between oral and
aboral surface is rarely evident on the body or arms,
and while the tube-feet always have suction tips, ped-
icellariae are rare.

One of the commonest spiny sea stars of western
Europe and the Mediterranean is Asterina gibbosa,
which is covered on both surfaces by tufts of small
spines. It is found along the Atlantic coast of Africa
as far as the Azores, and is known to vary its diet of
mollusks with meals on sponges and sea squirts.

The red or orange sea bat, Patiria miniata (Plate
126), is almost equally familiar along the Pacific
coast from Lower California to Alaska. Its oral sur-
face is decorated with tufts of spines in the form of
little fans fitted together, whereas the aboral surface
is granular, with curved plates forming an attractive
pattern. It seems to be particularly omnivorous, often
eating seaweed, sponges, sea urchins, squid eggs, or
spreading its thin surface against surfaces upon
which diatoms are growing. It will digest them away
from even the glass side of an aquarium.

Sometimes the appetite of a spiny sea star cannot
be predicted from an examination of its body. The
broadly pentagonal Anseropoda placenta of western
Europe and the Mediterranean is a burrowing species
of wafer thinness. Yet it engulfs other echinoderms,
snails, little clams, and a great variety of small crusta-
ceans—even hermit crabs. It seems impossible for
any animal to eat so much and stay so thin.

The blood star, Henricia sanguinolenta (Plate
125), is seldom more than 3 inches across, but its
rich red color and graceful pointed arms make it a fa-
vorite with beachcombers from Greenland to Cape
Hatteras on the western side of the Atlantic, and to
the Azores on the eastern side. Some individuals are
rose-colored, others orange, or purple, or even mottled
with creamy yellow. The arms are always smoothly

curved from aboral to oral surface, and the groove
containing the tube-feet is usually narrow.

Both H. sanguinolenta and H. leviuscula on the Pa-
cific coast of America stay hidden in dark crevices
during the winter months while they brood their rel-
atively large eggs. Henricia larvae omit the usual free-
swimming larval stage, and remain concealed among
the parent’s incurved arms until they have trans-
formed into miniature stars, ready to glide on their
own along the bottom.

The sun stars Crossaster and Solaster have a broad
body disk and many arms. Crossaster papposus
(Plate 127), found in the Pacific Ocean along coasts
as far south as Vancouver Island and in the Atlantic
to New Jersey on the west and the English Channel
on the east, is easily the handsomest of them. It may
have from eight to fifteen arms, each tufted conspicu-
ously with spines. The whole aboral surface wears a
sunburst of color perhaps more striking than on any
other echinoderm.

Solaster endica, by contrast, has slender arms and
no raised tufts of spines. It lives on both sides of the
Atlantic in cool water, and is usually a bright purple.
On Pacific coasts it is represented by S. dawsoni. Sun
stars are voracious creatures, eating large numbers of
smaller sea stars as well as sea anemones, bivalves,
and snails. Like Henricia, they have no free-swim-
ming stage, but develop directly. Older individuals
have more arms than younger ones.

Pteraster miliaris is one of several cushion stars
found in shore waters of Scandinavia, the British
Isles, down the Atlantic coast of America to New
Jersey, and along cooler shores of the Pacific. The
pinkish red body is covered by a membranous skin
draped from circlets of slender spines, as though it
were a tent roof. The membrane extends as a web
around the short, bluntly rounded arms, which may
span 6 inches. The skin over the aboral surface ac-
tually conceals a cavity used as a brood pouch for the
young and in respiration. Water enters it through
pores below, and emerges through a large cloacal
opening near the middle of the upper surface.

THE FORCEPS-CARRYING
SEA STARS

The special enemies of shellfishermen are sea stars
which, upon close inspection, prove to bear pedicel-
lariae raised above the surface on short stalks able to
turn in various directions. Most of these forceps-car-
riers (order Forcipulata) have long, rounded arms
and a small body disk. They include many of the most
persistent destroyers of clams, mussels, and oysters.

The forceps-carriers include the familiar stars of
wharf pilings and tide pools all over the world. As-
terias amurensis inhabits the Pacific coast from
Alaska to Korea, A. vulgaris the Atlantic coast from
Labrador to Long Island, A. forbesi from Maine to

Sun stars are denizens of shallow temperate seas.
Their arms vary in number, usually from seven to
thirteen, but may total as many as seventeen. The
exposed surface often wears a sunburst of color.
(Maine. Ralph Buchsbaum )

the Gulf of Mexico, and A. rubens (Plate 124) the
northern shores of Europe. All of them have a rough
body surface and four rows of tube-feet in the groove
below each arm. They also have two types of pedicel-
lariae: some with straight forceps, and others of a
cross-bladed type. A. vulgaris in Maine sometimes
reaches a span of 17 inches.

In opening a shellfish, these stars mount it with the
mouth opening directed toward the place where the
clam would gape if the mollusk did not clamp its
valves together. Then, with almost every tube-foot
affixed to one valve or the other, the sea star applies
the force of its body muscles. A pull of 7 to 10 pounds
has been measured, tending to open the shell.

Contrary to widespread belief, the sea star need
not wait for its victim to tire. A force of this size is
sufficient to bend the shell of clam or oyster, making it
gape a fraction. Even a hundredth of an inch is
enough for the sea star. Through the narrow slot it
slips its even thinner, everted stomach and proceeds
to digest the shellfish deep in the shell. For much of
the time the sea star does not even bother to hold the
valves apart. It lets them clamp on the extruded stom-
ach except at such times as a stream of liquefied prod-
ucts of digestion are ready for transfer into the sea
star’s body.

Not all forceps-carriers have the same tastes. On
the Pacific coast of America, Astrometis sertulifera
is expert at feeding on the large chiton Stenoplax
clinging to the rocks. Pisaster brevispinus on sandy
bottoms hunts for sand dollars, and the flavor of an
approaching star of this kind is distinctive enough to
sand dollars that they will cease feeding and burrow

[279

The starfish Asterias forbesi extrudes its stomach to
envelop the small dead fish which will be its dinner.
(Virginia. Robert Bailey )

out of sight when Pisaster comes within two feet of
them; half an hour after this star has passed by, they
come up again and resume feeding. They may have
an opportunity to repeat this vanishing act many
times, for Pisaster is believed to be one of the long-
est-lived of sea stars, reaching an age of twenty years.

In the Indo-Pacific, Coscinasterias calamaria is a
spinier star with from seven to fifteen arms. It opens
brachiopods as food, using the same method as
Asterias employs on clams. The giant twenty-rayed
Pycnopodia helianthoides of the Pacific coast from
southern California to the Aleutians often eats whole
sea urchins. In Puget Sound this sea star attains a di-
ameter of 22 inches. Apparently its mouth and appe-
tite are in proportion (Plate 128).

The Echinoids (Class Echinoidea)

Among the denizens of tide pools and seashores,
the sea urchins and sand dollars are second only to
sea stars as popular trophies. The smallest of them
are sand dollars barely 2 of an inch in diameter when
mature. The largest a skin diver can retrieve are black

280 |

sea urchins with a shell 6 inches across; long, slender
spines usually add another 10 or 12 inches to the
space needed to accommodate the prize without
touching. In much deeper waters live urchins with
leathery, flexible shells almost a foot across. The
largest urchin known is a leathery specimen of
Sperostoma giganteum, taken off Japan; it measured
nearly 13 inches in diameter.

Echinoids come in many different shapes: sea ur-
chins as regularly symmeirical as a doorknob; flat-
tened sand dollars and sea pancakes; broadly pointed
sea arrowheads; and heavy-bodied heart urchins.
Even their empty shells are things of beauty, for
without the skin covering them, they reveal a hand-
somely regular pattern of limy plates joined immoy-
ably. Knobs on certain plates are the balls of ball-
and-socket joints for spines under individual muscu-
lar control—the armament from which echinoids
get their name, suggesting echinos, the hedgehog.

As a sea urchin moves along a submerged rock or
the bottom, its spines seem constantly to be readjust-
ing themselves. Between them and often beyond them,
slender tube-feet may extend as feelers ready to detect
the approach of food or enemy. Other tube-feet bear
the weight, except in a few kinds of urchins in tropi-
cal waters that progress on their spines or lurch for-
ward by lifting themselves on their mouthparts. Their
tube-feet arise in five radiating areas, regions evident
in an empty, cleaned shell from the rows of circular
holes through which the tube-feet extended in life.

Pedicellariae on long stalks also reach about,
seizing on particles and transferring them as though
hand to hand around the body to the mouth, or de-
fending the urchin against attackers. The commonest
type of pedicellaria among echinoids has three jaws
coming together only at the tip. Special ones are
glandular, with a poison sac in each jaw producing
a toxic material. Each pedicellaria has its own nerv-
ous control and can act independently in policing the
body surface.

Echinoids replace tube-feet, pedicellariae, and
spines when these are damaged or lost. Cracks in the
shell can be mended, but new plates are produced
only during normal growth, keeping up with the en-
largement of the enclosed parts of the body.

Probably sea urchins occasionally live to be older
than eight years, but their growth is most rapid while
young. The common green urchin Strongylocentrotus
of the North Atlantic and North Pacific attains a
body diameter of about 4 of an inch by the end of
its first year, %s of an inch in the second year, | inch
at three years, 15%8 at four years, 2 inches at five
years, 2-8 at six years. Off the Norway coast this ur-
chin reaches a top diameter of about 3 inches.

In sea urchins and sand dollars the mouth is
equipped with an amazing dredgelike device with as
many as forty separate pieces, serving to control five

teeth that come together toward the outside and the
center of the oral surface. Aristotle, who discovered
this organ in the fourth century B.c., described it as
resembling “a horn lantern with the panes of horn
left out,” and it has been called “Aristotle’s lantern”
ever since. With it a sea urchin can chew a wide
variety of foods and possibly also excavate living
spaces in rocky shores.

So great a range of different echinoids inhabits the
coasts of the Indian Ocean and Malaya that those
areas are regarded as the world center for shore-
inhabiting kinds. In all directions from that center the
number of unlike types of echinoids decreases. It
shrinks too in progressively deeper water, and be-
low fifteen thousand feet none is known. Temperate
and polar seas have the largest number of individuals,
whereas in the tropics, communities of urchins are
less frequent although the number of different kinds
is more impressive. In the Arctic, urchins often con-
gregate in such abundance that it would be impos-
sible for a skin diver to set down a foot between one
urchin and the next.

About 750 species of living echinoids have been
identified, most of them members of groups with rep-
resentatives in shallow water. Some of these can be
recognized at a glance.

SEA URCHINS

Hatpin urchins, the bane of waders and skin div-
ers, are the most respected echinoderms in tropical
and subtropical waters. They include also the largest
of the regular echinoids to be found near shore.
Much larger ones, which belong to family Echino-
thuridae, are found in very deep waters.

The spines of these urchins may be | foot long,
shaped like needles, jet black, fragile, hollow and
probably poison-filled. They penetrate human skin
easily, break off, and cause intense stinging pain.
Eventually the lime of the spine is absorbed. Whorls
of minute teeth around each spine resist extraction,
and the material of the spine itself tends to crumble
in a pair of tweezers.

No one who has watched these big urchins on a
reef or experimented with them in an aquarium
tank has any doubts about the role of the long spines.
The urchin keeps them in constant motion, and re-
sponds to any shadow by turning even more spines
in that direction. With only a general sensitivity to
light in the black skin covering the shell, the urchin
seems very well aware of any change in its surround-
ings affecting the illumination falling upon it.

The hatpin urchin of the Mediterranean and tropi-
cal eastern Atlantic is Centrostephanus longispinus,
a black-bodied animal with brightly colored spines
kept constantly in motion, the tip of each spine trac-
ing a small circle in the water. Diadema setosum of
the East Indies and D. antillarum of the West Indies

and Florida keys present the same formidable appear-
ance. Commonly they cluster in cavities of coral reefs,
and all of the really large ones seem to have protec-
tion of this sort.

When stirred into movement a hatpin urchin can
travel at from one to one and one-half inches per
second, “walking” on the tips of shorter spines over
the oral surface. This is about sixty times as fast as
the maximum for the common sea urchins of New
England coasts on their multiple tube-feet.

Cidarid urchins differ in that they bear two very
different sizes and types of spines. The large ones
may be as long as the diameter of the shell, and are
widely spaced and covered by a wooly, hairlike ma-
terial to which foreign particles often cling. Their
small spines, by contrast, are as spotlessly clean as
those of other sea urchins. Some of the small spines
form a whorl around the base of each large spine.

Of cidarids, Cidaris tribuloides is familiar in tropi-
cal parts of the eastern Atlantic, and from North
Carolina to Brazil, throughout the West Indies, and
in Bermuda. It reaches a diameter of 2'4 inches and
is mottled in various shades of brown. Often its large
spines carry such a crust of moss animals (bryo-
zoans ) that the bands of purplish red and yellow are
concealed.

In scientific circles the sea urchins that have be-
come most distinguished are plain purplish brown,
measuring between | and 2 inches in diameter, with
the anus in the middle of the aboral surface clearly
equipped with four or five large plates acting as
valves. These urchins are poorly armed, usually
lacking glandular pedicellariae and bearing only mod-
erately slender spines about half as long as the width
of the shell. Shorter spines around the mouth wear
shiny caps.

These urchins of the genus Arbacia have provided
experimental biology with study material to a de-
gree paralleled only by the fruit fly in genetics, the
white rat in nutrition, and the frog in investigations
of muscle action. The most famous of them is Arbacia
punctulata, found from Cape Cod to Florida and
throughout the West Indies. A. lixula lives in the
Mediterranean and along tropical coasts of the east-
ern Atlantic. A. stellata is a very similar urchin oc-
curring from Mexico’s Baja California to Peru along
the eastern Pacific.

Most of the familiar sea urchins are not hatpin
urchins or cidarids or distinguished members of
the genus Arbacia. Instead, they are of types with
solid spines and an abundance of all four types of
pedicellariae.

On shores from the Carolinas through the West In-
dies, the good-sized, somewhat flattened urchin
whose solid, white spines against a darker body give
it a shaggy appearance, usually proves to be Lyte-
chinus variegatus. Close to the limit of low tide,

[281

os

The hollow spines of the hatpin urchin Diadema setosum are a menace to skin divers, for they
readily penetrate the skin, break off, and cause bad wounds. This one rested in a coral pool
at low tide on the Great Barrier Reef. (Fritz Goro: Life Magazine )

where waves break over it and the sun is particularly
bright, Lytechinus often uses the tube-feet on its
aboral surface to hold pieces of seaweed and bits of
coral or stones as a shield and shade. In deeper wa-
ter this habit is less frequent.

Echinus miliaris, found in British coastal waters,
tends to conceal itself in the same way. Apparently it
is a less active animal than its close relative, the edi-
ble urchin E. esculentus (Plate 136), for the latter
remains clean as it forages about for a mixed diet of
shellfish, tube-building worms, crustaceans, small
echinoderms, and hydroids.

The “sea egg” of Barbados and other islands in
the West Indies is Tripneustes ventricosus, a particu-
larly common urchin sought for human food at sea-
sons when the orange-colored ovaries are loaded
with eggs. Native people collect large numbers of
them, break them open, and either eat them raw or
roast them on the half shell or fry the ovaries as
though they were an omelet of hen’s eggs. In Italy the
egg masses of sea urchins are marketed in coastal
towns as “frutta di mare.” The favored Mediterra-
nean species is Paracentrotus lividus.

Recent immigrants to New England sometimes
seek out the largest specimens of a green sea urchin,
Strongylocentrotus droehbachiensis (recipient of one
of the longest scientific names on record). It takes
the place of Arbacia north of Cape Cod. It is found
also on northern European and Pacific coasts. This
animal is like Arbacia in being mostly a vegetarian,
feeding on seaweeds of definite kinds. Along the Ca-
nadian east coast, it has become addicted to a diet of
cannery wastes. In the Baltic Sea, it often varies its
diet with hydroids, tube-building worms, and other
foods. The big purple or red Strongylocentrotus
franciscanus (Plate 137) is sought by Italians in
California for its tasty ovaries, which are eaten raw.

A fair number of different urchins bore into rock,
seemingly by working on it with the hard teeth of the
Aristotle’s lantern or by abrading it with spines. An-
other possibility is that they keep the rock so free of
plant particles that erosion is hastened. Any loose
particles are probably removed by the tube-feet.
In any case the process is slow.

The commonest boring urchin along rocky coasts
from Norway and Iceland to the Cape Verde Islands
is Psammechinus miliaris. In the Mediterranean and
farther down the west coast of Africa, Paracentrotus
lividus has the same habit, and can be found in
honeycombed rock—a dark green animal with
spines of bright green, violet, and brown. Strongy-
locentrotus purpuratus, a purple urchin along the
Pacific side of North America, not only cuts cavities
in hard rock but has done extensive damage to steel
posts used as wharf pilings in California. Its food
consists mostly of plant materials.

If one of these boring urchins is disturbed, it at-

tempts to wedge itself at the bottom of its cavity.
Possibly this is its protection against wave action too.
Yet when the tide is in these animals apparently
wander away from their holes, feed on algae or other
material, and then return to the security of the
home they have prepared. Sometimes an urchin be-
comes imprisoned in its cavity, having opened a big
enough room but not enlarged the doorway through
which it entered at a smaller size and younger age.
On rocks of various Pacific islands, Colobocen-
trotus atratus demonstrates a very different technique
in resisting wave action. Its aboral spines are all
short, flat, bladelike organs that shield the body from
debris carried in the surf. Similar spines around the
somewhat flattened body suggest the petals of a
daisy. These too seem to aid the animal by using the
force of a wave to hold the body against a rock.
Heterocentrotus mammillatus is the slate-pencil ur-
chin of the Indo-Pacific and Hawaii. Its slightly flat-
tened spines may be 2 of an inch in diameter and
5 inches long. The lime of which they are composed
is hard and white; it can be used to make clear,
erasible marks on old-fashioned writing slates.

THE CAKE URCHINS AND
SAND DOLLARS

A bit of broken shell from a cake urchin or a sand
dollar shows many differences from any fragment of
a sea urchin’s test. The limy plates are thicker and
little vertical struts (such as no sea urchin possesses )
extend as braces between the aboral and oral sur-
faces.

The intact shell of a cake urchin or a sand dollar
shows, too, a bilateral symmetry through slight elon-
gation and in the displacement of the anal opening
toward the edge of the shell, on either the oral or the
aboral surface. The aboral surface itself bears a strik-
ing pattern of five petal-shaped marks (petaloids)
corresponding to the tracts of tube-foot holes in a sea
urchin’s shell.

Over much of the oral and aboral surfaces of both
cake urchins and sand dollars, short tube-feet extend
singly through a multitude of small openings. Along
with inconspicuous pedicellariae they serve to keep
the body clean and perhaps also in feeding. Those
on the undersurface aid the spines in locomotion and
in the digging movements by means of which these
animals sink themselves in the surface sediments.

Cake urchins are oval creatures with no distinct
edge to the shell. The common Clypeaster is cov-
ered by a dense, furlike coating of short dark-brown
spines. C. rosaceus is known as a “sea biscuit” in the
West Indies. C. subdepressus burrows shallowly in
tidal areas from North Carolina to Brazil.

Sand dollars are very flat, the edge of the body
thin and distinct. Most of those known live along
sandy shores of America and Japan. Echinarachnius

[283

The slate-pencil urchin Heterocentrotus mammillatus,
with its great clublike spines, is more than two hands-
ful in size. (Great Barrier Reef. Fritz Goro: Life
Magazine )

parma reaches a diameter of approximately 3 inches
along the Atlantic coast from New Jersey northward,
as well as around the Pacific from Vancouver Island
to Japan. Its petaloids end abruptly, as though in-
complete.

From Nantucket to Brazil, the sand dollar Mellita
testudinata has pointed petaloids and develops
notches in the rim of the body. These become sur-
rounded as slots when the sand dollar grows. In
the Gulf of California, certain members of Encope
acquire even more distinctive slots and holes, and
are popular as “sea arrowheads.” Echinodiscus auri-
tus, the yellow or purple “sea pancake” of Africa’s
east coast, excels most other sand dollars in size and
thinness of the body. The shells of many of these
animals can be ground up in water to make an indel-
ible ink.

HEART URCHINS

It is easy to tell a heart urchin from a sea biscuit,
even though both have a bulky oval body and a
heavy shell. The heart urchin has only four complete
petaloids on its aboral surface, and the mouth is a
transverse slot somewhat anterior of the middle on
the lower surface. The anus is well posterior. Inter-
nally the shell is braced, but the animal has no Aris-
totle’s lantern.

Heart urchins are burrowers, usually covered with
fine short spines that slant backward as though
combed. If large spines are present, they too are

284 |

aimed in a way that offers little resistance as the ani-
mal works along through the muddy bottom.
Spatangus purpureus, a violet-colored animal, ex-
cavates chambers for itself in the mud along shores
in western Europe, the Mediterranean and the west
side of Africa. Its presence can be suspected from the
small hole kept open between its chamber and the
water above. Mucus secreted by the heart urchin
keeps its cavity from shedding mineral particles while
extremely long tube-feet are extended from the petal-
oid areas through the hole in the chamber’s roof to
scavenge for food over adjacent areas of bottom.

The Serpent Stars

(Class Ophiuroidea)

By far the most active of all echinoderms are the
serpent stars. Yet because most of them are of small
size and retiring habits, they are less familiar than
sea stars and sea urchins. They are often called “brit-
tle stars” because of their readiness to throw off parts
of their arms when disturbed. Each arm may break
into many pieces. A few kinds go so far as to dis-
card the upper part of the body as well. Then the
missing portions are regenerated.

The five arms of a serpent star (only a few have
six or seven arms) are distinct from the disk-shaped
or pentagonal body. On the oral surface they lack the
grooves as well as the sucker-tipped tube-feet found
in sea stars. Only a pair of minute soft swellings at
each joint in the arms represent the tube-feet. Ap-
parently they are primarily sensory.

Flexibility of the arms in most serpent stars is
mostly in a horizontal direction. The animal curls
them around irregularities of the bottom and lifts its
body along, ordinarily holding it above the surface
on which the arms rest. The arms commonly are five
to six times as long as the diameter of the body, but
in some serpent stars the proportion reaches as much
as fifteen times.

The arms are so flexible that they suggest a ser-
pent’s tail, giving the common name to the animals
and also the word for the class to which they belong
(from ophis, a serpent, and ura, the tail).

Serpent stars frequently cluster together in aston-
ishing aggregations. The tangle of arms becomes im-
pressive enough to suggest that the group forms a
more efficient trap for suspended food matter than is
possible for a single individual.

The mouth at the center of the oral surface has five
sharp teeth but no Aristotle’s lantern. Close to the
mouth is the opening through which the water-vascu-
lar system is filled.

Serpent stars feed on a wide variety of bottom ma-
terial and take advantage of opportunites to include

flesh in their diet. They scavenge from the tide line to
at least twenty thousand feet below the surface, and
are found on every type of bottom in all seas at all
latitudes. A few burrow, but most creep over and
cling to seaweeds, sponges, hydroids, corals, and
other attached forms of life.

Most serpent stars are either male or female, and
they free their reproductive products into the sea.
Some do brood their eggs, providing this parental care
until the young are miniatures of the parent. Some
serpent stars are hermaphrodites, with both ovaries
and testes. A number of six-armed species reproduce
by transverse division of the body, followed by re-
generation of the missing parts by each half.

Almost all of the sixteen hundred different species
of serpent stars have unbranched arms. One order is
exceptional: the basket stars (Plate 134). These
creatures live in deeper water, and somehow control
a profusion of arm branches, walking about on the
branch tips or coiling them about submarine growths.
Gorgonocephalus, the gorgon’s head basket star, is a
big one, with a body as much as 4 inches across and
arms repeatedly branching to a total length of 1 foot
or more. If a living specimen is placed in fresh water,
it will die in an expanded position, completely re-
laxed. Then it can be preserved to show the great
maze of slender branchlets. Otherwise it curls up in
a confused mass.

Serpent stars with unbranched arms seldom have
a body disk more than 1 inch in diameter (Plates
131-133). A good many of them have remarkably
extensive geographic range, some being truly cosmo-
politan in coastal waters. The long-armed serpent
star Amphipholis squamata is one of the most wide-
spread from the subarctic to the subantarctic. It is
particularly abundant around the British Isles as a
grayish white or faintly bluish denizen of tide pools.
It is hermaphroditic and broods its young internally,
hence is viviparous.

Ophiactis savignyi is circumtropical, and is dis-
tinctive in having square teeth. Small, young individ-
uals with six arms can often be found in the cavities
of sponges; there they reproduce by transverse di-
vision of the body. Eventually, however, they reach
a larger size and become solitary. Then, after a final
fission, each half grows only two new teeth and two
new arms, becoming a five-armed serpent star.
Thereafter it is an adult, reproducing only by sexual
means.

Some serpent stars are quite colorful and show a
range of coloration from one individual to another.
This is particularly obvious in the common daisy brit-
tle star Ophiopholis aculeata found from Long Island
Sound to the Arctic, and in the spiny serpent star
Ophiothrix angulata of shallow waters from Chesa-
peake Bay to the West Indies and Rio de Janeiro.
The first-named actually spreads downward to a

The five-holed sand dollar Mellita testudinata has five
rays and a covering of movable spines that identify it
as a flattened relative of sea urchins. It digs into
sandy bottoms along the Atlantic coast of America
and in the West Indies. (Delaware Bay. William H.
Amos )

depth of over six thousand feet—ten times as deep as
O. angulata is found.

O. aculeata has a body just under 1 inch across
and arms to 312 inches long, and may be red or blue
on the body, deeper red or green or brown banded
with white on the arms. O. angulata seems always to
show a color difference between the banded arms
and the body: the latter may be red, pink, yellow,
brown, green, blue, or purple—almost the full spec-
trum among the individuals in a single tide pool.

At night a number of different serpent stars can be
found along the shore because the arms luminesce.
Ophiacantha bidentata, whose arms often appear to
be knotted, is dark brown by day but bluish gray in
the dark; it inhabits the Atlantic and Pacific, as far
south as Portugal and South Carolina, California and
Korea; it is commonest between thirty and fifteen
thousand feet below the surface. Ophioscolex gla-
cialis, whose S5-inch arms and 1-inch body are cov-
ered with a thick skin, varies from purple to yellow
in daylight; at night its body is invisible but the arms
are a bright violet, contrasting with muddy bottoms
from Virginia to Greenland.

nN
ioe)
wn

CHAPTER XX

(Top to bottom) salp, lancelet and sea squirt

L. it were not for the existence of sea squirts, salps,
and lancelets, the phylum Chordata would consist
only of vertebrate animals—those with a vertebral
skeleton or backbone. But sea squirts, salps, and
lancelets do exist. This fact necessitates a broader
view of the qualifications for membership in the
phylum Chordata.

This subdivision of the animal kingdom takes its
name from the notochord, a stiffening rod of charac-
teristic construction serving as the first, inner, skeletal
support of the body. A notochord consists of a fibrous
sheath around a multitude of translucent cells whose
turgid condition provides firmness with flexibility.

Possession of a notochord prevents a chordate’s
body from telescoping as an earthworm does when its
longitudinal muscles contract. Instead, a notochord-
bearing creature bends from side to side, undulating
as a fish does. Lancelets retain the notochord through-
out life, whereas sea squirts, salps, and vertebrates
possess one only during larval or embryonic stages of
development. No member of any other phylum has a
notochord.

Above its notochord, a chordate has a tubular
dorsal nerve cord, which may be enlarged at the an-
terior end into a true brain. This part of the animal
arises in a uniform manner in all chordates from sea
squirt to man, a procedure quite unlike any of the
ways in which a nervous system develops in mem-
bers of any other phylum.

286 |

The Invertebrate
Chordates

(Phylum Chordata)

Chordates also show a third feature, found else-
where only among acorn worms (hemichordates): a
series of openings between the pharynx region of the
digestive tract and the outside of the animal. Gill slits
of this kind are used throughout life by acorn worms,
sea squirts and salps, lancelets, and such vertebrates
as lampreys and fish. The tadpole stages of amphib-
ians use gill slits. Reptiles and warm-blooded verte-
brates possess pharyngeal clefts only during embry-
onic development.

The invertebrate chordates include a few hundred
members of the subphylum Urochordata (sea squirts,
pyrosomes, and salps) and about thirty different kinds
of lancelets in subphylum Cephalochordata. These
names refer to the fact that in urochordates the
notochord is restricted to the tail region, whereas
in cephalochordates it extends to the anterior end of
the body.

Invertebrate chordates resemble one another in
being exclusively marine and in possession of a pe-
culiar pocket, the atrium. Water from the pharynx
passes through the pharyngeal slits into the atrium,
and then to the outside world through a permanent
opening, the atrial pore. This current of water is
maintained by cilia on most inner surfaces of the
pharynx. It brings particles of food which become
entrapped in a film of mucus secreted over the same
pharyngeal surfaces. Cilia also move the loaded mu-
cus into a groove along the length of the pharynx

and within this narrow passageway as a food-charged
rope into the gullet and stomach. Thus the inverte-
brate chordates are filter feeders, depending upon
plankton and detritus particles for nourishment.

The Sea Squirts and
Their Kin (Subphylum Urochordata)

Most sea squirts consist simply of a saclike body
permanently attached to some solid object or buried
shallowly in the ocean bottom. One body opening ad-
mits a current of water. The other serves for the
escape of the same current as well as of wastes and
reproductive products.

The tadpole stage of most sea squirts could swim
through a buttonhole quite easily. Even in a shallow
dish with a black bottom, their tadpole-shaped bod-
ies are so transparent that it is easy to overlook them.
Yet the tail contains the complete notochord and the
slender nerve cord extending from a slightly enlarged
hollow brain in the dorsal portion of the body. A
light-sensitive simple eye and a minute organ of bal-
ance are embedded in the walls of the brain.

The anterior end of the larval sea squirt is occu-
pied by the adhesive organs with which the creature
will attach itself at the time of transformation into
adult form. Already, however, it shows a small mouth
(incurrent opening) well forward on the dorsal sur-
face, leading into a capacious pharynx. Gill slits
through the pharyngeal walls communicate with the
atrium, which opens dorsally farther back on the
body. The small stomach is connected by a short in-
testine ending in the atrium, nearer the excurrent
opening from which water is discharged.

When a sea squirt larva attaches itself and trans-
forms, it literally stands on its face while absorbing
and obliterating its tail, notochord, sense organs,
and so much of the nervous system that only a solid
ganglion remains, with nerves extending to the few
internal organs. At the same time the dorsal surface
becomes distorted through great enlargement of the
pharynx, until the incurrent and excurrent openings
are raised like two spouts on the squat body. Ex-
ternally the body surface secretes a covering of cellu-
lose as the tunic from which the attached animal
gains another common name, “tunicate” (Plate
144).

When a beachcomber disturbs a sea squirt, the
creature usually contracts. On a rock between tide
marks this event is made obvious by two little jets of
water, one from the incurrent opening (mouth) and
the other from the excurrent (atrium). If a person
wearing slacks inadvertently steps beside a large sea
squirt on the beach, one or both jets may easily go up

inside the trouser leg and reach the knee, to the
walker’s sudden dismay.

Along the Atlantic shores and also in California,
a common sea squirt with incurrent and excurrent
openings close together is Ciona intestinalis. Its pale
golden-yellow tunic and body wall are so transparent
that the inner organs can be seen through them.
The height of the slender body ranges from about
142 to 242 inches. Its favorite sites for attachment
seem to be rocks, floats, and submerged timbers.

Tethyum pyriforme, the sea peach (Plate 143), is
of the right size and shape to earn its name, and
varies in color from orange to yellow, suffused with
pink or red. It is a strikingly handsome member of
the coastal population from Maine northward in
cold, shallow water.

Sea grapes are clusters of Molgula manhattensis,
the commonest sea squirt along North America’s At-
lantic coasts from Massachusetts southward. Each
“grape” is almost spherical, about | inch in diame-
ter, and greenish yellow in color. The surface ap-
pears soft and spongy, and often serves as a site for
the attachment of other kinds of animals.

Many sea squirts reproduce by budding as well as
by sexual means. They often build large, complex
colonies coating the surface of stones, sea walls, and
pilings (Plate 142). The various colonial species of
the genus Amaroucium are popularly called ‘sea
pork” from the translucent gray, tough tunic linking
one individual to the next.

In addition to the attached sea squirts (class As-
cidiacea), the urochords include several types of
free-swimming pelagic animals. Appendicularians
(class Larvaceae) never metamorphose from the
swimming, tadpole-like larval stage. Instead, they
develop reproductive organs and reproduce their
kind without ever “growing up.” Their whole lives
are spent as minute creatures swimming in upper
levels of the sea, where they secrete complicated
food traps of mucus in the form of a lemon-shaped
house. Every few hours the trap is discarded because
it becomes clogged with particles unsuitable as food,
and the appendicularian spends about thirty min-
utes creating a new one into which it can move.

Members of class Thaliacea are transparent ani-
mals that reach far larger size or group themselves
together into colonies big enough to handle easily.
Among the most spectacular of them are the pyro-
somes (Pyrosoma), found swimming gently in the
sea, either near its surface or far down in the depths.
Pyrosoma means “fire body,” and refers to the fact
that in the dark these colonies can be detected as
luminous cylinders moving slowly through the water.

Each translucent cylinder consists of hundreds or
thousands of ¥s-inch sea squirts arranged radially
around a lengthwise central cavity, like the separate
parts of a pineapple around the hole where the core

[287

Tube sea squirt, Ciona intestinalis, 5 inches high, fil-
ters food out of the water that is drawn into the open-
ing on the left and discharged through the temporar-
ily closed one on the right. (England. D. P. Wilson)

has been removed. Each individual of the colony
takes water and food particles through incurrent
Openings on the outside of the colony, and discharges
the water again from atrial openings into the central

288 |

cavity. The combined flow is enough to propel the
colony endwise—jet propulsion of the mildest kind.

Pyrosomes found near the surf or netted from the
sea usually fall in the size range from | to 5 inches
long and from 8 to 7% of an inch in diameter. Oc-
casionally a really large one is collected at night,
when the display of its luminescence is so vivid. One
pyrosome colony 4 feet long and 8 inches in diame-
ter was brought up and handled by scientists and
crew aboard an oceanographic research vessel. Be-
fore preserving their trophy, the men amused them-
selves for half an hour by writing their names in
light on its surface—merely by tracing a finger tip
gently over the outer ends of the small animals that
composed it.

None of the other thaliaceans is colonial. They
are known as salps, and they combine a _ barrel-
shaped body with extreme transparency. Many of
them are evident in the water only as a regular
series of hooplike muscle bands, seemingly with no
connection. Slow pulsations of these muscles drive
water in through the mouth opening at one end,
through the huge pharyngeal sieve, and out of the
atrial opening at the other end.

One crustacean of almost equal transparency
(Phronima) is sometimes found riding along in this
transparent-walled cavity. Nearly always it turns
out to be a female feeding on larger food particles
swept in by the salp, and using the pharyngeal bas-
ket as a convenient place in which to raise her young.

Salps reproduce both sexually and by budding.
Often the buds develop into fully grown individuals
while still attached to the parent. In this way, long,
delicate trains of salps arise. In Doliolum the budded
individuals migrate over the surface of the parent and
attach themselves temporarily to a dorsal projection,
taking places in three rows of remarkable regularity.

The Lancelets

(Subphylum Cephalochordata)

Along sandy coasts of most oceans where the wa-
ter is as warm as in North Carolina, southern Eng-
land, the Mediterranean, or Japan, if a shovel is
thrust suddenly into the wet beach at the low-tide
line and the handle pulled back sharply, little trans-
lucent flesh-colored animals may jump out and bury
themselves rapidly close by. If a person is quick, a
few can be captured. Each turns out to have a flat-
tened slender body pointed at both ends, but no
paired appendages or very obvious fins. It is a lance-
let, a link between the vertebrates and the more
widely known kinds of invertebrates.

Through sand that is very wet or under water,
lancelets can swim almost as easily as a minnow in

water itself. They emerge, wriggle a few inches, and
dive in again so quickly that one naturalist realized
he could not tell whether they swam mouth forward
or tail first. To learn the answer, he caught some
lancelets and carefully dipped the tail of each into a
harmless dye. Then he released them in an aquar-
ium with a sandy bottom. Some dove into the sand
mouth first. Others went tail first. But when they
swam around of their own volition, the mouth was
always in advance.

Undisturbed lancelets rest in the sand with just the
mouth exposed. Water drawn into the pharynx passes
through oblique S-shaped slits into the atrium and
emerges into the sand about two-thirds of the way

along the ventral surface. The anus opens farther
back, at the base of the narrowly fin-bordered tail.

The reproductive organs, either testes or ovaries,
form a series of block-shaped bags that bulge into the
atrium and release their products into the water
being discharged through the atrial opening. Fertili-
zation occurs outside the body, and the development
of the embryo follows a pattern closely comparable
to that in many vertebrates. The early stages, how-
ever, suggest the steps in growth of an echinoderm
embryo. For this reason, lancelets have been of spe-
cial interest to scientists, and are still known by an
outmoded generic name as “amphioxi.” “Amphi-
oxus” merely indicates “pointed at both ends.”

[289

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INDEX

NOTE: A numeral in parentheses refers to a color plate; a page number followed
by an asterisk indicates a black-and-white illustration.

Abalones, 178*
Acanthobdella, 208
Acanthocephala, 15, 142
Acanthoptilum, 103
Achatina, 177, 183 (49)
Acmaea, 179*, 181*
Acoels, 120 (36)
Acorn worm, 146*, 147*
Acropora, 113 (31)
Actinophrys, 31
Actinopyga, 273, 275
Actinosphaerium, 31
Actinozoa, 97
Adamsia, 105
Aeolis, 182
Aequorea, 72
African sleeping sickness, 26,
2
A glaophenia, 72
Albatrossaster, 277
Alcyonaceans, 99, 100*
Alcyonaria, 98
Alcyonium, 99*, 102 (9)
Allopora, 75
Alpheus, 237
Amaroucium, 287
Amebas, 28*
Amebiasis, 29
Amoeba, 19, 20, 28*, 29
Amphihelia, 110
Amphineura, 159
“Amphioxus,” 289
Amphipholis, 285

Amphipoda, 234
Amphiporus, 131*, 132
Amphiscolops, 121
Amphitrite, 206*
Ancylostoma, 137
Anemones, see Sea anemones
Anemonia, 106 (14)( 19)
Annelida, 15, 200, 205*
Anodonta, 192
Anomia, 188
Anopheles, 49
Anseropoda, 278
Antedon, 256, 274*
Antennae, 226
Anthomastus, 101
Anthopleura, 106, 107* (13)
Anthozoa, 97
Antipatharians, 113
Aphrodite, 202 (85)
Aplacophora, 160
Aplysia (60)
Appendicularians, 287
Arachnida, 243
Araneae, 243

Arcella, 29
“Archiannelids,” 204
Architeuthis, 197
Arenicola, 203

Argiope, 244*
Argonauta, 199
Argulus, 232
Argyronecta, 244
Argyrotheca, 155

Ariolimax, 185*

Arion (71)

“Aristotle’s lantern,” 281
Armadillidium, 234, 236*
Arrow worms, 144*, 145*
Artemia, 229*
Arthropoda, 15, 226
Articulata, 155

Ascarids, 133

Ascaris, 133, 136
Aschelminthes, 133
Ascomorpha, 139
Asconema, 61

Asellus, 234

Asexual reproduction, 20
Astacopsis, 238

Astacus, 237

Asterias, 279, 280* (124)
Asterina, 278

Asteroidea, 276
Astrangia, 110, 111*
Astroides, 111 (24)
Astrometis, 279
Astropecten, 277

Atolls, 113

Atrium, 286

Auger snails, 177
Aurelia, 76*, 80
Avicularia, 245
Avicularium, 151
“Avoiding reaction,” 52
Axinella (3)

[293

Balanoglossus, 146
Balanophyllia, 110
Balantidium, 53

Balanus, 233, 234*, 235*
(90)

Barber-shop shrimp
Barnacles, 233, 234*
Barrier reefs, 113
Basket star, 285 (134)
Bathyplotes, 275
Bdelloid rotifers, 138
Bdelloura, 123

Beach fleas, 235

Bean shells, 188

Bear animalcules, 226*, 227

Beard worms, 148*
Bear’s-paw clam, 192

“‘Béche-de-mer,” 274, 275*

Beroé, 116, 118
Bilateral symmetry, 14
Binary fission, 20

Caecum, 177
Cake urchin, 283
Calanus, 231, 232*
Calcarea, 59

Calliactis, 106, 107 (15)

Callinectes, 239
Calliostoma (52)
Cambarus, 237 (94)
Cameos, 181
Cancer, 239 (96)
Caprella, 235, 238*
Carapace, 235
Carchesium, 54
Carcinides, 239 (95)
Carcinonemertes, 132
Carcinoscorpius, 243
Cardisoma (98)
Cardium, 191

294 |

Bipalium, 123

Birgus, 238 (102)

Bispira (84)

Black corals, 113

Black pearls, 187

Black widow spider, 245 (113)
Blood fluke, 119, 126
Bloodsucker, 225
“Bluebottle,” 75

Boat shell, 180

Bodo, 26

Bolinopsis, 118
Boloceroides, 108

Bonellia, 157*

Bootlace worm, 129, 130*
Botryllus (142)
Brachiopoda, 154, 155*
Brachyura, 238

Brain corals, 108*, 109 (27)
Branchellion, 225

Carteria, 25

Carybdea, 80
Caryophyllia, 110 (23)
Cassiopeia, 97, 98*

Cassis, 181

“Cat’s eyes,” 115

Caudina, 276

Centipedes, 226*, 240*, (117)
Centrostephanus, 281
Centruroides, 248

Cepaea (50)
Cephalochordata, 286, 288
Cephalodiscus, 147
Cephalopoda, 194
Cephalothorax, 235
Ceramaster, 277 (130)
Ceratia, 182

Ceratium, 23*, 24

Branchiocerianthus, 71, 72

“Brandling,” 206

Breadcrumb sponge (1)

Brine shrimp, 229*

Bristle-footed worms, 202*, 206

Brittle star, 254, 284 (131-133)

“Brown bodies,” 150

Bryozoay 155 1505 1516s)
(34)

Bubble shell (57)

Budding, 20

Bugula, 153 (34)

Bunodactis, 107 (21)

Busycon (104)

“Butterfly fish,” 159

“Butterfly shells,” 189, 191*

Byssus, 187

“By-the-wind sailor,” 75

Ceratosoma (65), (66)
Cercaria, 125
Cerebratulus, 131, 132
Cereus, 108
Cerianthids, 104
Cerianthus, 114, 149 (32)
Cestids, 118

Cestoda, 126
Cestodaria, 127
Cestum, 118
Chaetognatha, 15, 144
Chaetopleura, 160
Chaetopterus, 203, 204*
Chagas’s disease, 27
Chainworm, 201

Chalk, 30

Chama, 188

Charonia, 181

Cheilostomata, 153
Chelicerae, 226
“Chelicerate,” 226
Chelifer, 248
Chigger, 251
Chilomonas, 23
Chilopoda, 240
Chink shells, 160
Chiridota, 276
Chiropsalmus, 76, 80
Chiton, 158*, 159 (38)
Chlamydomonas, 25
Chlamys, 189*
Chlorophyll, 21
Choanoflagellates, 26
Chordata, 14, 15
Chromatophores, 21
Chromulina, 22
Chrysaora, 80
Chrysomonads, 22
Cidarids, 281

Cidaris, 281

Cilia, 51

Ciliata, 51

Ciona, 287, 288*
Cirripedia, 233
Cistenides, 202
Cladocera, 230, 232*
Clams, 158*, 184
Clamworm, 201*
Clathrulina, 31
Clava, 72 (4)
Clavellina (144)
Cliona, 63

Clione, 177*
Clionidae, 64

Dactylometra, 76, 79*, 97 (7)
Daddy longlegs, 249, 252*
Daphnia, 230*

“Date mussel,” 191

“Dead men’s fingers,” 99*
Decapoda, 236

Deep scattering layer, 231

Clitellio, 206
Clitellum, 206
Clonorchis, 125*

“Cloth of gold,” 187
Clypeaster, 283
Cnidaria, 67, 68
Coccidians, 49
Coccidiosis, 49
Coccoliths, 23, 30
Cockle, 191

Cocoon, 206

Codosiga, 26
Coelenterata, 15, 67
Coenobita (101)
Coleps, 52

“Collar cells,” 57
Colobocentrotus, 283
Colossendeis, 253
Colpoda, 52

Comb jellies, 115, 117*
“Compensation cavity,” 151
Conchoderma, 233
Conchs, 177, 180 (51)
Cone snails, 177
Conjugants, 51
Contractile vacuole, 21
Conus, 177 (59)
Convoluta, 121 (36)
Copepoda, 230, 231*, 232*
Coquinas, 188, 191*
Coral reefs, 111

Corals, 97 (23-29), (31)
Corallium, 102
Cordylophora, 72
Coronate jellyfishes, 80
Coronula, 233

Dendronotus (63)
Dendrophyllia, 110
Dendrosoma, 55
Dentalium, 193, 198*
Dermacentor, 252
Dermanyssus, 251
Dero, 306

Corymorpha, 72
Coscinasterias, 280
Cowries, 181, 184* (58)
Crabs, 239 (95-104)
Crangon, 236, 237
Crania, 154
Craspedacusta, 74
Craterolophus, 77*
Crayfishes, 237, 239* (93),
(94)
Crepidula, 180
Cresets, 197*
Crinoidea, 255
Cristatella, 152
Crossaster, 279 (127)
Crustacea, 229
Cryptochiton, 160
Cryptomonads, 23
Ctenidia, 177
Ctenodiscus, 277
Ctenophora, 15, 115
Ctenoplana, 118
Ctenostomata, 153
Cuboidal jellyfishes, 80
Cucumaria, 275 (140)
“Cultured pearls,” 186
Cuttlefish, 194 (75)
Cyanea, 76, 78*, 80, 97
Cyclops, 231*
Cydippids, 116
Cypraea, 184* (58)
“Cyprid” stage, 233
Cypris, 233
Cysts, 19

Diadema, 281, 282*
Diadumene, 108
Dibothriocephalus, 127
Didinium, 51, 52
Difflugia, 29

Digenetic flukes, 125
Dinobryon, 22

Dinoflagellates, 23*, 24*
Dinophilus, 204

Diodora (47)

Diopatra, 203
Diphyllobothrium, 127
Diplomonads, 28

Diplopoda, 241

Doliolum, 288

Dolomedes, 244 (109), (111)
Donax, 188, 191*

Dourine disease, 27
Dracunculis, 137

Drilophaga, 139
Dromia (103)
PSE. 23
Dugesia, 122*
Dysentery, 29

Ear shells, 178
Earthworm, 204, 207*
Echinarachnius, 283
Echinococcus, 128
Echinodera, 140
“Echinodere,” 140
Echinodermata, 15, 254
Echinodiscus, 284
Echinoidea, 280
Echinus, 283 (136)
Echiuroidea, 15, 157*
Echiurus, 157
Ectoprocta, 150
Ectyodoryx, 63

Edged sea stars, 277
Edwardsia, 105
Edwardsiella, 105
“Eelworms,” 133
Eimeria, 49

Eisenia, 206

Eledone (78-80)
Elephantiasis, 138
Elephant’s-ear sponge, 64*
Elephant-tusk shell, 193
Elkhorn coral, 112*
Elphidium, 31
Emplectonema, 132
Enchytraeus, 200, 206
Encope, 284
Encystment, 19

Ensis, 189, 192*
Entamoeba, 29
Enterobius, 138
Entoprocta, 15, 143*
Epiactis, 108 (16)
Epidinium, 21, 53
Ephippium, 230
Epistylis, 54

Epizoanthus, 113 (30)
“Errantia,” 202
Eubranchipus, 228*, 229
Eucestoda, 127
Eudistylia (81)
Euglena, 24, 25*
Euglenoids, 25
Eugorgia, 101
Eukrohnia, 145
Eunice, 202, 203*
Eunicella, 102 (11)
Eunoa, 202
Eupentacta (140)
Euphausiacea, 236
Euplanaria, 122
Euplectella, 61*
Euplotes, 54
Eurypterida, 242

Fairy shrimp, 228*, 229

“False spiders,” 247

Fan worms, 205* (83), (84)

Fasciola, 126

Feather-duster worms, 200*,
203 (81)

Feather stars, 255, 256, 274*
(135)

Filarial worms, 138

File shells, 187 (44-46)

Finger sponge, 63*

296 |

Fire worm, 202
Fish louse, 232
Fissurella, 179
Flabellum, 110
Flagellata, 16, 21
Flagellum, 21
Flatworms, 119, 123*, 124*
(35), (36)
Flukes, 119*, 124
Flustra, 153
Food vacuole, 51

Foraminiferans, 29, 30*, 31*
“Forams,” 29
Forceps-carrying sea stars, 279
Forcipulata, 279

Forskalia, 76

Fredericella, 152
Fresh-water clams, 192, 195*
Fresh-water mussels, 192
Fresh-water sponge, 62*
“Frutta di mare,” 283
Fungia, 109

Galathealinum, 148
Galatheanthemum, 104
Gammarus, 235

Garden snails, 187* (50)
Gastropoda, 160
Gastrotricha, 15, 139*, 140
Gattyana, 206*
Gemmules, 59, 64
Geoduck, 190
Geonemertes, 131
Geophilus, 241
Gersemia, 101

“Glacier worms,” 206

Glaucoma, 20
Glaucus, 182
Globigerina, 30
“Globigerina ooze,” 30
Glochidium, 192
Glossiphonia, 225
Glottidia, 155
Golfingia, 156*
Gonactinia, 104, 106, 108
Gonionemus, 69*, 74*
Gonium, 25
Gonyaulax, 23
Gordian worms, 141

Gorgonia, 102
Gorgonians, 101, 102*
Gorgonocephalus, 285
Grantia, 60
Gregarina, 49*
Gregarines, 33, 49*
Gribble, 234

Guinea worms, 133, 137
Gymnodinium, 23
Gymnolaemata, 153
Gyrodactylus, 124

Haematococcus, 25
Haemodipsa, 225
Haemopis, 225
Haemoproteus, 50*
Hairy stinger, 97
Halichondria, 62 (1)
Haliclona, 62
Haliclystus, 77*, 80
Haliotis, 178*
Halosydna, 202
Halteria, 53

Harenactis, 105, 108
Harvestmen, 249, 252*
Heart urchin, 284
Hectocotylized arm, 197
Heliometra, 256
Heliopora, 101
Heliozoans, 31

Helix, 183, 187*
Hemichordata, 15, 146
Hemosporidians, 49
Henricia, 278 (125)
Hermissenda (62), (64), (69)
Hermit crabs, 238 (101), (104)

Hermodice, 202
Herpetomonas, 27
Herpobdella, 225

Hesione, 202*
Heterocentrotus, 283, 284*
Heterodera, 136
Heteronemerteans, 132
Heteronereis, 201
Heteropsammia, 109
Hexacorallians, 98
Hexactinellida, 60

Hinge, 185

Hinnites, 187

Hippa, 240*

Hippopodius, 75, 76
Hippospongia, 57*
Hirudin, 208

Hirudinea, 208

Hirudo, 225

Holothuria, 273, 275 (141)
Holothuroidea, 273
Holotrichs, 52

Homarus, 237
Honeycomb worm (86) (87)

Hoof shells, 188
Hookworms, 137
Hoplonemerteans, 132
Hoploplana, 124
Hormiphora, 117
Horny corals, 101
Horse conch, 177
Horsehair worms, 141*
Horseshoe “crabs,” 225*, 242*
Hyalella, 235
Hyalonema, 61
Hydatid cyst, 128
Hydatina (57)
Hydractinia, 72
Hydra, 73
Hydras, 72*, 73*
Hydrocorals, 74
Hydroides, 204
Hydroids, 67*, 70*, 71* (4)
(5)
Hydrozoa, 70
Hymeniacidon, 62
Hymenolepis, 128
Hypermastiginads, 28

[297

Idotea, 234

Inarticulata, 155

India ink, 195
Infusorians, 16

Introvert, 156
Ischnochiton, 160

Isle of Wight disease, 252
Isopoda 234, 236*
Isospora, 49

Jackknife clam, 193*
Janthina, 179

Jellyfishes, 67*, 69*, 74*, 76%,

Vis TE, Sal (BD)
Jingle shells, 188
Julus, 241

Kala azar, 27

Katharina, 160 (39)

Keratosa, 64

Keyhole limpet, 179 (47), (48)
Kinorhyncha, 15, 139*, 140
Kirchenpaueria, 70*

Krill, 236

Lacuna, 160

Lambis (51)
Lamellaxis, 184*
Lamellisabella, 148
Lamp shells, 154*
Lancelets, 286*, 288
Land snails, 182, 184* (49)
Laqueus, 155
Larvaceae, 287
Latrodectus, 245 (113)
Leeches, 208
Leioptilus, 103
Leishmania, 27

Lepas, 233, 234*
Lepidochiton, 160
Lepidonotus, 202
Leptodora, 230
Leptychaster, 277
Leucosolenia, 59, 60*

Libinia, 239

Ligia, 234 (89)

Liguus, 183, 188*

Lima, 187 (44)

Limax, 183, 185*, 186*

Limestones, 30

Limnocnida, 74

Limnochares (115)

Limnoria, 234

Limpet, 178, 179*, 180*, 181*
(47), (48)

Limulus, 242*

Linckia, 278 (129)

Lineus, 129, 130*, 132

Lingula, 154*

“Lion’s mane,” 97

Lithophaga, 191

Littorina, 180, 183* (56)

Liver flukes, 125*

Lizzia, 72*, 73
Lobophyllia (27)
Lobsters, 226*, 237
Loligo, 194 (72), (73)
Lophelia, 110
Lophogorgia, 101
Lophophores, 155
“Loricates,” 160
Lucapina, 179
Lucernaria, 80
Lucernids, 78
Lugworm, 203
Luidia, 277 (123)
Lumbricus, 206
Luminodesmus, 242
Lycosa, 244 (110)
Lymnaea, 182
Lytechinus, 281

M

Macoma, 190
Macracanthorhynchus, 142
Macrobdella, 225
Macrocheira, 239

298 |

Macroperipatus, 228 (88)
Macrura, 238

Madrepora, 110
Madreporarian corals, 109

Madreporites, 276
Malacobdella, 132
Malaria, 49
“Mandibulate,” 226

Mantis shrimps, 240 (91)

Many-mouthed jellyfishes, 97*

Margaropus, 252

“Marine silk,” 187

Martesia, 190

Mastax, 139

Mastigophora, 21

Mastigoproctus, 248 (105),
(106)

Mediaster, 278

Medusa, 68, 70 (6)

Megalotractus, 177

Megascolides, 207

Megathura (48)

Melampus, 177

Meleagrina, 188

Mellita, 284, 285*

Meloidogyne, 136

Membranipora (33)

Mermis, 135*

Mermithid nematodes, 135*

Merostomata, 242

Mertensia, 117
Mesothuria, 275
Mesozoa, 15, 133
Metargiope (114)
Metazoa, 15
Metridium, 104, 105*, 108 (18)
(22)
Microciona, 64
Micron, 18
Microstomum, 121
Millepora, 113
Millepores, 74
Millipedes, 241*, 242 (116)
Milne-Edwardsia, 105
Minyads, 104
Mites, 249 (115)
Mnemiopsis, 117*
Modiolus, 187
Molgula, 287
Mollusca, 15, 158, 177*
Molpadonias, 275
Monas, 26

Monaxonida, 62
Moniliformis, 142
Monogenetic flukes, 124
Monogononta, 140
Monoplacophora, 159
Monoraphis, 61
Monosiga, 26
Montastrea, 65*, 113*
Moon snail, 179, 183* (55)
Mopalia (38)

Moss animals, 150*
“Mother-of-pearl,” 186
Multiple fission, 20
Murex, 181
Musculium, 191

Mya, 190

Mycale, 63

Mycetozoa, 18
Mysidacea, 235
Mytilus, 190* (40)

N

Nagana, 26

Nauplius stage, 231, 232, 233
Nausithoé, 80

Nautilus, 194, 195, 198* (74)
Necator, 137

Nematoda, 15, 134*
Nematomorpha, 15, 141
Nemertea, 15, 129, 131*

Neopilina, 159

Neothyris, 155

Nephila, 244*, 245

Nephridia, 156, 159, 200, 208,
228

Neptune’s goblet, 62

Nereis, 201*

Night crawler, 206

Noctiluca, 24*
Notochord, 286
Nucleus, 21

Nuda, 118
Nudibranchs, 177, 182
Nummulites, 30
Nuttallina, 160

Obelia, 71

Octocorallians, 98

Octopus, 158*, 194, 197, 199*
(76-80)

Ocypoda, 239 (99)

Odontosyllis, 202

Oikomonas, 26

Okenia (61)
Old-maid’s curl, 180
Oligochaeta, 204
Olivancillaria (53)
Oncicola, 142
One-celled animals, 15
Oniscus, 234, 236*

Onychophora, 227
Ooperipatus, 229
Opalina, 52
Opalinids, 52
“Opelet,” 106
Operculina, 30
Operculum, 160

[299

Ophiacantha, 285
Ophiactis, 285

Ophiocoma (132)
Ophiopholis, 285
Ophioscolex, 285
Ophiuroidea, 284
Ophlitaspongia, 62
“Opisthobranchs,” 177, 182

Ophiothrix, 285 (131)
Opisthorchis, 125*
Opossum shrimps, 235
Orb-weaver, 226*, 244*
Orchestia, 235

Oreaster, 278

Organelle, 21
Organ-pipe coral, 101

Oriental sore, 27
Ormers, 178

Osilinus, 182*
Ostracoda, 232, 233*
Ostraea, 188
Oxytricha, 54

Oyster drills, 177, 181
Oysters, 188

Pagurus (104)

Palaemonetes, 237 (92)

Paleonemerteans, 132

Palinurus, 237, 239*

Palolo worm, 202

Panope, 190

Panulirus, 237

Paper nautilus, 199

Paracentrotus, 283

Paracyamus, 235

Paragorgia, 101

Paramecium, 16*, 18*, 19, 20,
Deel

Paranemertes, 132

Parapodia, 201

Parasitic, 20

Parazoa, 15, 57

Parchment worm, 203, 204*

Patella, 180*

Patiria, 278 (126)

Peachia, 105

Peanut worms, 156*

Pearl, 186

Pearl oysters, 188

Pecten, 186 (42), (43)

Pectinatella, 151*, 152*

Pedicellariae, 276

Pedipalpi, 248

Pedipalps, 226

Pelagia, 80

Pelecypoda, 184

Pelomyxa, 29

Pen shells, 187

Peneus, 236

Pennatula, 103

Pennatulaceans, 102

Peranema, 25*

Peridinium, 24

300 }

Periostracum, 185
Peripatoides, 228
Peripatopsis, 228
Peripatus, 227* (88)
Periphylla, 80
Peritrichs, 54
Periwinkle, 180, 183 (56)
Petaloids, 283
Phalangida, 249
Phallusia (10)
Phanerozonia, 277
Phantom bottom, 198, 231
Phascolosoma, 156*
Pheronema, 61
Philodina, 138
Phoronida, 15, 149*
Phoronis, 149
Phoronopsis, 149
Photoreceptor, 21
Phronima, 235
Phylactolaemata, 152
Phyllangia (26)
Phyllopoda, 229*
Physa, 182

Physalia, 75 (8)
Physophora, 75, 76
Phytomastigina, 22
Phytomonads, 25
Phytomonas, 27
Piddocks, 190

“Pill bugs,” 234, 236* (89)
Pisaster, 279 (118-122)
Piscicola, 225

Pismo clam, 189

Pistol shrimps, 237
Placobdella, 225
Planarians, 119, 121
Planorbis, 182

Planula, 70, 97, 133
Plasmodium, 50
Platyhelminthes, 15, 119
Platynereis, 202
Pleurobrachia, 116*
Pleuroploca, 177
Plumatella, 152
Plumularia, 70*
Podocoryne, 73
Pogonophora, 15, 148
Poison) 23685 Lida 273
Polinices, 179, 183* (55)
Polychaeta, 201
Polyclads, 123
Polygordius, 204
Polymastia (3)
Polymastiginids, 27
Polyorchis (6)
Polyplacophora, 160
Polyps, 68, 70
Polystoma, 125
Pond snails, 182
Pontobdella, 225
Porcellio, 234
Porifera, 15
Porites, 111 (25)
Portuguese man-of-war, 69, 75
(8)
Poterion, 62
Prawns, 236 (92)
Precious coral, 102
Priapulida, 15, 141*
Priapulus, 141
Proales, 139
Proboscis worm, 129
Procambarus (93)
Procerodes, 123
Procotyla, 123

“Prosobranchs,” 177
Prostheceraeus, 124
Prostoma, 131
Prostomium, 157
Protista, 17
Protoplasm, 18
Protozoa, 15, 16
Psammechinus, 283
Pseudoceros (35)
Pseudopods, 28
Pseudoscorpionida, 248

Radial symmetry, 14
“Radiolarian ooze,” 32
Radiolarian shells, 32*
Radiolarians, 16*, 31
Radula, 158, 177, 194
Ragworm, 201

Razor clams, 189, 192*
Razor shell, 192*

Red snow, 25

Pseudoscorpions, 248
Pseudosquilla (91)
Psilaster, 277
Psolidium, 275
Psolus, 275

Pteraster, 279
Pteropods, 177
Pterosagitta, 145
Ptychodera, 146, 147*
“Pulmonates,’ 177
“Purple sailor,” 75

R

“Red spider,” 252

“Red tides,” 23

Reef corals, 109, 111 (28)
“Respiratory trees,” 273
Rhabdocoels, 121
Rhabdopleura, 147
Rhinophores, 182
Rhizopoda, 28
Rhizostoma, 97*

“Purple shell,” 179
Purples (54)
Pycnogonida, 252, 253*
Pycnopodia, 280 (128)
Pyrosoma, 287
Pyrosomes, 287

Quahog, 190
“Quarter-deck shell,” 180

Rhopilema, 77

Ribbon worms, 129, 131*, 132*
(37)

Robber crab, 238 (102)

Rotifera, 15, 18*, 138, 139*

Roundworms, 133

Royal purple, 181

Sabellaria (86) (87)

Sabellids, 203, 205* (83)

Saccoglossus, 146

Sacculina, 233

Sagartia, 108

Sagitta, 144, 145*

Salps, 286*, 288

Salt-marsh snails, 177

Salticus, 245

Sand dollar, 254, 280, 283, 285*

Saprozoic, 20

Sarcodina, 28

Sarcoptes, 251

Sarsia, 73

Saxicava, 190

Scale worms, 202, 206* (85)

Scallops, 158*, 186, 189*
(41-43)

Scaphopoda, 193, 198*

Schistosoma, 119, 126
Scleractinian corals, 109
Scolex, 126
Scolopendra, 241 (117)
Scorpio, 247
Scorpionida, 247
Scorpions, 247, 251*
Scuds, 235
Scutigera, 240*
Scyllaea (68)
Scyphozoa, 70, 76
Scyphozoans, 68, 77
Sea anemones, 104 (13-22),
(32)
“Sea arrowheads,” 284
Sea bat, 278 (126)
“Sea beef,” 159
“Sea biscuit,” 283
Sea blubbers, 80

“Sea butterflies,” 159, 177%,
197*

Sea collar, 179

Sea cradle, 158*, 159

Sea cucumbers, 254*, 273, 275*
(140) (141)

“Sea egg,” 283

Sea fans, 65*, 97, 101, 102 (11)

“Sea ferns,” 69

Sea fingers (9)

sea firs, 70

“Sea gooseberries,” 115, 116*

Sea grapes, 287

Sea hare, 182 (60)

Sea lilies, 254*, 255, 256

Sea mouse, 202 (85)

Sea nettle, 79*

“Sea pancake,” 284

[301

Sea peach, 287 (143)

Sea pens, 102, 103* (10)

“Sea plumes,” 70, 101

“Sea pork,” 287

Sea slugs, 177, 182 (61-69)

Sea spiders, 252, 253*

Sea squirts, 286*, 287, 288*
(10) (142)

Sea stars, 189*, 254*, 276, 280*
(118-125), (129), (130)
Sea urchins, 254*, 280, 281,

282*, 284* (136-139)
“Sea walnuts,” 115*, 117

Sea wasps, 76, 80
Sea whips, 65*, 97, 101, 102*
Seatworm, 138
“Sedentaria,” 202
Segmented worms, 200
Sepia, 194 (75)

Serpent stars, 254*, 284

Serpula, 204 (82)

Serpulids, 204 (82)

Sertularia, 69, 71

“Seven-year-itch,” 251

Sexual reproduction, 20

Shipworm, 191, 195*

Shrimps, 236, (90), (91)

Siboglinum, 148

Siliqua, 189, 192*

Siphon, 190

Siphonophores, 75

Sipunculoidea, 15, 156

Sipunculus, 156

Skeleton shrimp, 235, 238*

Slaters, 234

Sleeping sickness, African, 26,
ale

Slime molds, 18

“Slipper shell,” 180

Tachypleus, 243

Taenia, 127*

Tagelus, 193*

Talorchestia, 235
Tapeworms, 119*, 126, 127*
Tarantulas (107)
Tardigrada, 226

302 ]

Slugs, 158*, 182, 185*, 186*

(61=71)
Snails, 160 (49), (50), (55)
Snakelocks anemone, 106 (14)
Soft corals, 99*, 100*, 101* (9)
(29)
Soil nematodes, 135
Solaster, 279
Solenogasters, 160
Solpugida, 247
Sorocelis, 123
Sow-bugs, 234, 236*
Spadella, 145
Spaerium, 191
“Spat,” 188
Spatangus, 284
Sperostoma, 280
Spheciospongia, 62
Spicules, 58, 59, 60
Spiders, 243 (108-114)
Spinulosa, 278
Spiny-headed worms, 142*
Spiny lobster, 237, 239*
Spiny sea stars, 278
Spirorbis, 204
Spirobrachia, 148
Spirographis (83)
Spirostomum, 18*, 53
Spirotrichs, 53
Spirula, 194
Sponge fisheries, 66
Sponges, 15, 56* (1), (2), (3)
Spongilla, 62*
Spongillidae, 64
Sporozoa, 32
Sporulation, 20
Squids, 194, 197 (72), (73)
Squilla, 240
Stalked jellyfishes, 78

Tarentine fabric, 187
Tealia, 105, 107 (17) (20)
Tegula, 182*

Tentacles, 160

Tentaculata, 116
Terebratulina, 155

Teredo, 191, 195*

Stalked medusas, 80

Stalked tunicates, 144

“Star coral,” 110, 113*

Starfishes: see Sea stars

Statoblasts, 152

Stauromedusas, 78

Stenopus (90)

Stenostomata, 153

Stentor, 18, 51, 53*

Stichodacytyline anemones, 104

Stichopus, 275

Stigma, 21

Sting, 247

“Stinging corals,” 74, 113

Stoichactis, 104

Stoloniferans, 101

Stomatopoda, 240

Stomolophus, 97

Stomphia, 106

Stony corals, 104, 112*

Strombus, 181

Strongylocentrotus, 280, 283
(137) (138)

Stylatula, 103

Stylochus, 124

Stylonychia, 54*

Suberites (2)

Suberitidae, 64

Suctoria, 20, 54

“Sun animalcules,” 31

Sun stars, 279* (127)

Surf-dwelling clam, 189

“Swimmers’ itch,” 119, 126

Sycon, 60*

Symmetry, 14

Synaptula, 276

Synura, 23

Tethys, 182
Tethyum, 287 (143)
Tetilla, 58, 62
Tetractinellida, 62
Tetrahymena, 51
Tetrastemma, 131
Thais (54)

Thalassicola, 31
Thaliacea, 287
Theridion, 244

Thorny corals, 113
Threadworm, 138
Thyone, 275

Ticks, 249, 253*

Tiger cowrie, 184* (58)
Tivela, 189

Tjalfiella, 118
Tokophrya, 54

Tooth shell, 158*, 193
Tracheae, 228
Trachelobdella, 225
Trachyline medusas, 74
Tree snail, 183, 188*
Trematoda, 124

“Trepang,” 274, 275*
Trichina worm, 136
Trichinella, 136, 137*
Trichodina, 54
Trichomonads, 27
Trichomonas, 28
Trichonympha, 28
Triclads, 121
Tridacna, 192, 196*
Triopha (67)
Tripneustes, 283
“Tripoli stone,” 32
Trochophore, 156
Trombicula, 251
Tropiometra, 256
Trypanosoma, 27*
Trypanosomes, 26, 27*

Trumpet shell, 181
Tsetse fly, 27

Tubastrea, 111

Tube anemones, 104, 114 (32)
Tube-foot, 255

Tube shell, 177

Tube worm, (82)
Tubifex, 200, 206
Tubipora, 101
Tubulanus, 132* (37)
Tubularia, 72 (5)
Tubulipora, 153
Tunicates (144)
Turbatrix, 135
Turbellaria, 120
Turbellarians, 119*, 120
Tyrian purple, 181

Uca, 240 (100)
Umbellula, 103
Unio, 192
Urechis, 157
Urnatella, 143
Urochordata, 286
Urosalpinx, 181

Vacuole, 51

Vampire squid, 199
Vampyroteuthis, 198
Velamen, 118

Velella, 75

Velum, 70

Velvet worms, 226*, 227
Venom, 245

Venus, 190

Venus’ flower basket, 61*

“Venus’ girdle,” 115*, 118
Veretillum, 103 (10)
Vermicularia, 180
Victorella, 153
Vinegarone (105) (106)
Virgularia, 103

Vitamins, 231

Volvox, 25, 26*
Vorticella, 54, 55*

W xX

Wampum, 190
Water fleas, 226*, 230*
Water spider, 244

Water-vascular system, 254

Webs, 243

Wedge shells, 191*
Whale louse, 235

Wharf louse, 234

“Wheel animalcules,” 138
Wheel snails, 182

Whelks, 177, 180 (104)

Whipscorpion, 248, 251* (105),
(106)

Whipworm, 138

“Whiteweed,” 69, 71

“Wireworm,” 241

Worm shell, 180

Wrinkled purples (54)

Xiphosura, 242

Zirfaea, 190

Zoantharia, 104
Zoantharians, 98
Zoanthids, 104, 113 (30)
Zoochorellae, 22
Zoomastigina, 26
Zoothamnium, 54
Zooxanthellae, 22, 111

[303

THIS BOOK has been printed and bound by Kingsport Press, Inc.
Color engravings by Chanticleer Company. Design and typography
by James Hendrickson. Color layout by Nancy H. Dale.

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