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j

INVERTEBRAT=
ZOOLOGY

Crustacea

A TREATISE ON ZOOLOGY

A TREATISE ON ZOOLOGY

Demy 8vo, Cloth, price 15s. net each ; or in Paper
Covers, price 12s. 6d. net cach.

VOLUMES READY

Part I. (First Fascicle) INTRODUCTION AND
PROTOZOA. By Sir Ray LANKEsTER, K.C.B., F.R.S. ;
Prof. S. J. Hickson, M.A., F.R.S.; F. W. GAMBLE,
DSc, ERs: ; A. Waitimy, MsAS) Disc Ban: sas. dene.
Lister, F.R.S.; H. M. Woopcock, D.Se.; and the late
Prof. WELDON.

Part I. (Second Fascicle) INTRODUCTION AND
PROTOZOA. By J. B. Farmer, D.Sc., M.A., F.R.S. ;
Jaa eIStE Re CRAs abe AG MINCHIN, WINS & Ahovel Sed,
Hickson, F.R.S.

Part Hl. THE PORIFERA AND COELENTERA.
By Sir Ray LANKESTER, K.C.B., F.R.S.; HE. A. MINCHIN,
M.A.; G. HERBERT Fow Ler, B.A., Ph.D. ; and GILBERT
C. Bourne, M.A.

Part Ill. THE ECHINODERMA. by F. A. Barner,
M.A., assisted by J. W. Gregory, D.Se., and E. 8.
GoopricH, M.A.

Part IV. THE PLATYHELMIA, THE MESOZOA,
and THE NEMERTINI. By Prof. Brenna, D.Sc.

Part V. MOLLUSCA. By Dr. Pau PELSENEER.

Part VII. APPENDICULATA (Third Fascicle:
CRUSTACEA). By W. T. Caumay, D.Sc.

Part IX. VERTEBRATA CRANIATA (First Fas-
cicle: FISHES). By E. 8. Goopricn, M.A., F.R.S.

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A

TREATISE ON ZOOLOGY

EDITED BY

Str RAY LANKESTER

K.C.B., M.A., LL.D., F.R.S.

HONORARY FELLOW OF EXETER COLLEGE, OXFORD; CORRESPONDENT OF THE INSTITUTE

OF FRANCE 3; LATE DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS
OF THE BRITISH MUSEUM

Part VII
ae END © Ula
THIRD FASCICLE
CRUSTACEA.

BY

WT. CALMAN,, DSc. (St. Ann.)

.
ASSISTANT IN THE ZOOLOGICAL DEPARTMENT OF THE BRITISH MUSEUM

LONDON
ADAM AND CHARLES BLACK
19.09

een lnstit,, te»
g¢ APR 111910
a Vio 3.) He

onal Muses”

PREFACE

THE present volume is an instalment of that part of the

treatise dealing with the great phylum Appendiculata— a
phylum which includes the Arthropoda, Chetopoda, and
Rotifera. Dr. Calman having finished the present description
of the Crustacea, it has been considered advisable to publish
it at once, without waiting either for the general intro-
duction on the classification and characters of the phylum
Appendiculata or for the completion of the fascicles devoted to
the Peripatoids, Chilopods, Arachnids, Chilognaths, Hexapod
Insects, Cheetopods, and Rotifers.
KE. RAY LANKESTER.

January 1909.

CONTENTS

CHARTER!
THE CLASS CRUSTACEA : ; F , ; 1
CHAP TER» it
THE BRANCHIOPODA . 5 . : : ; 29
CHAPTER lit
THE OstTRACODA 56
CHAP RER IV
THE CoPEPODA : ; ‘ . : , al
CHAPTER V
THe CIRRIPEDIA : ; ; : : ‘ 106
CHAPTER. Vi
THE MALACOSTRACA . : . ; , / 143
CHAPTER VII
THe LeProsrRAca E E : ; : : 151
CHAPTER VIII

THE SYNCARIDA : . , 3 : : 162

vill

THE CRUSTACEA

THE MYSIDACEA

Tae CUMACEA

THE TANAIDACEA

THe Isopopa

Tort AMPHIPODA

THe EUPHAUSIACEA

THE DECAPODA

THE STOMATOPODA

INDEX

CHAPTER IX

CHAPTER X

CHAPTER XI

CHAPTER XII

CHAPTER XIII

CHAPTER XIV

CHAPTER XV

CHAPTER XVI

PAGE

7

183

190

196

333

CHAPTER I
CLASS CRUSTACEA.

Susp-Cuass I. BRANCHIOPODA.

Order 1. Anostraca.
» 2. Notostraca.
,, ¥. Conchostraca.
5, 4. Cladocera.

Sup-Cuass II. OsrracopDa.

Order 1. Myodocopa.
», 2. Cladocopa.
5 0. Podocopa.
» 4. Platycopa.

Sus-Ciass III. Coprpopa.

Order 1. Eucopepoda.
» 2. Branchiura.

Sus-CLass IV. CIrRRIPEDIA.

Order 1. Thoracica.

2. Acrothoracica,
3. Ascothoracica.

» 4. Apoda.

5. Rhizocephala.
Susp-CLass V. MALACOSTRACA.
SERIES A. LEPTOSTRAGA.

DIVISION PHYLLOCARIDA,
Order Nebaliacea.
SERIES B. EUMALACOSTRACA.
DIVISION 1. SYNCARIDA.

Order Anaspidacea.
1

2 THE CRUSTACEA

DIVISION 2. PERACARIDA.

Order 1. Mysidacea.
» 2. Cumacea.
» o Tanaidacea.
» 4. Isopoda.
,» 0. Amphipoda.

DIVISION 3. EUCARIDA.
Order 1. Euphausiacea.
_ 5 2. Decapoda.

Division 4. HOPLOCARIDA.
Order Stomatopoda.

Introductory.—The Crustacea form one of the Classes com-
posing the Sub-Phylum Arthropoda, and include, besides the
forms popularly recognised as Crabs, Lobsters, Crayfish, Prawns,
Shrimps, Sandhoppers, Woodlice, Barnacles, and Water-fleas, a
multitude of related organisms which are nameless in common
speech.

The Class presents so wide a range of structural diversity that
it is all but impossible to give, in a few words, a definition which
shall apply to all its members. Of the great majority it may be
said that they are Arthropoda of aquatic habits, breathing by gills or
by the general surface of the body, having two pairs of antenniform
preoral appendages, and having at least three pairs of postoral
appendages acting as jaws, the three corresponding somites being
coalesced with the head. But while these characters are found
in the more primitive members, actual or hypothetical, of all the
sub-classes and orders composing the Class, the more modified types
furnish exceptions to every statement of the definition. Thus, the
land-crabs and woodlice are not only completely terrestrial in their
habits, but are provided with special organs for aerial respiration ;
the preoral appendages may be modified for locomotor or prehensile
functions, or may be quite wanting ; and some or all of the mouth-
parts may be suppressed. The most extreme modifications are
found in parasitic forms, and some of these, such as the Rhizocephala,
have lost, in the adult state, almost every trace, not only of
Crustacean, but even of Arthropodous structure. In these cases,
however, the larval stages afford indications of affinity, while less
specialised forms provide connecting links with the typical Crustacea
and leave no doubt as to the natural character of the Class as a
whole.

Historical—In_ the Systema Naturae (12th edition, 1767),
Linnaeus placed most of the Crustacea then known in his Class
Insecta (equivalent to the sub-phylum Arthropoda as now under-

THE CRUSTACEA 3

stood), where they formed, with the Arachnida, one of the divisions
of the Order Aptera. Three genera were recognised, Cancer,
Monoculus, and Oniscus. The Barnacles, however, forming the genus
Lepas, were placed among the Vermes testacea, between Chiton and
Pholus, and the genus Lernaea, comprising certain parasitic forms,
was classed under Vermes mollusca. The adjective crustata or
crustacea had been applied, more or less loosely, by the older
naturalists to animals possessing a hard exoskeleton, and Brisson,
in 1756, had used it as the designation of a group. Pennant, in
1777, appears to be the first post-Linnaean author to suggest the
separation of a distinct class under the name Crustacea, and this
step was definitely taken in Cuvier’s Lecons d@ Anatomie comparde
(1800), where, however, the Isopoda still remained among the
Insects. Lamarck in 1801 included the Isopoda, and Latreille made
many changes in the classification, the most important being the
division of the class into Maualacostraca and Entomostraca (Genera
Crust. et Insect., 1806). This arrangement, with the further
division of the Mualacostraca into Edriophthalma and Podophthalma,
proposed by Leach in 1815, has been widely adopted down to the
present day.

The researches of J. C. Savigny on the structure of the mouth-
parts in Insects and Crustacea (1816) laid the foundations of modern
conceptions of Arthropod morphology. Among his immediate
successors in this line of research, perhaps the most prominent
names are those of V. Audouin and H. Milne-Edwards. The
Histoire Naturelle des Crustacés of the last-named author (1834-1840)
marks an epoch in the history of Carcinology and is still indispens-
able to the student. It is curious that, even at this date, Milne-
Edwards did not include the Cirripedia in his survey of the
Crustacea, although J. Vaughan Thompson had already in 1830
described their larval stages and recognised their Crustacean affini-
ties. Apart from this omission, the limits of the Class adopted by
Milne-Edwards differ from those now generally accepted in includ-
ing the Pyecnogonida, the Xiphosura, and the Trilobita. There can
be little doubt that the affinities of these groups are with the
Arachnida, though it is possible that the very primitive Trilobites
were also phyletically related to the Crustacea.

It is impossible to summarise here the numerous changes in
classification introduced since the date of Milne-Edwards’ work, but
it may be mentioned that the establishment of a phylogenetic basis
for classification is largely due to the numerous and important
works of C. Claus.

Further notes on the historical development of the subject will
be given in the chapters dealing with the separate sub-classes and
orders.

4 THE CRUSTACEA

GENERAL MORPHOLOGY.

Exoskeleton.—In the Crustacea, as in other Arthropoda, the exo-
skeleton of the body consists typically of a series of segments or
somites which may be movably articulated or more or less coalesced
together. In its simplest form the exoskeletal somite is a ring of
chitin, connected with the adjacent rings by areas of thinner
integument permitting movement in various directions, and having
a pair of appendages attached to its ventral surface. This ring may
be further subdivided into a dorsal fergite and a ventral sternite, and
the tergite may overhang the
attachment of the appendage on
each side as a free plate called the
pleuron + (Fig. 1).

At the posterior end of the
body is a terminal segment known
as the ¢elson, upon which the anus
opens. This segment never bears
typical limbs and its nature has
been variously interpreted. It has

been regarded as a true somite or
abiominal somites of the Crayfish (Astuens), 28 Tesulting from the coalescence
Dae) Pe yeaa ae of a number of somites, while some
: have described it as a “median
appendage” or as a fused pair of appendages. Its true nature,
however, is clearly shown by embryology. In the larval develop-
ment of the more primitive Crustacea the body increases in length
by the successive addition of new somites between the last-formed
somite and the terminal region which bears the anus. The “ grow-
ing-point” is, in fact, situated in front of this region, and when
the full number of somites has been reached, the unsegmented part
remaining forms the telson of the adult.

In no Crustacean, however, do all the somites of the body
remain distinct. Coalescence of somites or suppression of segmenta-
tion (lipomerism) involves more or less extensive regions where the
component somites are only indicated by the persistence of the
corresponding appendages. This is constantly the case in the
anterior part of the body, where a varying number of somites are
united to form the head. _This fusion of cephalic somites is
associated with what Lankester has termed the “adaptational shift-
ing of the oral aperture ” backwards from its primitive position at
the anterior end of the body. Asa result of this shifting, at least two
somites, corresponding to the antennules and antennae, come to lie

lie, al,

1 Sometimes called the epimeron, but this term has been used in different senses
and it seems better to abandon it altogether.

fm

THE CRUSTACEA

wal

in front of the mouth in all Crustacea (Fig. 2). Perhaps an anterior
somite bearing the paired eyes should also be recognised, but some
doubt remains as to the appendicular nature of the eye-stalks, and it
is possible that the eyes should be
referred to a primitively preoral region
corresponding to the prostomium of
annelid worms. In any case, a
prostomial element may be assumed
to share in the formation of the head,
and to it may be assigned the more
or less problematical ‘frontal sense-
organs” found in various larvae and
some adult Crustacea. It has been
suggested by Bernard that the back-
ward shifting of the mouth was Fig. 2.

accomplished by a bending round of-__Diasram of the Crustacean. head-

b i region. (Modified from Goodrich.) The

the anterior somites and that the nervous system is shown in black. a’,
p : : ; aid | ] ; antennule; a’, antenna; D, deutero-
prostomium 1s represented by the cerebrum, the division ‘of the brain
; : = = corresponding to the antennules; F,

labrum or upper lip Just in front of paired compound eye; e, unpaired
the mouth. There is, however, little “nauplius” eye; fp, frontal papilla
: ‘ ; - or sense-organ; m, mouth; md, man-
definite evidence in favour of this dible; mz’, maxilluia; mx’, maxilla; P,
protocerebrum, the division of the brain

vlew. corresponding to the paired eyes; 7,
In all existin o Crustacea in tritocerebrum, the division of the brain
2 5 z corresponding to the antennae. Behind

addition to the preoral somites, at the mouth is seen the transverse com-
least three postoral somites, corre- erat enang antennal ganglia or
sponding to the mandibles, maxillulae,

and maxillae, are included in the head-region. Even where a larger
number of somites are involved there is generally a more or less
marked change in the character of the appendages after the third
postoral pair, and, since the integumental fold which forms the cara-
pace seems to originate at this point, it is usual to take the third
postoral (maxillary) somite as the limit of the cephalon throughout
the Class. It is quite probable, however, that in the primitive
ancestral type of the Crustacea, the head-region included a smaller
number of somites. The three anterior pairs of limbs (antennules,
antennae, and mandibles), which alone are present in the “ nauplius ”
larva, show peculiarities of structure and development which seem
to place them in a different category from the succeeding limbs, and
there is some ground for regarding the three corresponding somites
as belonging toa “ primary head-region.” For descriptive purposes,
however, it is convenient to treat the two following somites also as
cephalic.

Mention must be made here of a remarkable feature found only
in the aberrant group of the Stomatopoda, among the Malacostraca.
This is the reappearance of segmentation in the anterior part of the
head, where two movably articulated rings carry the eye-stalks and

6 THE CRUSTACEA

antennules. Whether or not these rings correspond to the primitive
somites, their distinctness in the highly specialised Stomatopoda is
clearly a secondary condition since it is not found in their larvae nor
in any of the more primitive Malacostraca. For the same reasons
no great morphological significance can be attributed to the less
distinctly marked skeletal areas described as representing the
ophthalmic, antennular, and: antennal sternites in the higher
Decapoda.

In nearly all cases the post-cephalic somites can be further
grouped into regions or tagmata distinguished by the shape of the
somites or the character of their appendages. In descriptive
carcinology two such regions are commonly distinguished as thorax
and abdomen, but it must be pointed out that there is no morpho-
logical equivalence between the tagmata so named in different
groups. Throughout the Malacostraca, the thorax of eight and the
abdomen of six somites are sharply distinguished by the appendages.
In the other sub-classes the same names are sometimes applied to
the limb-bearing and limbless regions of the trunk, while in the
Branchiopoda they may denote respectively the regions in front of
and behind the genital apertures.

The total number of post-cephalic somites varies within very
wide limits. In the Ostracoda, where the body is not distinctly
segmented, the number of trunk-limbs does not exceed two pairs.
In some Branchiopoda the number of trunk-somites exceeds forty.

A structure which, from its occurrence in the most diverse
groups of Crustacea, is probably a primitive attribute of the Class,
is the dorsal shield or carapace, originating as a fold of the
integument from the posterior margin of the cephalic region. In
its simplest form, as seen in Apus among the Branchiopoda, the
carapace loosely envelops more or less of the trunk. In many
Branchiopoda and in the Ostracoda it forms .a bivalve shell
completely enclosing the body and limbs. In the Cirripedia it
forms a fleshy “mantle” usually strengthened by shelly plates.
In many cases among the Malacostraca the carapace coalesces with
the tergites of some or all of the thoracic somites, though it may
project freely at the sides, overhanging, as in the Decapoda, the
branchial chambers.

It is possible that, in those cases where some of the post-cephalic
somites seem to be simply fused with the head-region, a reduced
shell-fold is also involved in the coalescence. This is most probably
the case in the Isopoda and Amphipoda, where the fusion of the
first thoracic somite with the head is clearly the last vestige of a
shell-fold, traceable, with progressively diminishing extent, from the
primitive Mysidacea through the Cumacea and Tanaidacea. In the
Copepoda, on the other hand, in which one or two trunk-somites
coalesce with the head, there is less evidence that the dorsal

THE CRUSTACEA 7

“carapace” so formed really represents the shell-fold, and its lateral
extensions, which cover the bases of the legs, may be the pleura of
the coalesced somites. Apart from the Copepoda, the only
Crustacea in which there is no trace of a shell-fold are the
Anostracous Branchiopoda, and perhaps also the anomalous Mala-
costracan Anaspides. ——.

Before proceeding to discuss the true limbs, mention must be
made of certain appendages which have sometimes been regarded
as homologous with the limbs, but which probably do not belong to
that category. In most Malacostraca and in certain other forms,
notably among the Copepoda, the posterior margin of the oral
aperture is bounded by a fold forming a lower lip (metastoma or
hypostoma), usually cleft into two lobes, known as the paragnatha,
which may bear movable terminal lappets. Since there is never
any corresponding pair of ganglia on the ventral nerve-chain, or
other evidence of the existence of a corresponding somite, there is
little ground for the view that the paragnatha are a vestigial pair
of limbs. Claus has shown that in Apus the so-called paragnatha
are probably the proximal lobes of the maxillulae, and he has
suggested a similar connection in the Malacostraca, where, however,
an independent origin of the lower lip seems more probable. The
upper lip or /abrum, already mentioned, is plainly an unpaired
outgrowth.

The terminal segment or telson often bears a pair of processes
or rami forming the “caudal furca.” These may be multiarticulate
filaments as in Apus and a few Cirripedes; in the Anostracous
Branchiopoda, Copepoda, and Leptostraca they are unsegmented
rods articulated to the body; in other cases they may be simple
processes of the telson. There seems to be very little reason for
supposing that the furcal rami represent limbs, more especially
since the telson, as stated above, has not the value of a true somite.

Limbs - General Morphology.—£he limbs of Crustacea differ very
widely in form and structure, but it is generally possible to trace”
in them the modifications of a fundamental type consisting of a
peduncle, the protopodite (or sympodite), bearing two rami, the
exopodite and endopodite. This simple biramous form is seen, for
instance, in the swimming feet of the Copepoda (Fig. 3, B), the
cirri of the Cirripedia, and the abdominal appendages of the
Malacostraca (Fig. 3, A), and in the second and third pairs of limbs
in the earliest and most primitive type of larva, the nauplius
(Fig. 3, C). As a rule, the protopodite is composed of two segments
known as the coropodite (or cova) and basipodite} (or basis), but one
of these may be reduced or suppressed ; while, on the other hand,
Hansen has shown that in some cases a pre-coxal segment can be

1 By some writers the term basipodite is applied to the protopodite as a whole.

8 THE CRUSTACEA

distinguished. The two rami may become specialised for different
functions, as in the case of the thoracic limbs of Malacostraca
(Fig. 3, D, E), where the endopodite forms a walking-leg, while the
exopodite becomes a swimming-branch or may disappear altogether.

Fic. 3.

Various types of Crustacean limbs. A, abdominal limb (pleopod) of Crayfish. (After Hux-
ley.) B, swimming-foot of Calanus (Copepoda). (After Sars.) C, limb of second pair
(antenna) of nauplius larva of Apus (Branchiopoda). (After Claus.) D, first thoracic limb
of Anaspides (Syncarida). E, second thoracic limb of Anaspides. bs, basipodite ; ex, coxo-
podite ; en, endopodite ; ep, epipodite ; ex, exopodite ; gn, gnathobase ; prot, protopodite,

The coxopodite often bears on the outer side an appendage (rarely
more than one), known as the epipodite, which may function as a gill.
In the appendages near the mouth one or both of the segments of
the protopodite may develop, even in the nauplius, inwardly-turned
masticatory processes or gnathobases. The occurrence of epipodites
and gnathobases suggests that the primitive Crustacean limb was

THE CRUSTACEA 9

more complex than the simple biramous type. Lankester has
called attention to the lobed leaf-like appendages of the Branchiopoda
(Fig. 49, as probably approximating to the ancestral form. As will
be shown below, it is not altogether
easy to recognise the homologies
of the various lobes even within
the limits of the group Branchio-
poda, and their exact relation to
the parts of the biramous limb is
still open to doubt, but it is
probable that the Branchiopod limb
preserves characters belonging to
an early phyletic stage before the
biramous type had become fixed.
It does not seem profitable to — peartike trunk-limb of Lepidurus (Bran-
go beyond this and to attempt, chiopoda). (Atter Sars.) en, endites; ex,
as some have done, to compare =

the limbs of the Branchiopoda in detail with the Polychaete
parapodium.

The general character of the modifications which the original
type of limb undergoes is often, though by no means always,
plainly correlated with the functions which the limbs discharge.
In swimming-limbs the rami are often flattened and oar-like, and
fringed with plumose hairs or flattened spines. For walking or
creeping one of the rami, generally the inner, is stout and cylindrical,
tipped with a claw, and having the segments connected by definite
hinge-joints allowing movement only in one plane. The oral
appendages have the gnathobasic lobes developed at the expense of
the rest of the limb, the rami persisting, if at all, only as sensory
“palps.” A multiarticulate flagelliform modification of the rami is
generally associated with a sensory (tactile or olfactory) function,
as in the antennules and antennae. A pincer-like (chelate or sub-
chelate) form is frequently assumed by limbs used for prehension,
the terminal segment being flexed against the penultimate, or
opposed to a thumb-like process of the latter.

Special Morphology of Limls— Ocular Peduncles.—In many
Crustacea, notably in the Anostracous Branchiopoda and in the
majority of the Malacostraca, the eyes are set upon peduncles
which are movably articulated with the head, and which may be
divided into two or three segments. The view that these peduncles
are homologous with the limbs was first suggested by H. Milne-
Edwards, and has been widely but not universally accepted. In
spite of much discussion, however, it cannot be said that the point
has been finally decided. The fact that the eye-stalks are most
fully developed and most distinctly articulated not in the more
primitive forms, but among the highly specialised Decapoda, is

en.

Fia. 4.

fe) THE CRUSTACEA

against the appendicular theory, and the evidence of embryology
does not support it. In the development of the Branchiopod
Branchipus, Claus has shown that the eyes are, at their first appear-
ance, sessile, and only become pedunculated at a later stage, the
lateral lobes of the head on which they are set becoming produced
and separated from the rest of the head by a movable articulation
(Fig. 5).

The most important evidence in favour of the appendicular
nature of the eye-stalks is that afforded by the phenomena of

e.
\

s : =) Y, ‘\ IN asks Be S i

Pic. 5.

Development of ocular peduncles in Branchipus. (After Claus.) A, head of young larva ;
B, head of older larva. J (in A), lateral lobe of the head bearing #, the compound eye. In B
this lobe has elongated to form the ocular peduncle, not yet movably articulated, although one
of the muscles for moving it is developed (m). e, unpaired or nauplius eye; /, frontal sense-
organs.

regeneration. If the eye-stalk be removed from a living prawn or
lobster, it is found that, under certain conditions, a many-jointed
appendage, like the flagellum of an antennule, may grow in its
place. The bearing of such cases of “ heteromorphic regeneration ”
on questions of homology is, however, by no means clear, and their
discussion would involve a reconsideration of some of the most
fundamental conceptions of current morphology. For the present
it must suffice to point out that the appendicular nature of the
ocular peduncles cannot be assumed as definitely proved.

The antennules (or first antennae) are almost universally regarded

THE. CRUSTACEA 1a

as true appendages, although they differ from all the other append-
ages in the fact that they are always innervated from the brain (or
supra- oesophageal ganglia), and that they are uniramous in the
nauplius larva (Fig. 6, «)
and in the adults of all the
sub-classes except the Malaco-
straca. As regards the in-
nervation, an apparent excep-
tion is found in the case of
Apus, where the antennular
nerves arise, behind the
brain, from the oesophageal
connectives. This is un-
doubtedly a secondary
position, however, and the
nerve-fibres have been traced
forward to centres in the
brain. In the Malacostraca Pic.

the antennules are often — garly nauplius larva of ees (Cyclops sp.)
biramous (Fig, 7), but there Ponblow. eantennnla; at antenns: gm, gnatie
is considerable doubt as to

whether the two flagella correspond to the endopodite and exopodite
of the other limbs. In most cases the antennules are sensory in
function, but they may also be natatory or prehensile, and in the
Cirripedia they form organs of attachment.

The «antennae (or second antennae) are of special interest on
account of the clear evidence that, although preoral in position in
all adult Crustacea, they were originally postoral appendages. In
the nauplius larva (Fig. 6, a”) their position is beside
rather than in front of the mouth, and they may bear
‘hook-like masticatory processes (gn) which assist the
similar processes of the mandibles in seizing the food.
In the Branchiopoda and less distinctly in some other
groups, the nerves to the antennae arise not from the
brain, but from the oesophageal connectives, and the trans-
verse commissure of the corresponding ganglia can be traced
behind the oesophagus, even in those forms in which the
eee ganglia have moved forward into the brain (Fig. 2, pe)
of Crayfish. The functions of the antennae are very varied. As
Huxley.) already stated, they act as jaws in some nauplius larvae.

‘In many cases they are important organs of locomotion,
and they may serve as sexual ‘“‘claspers,” or as organs of attach-
ment in parasites. In the Malacostraca they are mainly sensory,
the endopodite being a long flagellum, while the exopodite may
form a flattened “scale” probably used as a balancer in swimming,
or may disappear altogether.

Fic. 7.

ies THE CRUSTACEA

The mandibles, like the antennae, are, in the nauplius, bira-
mous swimming-limbs with a masticatory gnathobase arising from
the basal segment of the protopodite. This form and function are
retained with little alteration in some adult Copepoda (Fig. 8, A).
In most cases, however, the exopodite is lost and the endopodite
(with the distal part of the protopodite) forms the “palp” (Fig.
8, B) or may disappear altogether (Fig. 8, C), while the ‘body ”
of the mandible is formed by the coxopodite (or perhaps by the
precoxa), and has a masticatory edge armed with tubercles, teeth,
or spines. In parasitic forms with suctorial mouth-parts the
mandibles may take the shape of piercing lancets enclosed in a
tubular beak formed by apposition of the labrum and metastoma.

Fic. 8.

A, mandible of Copepod (Calanus) (after Sars); ex, coxopodite (or precoxa, according to
Hansen), forming the ‘‘ body” of the mandible ; bs, basipodite ; en, endopodite ; ex, exopodite.
B, mandible of Crayfish (after Huxley); letters as above. In both cases the basipodite
and the segments distal to it form the ‘‘ palp.” ©, mandible of Lepidwrus (after Sars).

In Ostracoda the mandibular palp aids in locomotion, and in a few
cases the masticatory part is greatly reduced.

The mazillulae and mazillae (or, as they are often termed, the
first and second maxillae) are nearly always foliaceous appendages
having gnathobasic lobes or endites borne by the segments of the
protopodite (Fig. 9). The endopodite is reduced to a “palp” or
is absent. On the outer side, lobes representing the exopodite
and epipodite may be present. These appendages undergo great
modifications in the different groups and exact comparative in-
vestigations on their morphology are still wanting.

The post-cephalic or trunk appendages vary greatly in number.
In some Branchiopoda there are more than 60 pairs, while in
some Ostracoda it is uncertain whether there are any. They
present great diversity of form and function in the various groups

THE CRUSTACEA 13

and often also in the same animal. They may be nearly all alike
as in the Branchiopoda, where, at most, one or two of the anterior
pairs may be specialised as sensory or as grasping organs. Com-
monly, as in the Copepoda, one or two of the anterior pairs are
modified to assist the oral appendages and are known as mazillipeds.
It is very characteristic of the Malacostraca that the series of
trunk-limbs is differentiated into two well-defined “tagmata” or
groups of similarly modified appendages, corresponding to the

Fic. 9.

A, maxillula of Copepod (Calanus). (After Sars.) B, maxillula of Crayfish; C, maxilla of
Crayfish. (After Huxley.) en, endopodite ; ep, epipodite ; ex, exopodite ; gn, gnathobasic lobes.
(The plate lettered ep in C is possibly the exopodite rather than the epipodite ; see p. 268.)
thoracic and abdominal regions respectively. The thoracic limbs
have the endopodites forming, as a rule, more or less efficient
walking-legs, and the exopodites, when present, form swimming-
branches, while the abdominal limbs are usually biramous, with the
‘ami similar and, in the more primitive types, natatory in function.
The general similarity between the appendages of each tagma is
usually qualified by minor modifications, sometimes leading to
the formation of subsidiary groupings. Thus, for example, in
the Decapoda a group of three pairs of maxillipeds is differentiated
from the thoracic tagma.

14 THE CRUSTACEA

Branchiae.—In many of the smaller Crustacea there are no
special branchiae, and respiration is carried on by the general sur-
face of the body. When present, branchiae are usually formed by
differentiation of parts of the appendages, often the epipodites,
but the shell-fold has probably in many cases a respiratory function,
and processes from its inner surface (Cirripedia) or from the
surface of the body (some Ostracoda) may develop as branchiae.
In the more primitive of the Malacostraca, the gills are formed
by the epipodites of the thoracic limbs (podobranchiae), and this
was probably also the original nature of those branchiae which, in
the Decapoda, are attached to the articular membrane between the
limb and the body (arthrobranchiae), or to the body-wall itself
(pleurobranchiae). In the Isopoda the respiratory function is
assumed by the lamellar rami of the abdominal appendages.

Many terrestrial Crustacea have no special adaptations for
aerial respiration. In land-crabs of different families, however,
the lining membrane of the branchial chamber is covered with
vascular papillae and acts as a lung. Still more remarkable are
the breathing organs of many of the terrestrial Isopoda or Woodlice.
These are ramified tubular invaginations of the integument in
the abdominal appendages, and are precisely analogous to the
tracheae of other air-breathing Arthropoda.

Alimentary System.—In the great majority of Crustacea the
alimentary canal is nearly straight, except at its anterior end,
where it curves downwards to the ventrally placed mouth. The
only cases hitherto described in which it is actually coiled upon
itself are in certain Cladocera and in a single genus of Cumacea.
As in other Arthropoda, it consists of stomodaewm, mesenteron, and
proctodaewm, the first and last with a lining of chitin continuous at
mouth and anus with the exoskeleton. The ree proportions
of these three divisions vary greatly, and the extre né abbreviation
of the mesenteron found in the common Crayfish is by no means
typical of the Class. Even in the closely related Lobster this
section of the gut may be several inches long.

The whole length of the alimentary canal is provided, as a
rule, with circular and longitudinal muscle-fibres running in its
walls, and there are often also muscle-bands extending to adjacent
portions of the body-wall. In the anterior part of the stomodaeum
these muscles are more strongly developed to perform the move-
ments of deglutition. In a few Branchiopoda and Ostracoda the
chitinous lining of this region develops spines and hairs which
help to triturate and strain the food, and in some Ostracoda the
armature assumes a more complex form as a series of toothed
plates moved by special muscles. It is among the Malacostraca,
however, and especially in the Decapoda, that this apparatus, the
so-called ‘gastric mill,” reaches its greatest complexity. It con-

THE CRUSTACEA 15

sists of a framework of movably articulated ossicles developed as
thickened and calcified portions of the lining cuticle of the
“stomach” or dilated part of the stomodaeum. ‘These ossicles
bear teeth and are moved by a complex system of intrinsic and
extrinsic muscles. In the posterior division of the stomach a series
of pads and ridges beset with stiff hairs form a straining apparatus.

The mesenteron, in most Crustacea, has its surface increased by
pouch-like or tubular outgrowths, which not only serve as glands
for the secretion of the digestive juices, but may also become filled
by the more fluid portion of the partially digested food and
facilitate its absorption. These outgrowths vary much in their
arrangement in the different groups. Most commonly there is a
single pair, which may be more or less ramified, and may form a
massive digestive gland (‘‘ hepato-pancreas” or “ liver”).

In a few parasites (Rhizocephala and the Monstrillidae among
Copepoda) the alimentary canal is absent or vestigial throughout
life.

Circulatory System.—The heart of the Crustacea is of the usual
Arthropodous type, lying in a more or less well-defined pericardial
sinus, with which it communicates by valvular openings or ostia.
In some of the Branchiopoda, such as Branchipus, the heart is of
the primitive tubular form, extending the whole length of the
body, and having a pair of ostia in each somite. Even within the
group of Branchiopoda, however, a progressive abbreviation of the
heart, with a diminution in the number of ostia, can be traced,
leading to the condition found in the Cladocera, where the heart is
a sub-globular sac and the ostia are reduced to one pair. Among
the Malacostraca, an elongated heart with numerous ostia is found
only in the Leptostraca and Stomatopoda. In other cases the
heart is generally abbreviated, and even where, as in the Amphi-
poda, it is long and tubular, the ostia are restricted in number.
From the heart, the blood passes into one or more arterial trunks,
which may ramify into a more or less extensive system of arterial
vessels, or may open at once into the general lacunar system of
the body (haemocoel). Sometimes, as in the Branchiopoda, even
the arterial trunks are absent, and the blood is discharged from the
anterior end of the heart directly into the lacunae of the haemocoel.

In many Crustacea, especially those of small size (many
Copepoda and Ostracoda, Cirripedia), there is no heart and no
definite system of vessels, and the blood is simply driven hither and
thither by the movements of the body and of the alimentary canal.

Certain genera of parasitic Copepoda (Lernanthropus, ete.) are
unique among Arthropoda in possessing a closed vascular system,
containing a coloured fluid, and shut off from the general cavity
of the body. The morphological relations of this system are still
obscure.

16 THE (CRUSTACEA

Excretory System.—The most important organs of renal excre-
tion in the Crustacea are two pairs of glands, lying at the base of
the antennae and of the maxillae respectively, which are probably
the survivors of a series of segmentally arranged coelomoducts
present in the primitive Arthropoda. The two pairs are never
fully developed at the same time in one individual, although one
may replace the other in the course of development. Thus, in the
Branchiopoda, the antennal gland develops early and is functional
during a great part of the larval life, but it ultimately atrophies
and the maxillary gland takes its place as the excretory organ of
the adult. In the Decapoda, where the antennal gland alone is
well developed in the adult, the maxillary gland sometimes pre-
cedes it in the larva. The structure of both glands is essentially
the same (Fig. 10). There is a more or less convoluted glandular
tube (f), of mesoblastic
origin, connected internally
with a closed “ end-sac”
(¢.s), representing a vestigial
portion of the coelom, and
generally a thin-walled duct
which opens to the exterior.
In the Branchiopoda the
maxillary gland is lodged
in the thickness of the
shell-fold (when this is
present), and from this
circumstance it often
receives the somewhat mis-
leading name of ‘“‘shell-
gland.” In the Decapoda,

Fic. 10. the antennal gland is largely
Antennal gland of a larva of Estheria (Branchio- developed and often very
poda). (After Grobben.) con, connective-tissue fibres ; 6
é.s, end-sac ; 0, external opening ; ¢, glandular tubule. complex, and is known as
the “ green gland.”

Other excretory organs have been described in various
Crustacea, but although their excretory functions have been
demonstrated by physiological methods, their morphological rela-
tions are in most cases quite obscure. In some cases they consist
of masses of mesodermal cells, within which the excretory products
are stored up instead of being expelled from the body. In other
cases an excretory function is attributed to certain cells of the
mesenteron or to some of its diverticula.

Nervous System.—The central nervous system is constructed on
the same general plan as in the other Arthropoda, consisting of a
supra-oesophageal ganglonic mass or “brain,” united by circum-
oesophageal connectives with a double ventral chain of segmentally

THE CRUSTACEA 4

arranged ganglia. In the primitive Branchio-
poda the ventral chain retains the ladder-like
arrangement found in some Annelids and lower
worms, the two halves being widely separated
and the pairs of ganglia connected together
across the middle line by double transverse
commissures (Fig. 11). In the other groups
the two halves of the chain are approximated
and more or less completely coalesced, and, in
addition, a concentration of the ganglia in a
longitudinal direction takes place, leading
ultimately, in many cases, to the formation of an
unsegmented ganglionic mass. This is seen, for
example, in the Brachyura, among the Decapoda.

The brain consists, in the Branchiopoda,
mainly of two pairs of ganglionic centres, the
protocerebrum and deuterocerebrum (Fig. 2,
P, D), giving origin, respectively, to the optic
and antennular nerves. The antennal nerves
arise, in this group, from ganglionic swellings
on the oesophageal connectives. In the higher
groups, as already mentioned, the centres for
the antennal nerves have moved forwards and
are included in the brain, forming the trito-
cerebrum (Fig. 2, T), and other additional
centres are developed, so that in the highly
organised Decapoda the brain assumes an
extremely complicated structure. i |

Eyes. —Two kinds of eyes are found in
Crustacea, the unpaired median or nauplius eye, 1 |
and the paired compound eyes. The former | {
alone is present in the nauplius larva, and it
forms the sole organ of vision in the adult
Eucopepoda. It may coexist with the paired
eyes as in the Branchiopoda and in some of
the more primitive Malacostraca, although, in

the latter, it is generally vestigial. When
fully developed (Fig. 12), it usually presents
three divisions, each consisting of a cup-
shaped mass of dark pigment (), the cavity
of which is filled with columnar retinal
cells. The outer ends of these cells are con-
tinuous with the nerve-fibres (7), while at
their inner ends they contain rod-like bodies
(r). In some cases the three divisions of the
eye are each supplied by a separate nerve

Fig. 11.

Nervous system of Branchinecta
paludosa, one of the Branchiopoda (after
Sars), showing the ladder-like form ,of
the anterior part of the ventral nerve-
chain and the absence of ganglia and
of transverse commissures in the pos-
terior limbless part of the trunk. m
indicates the position of the mouth.
The existence of a transverse com-
missure in front of the mouth, as shown
by Prof. Sars in this drawing, is ex-
tremely doubtful. Possibly the structure
observed may be a portion of the
visceral nerve-ring encircling the gullet
in the region of the labrum.

2

18

RHE CRO SEA CE

arising from the brain.

In many cases there is no special refracting

apparatus, but a refractive body, or lens (/), is sometimes formed

Hig.) 12:

Horizontal section through

the median eye of Cypris.

(After Claus.) Only two of

the three divisions of the eye
are seen. J, lens; nm, nerve;
p, pigment; 7, rod-like bodies

on the outer side of the retinal cells, while
in the Copepoda, where the median eye may
undergo considerable modification, cuticular
lenses and other accessory structures may be
developed.

The compound eyes show considerable
agreement in the details of their structure
with those of Insects (Fig. 13). They consist
of a varying number of ommutidia or visual
elements, covered by a transparent region
of the cuticle, the cornea, which is usually
divided into lenticular facets. Typically
each ommatidium has the structure shown in

contained in the retinal cells. : :
the accompanying figure. Immediately under

the cuticle lie a pair of corneagen cells (hy), by which the cuticular
lens is secreted and renewed on ecdysis. Below these are a group,

generally two or four, of cells forming a refractive crystalline body (cr),

ans

"
!

eis

A

Fic. 13.

A, horizontal section of the eye and ocular peduncle of Branchipus. B, four ommatidia of
same further enlarged. b, basement membrane ; c, corneal cuticle, which in this case is not
thickened to form lenses; cr, crystalline body ; er.c, cells of the crystalline body ; f, nerve-
fibrils ; g, optic ganglia in the peduncle ; hy, hypodermis or corneagen cells ; m, muscle of the
pedunele ; 7, retinula cells surrounding the rhabdome, which is here concealed from view by the
black pigment. (After Claus.)

the lower end of which is embraced by the tips of the elongated
retinula cells (r). These surround a rod-like body, the rhabdome,
of cuticular nature but penetrated by nerve-fibrils, and usually

THE CRUSTACEA 19

divisible into rhabdomeres corresponding in number to the retinula
cells by which it is formed. At their bases the retinula cells pass
into nerve-fibres (f) which penetrate the basement membrane (/)) and
enter the optic ganglia. Each ommatidium is more or less com-
pletely isolated by a sheath of black pigment contained partly in
the retinular cells, partly in special cells lying between them. By
movements in the protoplasm of these cells the position of the
pigment changes according to the amount of light falling upon the
eye. <A layer of reflecting pigment, the tupetwm, may also be
present. It is impossible here to summarise the details of histo-
logical structure or of physiological interpretation. It may be
stated, however, that the variations in structure found in different
Crustacea appear to be determined not so much by the systematic
affinities as by the habits of the organisms. In this connection
the work of Chun and of Doflein on the structure of the eyes in
pelagic and abyssal species may be referred to.

In many Crustacea, as already stated, the paired eyes are set
on movable peduncles, and it is probable that this condition is the
primitive one. In the primitive Branchiopoda the eyes are either
pedunculated or, if sessile, movable in such a way as to suggest
derivation from the pedunculate condition.

Other Sense-Organs.—The other sense-organs of the Crustacea
are formed by modification of the hairs or setae on the surface of
the body and limbs (Fig. 14). As in other Arthropoda, many of
these setae are tactile. Each consists of a hollow conical outgrowth
of the cuticle, movably articulated at the base and containing
a prolongation of some of the cells of the hypodermis. One or
more nerve-fibrils may be traced into the interior, and, in some
cases, a ganglion-cell in connection therewith lies at the base of
the seta. When feathered, or provided with secondary barbs, the
setae will respond to movements or vibrations in the surrounding
water, and to some setae of this type an auditory function has
been attributed (Fig. 14, C). In certain Malacostraca more
specialised organs are found which have been regarded as auditory.
In most Decapoda there is an invagination of the integument in
the basal segment of the antennule having plumose “auditory ”
setae on its inner surface. In some cases the sac remains
open to the exterior, permitting the introduction of sand-grains
which act as “otoliths.” In other cases the sac is completely
closed, and may then contain a single “otolith” secreted by its
walls. Otocysts are found in a few other Malacostraca in various
positions ; for example, in the endopodites of the uropods in the
Mysidae.

Recent investigations have rendered it doubtful, however,
whether aquatic Crustacea can hear at all, in the proper sense of
the term, and it has been shown that one function, at least, of the

20 VHE CRUSTACEA

so-called “otocysts” is connected with the equilibration of the
body. They are more properly, therefore, termed “ statocysts.”

Another modification of sensory setae is believed to be
associated with the s nse of smell. In most Crustacea the
anntenules and often also the antennae bear groups of hair-like
filaments, sometimes slender, sometimes more or less swollen, in
which the cuticle is extremely delicate. These are known as
olfactory filaments or aesthetascs (Fig. 14, A, B). They are often
more strongly developed in the male sex, and are believed to guide
the males in pursuit of the females.

Fic. 14,

A, antenna of Daphnia magna bearing a group of “olfactory filaments.” g, nerve-ganglion
sending fibrils to the olfactory filaments. B, one of the filaments further enlarged. (After
Scourfield.) C, ‘‘auditory” seta from peduncle of antennule of Mysis relictu. . (After Sars.)

Glands.—Apart from the digestive and excretory glands already
mentioned, and from other glandular structures to be described in
connection with the reproductive system, many Crustacea possess
dermal glands scattered over the surface of the body and lmbs
or grouped at certain points for the discharge of special functions.
These consist of single cells or groups, traversed by ramified intra-
cellular canals, and communicating with the exterior by fine ducts.
Such glands occurring on the walls of the oesophagus or in the
neighbourhood of the mouth have been regarded as salivary in
function. Others on the surface of the body and limbs may be
used, as in some Amphipoda, for the construction of tubular cases
or nests in which the animals live, or, as in some Copepoda, may
secrete a gelatinous envelope enabling the animals to survive dessi-

THE CRUSTACEA 21

cation. Others, again, are believed to have a poisonous function.
The greatly developed cement-glands of the Cirripedia are possibly
related to the same group of structures.

Phosphorescent Organs.—In this connection may be mentioned
the power of phosphorescence possessed by many Crustacea. In
some cases this is due to a luminous secretion produced by certain
of the dermal glands. In the Euphausiacea and certain Decapoda,
however, complex and remarkable light-producing organs are present,
which were formerly described as ‘‘ accessory eyes.”

Leproductive System.—In the great majority of Crustacea, as in
other Arthropoda, the sexes are separate. Apart from certain
isolated instances, possibly abnormal and probably non-functional,
among Branchiopoda and Amphipoda, the only exceptions are the
sessile Cirripedia and some parasitic Isopoda (Cymothoidae and
Cryptoniscina), where hermaphroditism is the rule Partheno-
genesis is frequent among the Branchiopoda and Ostracoda, often
in more or less definite cyclical alternation with sexual reproduc-
tion. Where the sexes are distinct a more or less marked sexual
dimorphism often exists. The male is frequently provided with
clasping-organs for holding the female, and these may be formed
by the modification of almost any of the appendages, often the
antennules or antennae, or some of the trunk-limbs, or even the
mandibular palp (some Ostracoda). In addition, some of the
appendages in the neighbourhood of the genital apertures may be
modified for the purpose of transferring the sperms to the female.
In the higher Decapoda the male is generally larger than the
female and has stronger chelae. In the other groups the male
is often the smaller, and in many parasitic Copepoda and Isopoda
this disparity in size is carried to an extreme degree, and the minute
male is attached, like a parasite, to the enormously larger female.
The remarkable and complex sexual relationships of the Cirripedia
will be discussed in the section dealing with that group.

The gonads of the Crustacea, as of other Arthropoda, are hollow
organs, the cavity communicating with the efferent ducts. They
are primitively paired but often coalesce partially or completely
with each other on the dorsal side of the alimentary canal. The
ducts are present only as a single pair, except in certain parasitic
Isopoda (Hemioniscidae, Liriopsidae), where two pairs of oviducts
are found. Various accessory structures may be developed in
connection with the efferent ducts in both sexes. The oviducts
may have diverticula serving as receptacula seminis (in cases where
internal impregnation takes place), and may be provided with
glands secreting envelopes or shells around the eggs. Similarly
the glandular walls of the vasa deferentia may secrete spermatophores

1 According to recent observations (as yet unpublished) by Mr. Alf Wollebaek,
certain deep-sea Decapoda also are normally hermaphrodite.

THE CRUSTACEA

1S)
N

or capsules in which the sperms are transferred to the female.
The terminal portion of the male duct is sometimes protrusible,
and acts as an intromittent organ, or this function may be discharged
by some of the appendages.

The position of the genital apertures varies greatly in the different
groups. The most anterior position is found in the Cirripedia,
where the oviducts open on the first trunk-somite, while in certain
Branchiopoda (Polyartemia), on the other hand, the genital apertures
lie behind the nineteenth trunk-somite. It is characteristic of the
Malacostraca that the position of the genital apertures is different
in the two sexes, the female openings being on the sixth and the
male openings on the eighth trunk-somite. In all the other groups,
with exception of the hermaphrodite Cirripedia, the position is the
same in the two sexes.

While very few Crustacea are viviparous in the sense that the
eggs are retained within the body until hatching takes place (some
Branchiopoda), the great majority carry the eggs in some way or
other after their extrusion. The various devices by which this is
accomplished will be described in dealing with the different
groups ; but it may be mentioned here that a few cases are known
(Cladocera, terrestrial Isopoda) in which the developing embryos
are nourished by a special secretion while in the brood-chamber of
the mother.

EMBRYOLOGY.

The majority of the Crustacea leave the egg in a form more or
less different from that of the adult, and pass through a series of
free-swimming larval stages, but there are many cases of direct
development in which the newly hatched young resemble the
parent in general structure. The relative size of the egg is greater
in those forms which develop without metamorphosis, except where
other means exist for the nourishment of the developing embryos.

The details of the early stages of development differ consider-
ably within the limits of the class. They are chiefly of interest,
however, from the point of view of general embryology rather than
from that of the special student of the Crustacea, and can only be
very briefly referred to here. An admirable summary of the whole
subject will be found in Korschelt and Heider’s Yeat-book of the
Embryology of Invertebrates.

Segmentation is usually of the superficial or centrolecithal type,
or some modification thereof. The hypoblast is formed either by a
definite invagination or by the immigration of isolated cells which
wander through the yolk as “vitellophags” and later become
associated to form the mesenteron, or by some combination of the
two methods. ‘The blastopore generally occupies a position corre-
sponding to the posterior end of the body. The mesoblast of the

THE CRUSTACEA 23

cephalic (naupliar) region probably arises in connection with the
lips of the blastopore and consists of mesenchymatous cells. In
the region of the trunk, in many cases, paired mesoblastic bands’
are formed, growing in length by the division of teloblastic cells at
the posterior end and becoming segmented into somites. The
occurrence of true coelom-sacs is doubtful. The rudiments of the
first three pairs of appendages, antennules, antennae, and mandibles,
commonly appear simultaneously and, even in forms with embryonic
development, they often show differences in their mode of appear-
ance from the succeeding limbs. When this stage, corresponding
to the nauplius stage of larval development, is passed through
within the egg, it is often marked by the formation of a cuticular

oo?
membrane within which the further development proceeds.

The complex and varied larval metamorphoses of the Crustacea
have been the subject of much discussion in view of their bearing
on the phylogenetic history of the group. In those Crustacea in
which the series of larval stages is most complete the starting-point
is the form already mentioned under the name of nauplius. The
typical nauplius (Fig. 6, p. 11) has an oval unsegmented body and
three pairs of limbs, corresponding to the antennules, antennae,
and mandibles of the adult. The antennules are uniramous, the
others biramous, and all three pairs are used in swimming. The
antennae may have a spiniform or hooked masticatory process at
the base, and share with the mandibles, which have a similar
process, the function of seizing and masticating the food. The
mouth is overhung by a large labrum or upper lip, and the integu-
ment of the dorsal surface of the body forms a more or less definite
dorsal shield. The paired eyes are, as yet, wanting, but the median
eye is large and conspicuous. A pair of papillae or filaments,
probably sensory, are commonly present at the anterior end.
Nauplius larvae, differing only in details from the typical form
just described, are found in very diverse groups of the Crustacea,
such as the Branchiopoda, Copepoda, Cirripedia, and some Mala-
costraca. In many forms which hatch from the egg at a more
advanced stage there is, as already mentioned, more or less clear
evidence of an embryonic nauplius stage. It seems certain, there-
fore, that the possession of a nauplius larva must be regarded as
a very primitive character of the Crustacean stock.

As development proceeds, the body of the nauplius elongates
and indications of segmentation begin to appear in its posterior
part. At successive moults the somites increase in number by the
addition of new somites, behind those already differentiated, from
a formative zone in front of the telsonic region. In the most
primitive cases, the appendages posterior to the mandibles make
their appearance, like the somites which bear them, in regular

24 THE CRUSTACEA

order from before backwards. The limb-buds early become
bilobed and grow out into typically biramous appendages which
gradually assume the characters found in the adult. With the
elongation of the body, the dorsal shield of the nauplius begins
to project posteriorly as a shell-fold, which becomes the carapace.
The rudiments of the paired eyes appear under the integument of
the head, but only become pedunculated at a comparatively late
stage.

The course of development outlined above, leading from the
nauplius to the adult form by the successive addition of somites
and appendages in regular order, agrees so well with the process
observed in the development of the typical Annelida, that it must
be regarded as the most primitive. It is most closely followed by
such Branchiopoda as Apus and Branchipus, and by some Copepoda.
In the majority of Crustacea, however, this primitive scheme is
more or less modified. The earlier stages may be passed through
within the egg or in the maternal brood-chamber, so that the larva
only begins to lead an independent existence at a stage more
advanced than the nauplius. Further, the gradual appearance of
the successive somites and appendages may be accelerated, so that
great advances in structure take place at a single moult. For
example, in the Cirripedia, the latest nauplius stage gives rise
directly to the so-called Cypris-larva, which possesses all the
appendages of the adult. Another common modification of the
primitive method of development consists in the accelerated appear-
ance of certain somites or appendages, disturbing the regular order
of development. This modification is especially found in the
Malacostraca, in which, even among those which have most closely
adhered to the primitive order of development, the last pair of
abdominal appendages usually make their appearance before those
immediately in front of them. The same process, carried further,
leads to the very peculiar larva known as the zoéa, in the typical form
of which, found in the Brachyura, the posterior five or six thoracic
somites are greatly retarded in development, and are still repre-
sented by a short unsegmented region of the body at a stage when
the abdominal somites are fully formed and even carry appendages.

A remarkable phenomenon observed in the development of a
few Malacostraca is the temporary retrogression and even dis-
appearance of certain appendages which redevelop in later stages.
The best-known instances of this will be further alluded to in
describing the development of the Penaeidea among the Decapoda.

In addition to the nauplius and zoéa there are many other types
of Crustacean larvae distinguished by special names, though, as their
occurrence is restricted within the limits of the smaller systematic
divisions, they are of less general interest. We need only mention
here the metanauplius, a vaguely defined stage following the nauplius,

THE CRUSTACEA 25

possessing rudiments of some of the post-naupliar somites and
appendages.

Most of the larval forms are pelagic in habit, and many show
special adaptations to this mode of life, especially in the develop-
ment of spines and processes which are probably less important as
defensive organs than as aids to flotation.

PHYLOGENY.

The study of fossil Crustacea has hitherto contributed com-
paratively little towards a precise knowledge of the phylogenetic
history of the class. Although their remains are abundant in
nearly all formations, from the most ancient up to the most
recent, in very many cases only the carapace or shell is preserved,
the limbs being lost or represented only by indecipherable frag-
ments. Many important forms must have escaped fossilisation
altogether owing to their small size and delicate structure. Further,
many important groups were already differentiated when the geo-
logical record began. The Branchiopoda, Ostracoda, and Cirripedia
are represented in Cambrian or Silurian rocks by forms which seem to
resemble those now existing, so that palaeontology can have little
light to throw on the mode of origin of these groups. In the case
of the Malacostraca the material is a little more promising. It is
not improbable that the Phyllocarida, which are found from the
Cambrian onwards, may include the forerunners of the true Mala-
costraca, but nothing is definitely known of their appendages. The
recent discovery, in the Tasmanian Anaspides and the Australian
Koonunga, of what are believed to be representatives of the
Carboniferous and Permian Syncarida, has given a clue to the
affinities of forms hitherto problematical, and may throw light on
the relations of other Palaeozoic fossils hitherto vaguely referred
to “Schizopoda” or Decapoda. Remains of undoubted Decapods
are first met with in Mesozoic rocks. They are abundant in many
deposits, and are sometimes sufficiently well preserved to render
possible fairly accurate determination of their affinities. The
Isopoda and Stomatopoda are known from Mesozoic deposits, but
have hitherto yielded no results of phylogenetic importance.

In view of the scarcity of trustworthy evidence as to the actual
forerunners of existing Crustacea, phylogenetic conclusions based
on the data of comparative anatomy and embryology remain largely
speculative. They are none the less a necessary preliminary to the
attempt to construct a natural system of classification.

The earlier speculations on this subject started from the assump-
tion that the “theory of recapitulation” could be applied to the
larval history of the Crustacea. The various forms of larvae, more
especially the nauplius and the zoéa, were supposed to reproduce,

26 THE VCROSTACEA

more or less closely, the actual structure of ancestral types. As
regards the zoéa, this assumption was soon shown to be erroneous,
and the secondary nature of this type of larva is now generally
admitted. The nauplius, however, by the constancy of its general
characters in the most widely diverse groups, shows itself to he
a very ancient type, and the view has been advocated that the
Crustacea have arisen from an unsegmented nauplius- like
ancestor. To this view there are onsen objections. Several
structures which can hardly have been absent from the common
stock of the Crustacea, such as the paired eyes and the shell-fold,
are not found in the nauplius. Other characters common to
certain Crustacea and Annelids, such as the mode of growth of
the somites, the structure of the nervous system and of the heart,
can hardly be supposed to have arisen independently in the two
groups. The view now most generally adopted is that the
Branchiopoda, and especially Apus, which resemble the Annelids
in the characters just mentioned and also in the large number
and uniformity of the trunk-somites and their appendages, approach
most nearly to the primitive Crustacean type. On the other hand,
in some respects, such as the reduced mouth-parts, the Branchiopoda
are considerably specialised. In some Copepoda the cephalic
appendages are much more primitive than in the Branchiopoda,
and the first three pairs of appendages retain throughout life, with
little modification, the shape and function which they have in the
nauplius stage. It is possible, however, that in these characters
the Copepoda are persistently larval rather than phylogenetically
primitive, and in other respects, especially in the absence of paired
eyes and of a shell-fold, they are certainly specialised.

In order to reconstruct the hypothetical ancestral type, there-
fore, it is necessary to combine the characters of several of the
existing groups. It may be supposed to have approximated, 1
general form, to dpus, with an elongated body of numerous similar
somites, terminating in a caudal furca ; with the postoral appendages
all similar, and with a carapace originating as a shell-fold from the
maxillary region. The eyes were probably stalked and movable, the
antennules uniramous, and the antennae and mandibles biramous
and natatory, and both armed with masticatory processes. The
trunk-limbs were probably biramous but with additional endites
and exites, and all provided with gnathobases.

It is to be noted that the Trilobita, which, according to the
classification adopted in this work, are dealt with under Arachnida,
approximate to the structure of the primitive Crustacean here
sketched except in the absence of a shell-fold and in having the
eyes sessile.

It is not necessary, on this view, to deny all phylogenetic
significance to the nauplius. It may be regarded as an ancestral

THE CRUSTACEA 27

larval form, corresponding perhaps (as Hatschek suggests) to the
stages immediately succeeding the trochophore in the development
of Annelids, but with some of the later-acquired Crustacean
characters superposed upon it.

The five sub-classes into which the Crustacea are divided in the
classification here adopted appear to represent independent or
nearly independent lines of descent from the primitive stock.
Their relations to each other and the probable course of evolution
within each group will be dealt with in subsequent chapters.

It may be mentioned that the classification introduced by
Latreille in 1806, in which the Malacostraca are opposed to all
the other Crustacea grouped together under the name of
Entomostraca, is still frequently adopted. The Entomostraca,
however, like the Invertebrata, constitute a very heterogeneous
group, defined only by negative characters and having no claim
to retention in a natural system of classification.

LITERATURE.
(Selection of important works dealing with the Class as a whole. )

In this list and in those appended to the following chapters no attempt has
been made to give a complete bibliography of the subject. The references given
in the works mentioned will, however, provide the necessary guidance for the
student who desires a further acquaintance with the vast mass of carcinological
literature.

1. Bruntz, L. Contribution 2 1’étude de l’excrétion chez les Arthropodes. Arch.
Biol. xx pp. 217-422, pls. vii.-ix., 1903.

2. Claus, C. Untersuchungen zur Erforschung der genealogischen Grundlage
des Crustaceensystems. 4to. Wien, 1876.

3. Neue Beitriige zur Morphologie der Crustaceen. Arb. zool. Inst.
Wien, vi. pp. 1-108, pls. i.-vii., 1886.
4. Das Medianauge der Crustaceen. Arb. zool. Inst. Wien, ix. pp. 225-

266, 4 pls., 1891.
5. Dana, J. D. The Crustacea of the United States Exploring Expedition,
1838-1842. 2vols. 4to, and Atlas, fol. Philadelphia, 1852-1853.
6. Dohrn, A. Geschichte des Krebsstammes. Jenaische Zeitschrift, vi. pp.
96-156, 1871.
. Gerstaecker, A., and Ortmann, A. E. Crustacea, in Bronn’s Klassen und
Ordnungen des Thierreichs, Bd. v. Iste Abth. 1320 pp. 50 pls., 1866-
1879, by Gerstaecker. 2te Abth. viii + 1319 pp. 128 pls., 1881-1901, by
Gerstaecker-to p. 1056, continued by Ortmann.
8. Grobben, C. Die Antennendriise der Crustaceen. Arb. zool. Inst. Wien, iil.
pp. 93-110, pl. ix., 1881.

—— Zur Kenntniss des Stammbaumes und des Systems der Crustaceen.
Sitz.-Ber. Akad. Wien, ci. Abth. i. pp. 237-274, 1892. Translated in
Ann. Mag. Nat. Hist. (6) xi. pp. 440-473, 1893.

ba i

Le)

13.

14.

15.

THE CRUSTACEA

. De Haan, W. Crustacea, in P. F. v. Siebold’s Fauna Japonica. Fol.

Lugduni Batavorum, 1833-1849.

. Hansen, H. J. Zur Morph. der Gliedmassen und Mundtheile bei Crustaceen

und Insecten. Zool. Anz. xvi. pp. 193-198 and 201-212, 1893. Trans-
lated in Ann. Mag. Nat. Hist. (6) xii. pp. 417-4384, 1893.

. Huxley, T. H. The Crayfish, an Introduction to the Study of Zoology.

Internat. Sci. Series, vol. xxviii. London, 1880.

Korschelt, E., and Heider, K. Uehrbuch der vergleichenden Entwicklungs-
geschichte der wirbellosen Thiere. 8vo. Jena, 1890-1893. Translated
by M. Bernard, edited by M. F. Woodward, as Text-book of the
Embryology of Invertebrates. 4 vols. (Crustacea in vol. i.) 8vo.
London, 1899.

Milne-Edwards, H. Wistoire Naturelle des Crustacés (Roret’s Suites a
Buffon). 3 vols. and atlas, 8vo. Paris, 1834-1840.

Le Réegne animal... G. Cuvier. Illustrated edition. Crustacés,

1 vol. and atlas, 8vo. Paris, 1836-1849. (Only the plates are of much

importance. )

. Miller, F. Fiir Darwin. 8vo. Leipzig, 1864. Translated as Facts and

Arguments for Darwin. London, 1869.

. Parker, G. H. The Compound Eyes in Crustaceans. Bull. Mus. Comp.

Zool. Harvard, xxi. pp. 45-140, 10 pls., 1891.
The Retina and Optic Ganglia in Decapods, especially in Astacus.
Mitth. Zool. Stat. Neapel, xii. pp. 1-73, pls. 1-3, 1897.

CHAPTER II
THE BRANCHIOPODA

Sus-CLaAss BrANCHIOPODA, Latreille (1817).

Order 1. Anostraca.,
» 2. Notostraca.
» 0 Conchostraca.
» 4. Cladocera.
Sub-Order 1. Calyptomera.
Tribe 1. Ctenopoda.
» 2. Anomopoda.
Sub-Order 2. Gymnomera.
Tribe 1. Onychopoda.
», 2. Haplopoda.

Definition.—Crustacea in which the carapace may form a dorsal
shield or a bivalve shell or may be entirely absent ; the number of
trunk-somites varies greatly ; the posterior part of the trunk is
without limbs and usually ends in a candal furca; the antennules
are generally reduced and unsegmented; the mandibles have
no palp or only a vestige of one; the maxillae are reduced or
absent; the trunk-limbs, which vary greatly in number, are
generally of uniform structure, rarely pediform, generally foliaceous
and lobed; the position of the genital apertures varies greatly ;
the paired eyes are rarely absent; development usually with
metamorphosis ; young hatched in nauplius or metanauplius stage.

Historical.—The earliest mention of any of the Branchiopoda is
found in the works of Swammerdam, who, in 1669, described a
species of Daphnia as “ Pulex aquaticus arborescens,” and the name
of “ water-fleas” has since been commonly applied to the group of
Cladocera. Apus and Branchipus were described early in the
eighteenth century, and, together with Daphnia, formed the sub-
jects of a series of remarkable memoirs (1752-1756) by J. C.
Schiffer. The classical work of O. F. Miiller, ELntomostraca seu
Insecta testacea (1785), described a large number of new types and

29

30 DHE CRUSTACEA

laid the foundations of classification. The order Branchiopoda, as

Hig. 1d.

Branchinecta paludosa, one of the Anostraca.
x 4. (After Sars.) A, female; B, male. a’,
antennules ; a’, antennae, enlarged in the male
to form clasping organs ;
the male ; wt, ventral prolongation of the genital
segment in the female, containing the “ uterus ”
filled with eggs. On the front of the head,
between the antennules, is the unpaired eye,
and, just behind it, the stalked compound eye.
Dorsal to the pear-shaped mandible is seen the
groove which appears to divide the head-region
into two segments. Following this, the trunk
shows eleven limb-bearing and eight limbless
somites (besides the telson), the first and second
of the latter partly coalesced.

p, paired penes of

first defined by Latreille in
1817, included Ostracoda, Cope-
poda, and Limulus ; and Milne-
Edwards, in 1840, while exclud-
ing these, retains the later added
Nebalia. Later attempts to
extend the limits of the group
to readmit the Ostracoda and
Branchiura have not met with
support, while Claus’s demon-

stration of the Malacostracan
affinities of Nebalia and its

allies is now generally accepted.
Among the authors who, in the
first half of the nineteenth
century, contributed to a know-

ledge of the group, Jurine,

Fischer, and Baird may _ be
= F ?

mentioned. Zaddach’s mono-

graph on Apus is still the chief
source of information on many
points of anatomy. Leydig’s
work on the Cladocera is especi-
ally important as regards internal
anatomy and histology; and
Weismann’s series of papers
deal, among many other points,
with the remarkable phenomena
of their reproduction, which had
attracted attention from the
time of Schiffer. As is the case
with most other groups of Crus-
tacea, modern conceptions of
the morphology of the Branchio-
poda are largely indebted to
the works of Claus. Lankester’s
paper on the appendages and
nervous system of 4pus greatly
influenced opinion in favour of
the primitive position of the
Branchiopoda. Among the more
purely descriptive and faunistic
works the numerous papers of

G. O. Sars hold an important place, and mention may also be
made of the fine monograph on the Cladocera of Sweden, published

in 1900 by Lilljeborg, w

31

THE BRANCHIOPODA 3

ho had made important contributions to

the subject so long ago as 1853.

shape.

MorPHOLOGY.

The Branchiopoda present considerable diversity of general
In the Anostraca there is no shell-fold, and the elongated

ZO

een EE SOT

Fic. 16.
Lepidwrus glacialis, one of the Notostrava. x 21. (After Sars.) Dorsal view on the left,

lateral view on the right. In the latter, one-half of the carapace has been cut away to show
On the dorsal surface are seen the paired

the segmentation of the trunk and the appendages.
behind and between them, the median dorsal ridge of the

eyes with the ‘‘dorsal organ”
posterior part of the carapace, and the two transverse grooves just behind the eyes.

body, composed of many distinct somites, has an almost vermiform
aspect (Fig. 15). The flattened natatory feet are more laterally
placed than is usual in Crustacea, increasing the resemblance to
the Chaetopod worms. In the Notostraca also the body is

elongated, and composed of numerous somites, but its anterior
portion is covered by a broad arched carapace (Fig. 16). In the

32 THE CRUSTACEA

Conchostraca the body tends to be laterally compressed, and is
completely enclosed in a bivalved shell closely simulating that of
some lamellibranchiate molluscs (Fig. 17). In the Cladocera the
body is composed of few somites and its segmentation is more
or less obscured, while the bivalve shell, in most cases, covers the
body and limbs, leaving the head free (Fig. 18).

Hie. 17.

Estheria obliqua (Conchostraca). A, shell of female, from the left side. B, male seen fronr
the side, after removal of left valve of shell. (After Sars.) a’, antennule; a”, antenna; ad,
adductor muscle; jf, caudal furea; md, mandible. On the first and second pairs of trunk-
limbs are seen the ‘‘claspers”’ of the male.

Except in the Cladocera, the head is defined from the first trunk-
somite. In the Anostraca it is divided into two portions by a
transverse groove which crosses the dorsal surface just above the
mandibles. This groove is also found in the Conchostraca, and it
is no doubt. homologous with the anterior transverse groove on
the dorsal surface of the carapace in the Notostraca. In the
Conchostraca and Cladocera the front of the head is more or less
produced downwards forming a rostral process, and in the Notostraca
it is inflected, forming a sharp semicircular anterior edge continuous
on either side with the lateral margins of the carapace.

THE BRANCHIOPODA 33

The carapace may be directly continuous in front with the
dorsal integument of the head as in most Cladocera, or defined
from it by a groove as in some Cladocera and the Notostraca. In
the Conchostraca the con-
nection between the animal
and the shell is reduced to
a comparatively narrow neck

and the lateral lobes of the Ws
; RA(e

shell extend forwards on each as
side so as to enclose the — ad A
1a,

whole head (Fig. 17). Gener-
ally the shell-fold does not
coalesce with any of the
trunk-somites which it en-
velops, with the exception
of the one or two anterior
somites which in the Clado-
cera are fused with the head.
In the aberrant Cladoceran
Leptodora, however, it coal-
esces with the dorsal surface
of the leg-bearing somites,

and its free portion, which ai

here, as in some other Clado- eo:

cera, forms merely a_brood- aK ae
Fic. 18.

Sac, ae peans to Se from Daphnia, female. a’, antennule; @”, antenna ;
the posterior margin of the _ ?.c, brood-chamber ; br, brain; c, margin of carapace ;

: aa ae c.s, caudal setae; e, compound eyes coalesced into
sixth trunk-somite (Fig. £9); one; f, furea; gl, maxillary gland; h, heart; hep,

: hepatic diverticulum of gut; 7.e, nauplius eye ; ov,
The carapace May be ovary. (After Claus and Grobben.) .

more or less corneous, but

it is never strongly calcified. In a few Cladocera (Monospilus,
etc.) and in the Conchostraca (Fig. 17) the integument of the
outer surface of the shell is not cast off in ecdysis, but remains
in position, giving rise to a series of “lines of growth” marking
the increased size of the shell at each moult. Special modifica-
tions of the carapace for protection of the eggs will be referred
to below.

The number of trunk-somites varies very much. It is greatest
in the Notostraca, where 42 somites are found in certain
species of Apus. In the Conchostraca the number is from about
13 to 28, and in the Anostraca 19 to 23. In the Cladocera the
segmentation of the body is generally more or less obscured ; at
least the first two somites are always coalesced with the head. In
Daphnia, according to Claus, these are followed by three limb-
bearing somites, and the succeeding apodous region is divided in
the young into three “abdominal” somites and a ‘“ postabdomen ”

4
)

34 THE CRUSTACEA

or telson. This segmentation of the apodous region is distinctly
retained in the adult Leptodora (Fig. 19).

Apart from the presence or absence of appendages, the trunk of
the Branchiopoda is not differentiated into distinct regions. By
various authors the terms “thorax” and “abdomen” have been ap-
plied respectively, sometimes to the pre- and post-genital, sometimes
to the limb-bearing and limbless regions of the trunk. As the
limits between these regions do not coincide, even approximately,

Fia. 19.

Leptodora kindtii, female, x 10. a’, antennule; w’, antenna; ¢, carapace, reduced to a brood-
sac; ¢.s, caudal setae (compare figure of Daphnia, p. 33); e, compound eye; f, furca; p, first
trunk-limb. (After Lilljeborg.)

except in the Anostraca, it seems better to avoid altogether the use
of the terms “thoracic” and “abdominal” in dealing with this
group.

In the Notostraca a varying number (4-14) of the posterior
somites are without appendages. In the post-genital region of the
body the number of pairs of appendages greatly exceeds the number
of somites, some of the posterior somites carrying as many as six
pairs. In the Anostraca there are from four to nine limbless
somites, but at least the two anterior are coalesced to form the
genital segment. In the Conchostraca the short post-pedal region
is unsegmented.

i)

THE BRANCHIOPODA ' 35

The last segment of the body, or telson, carries, except in
Limnetis and Thamnocephalus, a pair of furcal rami, long antenni-
form filaments in the Notostraca (Fig. 16), unsegmented styles or
flattened plates in the Anostraca (Fig. 20, C). In the Conchostraca
and Cladocera the posterior part of the body is flexed ventrally
and the furea is represented by a pair of strong curved claws
(Fig. 17, f). The anus opens either at the end of the body

Fic. 20.

A, head-region of Lepidurus glacialis from below : a’, antennule ; a”, antenna; gn, gnatho-
base of first trunk-limb ; L, labrum or upper lip turned forwards (in the natural position it
covers the opposed edges of the mandibles) ; 1, lower lip (according to Claus, the inner lobes of
the maxillulae) ; m, mandible; mz’, maxillula; ix”, maxilla. B, posterior end of body of
Lepidurus glacialis ; a, position of anal opening ; pl, supra-anal plate; 7, rami of caudal furea;
T, terminal segment or telson. C, posterior end of body of Branchinecta paludosa ; letters as
above. (After Sars.)

between the furcal rami or, in many Cladocera, some distance in
front on the dorsal surface. In the genera Lepidurus (Notostraca)
and Thamnocephalus (Anostraca) the telson is produced as a thin
plate above the anal opening (Fig. 20, B).

Appendayes.—The antennules are, for the most part, purely
sensory in function, not segmented or obscurely so, and carrying
tufts of sensory filaments. In many Cladocera they are very small
and attached to the posterior surface of the deflexed beak-like

36 THE CRUSTACEA

process forming the front of the head (Fig. 18, a’). In the males
of some Cladocera they form clasping organs for holding the female.

The antennae differ very much in the various orders. In the
Notostraca they are vestigial (Fig. 20, A, a’) and may even be
absent in certain species of Apus. In the males of the Anostraca
they are converted into powerful claspers for seizing the female,
and may assume extraordinary and complex forms. A pair of
filaments, known as frontal appendages (Figs. 21 and 32, f.a),
arise, in many Anostraca, from the base
of the antennae, though sometimes they
are inserted on the front of the head
and seem quite unconnected with the
antennae. They may coalesce at the
base, and may be more or less ramified,
adding to the complexity of the apparatus

erik carried by the male. In the females the

Head of Chirocephalus diaphanus antennae are much simpler in form, and
(Aen Sigon)y Ww antennule; a”, are probably purely sensory in function.
antenna; fa, frontal appendages, It would seem from Claus’s observations
which in this species are large and c
branched. on the development of Branchipus that

the endopodite of the antenna atrophies,
and that the whole apparatus of the adult develops from the
protopodite and exopodite of the larval antenna.

In the Conchostraca and Cladocera the antennae are large
biramous swimming-organs. In the former group they have
multiarticulate rami, and they are protruded ventrally between the
valves of the shell (Fig. 17). In the latter order the rami have
few segments, and, since the head is not enclosed between the
valves of the shell, the antennae project freely (Fig\18). In
the genus Latona (Cladocera) a large process from the proximal
segment of the exopodite causes the antenna to appear as if three-
branched.

The mandibles (Fig. 8, C, p. 12) are devoid of palps in all existing
Branchiopoda with the exception of Polyartemia, in which a vestigial
palp has recently been found by Ekman. As a rule, they have
broad toothed triturating surfaces, but in some predatory Cladocera
(Leptodora) they become long sickle-shaped blades.

» The mazillulae (Fig. 22, A) are of small size and simple form.
As a rule, each consists of a single lobe armed with spines on
the inner edge. In the Notostraca they seem to consist of two
lobes, but it is possible, as Claus suggested, that the inner and
anterior lobes represent the lower lip, or paragnatha, otherwise
wanting in the group.

The mavillac (Fig. 22, B) are also greatly reduced and consist of a
simple lobe. In the Cladocera they are entirely wanting in the adult,
but a distinct rudiment is present in the embryo. In the Notostraca

THE BRANCHIOPODA a7

an external membranous lobe is present and was formerly regarded
as corresponding to the gill or bract of the succeeding appendages.
For this reason the appendage was regarded as belonging to the
series of the trunk-limbs, and was called a “foot-jaw” or “maxilliped.”
It has been shown, however, by Claus that the so-called “ bract ”
is really a tubular process bearing the external opening of the
maxillary gland, and is in no way related to the “bract” of the
following limbs. There is therefore no reason to doubt that the
appendage is homologous with the maxilla of other Branchiopoda.
It is of interest to notice, in connection with the great reduction of
this appendage, that there is, in Apus, no separate ganglion in the
ventral nerve-chain corresponding to it, but that the nerves supply-
ing it take their origin from the longitudinal connectives between
the ganglia corresponding to the maxillula and the first thoracic
appendage respectively.

A.

Fig. 22.
A, maxillulae, B, maxilla, of Apus cancriformis. (After Claus.) jp, the so-called inner lobes

of the maxillulae, representing, according to Claus, the paragnatha; 0, opening of maxillary
gland on a tubular process connected with the maxilla.

The trunk-limbs of the Branchiopoda are generally of very
uniform structure, and are not grouped into definite “ tagmata.”
On the other hand, these appendages present very great differences
in the different groups composing the sub-class, and it is not easy
in some cases to determine the exact homologies of the various
parts.

The most primitive form is probably that found in the Noto-
straca (4pus, Fig. 23, A). Each appendage consists of a flattened
corm or axis to which are attached eight lateral processes or lobes.
Six of these processes spring from the inner margin of the corm and
are termed endites, while two on the outer margin are termed evites.
The proximal endite (1), placed near the 4ttachment of the limb to the
body, is armed with strong spines and, like some or all of the other
endites, is provided with special muscles which permit‘of a limited
amount of movement on the corm. These basal endites working
against those of the opposite side function as jaws, seizing and
passing forward towards the mouth particles of food which are

38 THE CRUSTACEA

WIN
/ }) |

iG reves

Trunk-limbs of various Branchiopoda. A, seventh trunk-limb of Apus cancriformis
(Notostraca). B, third trunk-limb of Estheria obliqua (Conchostraca). C, fifth trunk-limb of
Branchinecta, paludosa (Anostraca). D, eleventh trunk-limb of Polyartemia forcipata
(Anostraca). (A after Lankester; B, C, and D after Sars.) br, branchia or bract; hie
\flabellum ; ¢, tactile process of the fifth endite in Estheria; 2, proximal exites of the Anostraca 5
1-6, the six endites, of which the first is the gnathobase. Between the flabellum and the
sixth endite in A is seen the “snb-apical lobe.” Regarding the homology of the plate lettered
jlin C and D, see the discussion in the text.

ae ae

THE BRANCHIOPODA 30

drawn in between them by the rhythmical movements of the
appendages in swimming. They are therefore distinguished as
- gnathobases. ‘The Branchiopoda are the only Crustacea in which
gnathobases are found on limbs far removed from the mouth. Of
the two exites, the distal, known as the flabellum (fl), is a thin plate
with setose margins. It is moved by special muscles and probably
serves chiefly as a swimming-plate. The proximal exite, known as
the bract (br), is branchial in function, having a very thin cuticle,
without setae, and is not provided with muscles. ‘The end of
the corm, external to the sixth endite, is produced into a rounded
process, the “ sub-apical lobe.”

While most of the postmaxillary appendages of the Notostraca
have the general structure of that just described, differing only in
details of shape and proportion of the various parts, certain of them
are specially modified. In the first and second pairs, the corm is
divided, in the former into four, and in the latter into two segments.
The endites, with the exception of the gnathobase, become more
elongated in passing forwards along the series of limbs, and in the
first pair the second, third, fourth, and fifth endites, counting from
the base, are produced into filiform multiarticulate rami (Fig. 20, A).
The fifth, in some species, is nearly as long as the body of the
animal. The sixth endite, however, is much reduced and of peculiar
form in the limbs of the first pair.

The trunk-limbs of the Conchostraca (Fig. 28, B) can without
difficulty be compared with those of Apus. The six endites are
distinct though reduced in size and less sharply marked off from
the unsegmented corm. The gnathobase is unprovided with
masticatory spines, but, like the following endites, is fringed with
setae. The fifth endite is produced in some cases into a long
tactile process (f). Only the sixth endite is marked off by a
distinct articulation. The flabellum is very large and the branchia
is reduced in size.

In the Anostraca (Fig. 23, C, D) the structure of the parts is
rather different and their exact homologies are not quite clear.
The flattened unsegmented corm has its inner edge more or less
distinctly divided into six lobes. At the distal end, towards the
outer side, is a broad oval plate (jl) defined by a well-marked
articulation and fringed with setae. On the proximal side of this,
on the outer edge, is the branchia, characterised as such by its
thin cuticle and by the lack of setae. Still nearer the base the
outer margin of the corm is produced into a rounded plate (7), very
thin and not defined by an articulation. In Polyartemia and in
some species, at least, of Chirocephalus there are two such plates
(Fig. 23, D). It appears most probable that the six lobes of
the inner edge correspond to the six endites of the Notostracan
limb, in which case the distal setose plate (//) will represent

40 THE CRUSTACEA

the flabellum. This view, however, is not accepted by Sars,
who regards the distal setose plate as the sixth endite and
supposes that the flabellum is wanting in the Anostraca. Sars’s
interpretation gains some support from a comparison with the
Conchostracan type of limb, where the sixth endite has much the
same position as the setose plate of the Anostraca. It is further
supported by the fact that, in the development of the limbs of
Apus, the flabellum only appears after some of the endites have
become marked off, while in Dranchipus the first differentiation to
take place in the limb-buds is a bifurcation defining the distal setose
plate from the terminal lobe of the inner edge. In any case it
seems certain that the external basal plate or plates of the
Anostraca are new formations unrepresented in the Notostraca and
Conchostraca, and not, as Lankester supposed, homologous with
the branchia (or bract) of these groups.

In the Cladocera the structure of the limbs is still more difficult
to interpret. In the Ctenopoda (Fig. 24, A), where the six pairs
of “thoracic” appendages are comparatively uniform, the inner
margin forms a small gnathobasic lobe followed by a broad lobe
carrying a comb-like series of long setae. A distal lobe may
correspond to the flabellum of Apus and Estheria, or perhaps to the
sixth endite. The branchia is present and has the usual characters.
In the Anomopoda there is considerable differentiation among
the members of the series. In Daphnia, for example, the first limb
(Fig. 24, B) is obscurely segmented and the five lobes on the inner
edge are slightly developed. The second limb (Fig. 24, C) has the
gnathobase enlarged and has an outer branch regarded as the
exopodite. Both of these limbs are adapted by the possession of
long curved setae to aid in the prehension of food. The third
(Fig. 24, D) and fourth pairs are characterised by the great
development of the proximal endite with its comb-like row of
setae. They serve to keep a current of water flowing between
the valves of the shell for the purposes of respiration and feeding.
The last pair in Daphnia are greatly reduced (Fig. 24, E).

In the Gymnomera, and especially in Leptodora (Fig. 19), the
trunk-limbs have lost the characteristic leaf-like shape and have
become cylindrical, elongated, and divided into four well-marked
segments, without any trace of endites or exites, serving only for
seizing and holding prey.

Modifications of certain of the trunk-limbs subservient to
the processes of reproduction are found in all divisions of the
Branchiopoda. In the males of most of the Conchostraca the first
two pairs have the terminal portion modified into a cheliform
clasper (Fig. 17, B), but in Limnetis and in the Cladocera only the
first pair is so modified. Sexual modifications of trunk-limbs in the
female are found only in the Notostraca and in some Conchostraca.

THE BRANCHIOPODA 41

In |the former the appendages of the genital somite (the eleventh
trunk-somite) are modified to form brood-pouches, and are known
as “oostegopods” (Fig. 25). The sixth endite is coalesced with

Fig. 24.

Trunk-limbs of Cladocera. A, first trunk-limb of Sida crystallina (Ctenopoda). B, first,
©, second, D, third, E, fifth trunk-limbs of Daphnia pulex (Anomopoda). Ur, branchia; gn,
gnathobase. (After Lilljeborg.)

the sub-apical lobe, and together with it forms a hemispherical
cup, closed by a movable lid formed by the flabellum. In some
species of Conchostraca two or three pairs of limbs near the genital
apertures have the proximal division of the flabellum produced

42 CHE CROSTACEA

and thickened, and to this the egg-masses are attached between

the valves of the shell.

As regards the homologies of the parts of the Branchiopod-limb
with those of the biramous type found in other Crustacea, two

Fic. 25.

Eleventh trunk-limb or oostegopod of Apus caneri-
formis, female. (After Lankester.) 1-6, the six endites,
of which the sixth is fused with the ‘‘ sub-apical lobe”
which forms the pouch, p, containing the eggs; fl,
flabellum forming the cover of the pouch; 67, the
vestigial bract.

views have been suggested.
According to the interpreta-
tion adopted by Huxley,
among others, the “ flabel-
lum” or distal exite of the
Apus-limb corresponds tothe
exopodite, while the distal
part of the corm represents
the endopodite. Lankester,
on the other hand, considers
the endopodite and the
exopodite to be represented
by the fifth and sixth
endites respectively, the
corm being the protopodite
and the flabellum the epi-
podite. The former view
is supported bya comparison
with the leaf-like thoracic
limbs of the Leptostraca,
while Lankester’sinterpreta-

tion is based chiefly on a comparison of the pre-oral with the post-
oral appendages in the larval Apus, and of -the trunk-limbs of Apus
with the maxilla and maxillipeds of various Decapods. Neither

view is quite free from difficulties, and the
divergences in structure mentioned above
as occurring in the Anostraca still further
complicate the matter, which requires
further investigation.

Alimentary System.—The oesophagus is
narrow and is provided with constrictor
and dilator as well as longitudinal muscles.
It usually projects a little way into the
more capacious mid-gut, and in Polyartemia
the terminal part is armed with setae.
The hind-gut is short and muscular. In
the aberrant Cladoceran Leptodora the
oesophagus is of great length and the
mid-gut hardly extends in front of the
terminal segment of the body. In many

Fie. 26.

Pleurowvus uncinatus (Cladocera)
(after Lilljeborg), showing the
coiled intestine and its ventral
diverticulum.

Cladocera belonging to the families Lyncodaphnidae and Lynceidae
the mid-gut is more or less coiled, forming a simple loop or a spiral

THE BRANCHIOPODA 43

of one and a half turns (Fig. 26). As a rule, the anterior part of
the mid-gut gives off a pair of diverticula. In the Notostraca and
Conchostraca these are much ramified, and in the Anostraca they
are saccular and lobulated. In the Cladocera they are often absent,
and when present are simple caeca. In some Cladocera of the
family Lynceidae the posterior part of the alimentary canal gives
off an unpaired diverticulum on the ventral side (Fig. 26). It
is usually short, but sometimes it is of considerable length. It is
stated to arise from the hind-gut, and its walls contain large

gland-cells. ‘
Circulatory System.—Except in the Cladocera, the heart is
elongated and tubular. In the Anostraca it traverses almost

the whole length of the trunk, and has paired ostia in each somite
except the first and last. In the Notostraca the heart extends
through the first eleven trunk-somites and has eleven pairs of ostia.
In the Conchostraca it is restricted to three or four somites, with
a corresponding number of ostia. In the Cladocera the heart is
greatly abbreviated, forming a sub-globular sac with a single pair of
ostia, lying in the region of the first trunk-somite (Fig. 18, /).
There are no distinct vessels and the blood is discharged directly
from the anterior end of the heart (through three openings in the
Notostraca) into the sinuses of the head-region.

In some genera (Apus, Branchipus, Artemia, and some Cladocera)
the fluid of the blood is coloured red, owing, as Lankester has
shown, to the presence of haemoglobin.

Excretory System.—The maxillary gland (Fig. 18, gl) is well
developed in all Branchiopoda. Except in the Anostraca and some
aberrant Cladocera (Leptodora), it lies within the thickness of the
shell-fold. It shows the typical structure, consisting of end-sac,
glandular coiled tube, and short terminal duct. In the Notostraca,
as already mentioned, the external opening is at the end of a
tubular process arising from the under side of the head, close to
the maxilla.

The antennal gland is well developed in the larval stages of
Anostraca, Notostraca, and Conchostraca (Fig. 10). A vestige of
it persists in the adult Artemia.

Glands.—Belonging to the dermal series of glands are the
segmentally arranged ventral and leg glands of some Anostraca,
and the groups of unicellular glands in the labrum which are
probably always present.

Special interest attaches to the structure variously referred to
as “neck gland,” “dorsal organ,” or “adhesive organ,” found in
many Branchiopoda. In its simplest form this consists of a
thickened and glandular area of the ectoderm, on the dorsal surface
near the posterior limit of the head-region. The adhesive secretion
reaches the exterior through pores or slits in the cuticle, and is used

ae

a”

44 LTE CRG SACRA

for the purpose of attaching the animal temporarily to plants or
other objects. In the Notostraca, however, where the organ is
apparently well developed, it is not used for this purpose. In the
Anostraca it is absent in the adult, though very large in the larva.
In some of the Conchostraca (Limnadia)
it is prominent and pedunculated. In
many Cladocera it is greatly reduced or
absent, but in some it is large and
functional. In the Sididae the organ is
divided into three parts, a large median
anterior and a pair of smaller ones posterior
to it. In this case certain muscles attached
to the integument in the neighbourhood of
the organ are believed to produce a sucker-

Fic. 27

Nervous system of Simocephalus (Cladocera) from the
dorsal side. (After Cunnington.) cer, brain; g.o, optic
ganglia, here partly fused in correlation with the fusion of
the paired eyes; n.a’, nerve to antennule; 7.@”, nerves to
antennae, arising from the oesophageal connectives ; 1.f.1-
n.f.5, nerves to the five trunk-limbs; n.Jbr, nerve ring
encircling oesophagus in region of the labrum; n.md, nerve
to mandibles ; n.mxz, nerve to maxillulae ; n.0, optic nerves ;
oe, position where oesophagus passes between the nerve-cords ;
ventrally the oesophagus curves backwards so as to pass
through the ring n.lbr before reaching the mouth. The
transverse commissure corresponding to the antennal ganglia
is on a level with the roots of the posterior antennal nerves.

like action, thus aiding adhesion. In some
Lynceidae two organs are found, one behind
the other.

Endoskeletal Structures.—In many
Branchiopoda there is a considerable de-
velopment of trabeculae and plates of
tendinous connective tissue giving attach-
ment to muscles. This system, which
almost merits the name of endoskeleton,
is most fully developed in the Anostraca,
where the external cuticle remains almost
membranous, but it is also found in the
Cladocera. In the Notostraca the chief
part of this endoskeletal system is a
tendinous plate, known as the entosternite,
lying under the anterior part of the
alimentary canal and giving attachment to the adductors of the
mandibles and to other muscles.

Muscular System.—In the Conchostraca and Cladocera the valves
of the shell are drawn together by a transverse adductor muscle.
In some, at least, of the Cladocera this muscle is double.

THE BRANCHIOPODA 45

Nervous System.—As has been mentioned above, the nervous
system of most Branchiopoda shows very primitive characters in
the ladder-like form of the ventral nerve-chain (Fig. 11, p. 17, and
Fig 27). In some Cladocera, however (Polyphemidae and Lepto-
dora), the ventral ganglia are more or less coalesced into a single
mass. In all cases, the nerves to the antennae arise not from the
supra-oesophageal ganglia, but from the first post-oesophageal pair
of ganglia. This pair of ganglia is quite distinct from the next
succeeding pair, which innervate the muscles of the mandibles,
and, like all the ventral pairs of ganglia (with the occasional
exception of the mandibular), it has a double transverse com-
missure. It is closely connected with the origin of a “ visceral”
nerve-ring which encircles the oesophagus and bears an unpaired
ganglion in the region of the labrum (Figs. 27 and 28, n.lbr).
So far as their nerve-supply is concerned
the antennae are, in the Branchiopoda,
unmistakably post-oral. In the Noto-
straca the nerves of the antennules (Fig.
28, ua’) arise from the oesophageal
connectives just in front of those of
the antennae. This was supposed by
Lankester to be a primitive condition
indicating the post-oral origin of these
appendages. Pelseneer showed, however,
that the fibres of these nerves pass
forward to a pair of nerve-centres in the
supra-oesophageal ganglion. In the other
Branchiopoda the corresponding nerves
arise from the posterior part of the brain,
and there can be little doubt that the
condition in Apus is a secondary one due
to the brain having been shifted forwards
and upwards in company with the paired
eyes which le on the dorsal surface of
the head, while the antennules are in- Fic. 28.
serted on its lower surface. In Apus Anterior part of the central

z : r nervous system of A pus, from below,
there is no ganglion corresponding to the semi-diagrammatic. cer, brain :

‘ mae F ee |S mage *-, gn’, antennal ganglion ; n.a’, nerve
reduced maxillae, and these limbs receive {)°* tennule® war nore te

a pair of nerves arising’ from the longi- antenna ; n.f’, nerves to first trunk-
z % 5 . © limb; m.Jbr, nerve-ring encireling
tudinal connective between the maxillular oesophagus; n.md, nerves to man-
. - On C dible; 7.mz’, nerves to maxillula;

and first thoracic ganglia (Fig. 28, nmz’, nerve to maxilla; oe, position

n.mz). In the Cladocera, also, where the oid Pabettons (After Lankester
maxillae are quite rudimentary or absent,

there is no ganglion corresponding to this somite. In Branchipus,
however, there is a distinct pair of ganglia with double transverse

commissures.

46 THE CRUSTACEA

Sense-Organs.—The compound eyes are present in all Branchio-
poda. In the Anostraca they are elevated on movable peduncles,
but in all other Branchiopoda they are sessile, preserving, however,
a certain degree of mobility owing to the fact that they are sunk
below the surface and covered by an invagination of the outer
cuticle, the cavity of the invagination generally remaining in
communication with the exterior by a pore (Fig. 29). Except in
the Anostraca, the two eyes
are Closely approximated ;
and in some Conchostraca,
and more completely in the
Cladocera, they fuse together
into a single eye. The cornea
is not distinctly faceted.
The crystalline cone is
divided into four parts. The
rhabdom is surrounded by
five rhabdom-cells, but (in
ranchipus) is not distinctly
divided into rhabdomeres.

Except in some of the
Cladocera, the nauplius eye
persists in the adult of all
Branchiopoda (Figs. 18 and

Fic. 29.

Diagrammatic longitudinal section through the
compound eye and associated structures of Apus.
(After Bernard.) br, brain; c, external cuticle of
head; ce, compound eye; m, muscle for moving
compound eye; 2.e, nauplius eye; p, pore leading
into the water-sac covering the compound eye and
sending a blind diverticulum into the nauplius eye ;
s, the water-sac, formed by an invagination of the
integument. The pore, p, is in the median line, so
that, as a matter of fact, a strictly longitudinal
section passing through it would pass between the
compound eyes,

29, ne). It is of the usual
tripartite structure, and may
be connected with the brain
by three separate nerves or
by gar single: sone. lila ithe
Cladocera it is reduced in
size and simplified in struc-
ture, and may be entirely

absent.

Frontal Organs.—In Branchipus a pair of organs, presumably
sensory, lie on the front surface of the head (Fig. 5, f). Each
consists of a large hypgdermis cell surrounded by a group of
ganglion cells and connected with the brain. Below this, in
Branchipus, is a group of club-shaped cells containing peculiarly
shaped rod-like bodies and connected with nerves. In the
Cladocera the first-mentioned frontal organs are vestigial, and
appear to be represented by a group of cells supplied by a
continuation of the nerve of the median eye. The club-shaped
cells, however (the ‘‘ Nackenorgan” of Leydig), are well developed,
but are situated high up on the sides or on the dorsal surface
of the head. The pair of nerves supplying them originate from
the ventral surface of the brain.

—-

THE BRANCHIOPODA 47

Reproductive System.—The gonads are generally paired, but in
some Cladocera they may be united in the middle line. In the
Notostraca they are much ramified, but in the other Branchiopoda
they are of simple tubular form. Probably all Branchiopoda are
of separate sexes. In the Notostraca Bernard has described testi-
cular tissue in the ovary, but the occurrence of normal functional
hermaphroditism is still unproved.

In the Notostraca the genital ducts open on the 11th trunk-
somite, and this is probably also the case in all the Conchostraca.
In the majority of the Anostraca the first two apodous somites,
namely, the 12th and 13th of the trunk, are more or less com-
pletely fused, forming a “genital segment” on which the genital
ducts open. The development indicates that the openings prob-
ably belong to the 12th somite. In Polyartemia, however, the
leg-bearing somites are 19 in number, and the 20th and 21st
somites form the genital segment in the male sex. In the female
all the apodous segments are coalesced. In the Cladocera the
female genital apertures are lateral or dorsal in position on the
posterior apodous division of the body. The male apertures are
lateral or ventral and often placed farther back, sometimes quite
at the end of the body.

The genital openings are generally paired, but the female
opening is unpaired in the Anostraca, where the oviducts unite to
form a uterine chamber (Fig. 15, A, uf) with groups of gland-
cells on its walls. In some Cladocera the male opening is un-
paired. The terminal part of the vasa deferentia forms a paired
eversible intromittent organ in the Anostraca (Fig. 15, B, p) and
in some Cladocera (Sididae).

The spermatozoa are immobile and usually spherical. In the
Cladocera, however, they present a remarkable variety of form,
differing greatly sometimes even in the species of one genus.

In the Anostraca the eggs are retained, sometimes till they
hatch, in the uterine portion of the oviduct. In the other Branchio-
poda they are carried after extrusion either in special receptacles
formed by the 11th pair of trunk-limbs (Notostraca) or enclosed
within the valves of the shell (Conchostraca and Cladocera). In
the Conchostraca the egg-masses are attached to certain pairs
of specially modified trunk-limbs. In the Cladocera a_ special
brood-chamber is formed between the dorsal surface of the body
and the shell, and is closed behind by fleshy folds or prominences.
Further, in some Cladocera, if not all, a modification of the hypo-
dermis of the dorsal surface takes place for the secretion of a
nutritive fluid by which the embryos are nourished within the
brood-chamber. In the Cladocera the sexually produced “ resting ”-
or ‘‘winter”-eggs are deposited within the cast-off shell, and in
many a part of the shell becomes thickened and indurated, and

48 THE CRUSTACEA

separates from the rest at ecdysis to form a protective case known
as the ephippium, containing the resting-eggs.
DEVELOPMENT.

Excepting the great majority of the Cladocera and a few
Conchostraca (Cyclestheria) in which the development is embryonic,

Fig. 30.

Larval stages of Apus cancriformis. A, metanauplius, just hatched; B, ‘‘second” larval
stage ; C, ‘‘ fourth” larval stage. 1, antennule; 2, antenna; 3, mandible; 4, maxillula; I-XIII,
first thirteen trunk-somites; js, frontal sense-organ; L, hepatic diverticula; s, carapace
(After Claus, from Korschelt and Heider’s Embryology.)

the Branchiopoda have a free-swimming nauplius or metanauplius
stage. Some differences exist even in closely allied forms in the
stage of development reached at hatching. In the Notostraca
(Fig. 30) and Anostraca the larva is a typical metanauplius with
an oval body, showing posteriorly the commencing division of
several trunk-somites and sometimes rudiments of their appen-
dages. The antennules are well developed, but simple. The
antennae have a movable masticatory process. The corresponding

THE BRANCHIOPODA 49

process of the mandible is feebly developed. The paired frontal
sense-organs in the form of papillae develop at an early stage,
though not present on hatching. The maxillulae and maxillae are
generally not marked off till after the succeeding limbs have been
differentiated. The ‘dorsal organ” or nuchal gland is very large
in the early stages even in those forms in which it is greatly
reduced or absent in the adult. The trunk-somites and their
appendages become differentiated in regular order from before
backwards.

In the Conchostraca the earliest larva has no trace of the
trunk-somites. The antennules are greatly reduced and the
labrum is very large. The nauplius of Limnetis is remarkable for
the broad dorsal shield and for the peculiar cruciform shape of the
front of the head. In the Conchostraca and in the Cladocera the
shell develops from paired rudiments. The later larval stages of

Fic. 31.

Metanauplius of Leptodora, hatched from a ‘‘ winter’-egg. a’, antennule; a”, antenna; md,
mandibular palp ; ol, labrum ; pi-p¥i, rudiments of the six pairs of trunk-limbs. (After Sars,
from Korschelt and Heider’s Lnbryology.)

the Conchostraca, as, for instance, Hstheria, correspond very closely
with the adult structure of the Cladocera.

In the Cladocera the eggs are usually large and rich in yolk,
or, when the reverse is the case, a special provision is made for the
nourishment of the developing embryos within the brood-chamber.
The egg-membrane, which in the parthenogenetic (“summer ”) eggs
is very thin, is early cast off, and the developing embryos lie free
within the brood- chamber. In the sexually produced (“winter ”
or “resting ”) eggs the whole development is gone through within
the egg- -membrane. A distinct nauplius stage is passed through,
and, at least in some cases, is marked by the formation of a cuticle
which is cast off later. The rudiments of the maxillulae and
maxillae do not appear until after some of the trunk-limbs have
already appeared, and the maxillae afterwards become reduced and
disappear in the adult. In the embryos of some Cladocera in
which only five pairs of trunk-limbs are present in the adult, six
pairs of rudiments are formed, but the last pair disappears later.

4

50 THE CRUSTACEA

The young of the Conchostracan Cyclestheria have an embryonic
development very similar to that of Cladocera within the shell of
the parent.

A remarkable exception to the rule of embryonic development
among Cladocera is afforded by the aberrant genus Leptodora. The
parthenogenetic ‘‘summer’”-eggs develop in the usual way within
the brood-pouch of the parent. The “ winter”-eggs, however, hatch
out as metanauplii (Fig. 31). The body is unsegmented, but the
six pairs of thoracic limbs are already visible as rudiments. The
antennules are very short. The antennae, on the other hand, are
unusually large, as they are also in the adult. They are without
any masticatory process. The mandibles have long unsegmented
palps. The compound eyes are not yet developed, but the nauplius
eye is present, and persists throughout life in the individuals
hatched from “ winter”-eggs, while it is absent in those hatched
from the “summer ”-eggs. In the reduction of the antennules this
larva shows some resemblance to that of Estheria.

REMARKS ON HABITS, ETC.

The great majority of the Branchiopoda inhabit fresh water.
A few species of Cladocera, belonging to three genera, occur in the
sea, and the Anostracan Artemia is found in salt lakes and brine-
pools. The Cladocera form an important part of the plankton of
lakes and ponds, and the larger Anostraca, Notostraca, and Con-
chostraca occur chiefly in small ponds and rain-water pools. The
occurrence, throughout the group, of sexually produced, thick-
shelled “resting egos, which can survive desiccation, in addition
to the thin-shelled eggs produced by parthenogenesis, probably
indicates the very ancient adaptation of the Branchiopoda to a
freshwater habitat.

No parasitic Branchiopoda are known.

The Cladocera are nearly all of microscopic size, and some species
which do not exceed 0°25 mm. in length are among the smallest
known Arthropoda. Of the other orders, the Notostraca comprise
the largest forms, some species of Apus reaching 70 mm. in
length.

PALAEONTOLOGY.

The Conchostraca are well known as fossils, and forms
referred to the existing genus Lstheria occur as early as the
Devonian. The Notostraca are more doubtfully represented by
Protocaris from the Lower Cambrian. From the delicacy of their
structure, the Anostraca are less likely to be preserved, and almost
the only undoubted example is Branchipodites of the Oligocene. The
Cladocera are not certainly known earlier than Post-tertiary deposits.

THE BRANCHIOPODA SI

Many palaeozoic fossils formerly classed with the ‘‘ Phyllopoda ”
are now referred to the Phyllocarida.

AFFINITIES AND CLASSIFICATION.

The alliance of the groups included in the Branchiopoda is
justified especially by the lobed foliaceous form of the trunk-limbs
which they have in common, but the divergences of structure in
other respects are greater than is the case in other sub-classes of
Crustacea. Thus, while the other sub-classes are more or less
strictly nomomeristic, each of the orders of Branchiopoda, and even
some of the families and genera, are markedly anomomeristic. This
is in agreement with the view that the Branchiopoda are a primitive
group which has not attained to the fixity of general structure
found in the other sub-classes.

Their primitive character is further shown, as has been pointed
out, by the general uniformity of the trunk-somites and their
appendages, by the presence of gnathobases on all the trunk-limbs,
by the “ladder-like” form of the ventral nerve-chain and the post-
oral position of the antennal ganglia, and by the tubular heart and
its segmentally arranged ostia. The primitive character of the
larval development has also been alluded to.

It may be mentioned here that, as in other groups of Arthro-
poda, the possession by many Branchiopoda of a large number of
somites can hardly be regarded as proof. of their primitive position.
In the Notostraca, the fact that the posterior pairs of appendages
exceed in number the somites which carry them, shows that
secondary changes, whether by coalescence of somites or, more
probably, by multiplication of appendages, have taken place. A
further argument in favour of a possible increase in number of
somites is afforded by a consideration of the aberrant Notostracan
genus Polyartemia (Fig. 32). Apart from the Cladocera, which the
abbreviation of the trunk excludes from the comparison, Polyartemia
forms the only exception to the rule that the genital apertures of
the Branchiopoda are situated, approximately, in the region of the
twelfth trunk-somite. Now, the.close resemblance in all other
respects between Polyartemia and the other Anostraca strongly
suggests that the nineteen somites interposed between the head
and the genital somite in that genus correspond, as a whole, to the
eleven somites which occupy the same position in the other
Anostraca ; and the agreement of the latter in this respect with
most of the other Branchiopoda seems to indicate that the smaller
number of somites is here the more primitive, the larger the more
specialised condition. If this be so, a similar multiplication of
somites in the post-genital region of Notostraca may well account
for the exceptionally large number found in that order.

52 THE CRUSTACEA

The classification of the Branchiopoda commonly adopted differs
from that given below in grouping together the Anostraca,
Notostraca, and Conchostraca as a single order, Phyllopoda
(Latreille, 1802),' distinguished from the Cladocera chiefly by the
greater number of somites and appendages and by the prevalence
of metamorphosis in development. The groups of the Phyllopoda,

Fie: 32.

Polyartemia forcipata, one of the Anostraca. x 5. (After Sars.) A, female, dorsal view ;
B, male, lateral view. a’, antennules; a’, antennae, very small in the female but greatly
enlarged and three-branched in the male; fa, ‘‘ frontal appendage”; p, paired penes of the
male. There are nineteen limb-bearing trunk-somites, followed, in the male, by six limbless
somites (besides the telson), of which the first and second are partly coalesced to form the
genital segment. In the female the limbless region of the trunk is unsegmented.

however, differ among themselves in characters which are at
least as important as those separating the Cladocera from the
Conchostraca, and it seems desirable to recognise this by giving
them the rank of orders.

! Unfortunately some writers, following Claus, have transposed the names
Branchiopoda and Phyllopoda, applying the latter to the sub-class and the former
to one of its divisions, but this use is not sanctioned either by priority or by
universal custom.

THE BRANCHIOPODA 53

Sup-CLass BRANCHIOPODA.
OrpER 1. Anostraca.

Rr caripace absent ; paired eyes pedunculate ; antennae prehensile in
male, reduced in female ; trunk-limbs, 11 or 19 pairs, none post-genital ;
furcal rami unsegmented ; development with metamorphosis. ~

Family Potyarremiupar. Polyartemia, Fischer (Fig. 32). Family
BRANCHIPODIDAE. Lranchipus, Schiffer ; Chirocephalus, Prévost (Fig.
21); Artemia, Leach; Branchinecta, Verrill (Fig. 15). Family
THAMNOCEPHALIDAE. Thamnocephalus, Packard,

OrpreR 2. Notostraca.

Carapace forming a dorsal shield; paired eyes sessile; antennae
vestigial ; trunk-limbs, 40 to 63 pairs, of which 29 to 52 are post-genital ;
furcal rami multiarticulate ; development with metamorphosis.

Family Apoprpar. Apus, Latreille ; Lepidurus, Leach (Fig. 16).

OrprR 3. Conchostraca.

Carapace bivalved, enclosing head and body; paired eyes sessile,
coalescent ; antennae biramous, natatory ; trunk limbs, 10 to 27 pairs,

_of which 0 to 16 are post-genital ; furcal rami claw-like ; development

usually with metamorphosis.
Family Limnapimpar. Limnadia, Brongniart; Estheria, Riippel
(Fig. 17) ; Cyclestherta, G. O. Sars. Family Limyetipar. Limnetis, Lovén.

OrperR 4. Cladocera.

Carapace bivalved, generally enclosing body but leaving head free,
sometimes reduced and serving only as a brood-sac ; paired eyes sessile,
coalesced ; antennae biramous (except in the female Holopedium), natatory ;
trunk-limbs, 4 to 6 pairs, none of which are post-genital ; furcal rami
claw-like ; development embryonic, rarely with metamorphosis.

SuB-ORDER 1. CALYPTOMERA.

Carapace completely enclosing body and limbs.

Tribe 1. Crrnopopa. Six pairs of trunk-limbs all similar and
foliaceous.

Family Siprpar. Sida, Straus; Latona, Straus; Penilia, Dana.
Family Honorepipar. Holopediwm, Zaddach.

Tribe 2. ANomMopopa. Five or six pairs of trunk-limbs, first two
pairs more or less prehensile.

Family Dapxniparn. Daphnia, O. F. Miller (Fig. 18); Moina,
Baird ; Simocephalus, Schodler (Simosa, Norman). Family Bosminipae.
Bosmina, Baird. Family LyNncopapHnipar. Ilyocryptus, G. O. Sars ;
Macrothriz, Baird. Family Lyncempar. Lynceus, O. F. Miiller;
Chydorus, Leach; Hurycercus, Baird; Pleurozus, Baird (Fig. 26) ;.
Monospilus, G. O. Sars.

54 LHE (CRUSTACEA

SuB-ORDER 2. GYMNOMERA.

Carapace not enclosing body and limbs.

Tribe 1. OnycHopopa. Four pairs of trunk-limbs, more or less
compressed.

Family PotypHemipar. Polyphemus, O. F. Miiller ; Bythotrephes,
Leydig ; Evadne, Lovén ; Podon, Lilljeborg.

Tribe 2. Hapnopopa. Six pairs of trunk-limbs, completely pediform.

Family Lerroporipar. Leptodora, Lilljeborg (Fig. 19).

LITERATURE.

1. Baird, W. The Natural History of the British Entomostraca. Ray Society,
London, 1850.

2. Bernard, H. M. The Apodidae: A Morphological Study. London, 1892.

3. Claus, C. Zur Kenntniss des Baues und der Entwickelung von Branchipus
stagnalis und Apus cancriformis. Abhandl. kgl. Ges. Wiss. Gottingen,
xviii. ; Phys. Cl. pp. 98-140, pls. i.-vili., 1873.

4, Zur Kenntniss der Organisation und des feineren Baues der Daphniden
und verwandter Cladoceren. Zeitschr. wiss. Zool. xxvii. pp. 362-402,
pls. xxv.-xxviii., 1876.

5. —— Untersuchungen iiber die Organisation und Entwickelung von
Branchipus und Artemia. Arb. zool. Inst. Wien, vi. pp. 267-370, 12 pls.,
1886.

6. Cunnington, W. A. Studien an einer Daphnide, Simocephalus sima. Jena.
Zeitschr. xxxvii. pp. 447-520, pls. xxiv.-xxvi., 1903.
. Ekman, S. Beitriige zur Kenntnis der Phyllopodenfamilie Polyartemiidae.
Bihang Svenska Vet.-Akad. Handl. xxviii, Afd. iv., No. 11, 38 pp.
4 pls., 1902.
8. Grobben, C. Die Entwickelungsgeschichte der Moina rectirostris. Arb. zool.
Inst. Wien, ii. pp. 203-268, 7 pls., 1879.
A9. Lankester, E. Ray. Observations and Reflections on the Appendages and on
the Nervous System of Apus cancriformis. Quart. J. Micr. Sci. xxi.
pp. 343-376, pl. xx., 1881.
10. Leydig, F. Naturgeschichte der Daphniden, pp. iv.+252, 10 pls. 4to.
Tiibingen, 1860.
11. Lilljeborg, W. Cladocera Sueciae. Nova Acta reg. Soc. Sci. Upsala, (3)
xix. vi+701 pp. 87 pls., 1900.
12. Packard, A. S.A Monograph of North American Phyllopod Crustacea.
Twelfth Ann. Rep. U.S. Geol. Survey, pp. 295-392, 39 pls. and map,
1883.
13. Pelseneer, P. Observations on the Nervous System of Apus. Quart. J.
Micr. Sci. xxv. pp. 433-444, pl. xxx., 1885.
14. Richard, J. Révision des Cladocéres. Ann. Sci. Nat. Zool. (7) xviii. pp.
279-389, pls. xv.-xvi., 1895 ; and op. cit. (8) ii. pp. 187-363, pls. xx,-xxv.,
1896.
15. Sars, G. O. Norges Ferskvandskrebsdyr. Cladocera Ctenopoda. 71 pp.
4 pls. 4to. Christiania, 1865.
Om en dimorph Udvikling samt Generationsvexel hos Leptodora.
Forh. Vidensk. Selsk. Christiania, 1873, pp. 1-15, 1 pl.

“I

16,

THE BRANCHIOPODA 55

. Sars, G O. On Cyelestheria hislopi (Baird). Forh. Vidensk. Selsk.
Christiania, 1887, No. 1, pp. 1-65, 8 pls.

18. Fauna Norvegiae. Vol. I. Phyllocarida and Phyllopoda. 4to, pp.
vi+ 140, 20 pls. Christiania, 1896.
19. Simon, Z. Etude sur les Crustacés du sous-ordre des Phyllopodes. Ann.

Soc. ent. France, (6) vi. pp. 393-460, pls. v.-vil., 1886.
Weismann, A. Ueber Bau und Lebenserscheinungen von Leptodora hyalina.
Zeitschr. wiss. Zool. xxiv. pp. 349-418, pls. xxxiii.-xxxviii., 1874.
Beitriige zur Naturgeschichte der Daphniden. Zeitschr. wiss. Zool.
XXVli.-xxxili., 1876-1879.
. Zaddach, E.G. De Apodis cancriformis, Schaeff., anatome et historia evolu-
tionis. Dissertatio inaug. vi+72 pp. 4 pls. 4to. Bonnae, 1841.

CHAPTER III
THE OSTRACODA

SubB-CLass OsrracopaA, Latreille (1802).

Order 1. Myodocopa.
» 2. Cladocopa.
», o Podocopa.
5 4. Platycopa.

Definition.—Crustacea in which the carapace forms a_ bivalve
shell; the trunk is indistinctly segmented, its posterior part is
without limbs and ends in a caudal furca; the antennules and
antennae are large and used for locomotion ; the mandibles have a
palp; not more than four pairs of limbs are distinctly developed
behind the mandibles and they vary much in form; the genital
apertures are behind the last pair of limbs; the paired eyes are
sometimes present; development with metamorphosis, the young
hatched in the form of a modified nauplius.

Historical—Although various species of Ostracoda were seen
and figured by the early microscopists, the scientific study of the
group may be said to begin with O. F. Miiller’s Hntomostraca
(1785). The bivalve shell caused these animals to be associated
in most of the earlier systems of classification with the Cladocera,
from which they were separated by Milne-Edwards (1840). Almost
the first to give an account of the internal anatomy was Zenker.
The knowledge of their development is based chiefly on the works
of Claus. The systematic and faunistic works of G. O. Sars, Brady,
and Norman are among the most important ; while in recent years
G. W. Miiller has made noteworthy advances towards a precise and
detailed knowledge of morphology and classification.

MorpPHOLOGY.

The bivalved shell which completely encloses the body and limbs
(Fig. 33) is usually elliptical in outline as seen from the side, often
(Podocopa) somewhat flattened ventrally, but it may be nearly

56

THE OSTRACODA oie

globular or, in some Halocypridae, greatly elongated. The two
valves are probably always more or less unsymmetrical, especially
along the ventral margin. On the dorsal side they are connected
by a hinge-joint, which may be merely an uncealcified strip of
the integument (Halocypridae), or may be strengthened by inter-
locking ridges and teeth. The most complex hinges are found
among the Cytheridae. The almost globular shell of Gigantocypris
is exceptional in that the free edges of the valves occupy only
about one-third of the circumference.

The outer surface of the valves is seldom quite smooth. It
may be beset with setae or pitted or sculptured (Fig. 33, C), and
is sometimes produced into wing-like processes. When the shell
is‘strongly calcified and opaque more transparent spots may mark
the position of the eyes (Podocopa, Fig. 33, ¢). The attachment
of the adductor muscle is usually visible externally as a group of

Fic. 33.
Lateral view of shell of A, Philomedes brenda (Myodocopa), x 8; B, Cypris fuseata (Podocopa),
x 19; C, Cythereis ornata (Podocopa), x 33. a, attachment of adductor muscles; e, median

eye 3.n, antennal notch. (A after Brady and Norman; B and C after G. W. Miiller.)

spots, the arrangement of which affords characters of systematic
importance (a). When the edges of the valves are brought
together they usually fit closely, but in some cases openings are
left. The most important of these is the “antennal notch” found
in most Myodocopa, and permitting the protrusion of the antennae
(Fig. 33, A, m). Unicellular glands opening by pores on the
surface of the shell are frequent in Myodocopa, less so in Podocopa.

The fold which marks off the shell from the body on each side
does not extend very far towards the dorsal surface, and certain of
the viscera may extend, as in some Cirripedia, into the cavity
between the outer and inner integument of each valve. This is
the case with the hepatic caeca in some Cyprididae (Pontocyprinae),
and more commonly with the reproductive organs, especially the
ovaries, which in the Cyprididae are completely and in the
Cytheridae partly lodged in the cavity of the shell-fold. In the
Cypridinidae a network of blood-channels traverses each valve,
radiating outwards from the muscle-impression.

The posterior part of the body, which is free within the shell,

58 THE CRUSTACEA

shows, at most, only indistinct traces of segmentation (Cytherella).
The terminal part is curved ventrally, and ends in a caudal furea.
In the Myodocopa the fureal rami are flattened triangular plates,
with short, stout spines or teeth on the hinder margins (Fig. 37, E).
In the Podocopa they are slender or styliform, bearing setae, or
may be much reduced, as in the Cytheridae.

Fic. 34.

A, antennule of Cypridina mediterranea, 2. B, antenna of Conchoecia magna, 2. C, antenna
of Cytherella sordida. D, antenna of Darwinula stevensoni. (After G. W. Miller.) en, endopo-
dite, ev, exopodite, according to Miiller’s interpretation.

Appendages.—The antennules may function as sensory organs,
or they may be used for swimming, creeping, or digging in sand,
and their form and armature of setae or spines are correspondingly
varied. Kach is composed of eight segments in Cypridina (Fig.
34, A) and in Pontocypris, and this seems to be the typical number
from which the others have been derived by reduction. In the
Halocypridae the segments are reduced to two or one. Sometimes

THE OSTRACODA 59

the antennules are modified in the male sex as organs for clasping
the female. This appears to be the function of certain highly
peculiar setae provided with sucker-like organs found in the male
of Cypridina.

With very few exceptions the antenna appears to be the chief
organ of locomotion, whether swimming or creeping. In the
Myodocopa it is biramous, and the outer branch is more strongly
developed than the inner, with eight or nine segments carrying
natatory setae. The inner branch has not more than three
segments, and is often modified as a clasping organ in the male.
It is characteristic of the Myodocopa that the single segment of
the peduncle is greatly expanded and occupied by large muscles
(Fig. 34, B). In Polycope (Cladocopa) the two rami do not differ
greatly in length. In the Podocopa only one ramus of three or
four segments is well developed, and, according to the view of
G. W. Miiller, it is the inner ramus, the outer being represented
by a small process tipped with setae or being altogether absent
(Fig. 34, D). In Cytherella (Platycopa) the antenna differs from
that of all other Ostracoda in having the peduncle divided into
two segments and bent or geniculate between them (Fig. 34, C).
The two rami are well developed—the inner, of three segments,
resembling that of the Podocopa in the disposition of the sensory
setae. The outer ramus has two segments. In the Cytheridae a
large seta, bent at the tip, occupies the place of the vestigial outer
ramus present in the other families of Podocopa. It serves as
duct to a large unicellular gland. This was formerly regarded as
a poison-apparatus, but, according to Miiller, it is a spinning organ,
by means of which the Ostracod covers with a network of fine-
threads the surface on which it is creeping, in order to obtain a
secure foothold.

The labrum is usually well developed, and is especially large in
Cypridinidae, where it contains a group of gland-cells. The lower
lip is usually small, and only rarely shows traces of a division into
paragnatha,

The mandible is characterised by the large size of the palp,
which is often biramous and is sometimes pediform or variously
modified. The gnathobase may be reduced to a small setose lobe
(Cypridina), or to a curved serrated process extending into the gullet
(Asterope). In Sarsiella it seems to be entirely absent, and the
strong curved spines with which the tip of the palp is armed
probably serve for seizing food and passing it into the mouth
(Fig. 35, C). In the other families the gnathobase is usually well
developed, and armed with spines and teeth. The palp usually
consists of four segments, but the number is often reduced. In
the Cypridinidae it is long and pediform, and is used in creeping.
In Sarsiella, as already noted, it serves for the prehension of food,

60 THE CROSLAGEA

and in the male of that genus it is apparently a clasping organ.
In the Halocypridae (Fig. 35, B) and Polycopidae (Fig. 35, A)
the first segment of the palp sends inwards a process tipped
with spines, which lies alongside the gnathobase and assists in
mastication. In Cytherella and some other genera the inner surface

of the first and second segments of the palp bears a comb-like series

Fie: 35.

A mandible of Polycope frequens. B, mandible of Conchoecia magna. C, mandible of Sar-
siella levis, 2. D, maxillula of Philomedes interpuncta. E, maxillula of Polycopsis serrata. F,
maxillula of Macrocypris swccinea. (After G. W. Miiller.) ex, exopodite.

of long setae. The ezxopodite is represented in most Myodocopa
by a small unsegmented appendage. In the Cyprididae and allied
families it is a flattened plate with radiating fan-like setae or
setiform processes, the so-called branchial appendage. In Para-
doxostoma and some allied genera the mouth-parts are modified for
piercing and sucking. The mandible is styliform, with a slender
palp, and is enclosed in a conical beak formed by the labrum and
hypostoma.

"oY

LHE ‘OSTRACODA 61

The structure of the mazillula varies very much in the different
genera. The most primitive form is probably that found in the
Cladocopa, where it consists of a protopodite of two segments, a
three-segmented endopodite, and a small exopodite of one or two
segments (Fig. 35, E). The segments of the protopodite are
each produced inwards into a slight masticatory lobe. In the
Halocypridae and most Cypridinidae (Fig. 35, D) the structure
is similar, save that the exopodite is wanting. In most Podocopa
the masticatory lobes are greatly produced, and the distal one is

Fic. 36.

A, third post-oral appendage (so-called ‘‘ second maxilla”) of Cypridina mediterranea (young).
B, third post-oral appendage (so-called ‘first leg”) of Cythereis convexa. C, third post-oral
appendage (so-called ‘*‘ maxilliped ””) of Macrocypris succinea, male. D, the same, female. (After
G. W. Miiller.) en, endopodite ; ex, exopodite.

divided into two. The three segments of the endopodite may be
distinct or may fuse into one. A large “branchial appendage,” with
radiating setae, may perhaps represent the exopodite (Fig. 35, F).
The third post-oral limb is of very diverse form, and has received
different names in the various genera. Thus in the Cypridinidae
it has been called the “second maxilla,” in the Halocypridae and
Cyprididae the “maxilliped,” and in the Cytheridae and other
families the ‘‘first leg.” In the Cypridinidae it is quite maxilli-
form, and in the adult shows hardly any trace of segmentation.
In young stages, however, Miiller finds that it consists of six
more or less distinct segments, of which two are assigned to the
protopodite and the remainder to the endopodite (Fig. 36, A).
A “branchial appendage” is present and is probably to be regarded

62 THE CROSTAGCEA

as the epipodite. In the other families the appendage is more leg-
like. The “branchial plate” is commonly present, and sometimes
an unsegmented appendage which is regarded as the exopodite.
In many Cyprididae the limb forms, in the male, a strong clasp-
ing organ (Fig. 36, C), which may be unsymmetrically developed
on the two sides. In Cytherella it has, in the male, much the
same structure as in the Cyprididae, while in the female it is
entirely absent. Finally, in the Bairdiidae and Cytheridae it is
quite pediform (Fig. 36, B), with a strong terminal claw, and
with or without a branchial plate.

The completely pediform character of this appendage in many
Ostracoda suggests a doubt as to its homology with the maxilla of
other Crustacea. This doubt is further strengthened by Miiller’s
statement that the limb appears to belong to the thoracic rather
than to the cephalic division of the body. More important still is
the fact that in the course of development a pause in the successive
appearance of the limbs occurs before this limb is added to the
series. On these grounds there seems to be considerable proba-
bility in Miiller’s view that the maxilla has been entirely lost in
the Ostracoda and that the appendage which occupies its place is to
be regarded as homologous with the first thoracic appendage of
other Crustacea.

In most Myodocopa the fourth post-oral limb is a maxilliform
lobed plate, distinctly segmented only in Cypridina (Fig. 37, A).
In Sarsiella and Asterope it is laminar and not lobed. In the
Polycopidae it is absent. In the other families it is more or less
leg-like (Fig. 37, B), with or without a branchial plate. In some
Cytherellidae it forms a clasping organ in the male, while in the
female it is reduced to the branchial plate.

In the Cytheridae, Bairdiidae, and Darwinulidae the jifth post-oral
limb is pediform, with a strong terminal claw, and is used for
creeping. In the Cyprididae (Fig. 37, D) it appears less adapted
for locomotion, and is probably chiefly used as a “cleaning foot”
for cleaning the other appendages and the inside of the shell.
This is its only function in the Myodocopa (except Halocypridae),
where it has a remarkable structure, being long and cirriform,
divided into numerous segments moved by two muscles running
along its whole length (Fig. 37, C). It is set high up on the side
of the body, and the terminal part is armed with setae and
chitinous teeth. In the Halocypridae the limb is greatly reduced
and in the Cladocopa it is altogether absent.

A peculiar brush-like appendage found on the side of the body
in the males of some Ostracods has been regarded as a vestigial
sixth post-oral limb. It is found ina few Cyprididae and in Cytherella
behind the last leg, and its position near the first leg (third post-oral)
in the Bairdiidae and Cytheridae is explained as the result of a

a

THE OSTRACODA 63

secondary shifting of position. A similar organ has been found in
one species of Cypridina.

It is not unlikely that at least one pair of limbs is involved in
the composition of the penes of male Ostracods.

Alimentary System.—The oesophagus is narrow and has muscular
walls. Its upper or posterior end projects into the capacious mid-

Fic. 37.

A, fourth post-oral appendage of Cypridina mediterranea. B, the same of Macrocypris
succinea. _ C, fifth post-oral appendage of Cypridina mediterranea. D, the same of Macrocypris
succinea. HH, one ramus of the caudal furea of Cypridina squamosa, seen from the side. (After
G. W. Miiller.)

gut, and in the Podocopa is armed internally with chitinous ridges
and teeth. In the Bairdiidae this apparatus is most fully developed
and forms an efficient “gastric mill,” moved by extrinsic and
intrinsic muscles, for the trituration of the food.

The mid-gut in the Podocopa is divided into two parts by a con-
striction. Hepatic caeca may be absent as in Cypridina, numerous
and small as in Halocypris, or large and reduced to a single pair
which may extend into the shell-cavity, as in Cyprididae.

64 THEE ICROSTA CEA

The short rectum opens on the ventral side of the furea in
Myodocopa, but on the dorsal side in the Cyprididae and allied
families.

Circulatory System.—A. heart is present only in the Myodocopa
(Fig. 38, HT). It is placed near the dorsal surface just above the
mandibles, and has one pair of lateral ostia and an opening in
front through which the blood is expelled. No definite vessels
exist, but a network of blood-channels is found in the shell of the
Cypridinidae. The blood is coloured red in Krithe.

Respiratory System.—In the majority of Ostracoda the respiratory
function is probably discharged by the general surface of the body
and limbs and by the inner surface of the shell. The so-called
‘branchial appendages” found on the various limbs serve to
keep up a current of water within the shell. Only in the genus
Asterope, and less distinctly in one or two species of Cypridina, are
definite branchiae found. These are lamellar appendages attached
to the dorsal surface of the posterior part of the body. Seven
pairs are present in Asterope.

Excretory System. — Little :is known regarding the excretory
svstem of the Ostracoda. ‘ Segmental” organs in the form of
small sacs lying at the bases of the ambulatory legs are described
in Paradoxostoma and Bairdia. It is doubtful whether they open to
the exterior. In Cypris a gland lying in the labrum and opening
on the first segment of the antenna and a second gland opening on
the basal segment of the third post-oral appendage (maxilla ?) have
been described.

Glands.—As already stated, dermal glands are frequently found
in the valves of the shell. In some Cypridinidae their secretion
serves to agglutinate the sand in which these animals burrow, and
in some cases to form definite tubular dwellings. In the Halo-
cypridae the glands are most numerous near the edge of the
anterior part of the shell, and it is stated that their mucus-like
secretion serves to entangle food-particles and is then swallowed.
Specially large glands opening near the margins of the valves
anteriorly are found also in some other Ostracoda, and, from their
position, suggest a comparison with the “fronto-lateral glands”
similarly situated in the “‘ Cypris-larva” of Cirripedes. Glands are
sometimes found in the labrum (Cypridinidae and Cyprididae), and
are believed, in Pyrocypris, to produce a luminous secretion. The
spinning-glands of Cytheridae have already been mentioned.

Musculature.—The adductor muscle (Fig. 38, S.J7) runs between
the valves of the shell on the ventral side of the alimentary canal.
In some Ostracoda, especially in Cyprididae, a tendinous plate is
found below the anterior part of the alimentary canal, serving for the
attachment of the mandibular and maxillary muscles. It is worthy
of note that the adductor muscle does not share in its formation.

THE OSTRACODA 65

Nervous Systen.—The supracesophageal ganglion is largest in
the Cypridinidae in correlation with the presence of paired eyes in
that family. The ventral nerve-chain is represented by a single

Fic. 38.

Cypridina mediterranea. Female (above) and male (below). One valve of shell removed to
show appendages and internal organs. A”, antenna (the antennule is just above); F’ (below),
fourth post-oral limb; #” (above), fifth post-oral limb; Fu, caudal furea; G, brain ; H, heart ;
M, mid-gut; Mdf, mandibular palp; Ma’, maxillula; Mx”, third post-oral limb (maxilla); 0,
paired eye; 0’, median eye; P, penis; S.J, adductor muscle of shell; Sfz, frontal tentacle ; 7’,
testis. (From Claus's Textbook.)

5

66 THE CRUSTACEA

undivided mass in the Cyprididae, but in the Myodocopa it may be
more or less completely divided into two or three (Halocypridae)
ganglionic masses.

Sense-Organs.—Paired compound eyes are present only in the
Myodocopa (excluding Halocypridae), where they project slightly
from the surface of the head within the shell (Fig. 38, 0). The
number of ommatidia in each varies from four in Sarsiella to about
fifty in some species of Asterope. The crystalline body in each is
bipartite, and the rhabdom is longitudinally ribbed. There are no
facets or cuticular lenses on the overlying cuticle, nor ‘‘ eye-spots ”
on the shell. In Philomedes the eyes, though well developed in
the male, are rudimentary in the female.

The nauplius eye is present in the majority of the Ostracods
(Fig. 38, O’), and consists of the usual three pigment-cups contain-
ing each from 3 to about 100 retinal rods. In some Podocopa
the three parts are widely separated from each other. A uni-
cellular lens, or “crystalline body,” is found in many Podocopa
(Fig. 12, p. 18), and transparent “‘eye-spots” on the shell are
common. In the Myodocopa the nauplius-eye lies at the base of
a rod-like median process from the front of the head, the “ frontal
tentacle” (Fig. 38, Stz). Sometimes (Halocypridae) the distal
portion of this tentacle is segmented off and is known as the
“ capitulum,”

Olfactory filaments are present, commonly in greater numbers in
the male than in the female, on antennules and antennae, and also
on the “ brush-like appendage.”

Reproductive System; Female.—The ovaries are paired, and are
generally lodged in the posterior part of the body. In the
Cyprididae, and partly in the Cytheridae, they lie in the cavities
of the shell-valves. The oviducts usually open separately behind
the last pair of legs. In the Halocypridae the two oviducts unite
shortly after leaving the ovaries, and the unpaired opening is
situated on the left side just in front of the caudal furca. A
receptaculum seminis, paired except in the Halocypridae, is always
present. Asa rule, it opens to the exterior by a special copulatory
pore, and communicates internally with the oviduct, but sometimes
only the external opening appears to be present, while in the
Cyprididae the opening into the oviduct serves both for entrance
and exit.

Male.—The testes are simple in the Myodocopa (Fig. 38, 7’),
four-lobed in most of the other families. _In the Cypridinidae
the two vasa deferentia unite to open by a single median pore
lying between the paired penes, which in this family alone are
not traversed by the ducts (Fig. 38, P). In the Halocypridae the
penis is unpaired and lies to the right of the middle line. The
vasa deferentia unite just before entering it. In the other families

THE OSTRACODA 67

the vasa deferentia are probably always united by a_ transverse
duct shortly after leaving the testes. They are often of great
length and are coiled in a very complex fashion, differing in the
different groups. The distal part forms a ductus ejaculatorius of
complicated structure, with muscular walls. The paired penes are
traversed by the vasa deferentia, the terminal portion forming a
protrusible copulatory tube, and the penis is often armed with
chitinous hooks moved by special muscles.

The spermatozoa are sometimes spherical (Asterope), more
commonly filiform. In the Cy prididae they are of a size which
relatively, if not absolutely, is unique in the animal kingdom. In
Pontocypris monstrosa the total length of the animal is ‘6 mm., while
the spermatozoa are 5:0-7°0 mm. long.

DEVELOPMENT.

The eggs are carried within the valves of the shell dorsally to
the body of the animal in the Cypridinidae, Cytherellidae, some
Cytheridae, and in the freshwater genus Darwinula, and in a
few cases the young are carried for some time after hatching. In
other cases the eggs are deposited on water-plants or shed free
in the water. The course of development is best known in the
Cyprididae. On hatching, the larva is already enclosed within a
bivalve shell, but otherwise corresponds in structure to a nauplius
(Fig. 39). Three pairs of appendages are present, antennules,
antennae, and mandibles, the last
two, however, not distinctly biramous. _-&:

In the Cytheridae the mandible at *Q
this stage is rudimentary. The
remaining limbs are added at suc-
cessivé moults in regular order from
before backwards. According to
Miller, it is not the case that, as
stated by Claus, the fourth post-oral
limbs appear before the third. There
is, however, a marked pause in the yy .piiusstageof Cypris. a’,antennule;
development before the appearance a, antenna ; ad, adductor muscle of cara-
: 5 ‘ 4 pace; ¢, nauplius eye; md, mandible.
of the third post-oral pair, and this, (Arter Claus.) :

as already pointed out, supports the

view that a pair of appendages corresponding to the maxillae of
other Crustacea is missing.

Fic. 39.

REMARKS ON HABITS, ETC.

The Ostracoda are abundant both in fresh waters and in the
sea, generally burrowing in mud or creeping among weeds. The
marine Halocypridae belong to the plankton. None are definitely

i

68 THE CRUSLAGCEA

known to be parasitic, but one species found in the gill-chambers of
Crayfish in North America may be so. The majority are minute,
very many not exceeding 0°5 mm. in length. The Myodocopa are
usually larger than the Podocopa, many being 1 or 2 mm. long.
The largest known Ostracod, a species of Gigantocypris, is 23 mm.
in length.

PALAEONTOLOGY.

Fossil Ostracoda are abundant in all geological formations from
the oldest to the most recent, but, with hardly an exception, only
the shell is preserved and the affinities of the numerous genera
which have been established remain quite uncertain. Most of the
Ostracoda from Cambrian rocks belong to the genera Primitia,
Jones, and Leperditia, Roualt, while Leyrichia, M‘Coy, is common
in the Silurian. Species referred to the recent genus Cypridina
occur in the Carboniferous, and Cythere and other recent genera are
stated to make their appearance in the Permian.

AFFINITIES AND CLASSIFICATION.

In the bivalved form of the shell, the ventrally flexed posterior
part of the body, the form of the caudal furea (in the Myodocopa),
and the biramous natatory antennae (especially of the Cladocopa
and Platycopa), the Ostracoda present important resemblances to
the Conchostraca and Cladocera among the Branchiopoda. There
might, indeed, be little difficulty in regarding them as derived from
the Conchostraca, were it not for the presence of the mandibular
palp, which is absent from the Branchiopoda. The possession of
this appendage and its biramous form in many cases point to
the origin of the Ostracoda as an independent branch of the
primitive Crustacean stock. There appears to be no reason,
however, to suggest, as Claus has done, that the small number of
appendages is a primitive character.

In the possession of paired eyes and a heart, the Cypridinidae
are more primitive than the other Ostracoda, although in the form
of the antennae and in some other points they are probably more
specialised than the Cladocopa and Platycopa.

The classification given below is that of Sars, as modified by
Brady and Norman. In the more recent arrangement of G. W.
Miiller the Cladocopa are included in the Myodocopa and the
Platycopa in the Podocopa, and the number of families is considerably
reduced.

SuB-CLASS OSTRACODA.
OrpER 1. Myodocopa.

Shell generally with antennal notch; antennae with massive basal
seginent, generally biramous, exopodite generally with eight or nine

THE OSTRACODA 69

segments, endopodite minute and generally prehensile in male ; five pairs
of post-oral limbs ; caudal furca with lamellar rami armed with spines.

Family HatocypripAE (CONCHOECIIDAE). Halocypris, Dana ;
Conchoecia, Dana. Family AstEropipar. Asterope, Philippi (= Cylindro-
leberis, Brady). Family Cypripinipar. Cypridina, H. Milne-Edwards ;
Philomedes, Lilljeborg (Fig. 33, A); Pyrocypris, G. W. Miiller ; Giganto-
cypris, G. W. Miiller. Family Rurmpermatipar. Rutiderma, Brady and
Norman. Family Sarstecnipar. Sarsiella, Norman.

OrpreR 2. Cladocopa.

Shell without antennal notch; antennae biramous, both rami well
developed and natatory ; only three pairs of post-oral limbs; other
characters as in Myodocopa.

Family Potrycopipar. Polycope, G. O. Sars; Polycopsis, G. W.
Miiller.

OrpER 3. Podocopa.

Shell without antennal notch; antennae with basal segment not
enlarged, one ramus (exopodite, Miiller) vestigial or absent, the other of
not more than four segments ; five pairs of post-oral limbs ; caudal furea
with styliform or vestigial rami.

Family PARADOXOSTOMATIDAE. Paradoxostoma, Fischer. Family
CYTHERIDAE. Cythere, O. F. Miiller; Cythereis, G. O. Sars (Fig. 33,
C); Krithe, Brady. Family Darwinuiipar. Darwinula, Brady and
Robertson. Family Batrpupav. Bairdia, M‘Coy. Family CypripIDAe.
Cypris, O. F. Miiller (Fig. 33, B); Pontocypris, G. O. Sars. Family
CYPRIDOPSIDAE. Cypridopsis, Brady.

OrprER 4. Platycopa.

Antennae biramous, protopodite of two segments, endopodite of three,
and exopodite of two segments ; only four pairs of post-oral limbs ; other
characters as in Podocopa.

Family CyrHERELLIDAE. Cytherella, Bosquet.

LITERATURE.

1. Brady, G. S.A Monograph of the Recent British Ostracoda. Trans. Linn.
Soc. xxvi. pp. 353-495, pls. xxiii.-xli., 1868.

Report on the Ostracoda. Rep. Voy. ‘‘ Challenger,” Zool, i. 184 pp.
44 pls., 1880.

8. Brady, G. S.,and Norman, A. MW. A Monograph of the Marine and Freshwater
Ostracoda of the North Atlantic and of North-Western Europe. Trans.
Roy. Dublin Soc. (2) iv. pp. 63-270, pls. viii.-xxiii., 1889; and v.
pp. 621-746, pls. 1.-lxviii., 1896.

4. Claus, C. Beitr. zur Kennt. der Ostracoden. 1. Entwicklungsgeschichte
von Cypris. Schr. Ges. Naturwiss. Marburg, ix, pp. 151-166, 2 pls.,
[1868] 1872.

9
“

7O

10

11

THE CRUSTACEA

Claus, C. Schriften zoologischen Inhalts. 1. Die Familie der Halocypriden,
pp- 1-16, pls. i.-iii. 4to. Wien, 1874.
Die Halocypriden des atlantischen Oceans und Mittelmeeres.
iv+81 pp. 26 pls. 4to. Wien, 1891. ,
Beitr. zur Kennt. der Siisswasser Ostracoden. Arb. zool. Inst. Wien,
x. pp. 147-216, 12 pls., 1893.
. Miller, G. W. Die Ostracoden. Fauna und Flora des Golfes von Neapel,
Monogr. xxi., 1894.
— Deutschlands Siisswasser Ostracoden. Zoologica, xii. Heft 30,
112 pp. 21 pls., 1900.
. Sars, G. O. Oversigt af Norges marine Ostracoder. Forh. Vid.-Selsk.
Christiania, 1865, pp. 1-130, [1865] 1866.
. Zenker, W. Monographie der Ostracoden. Arch. Naturgesch. xx. pp.
1-87, pls. i.-vi., 1854.

a

CHAPTER IV
THE COPEPODA

Sus-CLass Coprepopa, H. Milne-Edwards (1830).

Order 1. Eucopepoda.
Sub-Order 1. Gymnoplea.
Tribe 1. Amphaskandria.
» 2. Heterarthrandria.
Sub-Order 2. Podoplea.
Tribe 1. Isokerandria.
», 2. Ampharthrandria.
Order 2. Branchiura.

Definition.— Crustacea in which there is no distinct shell-fold,
though the dorsal shield of the cephalon may be enlarged by the
coalescence of one or more of the trunk-somites ; there are typically
nine free trunk-somites (besides the telson), the last four without
appendages ; the telson bears a caudal furca; the antennules and
antennae are generally large, the latter sometimes biramous,
and both may be used for locomotion or for prehension; the
mandibles may have a palp, sometimes biramous; there are
typically six pairs of trunk-limbs, the last five biramous and
natatory, but the sixth pair are frequently reduced or absent ; the
genital apertures are on the seventh trunk-somite (except in
Branchiura) ; the paired eyes are absent (except in Branchiura) ;
development with metamorphosis, the young generally hatched in
nauplius stage. (Most of these characters are subject to modifica-
tion in parasitic forms.)

Historical.—The relatively large size attained by some of the
parasitic Copepoda renders it probable that they were the first to
attract attention, and it is possible, though not certain, that they
are referred to in certain passages of Aristotle. The minute free-
living forms remained unnoticed till some of the microscopists of
the seventeenth century—notably Leeuwenhoek—described and
figured the common freshwater Cyclops. It was long, however,

71

Wee TALE VORUSTACEA

before the affinity of the two groups was recognised. Linnaeus
included some free-living Copepods in his genus Monoculus, among
the Crustacea, but some of the parasites were placed under “ Vermes
mollusca” in the genus Leruaea, and others among the “ Zoophyta”
in the genus ennatula. O. F. Miiller’s great work on the
“Entomostraca” marks the beginning of a new epoch in the study
of the group. The genera Cyclops, Caligus, and Argulus were
established by Miiller, besides two others based on larval stages,
one of which, the Nauplius, still bears the name given to it by
Miller. Jurine’s Histoire des Monocles (1820) is noteworthy,
among much else, for the description of the larval metamorphosis
of Cyclops, the earlier stages of which had been seen long before by
Leeuwenhoek and de Geer. Although an affinity between the
highly modified Lernaeidae and the less-specialised parasites hke
Caligus was suggested, more or less definitely, by Oken, Lamarck,
and others, it was not until von Nordmann’s researches (1832)
threw light on their development that the Lernaeidae and their
allies were definitely accepted as Crustacea. In most systems of
classification, however, the parasites were more or less widely
separated from the free-living forms, and by Milne-Edwards they
were even placed alongside of the Pycnogonida in a different sub-
class. Milne-Edwards introduced the name Copepoda for the
free-living forms alone. Zenker, in 1854, seems to have been the
first to associate together free-living and parasitic forms under the
name Entomostraca. Modern conceptions of the morphology and
classification of the Copepoda are largely based upon the long series
of highly important memoirs (1857-1895) by C. Claus. Among
faunistic workers, J. D. Dana, H. Kroyer, Steenstrup and Liitken,
van Beneden, and Brady, may be specially mentioned. In more
recent years, W. Giesbrecht, in his splendid monograph of the
pelagic Copepoda and other important works, has given a new
aspect to the problem of classification, by showing that the
parasitic habit has been acquired not once but many times in the
evolution of the group, and that the line of division, maintained
even in Claus’s classification, between free-living and parasitic
forms must be abandoned. MHansen’s fine monograph of the
Choniostomatidae has raised that family, previously obscure, to the
position of one of the best known among the parasitic groups.
Finally, G. O. Sars’s work on the Copepoda of Norway, now in
course of publication, is especially important as regards the bottom-
living marine forms, which in recent years have been less studied
than the more easily collected pelagic species. The small group of
the Branchiura, associated by the older authors with the parasitic
Copepoda, were removed by Zenker to the Branchiopoda. Claus
restored them to the Copepoda, and his arrangement is followed
here, but in view of the important differences which separate them

ie

THE COPEPODA 73

from the Eucopepoda, it will be more convenient to deal separately
with the morphology of the two groups.

MorPHOLOGY OF EUCOPEPODA.

Apart from the parasitic forms, which exhibit an endless
variety of modifications, the Eucopepoda present a considerable
uniformity in general shape. The body is divided into two
regions, of which the anterior is sub-cylindrical or flattened,
and is more or less sharply marked off from the posterior
region, which is usually much narrower and terminates in a well-
marked caudal furca. There are typically ten free segments (in-
cluding the telson) behind the head, and the limit between the two
regions is marked by a very movable articulation which falls either
between the fifth and sixth of these (Gymnoplea) or between the
fourth and fifth (Podoplea) (Fig. 40). Giesbrecht has suggested
that the limit between these
regions is really in the same,
position in both cases, that the
fifth thoracic somite of the
Gymnoplea is unrepresented in
the Podoplea, and that the
so-called fifth thoracic somite
of the last-named group is a
“pre-genital” somite which is
suppressed in the Gymnoplea.
The evidence in favour of this
view, however, is very slight.
The head-region is usually g
stated to include, in addition to
the primitive cephalic somites,
that corresponding to the
maxillipeds or first post- ¢-
maxillary appendages. It Tete
appears, however, that in some Segmentation of the body in Gymnoplea and
ieee the) line -of articulation 7OtoPles Ay Oren ene oot Nbdoman

Calamus (Gymnoplea), dorsal view. , abdomen

definine the first free somite of male Calanus. C, outline of aan Cyclops
5 (Podoplea). ii, iii, vi, second, third, and sixth

runs in front of the maxillipeds, thoracic somites (commonly reckoned as first,
2 = ; second, and fifth respectively); 1+-2, first and
and it is possible that the second abdominal somites, coalesced in the female
<) meet sex in both instances ; t, telson; f, caudal furca.
somite bear ing these appendages * marks the position of the movable articulation
should he regarded as coalesced are, the anterior and posterior divisions of
: ‘ the body.
not with the head-region but
with the following somite. The next five somites bear swimming-
feet, and constitute what is commonly called the thoracic region.
It seems advisable, however, to extend the meaning of the term

thorax to include also the somite of the maxillipeds. The remaining

Ce

74 THE CRUSTACEA

four somites with the telson constitute the abdomen, and are limb-
less, with the possible exception of the first or genital somite, which
bears, in both sexes, the external openings of the genital organs,
and may have what are sometimes regarded as the vestiges of a
pair of appendages.

In the majority of cases the number of free somites is reduced
by coalescence. Very often the second (commonly reckoned as
the first) thoracic somite, bearing the first pair of swimming-feet, is
fused with the head, and not infrequently (in the Gymnoplea) the

hig ol ea aaa
ey y . Q= = = yy
S ae {8s SOD wre Ses ae es ee es
= } . y : “oN

\

Fic. 41.

A, Calanus finmarchicus, female, from the side, x 16; B, antenna; C, maxilla; D, maxilliped.
ii and vi, second and sixth thoracic somites ; 1+-2, first and second abdominal somites coalesced ;
a, antennule ; en, endopodite ; ex, exopodite; f, caudal furca. (After Sars.)

last two thoracic somites fuse together. The abdominal somites
are usually all distinct in the male sex (Fig. 40, B), but in the
female this is rarely the case, the first two being generally fused
(Figs. 40 and 41, A), and the number may be still further reduced.

While there is no distinct shell-fold, the head-region usually
possesses more or less well-developed pleural folds, which may be
directed downwards or even inwards so as partially to enclose the
bases of the limbs. These pleural folds are repeated on the free
thoracic somites, but are as a rule absent on the abdomen. An-
teriorly the tergal plate of the head-region is often produced into
a rostral process which may be a flattened plate, movably articu-

THE COPEPODA 75

lated with the head in some Uarpacticidae, and resembling the
rostral plate of the Leptostraca. More usually the rostrum is
bent down under the head and is often forked. A very remark-
able modification of the rostrum found in some Pontellidae is
mentioned below in connection with the eye.

The two rami of the caudal furca are usually movably
articulated with the telson or terminal segment. ‘Their setae
are very constant in number and position, and afford valuable
systematic characters. In some pelagic forms these setae attain
an exaggerated development (Fig. 42), while in some commensal or
parasitic forms they become converted into hook-like organs of
adhesion (Doropygus). Between the furcal rami and somewhat on
the dorsal side is the anal aperture, covered by a small supra-anal

Fic. 42.
Calocalanus pavo, X 16. (After Giesbrecht.)

plate which may represent the post-anal region of the telson in the
Branchiopod Lepidurus and the Malacostraca.

A modification of the thoracic region which may be mentioned
here is the development in several Ascidicolidae of a dorsal brood-
pouch formed by a fold of the integument arising sometimes from
the fourth, sometimes from the second free thoracic somite.

The modifications which the form of the body undergoes in
parasitic EKucopepoda consist in the coalescence of somites leading
ultimately to the disappearance of segmentation, and in the develop-
ment of lobes and processes from the various regions of the body.
The free edges of the thoracic somites may be produced into
lamellar appendages, or wing-like lobes may be developed on the
dorsal surface (Notopterophorus).

Appendages.—The antennules are always uniramous, and in many

76 THE CRUSTACEA.

of the free-living Eucopepoda they assist in swimming. ‘They are
further modified in many cases, in the male sex, to act as prehensile
organs for seizing the female. They are most fully developed in
the Gymnoplea, where they may exceed the body in length and
may consist of twenty-five segments (Fig. 41, A, a’). Throughout
the Gymnoplea and also in the Cyclopidae and Asterocheridae,
where the number of segments is less, Claus and Giesbrecht have
demonstrated their homology with those of the twenty-five-
segmented form. As an example we may give Giesbrecht’s com-
parison of the segmentation of the antennules in a species of
Cyclops, with the typical arrangement as found in many Gymnoplea.

Gymnoplea 1, 2, 3, 4, 5, 6, 7, 8 9, 10, 11, 12, 18, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25

——_—“— —— Oe i ee eee
Cyclops & 1s DPS Gay, (85 O Os Mla Ormis pel ae 15, alee cell
—SS— “~— —— JS Oe eee
Cyclops 9 1 eee De 165 7, 8, 0 NO. IM, 2 18 sae Thee ten

In the Harpacticidae and other families with a reduced number
of segments the homology has not been demonstrated, but there
can be little doubt that the twenty-five segments of the Gymnoplea
represent the typical and primitive arrangement from which the
others have been derived. In the parasitic forms the antennules
are usually greatly reduced. In the Caligidae the basal portions
of the antennules become coalesced with the front of the head, form-
ing a bilobed prominence. In some genera this bears, on either
side, a sucker which serves to attach the parasite to its host. Ex-
cept in this instance, however, the antennules do not become con-
verted into organs of attachment as the antennae frequently do.

In most, perhaps in all cases, the antennule, as in other Crustacea,
bears sensory setae of the type to which Giesbrecht has given the
name ‘aesthetascs,” and these are commonly more numerous in the
male sex. In some cases each antennule bears only a single
aesthetase, which may then be of relatively great size.

In those Eucopepoda in which the antennule of the male is
transformed into a clasping organ for seizing the female, the distal
is flexed upon the proximal portion (Fig. 43, A). It is probable
that the point at which this flexion takes place is the same in all
cases, corresponding to the articulation between the eighteenth
and nineteenth of the primitive series of segments. The proximal
portion of the appendage becomes more or less swollen, owing to
the strong development of flexor and extensor muscles of this joint,
and the opposed edges are often armed with teeth or spines. In
those Gymnoplea in which this clasping apparatus is developed,
only one, generally the right, antennule is modified (Heterarth-
randria). In the Podoplea, on the other hand, the modification,
when present, is bilateral. The occurrence of this modification of
the male antennules in many families of Eucopepoda which, in any

THE COPEPODA 77

scheme of classification, are widely separate from each other, and
especially the fact that the geniculation occurs in the same place
in some, probably in all cases, suggests that this character is a
primitive one for the whole group, and that its absence is a
secondary modification. This view is supported by the interesting
fact observed by Claus, that in some Gymnoplea Amphaskandria
a trace of this modification persists in the coalescence of the
twentieth and twenty-first segments of the antennule in the male,

Fic. 43.

A, clasping antennule of male Centropages typicus (Gymnoplea, Heterarthrandria) ; *, position
of the hinge-joint. 3B, last pair of thoracic limbs of the same. en, endopodites ; ea, exopodites,
that of the right side modified as a chelate grasping organ. (After Sars.)

and that in some cases this coalescence only appears in the antennule
of one side as in the allied Heterarthrandria.

The antennae, like the antennules, preserve in many Euco-
pepoda the general structure and the natatory function which
they have in the nauplius. They are most fully developed
in the Gymnoplea, where they consist of a protopodite of
two segments, an endopodite of two segments, and a multi-
articulate exopodite, and bear numerous long natatory setae (Fig.
41, B). In the Podoplea the natatory function is less well marked,

78 THE*CRESTACEA

being usually superseded by that of clinging organs. In the
Harpacticidae and Asterocheridae the exopodite is retained, though
often reduced to a single segment. In the other families it dis-
appears altogether. The endopodite never consists of more than
two segments, so that in the absence of the exopodite the
appendage is usually composed of four segments. In the parasitic
families the antennae generally form organs for attachment to
the host, provided with a strong curved claw and, in some cases,
even with a chelate termination.

The labrum and metastoma are very variously modified, especi-
ally in the parasitic forms, and will be described below in connec-
tion with the other mouth-parts. In the free-living forms the
metastoma may either form a simple ridge or may be provided
with a pair of movable lateral lappets.

The mandibles are especially interesting from the fact that in
many Eucopepoda (especially the Gymnoplea) they retain more
completely than in any other Crustacea the form of biramous
swimming-limbs which they possess in the nauplius. The body of
the mandible is formed by the proximal segment, and the remainder
of the protopodite, together with the endopodite and exopodite,
forms the “palp” (Fig. 8, A, p. 12). Hansen has pointed out the
existence in some Gymnoplea of a minute intermediate segment
between the body of the mandible and the large segment which
bears the endopodite and exopodite. It would seem, therefore,
that the body of the mandible in the Eucopepoda, and no doubt
also in other Crustacea, represents the precoxal segment of the
limb. The endopodite, as in the case of the antennules, consists
of, at most, two segments, while the exopodite may consist of
five or six. The cutting edge in most free-living forms is armed
with teeth and setae.

The type of mandible just described is universal among the
Gymnoplea and is found in some Harpacticidae and Ascidicolidae.
More usually, however, among the Podoplea the palp is reduced,
as in Cyclops, to a papilla bearing a tuft of setae, or is altogether
absent. The form of the cutting edge is variously modified, especi-
ally in the parasitic and semiparasitic forms. In many of these the
mandibles have a sickle-shaped blade, with the point directed into
the cavity of the mouth, but in those forms which have completely
suctorial mouth-parts (formerly grouped together as Siphonostomata)
the mandibles become simple piercing stylets, and are enclosed
within a conical or tubular “siphon” formed by the upper and
lower lips. In some cases the siphon may be as long as the body
(Acontiophorus) (Fig. 44, A). The structure of this siphon is not
in all cases the same, though it does not seem to be the case, as
has been stated, that it is ever formed from the labrum alone.

The mazillulae (commonly called the maxillae) are most com-

THE COPEPODA 79

pletely developed in the Gymnoplea and some Harpacticidae, in
which endopodite, exopodite, and epipodite are distinct, and the
protopodite is produced internally into a large masticatory lobe and
two smaller distal lobes (Fig. 9,
A, p. 13). In the Cyclopidae
the epipodite has vanished, the
exopodite and endopodite are
very small, and only the large
masticatory process of the proto-
podite persists. In many Har-
pacticidae and in the other
families the maxillula undergoes
various degrees of reduction.
The two pairs of appendages
succeeding the maxillulae are
commonly designated the outer
(or anterior) and inner (or
posterior) maxillipeds, and were
for long considered to represent
the separated rami of a single
pair of appendages. This in-
terpretation was put forward MiG e a _0
by Claus, who found that, in, 4 4gptigrtgras suatus, ©, from the side
the metanauplius stage of * Suctorial siphon; vi, the rudimentary sixth

: pair of thoracic limbs ; 1+2, the coalesced first
Cyclops and other forms, the and second abdominal somites ; 4+5, the fourth
; A abdominal somite coalesced with the telson.

two appeared to arise from a (After Giesbrecht.) B, larva of Rhinealanus
: : - , ndsutus in last metanauplius stage. The outline
single rudiment. Hansen, how- of the body as seen from above. The first three

ever, has discovered, and the _ pairs of appendages are omitted, but the rudi-

observation has been confirmed GrauShateny AO Ane hal ope Seen
by Giesbrecht and by Claus Wy? impnngn sora fn, marie
himself, that in the larvae of £31”, ttst and second pairs of swimming-feet.
certain marine Gymnoplea

(Eucalanus, Echinealanus, Pontella, ete.) in which the body is more
elongated than usual, the rudiments of the two appendages are not
only quite distinct, but are separated from each other by the suture
line which marks off from the head the so-called first thoracic
somite (Fig. 44, B). The “outer (or anterior) maxillipeds” are
therefore the mazillae, while the inner (or posterior) pair, for which
the name mazillipeds may be retained, must be regarded as the
first of the thoracic series, and the somite corresponding to them
is, at least in some cases, coalesced with that which bears the first
pair of swimming-feet. The maxilla in its most fully developed
form consists of a flattened and shortened axis of, at most, eight
segments, of which the first and second each bear two, and the
third a single endite (Fig. 41, C). In the Gymnoplea this appendage
is beset with plumose setae, which act as a net in collecting food-

A.

fe) THE CRUSTACEA

particles. In the Podoplea the setae are generally much reduced,
and stout spines are developed on the endites. In many cases,
especially in parasites, the armature is reduced to a single terminal
claw-like spine and the limb is exclusively a clinging organ.

In the parasitic family Lernaeopodidae, a very remarkable
apparatus of attachment is formed by two appendages which unite
to form a sucker-like organ of complicated structure (Fig. 45, B).
In some cases, when the appendages are short, they coalesce com-
pletely to the base, but in other cases they have the form of

Fic. 46.

Achtheres percarum (Lernaeopodidae). A, larva in first Copepodid stage, dorsal view. B,
adult female, ventral view, x 24. a’, antennule; @”, antenna; c.g/, cement gland opening into
oviduct ; e, median eye; f,caudalfurea; f.gl, frontal cement gland ; ma’, maxilla; map, maxil-
liped ; 0, opening of oviduet; ovd, oviduct distended with eges ; sp, openings of spermathecae.
(After Claus, slightly modified.)

long arms, united only at the tip. These appendages have been
regarded sometimes as the ‘first maxillipeds” (maxillae) and
sometimes as the “second maxillipeds” (here called maxillipeds).
The fact that a pair of glands, identified as the maxillary
(excretory) glands, open at their base, seems to show that the
former interpretation is the correct one. An apical coalescence
of paired appendages is not known to occur in any other
Arthropods.

The mazilliped (first thoracic limb) is always uniramous, and is
generally more elongated than the maxilla (Fig. 41, D). It consists

ee

ide COPEPODA 81

of, at most, seven (perhaps eight) segments, but the number is
often much reduced, and, as in the case of the maxilla, the limb
is commonly modified into a clinging organ with a strong terminal
claw, or, as in a section of the Harpacticidae, into a subchelate,
prehensile “ hand.”

The five following pairs of appendages (the thoracic limbs of
the ordinary terminology, the second to the sixth of the system
here adopted) are in some Gymnoplea all similar and in the form
of biramous swimming-legs. This form is retained by some, at
least, of these limbs in “all ‘Copepoda i in the later larval if not in the
adult stage, and constitutes one of the most general characters of
the sub-class.

Each consists typically of a broad and flattened protopodite :
two segments, and of an endopodite and exopodite, each with, a
most, three segments, flattened, and bearing marginal natatory alee
together with, on the outer edges, strong spines (Fig. 3, B, p. 8).
The proximal segments of the ‘protopodites of each pair are con-
nected with each other across the middle line by a plate formed
by a transverse fold of the sternal integument (the “ Bauchwirbel”
of Zenker), so that in the backward and forward movement in
swimming the two appendages move as one.

The last (sixth) pair of thoracic limbs are similar to the preceding
pairs only in the females of some genera of Gymnoplea. In the
male sex of that order they are always modified into copulatory
organs, often very complex, by means of which the spermatophores
are affixed to the copulatory aperture of the female. This modifica-
tion is asymmetrical on the two sides in correlation with the
asymmetrical development of the internal generative organs in
the group (Fig. 43, B). In the females of many Gymnoplea the
appendages exhibit every stage of reduction even to complete dis-

‘appearance. In the Podoplea the appendages are always present

(Fig. 44, A, vi.), except in the more degraded parasites ; always
vestigial, consisting of one or two small segments; and are not
specially modified in the male.. In some Harpacticidae and Ascidi-
colidae, however, they become enlarged in the female sex into
plate-like appendages serving to protect the egg-masses. It is
noteworthy that these vestigial limbs of the last pair may persist
even in cases where the pr eceding pair of limbs is suppressed.

In the Podoplea (but not in Gymnoplea) the genital apertures
of the female on the first abdominal somite are guarded by valvular
plates moved by muscles. These valves have been supposed to
represent a vestigial pair of appendages.

In the parasitic forms, with the loss of the power of locomotion,
the thoracic limbs become more or less reduced. In Lernaeocera,
for example, they persist as microscopic though completely formed
limbs set at long intervals along the length of the unsegmented

6

82 THE CRUSTACEA

body. In the Chondracanthidae the anterior two pairs alone are
developed, and these become enlarged in the adult into clumsy,
unsegmented bifid lobes. In other cases the thoracic limbs are
reduced to minute, unsegmented processes, or some or all of them
may disappear. In a few cases the adult is entirely without
appendages, as in the Herpyllobiidae.

Alimentary System.—The alimentary canal is in many cases of
simple form, not divided into sharply defined regions and without
diverticula. The stomodaeum and proctodaeum are short. In
many Gymnoplea there is a short median diverticulum anteriorly,
and in some cases, immediately behind this, a pair of small lateral
(hepatic) caeca which may be bifid (Hucalanus). In some Cory-
caeidae and Asterocheridae these caeca are large and much
branched (Fig. 46). Groups of gland-cells described as salivary
occur in the region of the
labrum and epistome.

The extrinsic muscles of
the alimentary tract are well
developed in Eucopepoda.
Certain muscles running
from the anterior part of the
gut to the dorsal and anterior
region of the body-wall are
of importance in producing a
rhythmical displacement of
the whole alimentary canal,
and serving, in the absence
of a heart, to cause a circu-
latory movement of the blood.
In some parasites the dilator
muscles of the oesophageal

SESS region are greatly developed

Artotrogus orbicularis. Outline of body, fom and act as a suctorial

above, showing ramified lateral diverticula of the

alimentary canal. (After Giesbrecht.) apparatus. The short rectum

(proctodaeum) is usually pro-

vided with dilator muscles running outwards to the body-wall

in addition to the usual constrictors, and the rhythmical movements

of dilatation and contraction produced by them have been regarded
as subservient to a process of anal respiration.

The alimentary canal is usually nearly straight (except for the
sternal flexure of the oesophageal portion), but in a few Gymnoplea
and in Cancerilla (Asterocheridae) its course is slightly sinuous.

Circulatory System.—A heart is present in most Gymnoplea and
in the genus Misophria among the Podoplea. In all other Cope-
poda it appears to be wanting. When present it has an abbreviated
saccular form, and is situated in the region of the first or second

ty.” i

THE COPEPODA 83

free somite. ‘There are three ostia, one median on the posterior
surface and a lateral pair. Anteriorly the heart gives off an aortic
vessel, usually very short. Only in Zucalanus is the aorta described
as extending into the frontal region of the head and dividing into
two pairs of lateral vessels.

In the majority of the free-living Podoplea where the heart is
absent the blood is kept in motion mainly by the continuous
rhythmical backward and forward movements of the alimentary
canal, effected by the extrinsic muscles already mentioned. In
certain parasitic forms (Caligus, young Achtheres) a heart, or an
apparatus having an analogous function, is said to be present, but
exact details as to its structure are wanting.

In Ler nanthropus and some other Dichelestiidae a closed system
of vessels is present containing a yellowish or reddish fluid. There
is no heart, and the relation of this system to the circulatory
apparatus of other Copepoda is quite obscure.

Exeretory System.—The maxillary (“shell”) gland is the fune-
tional excretory organ in the adult stage of most, if not all,
Copepoda. It is much larger in the freshwater forms, where the
duct is long and convoluted, than in the marine forms, in which it
is often hard to find, and sometimes apparently absent. The end
sac is small, and the tube terminates in a short chitin-lined duct
opening on the posterior surface of the maxilla.

In the freshwater Harpacticid Selisarius a curious vibratile
organ is found connected with, or in close proximity to, the
maxillary gland. It has been supposed to be of the nature of
a “flame-cell,” but it is more probably a muscular fibre or
membrane aiding the circulation of the blood in the neighbour-
hood of the gland.

Glands.—Unicellular dermal glands are present on the body and
limbs of most Eucopepoda. Certain pelagic forms belonging to
various genera of the Centropagidae and Oncaeidae are known to
be phosphorescent, and Giesbrecht has shown that this is due to
certain of the dermal glands, the secretion of which becomes
Juminous on issuing from the apertures of the glands. In fresh-
water Cyclopidae and Harpacticidae the secretion of the dermal
glands envelops the body when the water dries up, and forms a
protective case enabling the animal to survive prolonged desiccation.

Nervous System.—The ventral nerve-cord is always short, not
reaching beyond the fourth free thoracic somite. It is divided
into distinct ganglia in the Gymnoplea, but in the Podoplea, so far
as is known, the ganglia are all coalesced. In the Corycaeidae and
in the parasitic families the whole system is still more concentrated,
forming a thick perioesophageal- ring. Even in the Gymnoplea the
distinction between ganglia and commissures is not sharp, nerve-
cells being present abundantly on the latter as on the former.

84 THE CRUSTACEA

In Cyclops it has been observed that the pair of nerves to the
antennae originate from the oesophageal connectives, so that
as regards their nerve-supply these appendages are parastomial.

Sense-Organs.—The paired compound eyes of other Crustacea
appear to be unrepresented in the Eucopepoda, although rudiments
of them were observed by Grobben in the development of Calanus.
The nawplius-eye, on the other hand, is almost universally present
in the free-living EKucopepoda, and even in many of the parasitic
forms, and in some cases, especially among the Gymnoplea, it
attains a complexity of structure not observed in any other class
of Crustacea,

In the simplest and typical form it consists of three ocelli, each
supplied by a separate nerve from the brain. Two of the ocelli are
dorsal and look upwards and forwards, while the third is ventral,
looking downwards. Each consists of a cup-shaped mass of pigment,
containing in its cavity a number (up to ten) of retinal cells con-
tinuous at their distal ends with the nerve-fibres, and having (at
least in some cases) a rhabdome near the proximal end. In the
genus Anomalocera (Pontellidae) and in some Asterocheridae the
number of ocelli is increased to five, those of the dorsal pair being
doubled.

In some Eucopepoda the eye is movable by means of special
muscles. These are wanting, however, in many cases (Cyclops).

In some cases the visual apparatus is perfected by the addition
of a pair of corneal lenses formed by thickening of the cuticle
over the dorsal pair of ocelli. These may be inconspicuous as in
Cyclops, or large and well-defined as in Miracia (Harpacticidae). It
is, however, in the two widely separate families of Pontellidae and
Corycaeidae that the structure of the visual apparatus reaches
its highest degree of complication. In the former the dorsal ocelli
are often provided with cuticular lenses, and in addition there may
be developed a vesicular crystalline body interposed between the
retinal cells and the cuticle. The ventral ocellus approaches the
sternal surface and sometimes projects as a papilliform or peduncu-
late prominence, while the deflected rostrum in front of it becomes
thickened in such a manner as to form a biconvex lens, serving to
concentrate the rays of light upon it.

In the Corycaeidae (Fig. 47) the three ocelli are widely
separate and the median element remains small, while the dorso-
lateral pair attain a much greater—sometimes relatively enormous
—development. ach is provided with a large biconvex cuticular
lens (/), and the retinal apparatus is at a considerable distance
from this, at the apex of a conical space the base of which is
formed by the lens and the walls by a delicate membrane. The
pigment-cup (p) is elongated into a tubular form and at its mouth
is set a vesicular “crystalline body” (¢). In Corycaeus the posterior

THE COPEPODA 85

part of the ocular apparatus reaches back into the region of the
anterior thoracic somites, and in Copilia the pigment-cups enclos-
ing the retinal cells lie together in a conical protuberance on the
sternal surface of the body.

In this account it has been assumed that the “paired eyes” of
Pontellidae and Coryeaeidae are derived from the dorso-lateral
elements of the nauplius-eye. It must be mentioned, however,
that Claus, while admitting this derivation in the case of the
Corycaeidae, regarded the lateral eyes of the Pontellidae as homo-
logous with the paired compound eyes of other Crustacea. If it be
the case, however, that in the Pontellid eye, as in those of other
Eucopepoda, the retinal cells are “inverted” (or are connected
with nerve-fibrils at the end turned towards the light), this
homology would seem to be impossible.

A problematical organ to which a visual function has been
attributed is found in the genus Pleuwromamma. It lies on one side

Corycaeus anglicus, male, from the side, showing one of the large paired eyes. /, lens; ¢,
crystalline body ; p, tubular pigment-cup. (After Leuckart.)

of the cephalic shield, in the region of the maxillipeds, and consists
of a globular refractive body enclosed in a mass of pigment, the
whole projecting from the surface of the body in a little papilliform
elevation. It has also been suggested that this is an organ of
phosphorescence, but according to Giesbrecht this is not the case.

The “«esthetascs,’ or “olfactory filaments,” of the antennules
have already been mentioned. Their number and arrangement
vary very much in different forms, and afford valuable systematic
characters.

The “frontal sense-organs” are certain sensory setae, generally
a single pair, on the front surface of the head above the rostrum,
which are supplied by a pair of nerves arising from the brain,
and which have been supposed to be the seat of some special
sense.

The existence of “auditory” organs in the Eucopepoda is
doubtful. A pair of statocysts have been described in the
anterior part of the brain in Lucalanus.

86 THE sCROSPAGEA

Reproductive Systen.—The ovary may be paired or single. It is
generally of small size and the ova pass at an early stage into the
oviducts, which are large and give off blind diverticula (Fig. 48,
ut). In the parasitic forms the ramifications
of the oviducts (or uteri) occupy the greater
part of the body-cavity, and even, in Chondra-
canthus, invade the misshapen thoracic limbs.
In the terminal portion of the oviducts the
walls are glandular and secrete the cement
by which the eggs when expelled are agglu-
tinated together. The openings of the oviducts
are on the first abdominal somite, and may
be ventral, lateral, or dorsal in position. The
genital valves covering the openings have been
already mentioned.

In the great majority of Eucopepoda the
female generative apparatus possesses another
opening or pair of openings on the ventral
side of the genital somite, serving for the

Fie. 48. entrance of the sperm and communicating
Reproductive system of internally with a single or double spermatheca

female Cyclops. ap, external a i
opening of oviduct; ov, (Fig. 48, sy). On each side the spermatheca

eT Loren nies: gives off a duct which communicates with the
eee (Atte Hertos) OViduct close to its external aperture. Rarely

(Plewromamma) only one sperm-duct is present.
This sperm-duct is lined with chitin, but, in some cases at least,
the spermatheca is devoid of such a lining and is difficult to
detect except when distended with spermatozoa. It is stated to
be altogether absent in Heterocope (Gymnoplea). While the details
of this apparatus have been investigated only in a relatively small
number of forms, it seems probable that the possession of special
copulatory pores apart from the openings of the oviducts is a
characteristic of all Eucopepoda. Canu has proposed to divide
the order into two groups, Monoporodelphya and Diporodelphya,
according as the copulatory pore is single or paired, but it appears
from Giesbrecht’s researches that the two conditions may be found
in closely allied forms. The last-named author has observed that
in Scottocheres (one of the Asterocheridae) the sperm-duct opens
not into the spermatheca but to the outside by a separate pore
close to the opening of the latter.

The eggs are sometimes deposited singly in the water
(some Gymnoplea), but in the great majority of the Eucope-
poda they are cemented together into packets by means of a
secretion formed by the oviduct. In all except a very few
eases (Choniostomatidae) these packets are carried by the female
attached to the openings of the oviducts until the eggs hatch.

THE COPEPODA 87

The brood-pouches of the Ascidicolidae have already been
alluded to.

The festis, like the ovary, may be paired or single, the former
condition occurring chiefly aniong the parasitic forms. The vas
deferens is sometimes developed only on one side of the body.
This arrangement is universal among the Gymnoplea and is found
also in some Harpacticidae. Three regions are distinguished in the
vas deferens, which, however, are not sharply defined from each
other. A narrow proximal portion is followed by a wider part in
which the spermatozoa accumulate and become surrounded by a
layer of secretion giving rise to the sheath of the spermatophore
and a widened terminal part in which the development of the
spermatophore is completed.

The possession of definite spermatophores seems to be a universal
character of the Eucopepoda, distinguishing them from all the
other ‘‘Entomostracan” orders. The spermatophores may be
globular, pyriform, or, commonly, sausage-shaped, and consist of a
firm cuticular (not chitinous) investment enclosing a mass of
spermatozoa together with a substance which by its expansion
serves to expel the spermatozoa. In addition, the spermatophore
contains a coagulable secretion which is expelled before the
spermatozoa and forms a sheath surrounding them within the
female spermatheca. Externally the “neck” of the spermatophore
is surrounded by a mass of a cementing substance secreted in
the terminal portion of the vas deferens for attachment to the
copulatory aperture of the female. In the Gymnoplea the last pair
of thoracic feet of the male are modified to form an apparatus by
which the spermatophores are transferred to the female. In the
other Eucopepoda special copulatory appendages are absent.

DEVELOPMENT OF EUCOPEPODA.

The majority of the Eucopepoda hatch in the form of a very
typical Nauplius larva, though many parasitic forms reach a later stage
of development within the egg. The adult stage is reached by a very
gradual metamorphosis, the most marked change of shape occurring
(in the free-living forms) in the transition from the last metanauplius
to the first ‘‘ Copepodid stage.” In the parasitic forms great changes
occur in the later stages, some of which are described below.

The youngest nauplius stages (Fig. 6, p. 11, and Fig. 49, A)
have an oval unsegmented body from which the dorsal shield is
not yet defined, a large labrum, and the usual three pairs of
appendages, the second pair (antennae) bearing a masticatory
process, while the third pair (mandibles) are often without such a
process at this stage. A large unpaired eye and a pair of antennal
glands (which later degenerate) are present.

88 THE CROSTACEA

The later nauplius stages pass without any sudden change into
the metanauplius (Fig. 49, B, C), in which the dorsal shield becomes
marked off and several pairs of appendages appear as rudiments
behind the mandibles. According to the earlier investigations of
Claus, the second pair of these rudiments were believed to give
rise to the ‘outer and inner maxillipeds,” but, as stated above,
it is now known that this is an error arising from the fact that

Fie. 49,

Larval stages of Calanus finmarchicus (= Cetochilus septentrionalis). A, nauplins; B, early
metanauplius ; C, later metanauplius. 1, antennule; 2, antenna; 3, mandible; 4, maxillula ;
5, 5, maxilla and maxilliped (formerly regarded as parts of one appendage); I, II, first and
second pairs of swimming-legs ; an, anus; g, brain; gz, genital cells ; m, mouth ; me, primitive
mesoderm cells; ol, labrum. (After Grobben, from Korschelt and Heider’s Lmbryology.)

in the metanaupliar stages of most Copepods the appendages are
very much crowded together.

The transition from the metanauphar to the Copepodid stages
(sometimes known as the “ Cyclops stages”) is marked by a straighten-
ing of the body, which in earlier stages is ventrally curved, and by
the unsegmented posterior region becoming sharply marked off from
the broader anterior part. The limbs begin to show the characters
which they have in the adult, the antennules elongating and becom-
ing divided into more numerous segments, the antennae losing the
masticatory process, and the mouth-parts and swimming-feet

THE COPEPODA 89

approximating to their permanent form. The caudal furea is also
developed at this stage. There are typically four somites defined
in front of the unsegmented abdominal region in the first Copepodid
stage, and three pairs of swimming-feet. In each of the five
succeeding Copepodid stages a somite is added, giving, together
with the terminal segment or telson, the typical number of ten free
segments. In the majority of cases, however, as already mentioned,
the number of somites in the adult is reduced by coalescence or
suppression, with corresponding changes in the course of develop-
ment. The constriction which marks off the broad anterior from
the narrow posterior region falls, in the first Copepodid stage,
behind the third free somite. It is moved backward one somite at
each moult, the Podoplea reaching the final limitation of the regions
at the second and the Gymnoplea at the third Copepodid stage.
In the more primitive forms (Calanus) the development of the
limbs, like that of the somites, takes place in regular order from
before backwards. In the more specialised forms, while the rudi-
ments of the limbs appear in this order, there is a tendency for the
anterior swimming-feet to outstrip in their development the maxillae
and maxillipeds, which remain for some time as rudimentary buds.

LIFE-HISTORY OF PARASITIC EUCOPEPODA.

In no other group of Crustacea has parasitism: led to such
diversity of structure and of life-history as in the Eucopepoda.
The parasitic habit of life has been adopted to a greater or less
degree by many very different families, and every transition is
found from the normal free-living types to those most completely
adapted to a parasitic life.

In those Eucopepoda which, while parasitic, retain to some
extent the power of locomotion, the general structure of the adult
does not differ greatly from that of the free-living types and the
sexual dimorphism is not accentuated. Thus in the family Astero-
cheridae, which have, as a rule, completely suctorial mouth-parts
and are parasitic on various Invertebrata, most of the species are
capable of swimming and retain the general Copepod form. In
the Ascidicolidae, which live rather as commensals than as parasites
in the alimentary tract of Tunicata and Echinoderma, we find a
series leading from the little-modified forms (Votodelphys, ete.) which
live in comparative freedom in the pharyngeal sac of the Tunicata,
and in which the adults of both sexes possess natatory thoracic limbs,
to those species which live in the stomach and intestine, and have
assumed in the female an almost vermiform shape, with limbs adapted
to push their way through the contents of the alimentary canal of
the host. The male in most cases is free-swimming, at least in the
adult stage, and is correspondingly less modified in general form.

go THE CRUSTACEA

As an example, we may take Hnterognathus, recently described
by Giesbrecht. This form differs from most other Ascidicolidae in
infesting, not a Tunicate, but the Crinoid Antedon rosacea. The
female (Fig. 50) has an elongated body which presents the full
number of segments. Antennules and
antennae are short and consist of few
segments. The mouth-parts are not suc-
torial. The mandible consists of a long
and narrow blade, with toothed cutting
edge and a vestigial palp of two seg-
ments. The maxillipeds are absent. The
first four pairs of thoracic feet are
short and biramous, with the endopodite
forming a broad, spoon-like plate, without
setae, while the exopodite forms a strong
curved claw. By movements of these feet,
and by elongation and contraction of the
body, the parasite pushes its way through
the contents of the intestine of its host.
The last pair of feet are broad lamellae
fringed with hairs, covering the point of
attachment of the egg-masses, and prevent-
ing these from being detached in the
movements of the animal. The abdomen

Enterognathus comatulae, aduit CNS in a well-marked furca, bearing a few
female, x 17. (After Giesbrecht.) ghort setae.
II, VI, second and sixth thoracic : : :
somites; 1, first abdominal The male is free-swimming, and _ pre-
eee Fane eeeeaGee fine sents the typical Copepod form, with fully
segmented body and natatory thoracic
feet. Its most striking feature is the entire absence of mouth-
parts, there being no trace of the appendages between the antennae
and the first pair of swimming-feet.

The life-history is as follows. The earlier stages are unknown,
but it appears that the first Copepodid stage is free-swimming, and
that both sexes enter the alimentary canal of the host in the second
Copepodid stage. Retrogressive changes then take place, the suc-
ceeding stages of the female resembling the adult in general shape,
while those of the male lose the natatory setae of the thoracic feet.
In the adult male, however, these are reacquired, while the mouth-
parts disappear and the animal escapes from the host. Where it
meets with the female is not definitely known, but it is at least
probable that the latter temporarily leaves the alimentary canal of
the Crinoid, and clinging to the surface of its body, is there fertil-
ised by the male.

In certain families of the truly parasitic forms with suctorial
mouth-parts (Caligidae, Lernaeidae, Lernaeopodidae) a community

Fic. 50.

THE COPEPODA 9!

of origin is indicated by the possession of a larval glandular organ
of adhesion in the frontal region (Fig. 45, A, fgl). In the
Caligidae the first Copepodid stage becomes attached to the skin of
a fish by a long filament (frontal band) which appears to be formed
by the consolidated secretion of a convoluted tubular gland lying
in the frontal region. Larvae in this stage were described by
Burmeister as a distinct genus, under the name Chalimus, and it
may conveniently be designated the Chalimus-stage. In later
stages both sexes become free, and in some species at least
retain the power of swimming freely, attaching themselves only
temporarily to fishes for the purpose of sucking their blood.
The males and females, at the stage at which fertilisation takes
place, do not differ greatly, but after impregnation the genital
somite of the female becomes greatly distended and filiform egg-
masses are produced.

A more complex life-history is that of the Lernaeidae. Lernaca
branchialis is hatched as a nauplius, and when it reaches a stage
corresponding to the first Copepodid stage (Fig. 51, A) it becomes
parasitic on the gill-filaments of
a fish, usually one of the Pleuro-
nectidae, attaching itself at first
by the subchelate antennae and
the maxillae, and later by the
frontal cement-gland. It then
passes into a “pupal” stage
(Fig. 51, B), in which the power ---O€
of movement is lost and retro-
gressive changes occur, especially
in the swimming-legs, which
lose their setae and become
unsegmented stumps. Later,
the power of locomotion is
regained, and the parasite leaves
its first host in a form which
corresponds to the adult stage
of free-living Copepods. Sexual
maturity is now reached and
the female (Fig. 52, B) is dis. | des
tinguished by the great elonga- 4. ji. Copano eigen Pnate
tion of the region of the genita] artennule; a”, antenna; J, f”, first and second

5 5 pairs of swimming-feet; k, mass of cement
segment. Impregnation takes produced by frontal gland; oc, nauplius-eye.
place in. this free-swimming Gnoryoiogy)) nt SM Heicens
stage and the male does not
develop further. The female, however, seeks a second host, a
fish of the family Gadidae, and becoming attached to the gills,
burrows into the flesh so that the whole anterior region of the

92° THE CRUSTACEA

body is embedded. Three ramified processes grow out from the
head into the tissues of the host, and the region of the genital
somite becomes enormously enlarged, forming the greater part of

IGS 2s

Lernaen branchialis. A, male; B, female, at copulatory stage. C, D, later stages of female
after attachment to second host. «’, antennule; a”, antenna; f%, fi”, first and fourth pairs of
swimming-feet ; g, opening of spermatheca; ma, maxilliped ; oc, nauplius-eye; sp, spermato-
phore sac; t, testis. (After Claus, from Korschelt and Heider’s Embryology.)

the vermiform body (Fig. 52, C, D). The swimming -feet are
retained in a vestigial condition near the anterior end.

In some other forms parasitic on fish (Lernaeopodidae, Chon-
dracanthidae) the male is attached to the female in a dwarfed
condition throughout life. The larva becomes parasitic in the

J

THE COPEPODA 93

first Copepodid stage, and the later stages of the typical series are
suppressed, the characteristic features of the parasite being assumed
at the next moult.

In the Choniostomatidae, which are parasitic on other Crustacea,
the larva hatches in the first Copepodid stage, with two pairs of
swimming-feet, and becomes attached to the host by an adhesive
frontal plate, corresponding probably to the “frontal thread” of other
forms. This larva may give rise at once to the adult form, or a
pupal stage with reduced limbs may intervene. The male is similar
to the female in essential structure, but of much smaller size.

The most extreme stage of degeneration is reached in the
Herpyllobidae, which are parasitic on Polychaete worms and on
Crustacea. In Lhizorhina, which is the most thoroughly known,
the adult female is entirely without appendages, and is attached by
a tubular process which ramifies within the body of the host in a
fashion recalling the “roots” of the Rhizocephala. The adult male
is also entirely limbless, but remains enclosed within the last larval
skin (of the first Copepodid stage). Within it are formed a pair of
relatively enormous spermatophores, which are not expelled from
the body but discharge their contents through ducts which pass
out close to the point of attachment, and in front of the position
of the larval mouth. A number of males are attached to the body
of the female near the genital apertures.

The Monstrillidae have a very remarkable life-history, which
has only recently been made known. The adults of both sexes are
free-swimming, and are without mouth-parts or alimentary canal.
The newly hatched young are also free-swimming, but the inter-
mediate stages are endoparasitic within various Polychaete annelids.
The life-history is most fully known in the case of Haemocera dunae,
investigated by Malaquin (Fig. 53). The adults (F) have antennules
and four pairs of swimming-feet, but no trace of antennae or
mouth-parts. The fifth pair of thoracic feet are vestigial in the
female and are stated to be absent in the male. The alimentary
system is represented by a blind stomodaeal invagination and a
mass of undifferentiated endoderm cells. The female carries a
single packet of eggs (ov) adhering to a pair of very long setae
(g-8) which spring from the genital valves. The young are hatched
as nauplii, without mouth or alimentary canal, and with strong
hook-like mandibles (A). The nauplius burrows into the body of
its host (the Polychaete Salmacina), casting its cuticle in the
process and losing its limbs, so that when it reaches the body-
vavity it consists merely of a mass of embryonic cells without a
cuticle (B). From the body-cavity the parasite passes into the
vascular system of the host, where it undergoes its further develop-
ment. A thin cuticle is now secreted, and a pair of processes begin
to grow out from one end of the ovoid body (C, pr). These

94 THE CROSTAGEA

increase in size, in some cases, to several times the length of the
body, and as the cuticle covering them is very thin it is believed

IMieh BR)

Stages in the life-history of Haemocera danae, A, free-swimming nauplius-larva, x 280. B,
embryo after penetrating into the body-cavity of the host; no organs remain except the
degenerating nauplius-eye. C, later stage, from the vascular system of the host ; the absorptive
processes have begun to develop. 0D, still later stage; the absorptive processes are fully
formed and the posterior end of the embryo is provided with rows of recurved hooks. E, the
adult female, just before emergence from the host; the anterior part of the body is distended
with eggs. F, free-swimming female, carrying the extruded eggs, x 28 ; the hypodermis in the
anterior part of the body has separated from the cuticle after expulsion of the eggs and forms
a sheath around the nerve-cord. a’, antennule; b7, brain; e, nauplius-eye ; f, swimming-feet 5
g.s, genital setae; m, position of mouth ; md, mandible of nauplius ; n, nerve-cord connecting
brain with ventral nerve-chain; ov, mass of eggs carried on genital setae; ovy, ovary; pr,
absorptive processes. (After Malaquin.)

that they act as absorptive organs. In some cases, but not always,
a second pair of these processes is found behind the first. From
the position which they occupy relatively to the rudiments of

THE COPEPODA 95

appendages afterwards appearing, it is believed that they represent
the antennae and mandibles of the nauplius. The organs of the
adult are gradually differentiated within the cuticular sac, which
enlarges with the growth of the animal. The pointed posterior
end of the sac is surrounded by rows of recurved hooks (D), and
these appear to be used in boring a way out through the tissues
of the host when development is complete (E). The reproductive
organs are developed before the parasites escape from the host.
After escaping, a single moult takes place and sexual maturity
is reached.

The life-history of the Monstrillidae may be compared with that
of the male Hnterognathus described above, in which the earlier
larval stages and the adult are free-swimming, while the intervening
stages are parasitic and degenerate, and in which also the adult is
incapable of feeding.

MORPHOLOGY OF BRANCHIURA.

The body is much flattened, and is divided into three regions,
an unsegmented, cephalothoracic region followed by three free
thoracic somites and an unsegmented abdomen (Fig. 54). The
cephalothoracic region is covered by a greatly developed head-shield
or carapace, which, while not projecting beyond the articulation of
the succeeding somite as a distinct “ shell- fold,” is expanded on each
side in a creat wing-like pleural fold. In many species the lateral
folds are produced backwards and cover the thoracic somites and
their appendages, and sometimes even the abdomen. The abdomen
is notched or bilobed, and bears a pair of minute furcal rami (/).

Appendages.—The antennules are small, consisting of four
segments, of which the first is divided into two parts and is
provided with a large hooked claw and some smaller spines, used
for attachment to the host. The antennae are also short, uniramous
in the adult, of four segments, the basal part provided with stout
spines.

The mouth-parts are suctorial, the upper and lower lips together
forming a proboscis (Fig. 54, p) within which are enclosed the
mandibles and maxillulae. The maxillulae are never included in
the proboscis in suctorial Eucopepoda.

The mandibles are without palps in the adult and have sickle-
shaped, serrated tips. The mavillulac are stated to be wanting in
the genus Dolops. In Argulus they are simple, lancet-like blades.
The mazillae (“first maxillipeds”) are very remarkably modified.
Except in the genus Dolops, where they end in stout hooked claws,
they are represented chiefly by a pair of large adhesive suckers
(Fig. 54, mx”), situated some distance in front of the proboscis. The
sucker is developed from the basal portion of the appendage, the

96 THE (CRUSTACEA

distal segments which are present in the larva persisting as a
vestige under the outer margin of the sucker or disappearing
altogether. The sucker itself is provided with strong muscles and
its margin is strengthened by radiating chitinous rods.

The first thoracic appendage (“second maxilliped ”) (map) consists
of five segments, the basal one produced into a lobe armed with
strong teeth and the end of the limb carrying two stout claws.

The next four pairs of appendages are biramous natatory feet.
The first pair is attached to the cephalothoracic region, the remain-
ing three correspond to the three free thoracic somites. Each
consists of a stout protopodite, which, in some species at least, has

NT Sy =

Fig. 54.

Argulus americanus, female, from below, x 5. a’, antennule; a”, antenna; e, paired eye ;
f, caudal furca; ma”, sucker formed by maxilla (“first maxilliped”); map, first thoracic
appendage (‘* second maxilliped ”); p, suetorial proboscis ; sp, poison spine. (After Wilson.)

three segments, and an exopodite and endopodite of about equal
length. The exopodite is unsegmented, and the endopodite consists
in the first pair of three segments, in the second of one, and in
the last two pairs of two segments. Both rami are furnished with
two rows of long plumose setae, set along the dorsal and ventral
margins respectively. The insertion of the broadened bases of
these setae gives to the exopodite and endopodite the appearance of
being divided into numerous short segments, and they have been
so described, but the arrangement of the musculature shows that
these do not represent true segments of the limb.

On certain of the anterior legs in most of the species the
protopodite carries at its distal end, besides the endopodite and
exopodite, a slender appendage, known as the flagellum, which

THE COPEPODA 97

originates to the outer (or dorsal) side of the exopodite, and is bent
backwards upon the protopodite. It is provided with two rows of
plumose setae, and its probable function is to cleanse the lower
surface of the carapace. The homology of this appendage is
doubtful. It cannot be an epipodite since it springs from the
distal segment of the protopodite. Nothing equivalent to it is
found in the Eucopepoda.

In the male sex the peduncles of the last two, sometimes of the
last three, pairs of legs are modified for purposes of copulation.
The details differ in the different species, but in all the peduncle of
the penultimate pair is excavated to form a seminal pouch which

A, nervous system of Argulus americanus. e, nauplius-eye ; immediately below is the opening
through which the oesophagus passes. B, female reproductive organs. ovy, ovary ; od, open-
ing of oviduct ; sp, spermatheca ; the papillae on which the spermathecal ducts open are seen
just below the opening of oviduct ; t.p, ‘‘ tactile papillae.” C, male reproductive organs. 1,
accessory gland ; 0, external opening ; s.v, seminal vesicle; t, testis. (After Wilson.)

opens on the dorsal surface of the limb. On the anterior surface
of the peduncle of the last pair is a peg-like process which seems to
be used for opening the mouth of the seminal pouch so that the
latter can be filled with sperm. In some species in the female sex
a pair of finger-like processes (Fig. 55, B, t.p) are situated at the
sides of the genital orifice between the last pair of legs. These
may possibly represent a vestigial sixth pair of thoracic appendages.

In the genus Argulus a very peculiar poison apparatus is
situated in front of the mouth. It consists of a hollow spine (Fig.
54, sp), which can be withdrawn into and protruded from a sheath
by the action of special muscles. The duct which traverses it com-
municates with three groups of large unicellular glands lying at its

~

/

98 THE CRUSTACEA

base. These glands appear to be a specialisation of some of the
dermal glands which (as in many Eucopepoda) are abundantly dis-
tributed over the surface of the body.

Alimentary System.—The alimentary canal has a narrow oeso-
phageal region, with strong circular and longitudinal muscles, which
projects, funnel-like, into the wide stomach. The latter gives off
a pair of diverticula, which are much ramified, and occupy the
greater part of the lateral lobes of the cephalothorax. When feed-
ing, these diverticula, as well as the stomach and intestine, become
filied with the juices of the host. The stomach is followed by a
wide intestinal region which is separated by a sphincter from the
narrow rectum. The latter is without the dilator muscles found
not only in Eucopepoda but in most Crustacea.

Circulatory System.—The heart is situated at the junction of
thorax and abdomen, and sends off an aorta which reaches as far
forward as the brain. It is provided with one or two pairs of
lateral and inferior afferent ostia and sometimes a median inferior
efferent opening at the base of the aorta. There appears to be
doubt as to the existence of a posterior median efferent opening.
In the earliest larval stages the heart is absent, and the circulation
is mainly carried on, as in the later stages it is assisted, by
rhythmical contractions of dorso-ventral muscles in the abdomen.

Excretory System.—An excretory gland of the usual type is
present, and has been identified as the maxillary gland (shell-
gland). It appears from the investigations of Claus and of
Nettovich, however, that it differs from the maxillary gland of
the Eucopepoda and other Crustacea in opening not on the maxilla
but on the first thoracic limb (the so-called “second maxilliped ”),
or on the sternal surface of the body close to the base of that
appendage.

Nervous System.—The ventral nerve-chain (Fig. 55, <A) is
shortened, but six ganglia can be distinguished. The statements as
to the origin of the nerves to the two pairs of maxillipeds are con-
flicting, but the last four ganglia supply the somites of the four
pairs of swimming-feet, the last also sending nerves to the abdomen.

Sense-Organs.—A median (nauplius) eye of the usual structure
is set upon the dorsal surface of the brain (Fig. 55, A, ¢). In
addition, there are a pair of large compound eyes (Fig. 54, ¢)
visible through the transparent integument of the dorsal surface.
Each is supplied by a stout optic nerve which swells into a
ganglion before entering the eye. The eye is movable, but it
differs from the similarly movable, non-pedunculated eyes of the
Branchiopoda in the fact that it moves not in a “corneal pouch”
but in a blood-space which intervenes between the outer ends of
the quadripartite crystalline bodies and the integument. Seen
from above this blood-sinus is bounded on the anterior, external,

THE COPEPODA 99

and posterior sides by a chitinous wall. It seems not unlikely
that further research will show the wall to be formed by an
invagination of the cuticle, in which case it may represent the
vestige of a corneal pouch like that of the Branchiopoda.

Reproductive System.—The ovary (Fig. 55, B, ovy) is unpaired
and, at its first appearance in the larva, asymmetrically placed,
afterwards assuming a median position. Rudiments of two ovi-
ducts are found in the larva, but that situated on the same side
of the body as the ovary atrophies, while the other develops
further and ultimately opens (od) in the middle line between the
bases of the last pair of legs.

A pair of spermathecae (Fig. 55, B, sp) are found in the
abdomen. ‘They are not connected with the oviducal opening, but
each has a short duct which gives off a blind diverticulum and
terminates on a papilla with a retractile spiniform tip close to
the anterior margin of the abdomen. It is believed that the
sharp points of these papillae pierce the envelopes of the eggs
when the latter are laid, so as to permit the entrance of the
spermatozoa. The eggs are laid attached to stones or other objects.

The testes (Fig. 55, C, ¢) are paired and lie in the abdomen.
Their ducts unite to form an unpaired seminal vesicle (s.v), and
after receiving the ducts of a pair of accessory glands (q/) lying
in the thoracic region again unite to open by a median pore (0)
between the bases of the last pair of legs. The seminal pouches
on the penultimate legs of the male and the structures connected
therewith have already been mentioned.

DEVELOPMENT OF BRANCHIURA.

In some species of Argulus the newly hatched larva has all the
appendages similar to those of the adult with the exception of the
first maxillipeds, which are not modified into suckers but are stout
clasping limbs, each consisting of four segments and ending in a
double claw. In other species, however, among which is the
common European 4. foliaceus, the newly hatched larva differs still
more from the adult (Fig. 56). The antennae are biramous, having
a large unsegmented exopodite which is lost in the adult, and the
mandibles have a large uniramous palp of two segments. The
antennal exopodite and the mandibular palp are tipped with plumose
setae and serve as swimming-organs. ‘The heart is not found in
the earliest larvae but develops after the first moult.

REMARKS ON HABITS, ETC.

The majority of the Eucopepoda are marine, but numerous
species, belonging chiefly to the families Centropagidae, Harpac-

100 THE CRUSTACEA

ticidae, and Cyclopidae, are very abundant in fresh water. Most
of the Gymnoplea are pelagic, forming a very important part
of the plankton of the sea and of lakes. The non-parasitic
Podoplea, on the other hand, with the exception of a few pelagic
groups like the Corycaeidae, belong to the bottom-fauna. A large

Newly hatched larva of Argulus foliaceus. a’, antennule; a”, antenna; md, mandible ; mdt,
mandibular palp; mf’, maxilla (first maxilliped); mf”, (second); maxilliped ; pl, p4, first and
fourth pairs of swimming-feet. (After Claus, from Korschelt and;Heider’s Lnbryoloyy.) -

proportion of the parasitic forms of various families attack fish, and
some of these, such as Lernaeocera and Achtheres, occur in fresh water.
Pennella is sometimes found on whales. - Other parasitic and semi-
parasitic forms are found on various groups of marine inverte-
brates. The Branchiura are temporary parasites on fish and occur
both in the sea and in fresh water.

Most of the free-living Eucopepoda are minute, but some of the

eee

THE COPEPODA 10I

parasitic species attain a greater size, the largest (Pennella) being
more than a foot in length.
No fossil remains of Copepoda are known.

AFFINITIES AND CLASSIFICATION,

On the hypothesis that the Nauplius represents the ancestral
type of the Crustacea, the Eucopepoda would be regarded as the
most primitive existing members of the class, retaining, as they
do, nauplar characters in the form of the first three pairs of
appendages and in the absence of paired eyes and of a shell-fold.
As already indicated, however, it is much more probable that they
are to be regarded as a specialised and in some respects degenerate
group which, while retaining, in some cases, a very primitive
structure of the cephalic appendages, has diverged from the
ancestral stock in the reduction of the number of somites, the loss
of the paired eyes and shell-fold, and the simplified form of the
trunk-limbs. The prevalence of parasitism and the great structural
changes associated therewith render the classification of the Euco-
pepoda a matter of peculiar difficulty, and none of the schemes
hitherto proposed is altogether satisfactory. In Claus’s system
(1880) the distinction drawn by most of the older authors between
free-living and parasitic forms is still maintained in the two chief
divisions of Gnathostomata and Siphonostomata, the latter includ-
ing forms in which the. mouth-parts are more or less distinctly
suctorial. Giesbrecht has shown, however, that this arrangement,
and also that proposed by Canu, based on the copulatory pores of
the female, are quite unnatural, since forms with biting and suc-
torial mouth-parts and with paired and unpaired copulatory pores
may occur within the limits of the same family. Giesbrecht’s own
classification of the Eucopepoda, which is given below, marks a
distinct advance, especially as regards the separation of the more
primitive pelagic families to form the group Gymnoplea. His
arrangement of the remaining families, which he groups together as
Podoplea, is, however, less convincing, and he does not attempt to
define the position of many of the parasitic forms. The system is
therefore incomplete and can only be adopted as a temporary
expedient pending further investigation.

Some modern writers follow Zenker and Thorell in referring
the Branchiura to the Branchiopoda, although the only character
which can now be referred to in support of this arrangement is the
presence of paired compound eyes. On the other hand, the com-
parison instituted by Claus between the appendages of Branchiura
and Eucopepoda shows a general similarity of structure which can-
not be disregarded. The ‘only serious difficulty in the way of this
comparison is the difference in the position of the maxillar y gland,

102 THE CROSTACEA

which in the Eucopepoda, as in other Crustacea, opens on the
maxilla, but in the Branchiura on the first thoracic appendage. It
seems more probable, however, that a shifting of the aperture has
taken place than that the appendages do not correspond serially
in the two groups. ;

Sus-Ciass Coprepopa, H. Milne-Edwards (1830).

ORDER 1. Bucopepoda, Claus (1875).

Paired compound eyes absent; genital apertures on the seventh
trunk-somite; thoracic limbs without flagellum; fertilisation by
spermatophores.

Sup-Orper 1. Gymnoplea, Giesbrecht.

Last thoracic somite firmly connected with the preceding somite and
movably-articulated with the first abdominal somite ; last pair of thoracic
appendages in female similar to preceding pair, or reduced or absent, in
male always present and modified as copulatory organs; one or neither
of the antennules geniculate in male; eggs deposited singly or carried in
a single packet; heart generally present; vas deferens unpaired, its
opening unsymmetrically placed. Free-living forms, mostly pelagic.

TRIBE 1. AMPHASKANDRIA, Giesbrecht.

Antennules of male not geniculate, with more numerous aesthetascs
than in female.

Family Cananmarn. ‘This extensive group is divided by Sars into
twelve families. Most of these correspond to sub-families recognised by
Giesbrecht. Calanus, Leach (Fig. 41); Hucalanus, Dana; Rhincalanus,
Dana; Calocalanus, Giesbrecht (Fig. 42); Paracalanus, Boeck; Pseudo-
calanus, Boeck; Aetideus, Brady ; Euchaeta, Philippi; Phaénna, Claus ;
Scolecithriz, Brady ; Diaixis, G. O. Sars; Stephos, Scott; Tharybis, G. O.
Sars; Pseudocyclopia, Scott. (The families represented by the last eight
genera are separated from the Amphaskandria by Sars to form a division
Tsokerandria.)

One of the antennules geniculate in male.

Family CENTROPAGIDAE. Divided into eight families by Sars :—
Centropages, Kroyer ; Diaptomus, Westwood ; Pseudodiaptomus, Herrick ;
Heterocope, G. O. Sars; Lucicutia, Giesbrecht ; Temora, Baird ; Metridia,
Boeck ; Heterorhabdus, Giesbrecht ; Plewromamma, Giesbrecht ; Arietellus,
Giesbrecht. Family Pseupocyctoripan. Pseudocyclops, Brady. Family
Canpacupar. Candacia, Dana. Family Ponretiipar. Divided into
four families by Sars :—Pontella, Dana; Parapontella, Brady ; Acartia,
Dana; Anomalocera, Templeton ; Tortanus, Giesbrecht.

i.

THE COPEPODA 103
cc a a A NN

SuB-OrDER 2. Podoplea, Giesbrecht.

(Most of the following characters are subject to modification in parasitic
forms.)

Last thoracic somite movably articulated with the preceding, and
firmly united with the first abdominal somite, which it resembles in size
and form. Last pair of thoracic feet vestigial in both sexes ; not
modified as copulatory organs in male. Both or neither of the antennules
geniculate in the male. Eggs generally carried in paired or unpaired
masses. Heart absent (except in Misophria). Male reproductive system
usually paired. Free-living (rarely pelagic) or parasitic.

TRIBE 1. IsoKERANDRIA, Giesbrecht.

Swimming forms with antennules not geniculate in male, generally
similarly segmented in both sexes, and parasitic forms allied to these.

Family Cuaustpipar. Clausidiwm, Kossmann. Family Corycarrpan,
Corycaeus, Dana (Fig. 47); Copilia, Dana; Sapphirina, J. V. Thompson.
Family ONcaEIDAE. Oncaea, Philippi. Family Lichomoneipan. Licho-
molgus, Thorell. Family Ercastuipar. Ergasilus, Nordmann. Family
Bomotocnuiwak. Bomolochus, Nordmann. Family Crausipar. Clausia,
Claparede. Family Neretcontmpar. Nereicola, Keferstein.

TRIBE 2, AMPHARTHRANDRIA, Giesbrecht.

Swimming forms, with both antennules geniculate in male, generally
differently segmented in the two sexes, and parasitic forms allied to these.

Family MisopHrupar. Misophria, Boeck. Family HaRpacticIDAk.
This extensive group corresponds rather to an assemblage of families (ef.
Sars) : — Harpacticus, Milne-Edwards ; Longipedia, Claus; Cervinia,
Norman ; Ectinosoma, Boeck ; Peltidium, Philippi; Tegastes, Norman ;
Porcellidium, Claus; Idya, Philippi; Thalestris, Claus ; Miosaccus,
Boeck ; Canthocamptus, Westwood ; Belisarius, Maupas; Laophonte,
Philippi ; Setella, Dana; Miracia, Dana ; Aegisthus, Giesbrecht ; Clytem-
nestra, Dana. Family Cyciopipar. Cyclops, Miiller ; Oithona, Baird.
Family Monstrinuipan. Monstrilla, Dana ; Haemocera, Malaquin (Fig.
53). Family Ascrpiconipar. Ascidicola, Thorell : Notodelphys, Allman ,
Doropygus, Thorell ; Notopterophorus, Costa ; Enterognathus, Giesbrecht
(Fig. 50). Family AsTEROCHERIDAR. Asterocheres, Boeck; Acontio-
phorus, Brady (Fig. 44); Cancerilla, Dalyell; Scottocheres, Giesbrecht ;
Artrotrogus, Boeck (Fig. 46). Family Nrcornorar. Nicothoé, Audouin.
Family DicueLestipar. Dichelestivm, Hermann; Lernanthropus,
Nordmann.

The position of the remaining families (consisting wholly of parasitic
forms) with respect to this system of classification is not yet determined.
The groups most usually accepted are :—

Family Canierpar. Caliqus, Miiller. Family LERNAEIDAR. Lernaea,
Linn. (Figs. 51, 52); Pennella, Oken; Lernaeocera, Blainyille. Family
LERNAEOPODIDAR. Lernaeopoda, Kroyer; Achtheres, Nordmann (Fig.
45). Family CHonpracanratpar. Chondracanthus, La Roche. Family

104

THE CRUSTACEA

CHONIOSTOMATIDAE. Choniostoma, Hansen. Family HErRpPYLLOBIIDAE.
Herpyllobius, Steenstrup and Liitken ; Rhizorhina, Hansen.

OrDER 2. Branchiura, Thorell (1864).

Paired compound eyes present; genital apertures on fifth trunk-

somite ; thoracic limbs sometimes with flagellum ; no spermatophores.

Family Ara@uLIpAE. Argulus, O. F. Miller (Fig. 54); Dolops,

Audouin ; Chonopeltis, Thiele.

LITERATURE.

1. Brady, G. S. A Monograph of the Free and Semiparasitic Copepoda of the
British Islands. Ray Society, 3 vols. 8vo, 1878-1880.
2. —— Report on the Copepoda. Rep. Voy. ‘‘Challenger.”” Zool. viii. pp.
142, 55 pls., 1883.
3. Canu, E. Les Copépodes du Boulonnais. Trav. du Lab. de Wimereux, vi.
pp. 292, 30 pls., 1892.
4, Claus, C. Ueber den Bau und die Entwicklungsgeschichte parasitischer
Crustaceen, pp. 34, 2 pls. 4to. Cassel, 1858.
5. Ueber den Bau und die Entwicklung von Achtheres percarwin.
Zeitschr. wiss. Zool. xi. pp. 287-308, pls. xxiii. and xxiv., 1861.
6. Die freilebenden Copepoden. pp. x+230, 37 pls. 4to. Leipzig,
1863.
le Beobachtungen iiber Lernaeocera, Peniculus, und Lernaea. Schrift.
Ges. Naturw. Marburg, ii. pp. vi+32, 4 pls., 1868.
8. Ueber die Entwicklung, Organisation und systematische Stellung der
Arguliden. Zeitschr. wiss. Zool. xxv. pp. 217-284, pls. xiv.-xvili., 1875.
9, —— Ueber Lernacascus nematoxys, Cls., und die Familie der Philichthyden.
Arb. zool. Inst. Wien, vii. pp. 281-315, 4 pls., 1887.
10. —— Ueber die Maxillarfiisse der Copepoden und die morphologischen
Deutung der Cirripedien-Gliedmassen. Arb. zool. Inst. Wien, xi. pp. 49-
64, 1 pl., 1895.
11. Giesbrecht, W. Pelagische Copepoden. Fauna und Flora d. Golfes von
Neapel. Monogr. xix., 1892.
12. —— Asterocheriden. Op. cit. Monogr. xxv., 1899.
13. —— Mittheilungen iiber Copepoden. (14 papers.) Mitth. zool. Stat.
Neapel, xi.-xiv., 1893-1900.
14, and Schmeil, O. Copepoda Gymnoplea. Das Tierreich, Lief. 6, 1898.
15. Grobben, C. Die Entwickelungsgeschichte der Cetochilus septentrionalis.
Arb. zool. Inst. Wien. iii. pp. 243-282, 4 pls., 1881.
16. Hansen, H. J. The Choniostomatidae. 205 pp. 13 pls. 4to. Copenhagen,
1897.
17. Hartog, M. The Morphology of Cyclops and the Relations of the Copepoda.
Trans. Linn. Soc. Zool. v. pp. 1-46, pls. i.-iv., 1888.
18. Malaquin, A. Le parasitisme évolutif des Monstrillides (Crustacés copé-
podes), Arch. Zool. exp. (3) ix. pp. 81-232, pls. i.-vil., 1901.
19. Nettovich, L. v. Neue Beitrage zur Kenntniss der Areuliden. Arb. zool.
Inst. Wien, xiii. pp. 1-32, 2 pls., 1900.
20. Nordmann, A. v. Mikrographische Beitrage zur Naturgeschichte der

wirbellosen Thiere, Heft 2, 4to, Berlin, 1832.

21.

26.

THE COPEPODA 105

Sars, G. O. An Account of the Crustacea of Norway. IV. Copepoda
Calanoida, 1901-1903. V. Copepoda Harpacticoida, 1903—(in progress).

. Schmeil, O. Deutschlands freilebende Siisswasser-Copepoden. Bibliotheca

Zoologica, iv. Heft 11, 1892; v. Heft 15, 1894; vii. Heft 21, 1896-
1898.

3. Steenstrup, J. J. S., and Liitken, C. F. Bidrag til Kundskab om det aabne

Havs Snyltekrebs . . . Kgl. Danske Vidensk. Selsk. Skrifter, (5) v. pp.
341-432, pls. i.-xv., 1861.

. Thiele, J. Beitraige zur Morphologie der Arguliden. Mitt. Mus. Naturkunde,

Berlin, ii. (4), pp. 1-51, pls. vi.-ix., 1904.

Wilson, C. BL. North American Parasitic Copepods of the Family Argulidae,
with a bibliography of the group and a systematic review of all known
species. Proc. U.S. Nat. Mus. xxv. pp. 635-742, pls. vili.-xxvii., 1902.
A New Species of Argulus. . . . Op. cit. xxvii. pp. 627-655, 1904.

North American Parasitic Copepods belonging to the Family Caligidae.

Pt. I. The Caliginae. Proc. U.S. Nat. Mus. xxviii. pp. 479-672, pls.

v.-xxix., 1905. Pt. IJ. The Trebinae and Euryphorinae. Op. cit. xxxi.

pp. 669-720, pls. xv.-xx., 1907. Pts. III. and IV. A Revision of the

Pandarinae and the Cecropinae. Op. cit. xxxiii. pp. 323-490, pls.

XVli.-xliii., 1907.

CHAPTER V
THE CIRRIPEDIA

Sus-CLAss CirriPpeDiA, Burmeister (1834).

Order 1. Thoracica.
Sub-Order 1. Pedunculata.
3s 2. Operculata.
Tribe 1. Asymmetrica.
5 2. Symmetrica.
, 2. Acrothoracica.
, ». Ascothoracica.
» 4. Apoda.
», 0. Rhizocephala.

Definition.—Crustacea which are sessile in the adult condition; the
carapace (very rarely absent) forms a mantle completely enclosing
the body and limbs, usually strengthened by shelly plates; the
posterior limbless part of the trunk is vestigial and usually ends in
a caudal furea ; the antennules are organs of attachment, becoming
vestigial in the adult, and the antennae generally disappear ; man-
dibles without palp ; typically six pairs of biramous cirriform trunk-
limbs ; usually hermaphrodite, female genital apertures on first
trunk-somite, male apertures behind last pair of limbs; paired eyes
absent in adult ; development with metamorphosis ; young generally
hatched in nauplius stage and passing through a so-called “ cypris
stage” with bivalved shell.

Historicul.—Some of the Cirripedia are sufficiently common and
conspicuous to have attracted attention from remote times. They
are probably referred to by Aristotle, and they formed the subject
of a curiously persistent mediaeval myth, current in literature from
the twelfth to the beginning of the eighteenth century, regarding
the origin of the Barnacle Goose. While the earlier systematists
not unnaturally classed the barnacles and acorn-shells as Mollusca,
it seems strange to find this view of their affinities surviving the

106

naa,

THE CIRRIPEDIA 107

anatomical investigations of Cuvier. Lamarck, who was the first
to give them the name “ Cirrhipédes ” (later corrected by Burmeister
to Cirripedia), referred more or less vaguely to their affinities with
Crustacea, as did also Oken and others, without definitely removing
them from the Mollusca.

It was not until J. Vaughan Thompson, in 1830, described the
development of Balanus from the “ Cypris” larva that the Crustacean
nature of the group was placed beyond dispute. A little later
Burmeister (1834) and Thompson himself (1835) completed the out-
line of the life-history by discovering the earlier nauplius stage,
confirming the long-forgotten observations of Slabber, who had
figured the nauplius of Lepas as early as 1767. Although notable
contributions to the anatomy of the group were made by Martin
Saint-Ange (1835) and others, its taxonomy remained in the hands
of conchologists, and new genera and species were established on
the superficial characters of the shell alone. It is curious to note,
as a survival of this period, that so recently as 1906 it was thought
necessary to include a chapter on Cirripedes in a conchological
work. Darwin’s Monograph of the Cirripedia (1851-54) placed
the study of the group upon a new basis, and indeed still remains
the chief work of reference on the subject. The discovery of the |
“complemental males” and of the remarkable genera Cryptophialus
and Proteolepas (the latter not since re-observed) are due to Darwin,
while his systematic treatment of the normal Cirripedia (Thoracica)
has scarcely been modified by subsequent workers, except as regards
the addition of new species, for the most part from the deep sea.
Some anatomical errors in Darwin’s work were soon after corrected
by Krohn (1859). J. V. Thompson had already in 1836 pointed
out the resemblance of the nauplius larva of Sacculina to that of the
Cirripedia, and Lilljeborg (1859-60) established for that genus and
its allies the group of “ Cirripedia Suctoria,” and showed that they
passed through a “Cypris” stage. Fritz Miiller (1862-63) gave a
more detailed account of the anatomy and larval stages of this group,
to which he gave the name Rhizocephala. Delage, in a remarkable
memoir (1884), made known, for the first time, the complete life-
history of Sacculina, and his results, though received with scepticism
by some, have recently been confirmed by G. Smith (1906). The
group of Ascothoracica was established by Lacaze-Duthiers (1883)
for the very remarkable genus Laura, and other genera have been
added by Norman, Fowler (1889), Knipowitsch, and others. Among
the more important contributions to the study of the normal Cirri-
pedes may be mentioned the works of Hoek on the “Challenger”
collections (1883-84), Aurivillius (1892-95), and Gruvel (1904),
and on the larval stages those of Claus (1869), Groom (1895), and
Hansen (1899)

108 LHE CRUSTACEA

MORPHOLOGY OF THORACICA AND ACROTHORACICA.

In general form and in many details of structure the Cirripedia
as a whole depart more widely from the common type than do any
of the other sub-classes of the Crustacea. This is correlated with
the sessile habit of life which is universal within the group.
In those forms which have become purely parasitic, as in the
orders Ascothoracica, Apoda, and Rhizocephala, the modifications
are still more profound, leading, in the last-named order, to the
- disappearance of every trace of Arthropod organisation. Neverthe-
less, the life-history and even the minute characters of the larvae
are so constant throughout the group that it is impossible to
question the close relationship of the various forms.

Fie. 57.

A, Lepas anatifera; B, Balanus hameri. (After Darwin.) c¢, carina; ¢./, carino-lateral ; J,
Jateral ; p, peduncle ; r+r.l, rostrum coalesced with rostro-lateral ; se, seutum ; ¢, tergum.

Leaving aside for the present the parasitic orders named above,
the remaining Cirripedia, forming the orders Thoracica and Acro-
thoracica (Abdominalia of Darwin), show considerable uniformity
of structure, though differing widely in general appearance. In all
cases, the animal is attached to some foreign object by the anterior
portion of the body in the region of the antennules. The shell-
fold is greatly developed, forming a “mantle” enclosing the body
and limbs, and strengthened, as a rule, by shelly plates on its outer
surface. Owing to a strongly marked dorsal flexure of the preoral
region, the greater part of the body within the mantle comes to lie
nearly at right angles to the anterior part. The anterior part of
the cephalic region may be elongated into a flexible and muscular
peduncle (Fig. 57, p), as in the Pedunculata, or represented only by

THE CIRRIPEDIA 109

a flattened disc of attachment, as in the Operculata and Acrothoracica.
When a peduncle is present, the rest of the body enclosed by the
mantle is distinguished as the capitulum.

On account of the confusion which would arise from applying
the usual terms of orienta-
tion to animals of such com- A B
plex form, it is customary, C R
in describing Cirripedia, to x ve
employ an arbitrary termin-
ology in which the animal
is supposed to be placed
vertically with the capitulum
above, and the peduncle or
base of attachment below.
What is, morphologically, Cols, aie R.L.
the sternal aspect of the
peduncle and the anterior Turrilepas Wrightii. A, view of the whole fossil.
side of the capitulum is called B, a portion) further enlarged. C, carinal scales ;

a C.L, carino-Jateral; L, lateral; &.L, rostro-lateral ;
the “rostral, the opposite pR, rostral. (From Gruvel’s Monographie.)
being the “ carinal ” side.

The number and arrangement of the calcareous plates on the
outer surface of the body afford valuable systematic characters,
throwing light on the phylogenetic history of the group. It seems
probable that in the most
primitive Cirripedia there
was no distinction of capit-
ulum and peduncle, the
whole body being en-
veloped by a_ mantle,
probably bivalved, and
strengthened with shelly
plates. Such a form is
perhaps represented by
the fossil Turrilepas (Fig.
58) from Silurian and
Devonian rocks, in which
the whole animal appears

Fic. 59. to be covered with im-
mamas Pilea © carpal scaen: CZs cure bricating scales arranged
The capitular plates are not correctly shown. (From in transverse rows of five
Gruvel’s Monographie.) :

on each side. The genus
Loricula (Fig. 59), appearing in the Lower Cretaceous, has been
supposed to represent the next stage of evolution, showing the
beginning of the differentiation between peduncular and capitular
plates. In the peduncular region the arrangement of the plates
is the same as in Turrilepas. At one end of the animal, several

Fic. 58.

OD. Ee RAL.

110 LAERVCRUSTACEA

plates of the terminal row on each side are much enlarged and
represent the capitular plates. Much older than Loricula, however,
and probably much more primitive, is the still-existing genus
Pollicipes, which dates back to the Silurian, possibly to the
Ordovician epoch. In Pollicipes the peduncle is covered with small
scale-like plates which increase in size towards the capitular end,
and in some cases (P. sertus (Fig. 60)) show a complete gradation
of size and arrangement up to the capitular plates themselves.
The latter consist of unpaired rostrum and carina, with paired terga
and scufa, with a varying number of lateral plates, forming a
transition to the scales of the peduncle.

From the type of Pollicipes two lines of modification may be

BN AA ra a\l
Fic. 60.

Pollicipes sertus, showing Fic. 61.
transition from peduncular Scalpellwm stearnsti, X 3.
seales to capitular plates. (After Stebbing, from Mn-
(From Gruvel’s Monographie.) cyel. Brit.)

traced. On the one hand, in the group Pedunculata, we find the
scales of the peduncle becoming horny and disappearing, while
the capitular plates diminish in number as we pass from
Scalpellum (Fig. 61), through forms like Lepas (Fig. 57, A) and
Dichelaspis, to Alepas and Anelasma, where the mantle is entirely
membranous.
On the other hand, the Operculata may be supposed to have
originated from a form resembling ollicipes, or intermediate
between it and Loricula. The peduncle has disappeared, but the
whorl of plates immediately below the capitular valves have
persisted, and, together with the rostrum and carina, have become
united to form the outer ‘‘ wall” of tubular or conical form, within
the opening of which the scuta and terga are articulated to form
the movable operculum. The most primitive genus among the

THE CIRRIPEDIA 111

Operculata is apparently Catophragmus (Figs. 62, 63), where the
“wall” consists of eight pieces (or “compartments,” as Darwin
termed them), the unpaired rostrum and carina, and the paired
lateral, rostro-lateral, and carino-lateral plates, and is further
surrounded by several whorls of imbricating scales diminishing
in size towards the periphery, and representing the armature of
the vanished peduncle. In the other Operculata these scales are
wanting, and a series can be traced in which the compartments
diminish successively in number by coalescence, from Octomeris,
which has eight plates, through Lalanus (Fig. 57, B) with six, and
Elminius with four, to Pyr-
goma, where all the plates
have coalesced and_ the
“wall” is undivided. Each
compartment presents three

1s

io,

Ae

Sar

Fic. 62. Diagram showing the constitu-

Catophragmus polymerus. The upper tion of the *‘ wall” in Catophragmus.

figure represents the entire shell viewed The eight principal compartments

from above. S, scutum; 7’, tergum, are surrounded by several whorls

separated and further enlarged. (From of scales. (From Gruvel’s Mono-
Gruvel’s Monographie.) qraphie.)

divisions, a central paries flanked by two lateral portions known as
radii or alae according as they overlap or are overlapped by the
adjacent compartments. The exact manner in which the over-
lapping takes place varies in the different genera and affords a
basis for systematic divisions. Thus Darwin divided his Balanidae
into two sub-families: (1) the Chthamalinae, in which the rostrum
has alae on both sides, or, in other words, is overlapped by the
adjacent compartments; and (2) the Balaninae, in which the
apparent rostrum is really formed by the fusion of the rostrum
with the rostro-lateral compartments (Fig. 57, B, 7+7/), and con-
sequently has radii overlapping its neighbours on both sides. By
some recent writers the arrangement of the plates is interpreted
somewhat differently, and, though its phylogenetic importance is
recognised, the classification adopted is made to rest upon the
number of compartments distinct in the adult.

riz TAENCROUSTAGEA

Generally included with the Operculata, though possibly deserving
to rank as a separate sub-order, is the curious little group of Asym-
metrica, comprising the single genus Verruca. These are sessile,
like the true Operculata, and have the shell composed of a wall
and closed by a movable operculum. But the operculum consists
of the scutum and tergum of one side only, those of the other side
being fused to form one-half of the wall, which is completed, on
the side of the movable opercular plates, by the greatly developed
and displaced rostrum and carina.

Fic. 64.

Diagrammatic vertical section of Balanus. The cirri are cut short. A, anus; ant,
antennule; B, mouth; C, carina; c, cerebral ganglion; cap, lamellae of the ‘* wall”;
ci, cirri; ¢.p, parietal canal; c.pal, mantle-cavity; c.r, radial canal of the base; c.t,
testicular caeca; H, stomach ; gl.ce, cement-glands ; 7, intestine; inf, ‘‘ infundibulum” (con-
taining a prolongation of the mantle); /.ext, external lamina of the wall; m.a.s, adductor
scutorum muscle; m.d.s, depressor scuti muscle; m.d.t, depressor tergi muscle; 7, ventral
nerve-mass ; 0, opening of mantle-cavity ; ov, ovary; p, penis; R&R, rostrum; S, scutum ; s.oe,
egg-mass in mantle-cavity ; s.ro, rostral blood-sinus ; 7, tergum; v.s, seminal vesicle. (From
Gruvel’s Monographie.)

In the Pedunculata the shell is formed of simple calcified plates,
increasing in thickness by the application of successive layers on
the inner surface, while the uncalcified cuticle between them scales
off periodically to admit of growth, with the formation of a new
cuticle underneath. In the simpler Operculata (Chthamalus), the
compartments forming the wall are of this nature, but in most of
the genera composing this group they have a more complex
structure, being traversed by canals running parallel with the
surface and containing prolongations of the hypodermis (Fig. 64,
cp and inf). The complexity of the shell reaches its maximum
in the genus Coronula, the species of which attach themselves to
the skin of whales. In these, the folding of the wall gives rise to

~

TE CIRRIPE DTA 113

chambers on the inner and outer surfaces, receiving respectively
branches of the ovaries of the Cirripede and prolongations of the
epidermal tissue of the host.

The base of the shell in the Operculata may be simple and
membranous or it may become calcified, and in the latter case it
may be traversed by radial canals (Fig. 64, cr) carrying prolonga-
tions of the hypodermis.

In Xenobalanus (Figs. 65, 66) among the Operculata the wall is
reduced to a small vestige and the opercular plates are absent.
The mantle-sac is elongated and appears as if divided into capitular
and peduncular portions, giving the
animal an extraordinarily close re-
semblance to certain Pedunculata such
as Alepas.

It may be mentioned here that in
the Pedunculate Anelasma, which is
parasitic on sharks, the peduncle
becomes imbedded in the muscles of

Cc
CL+l
R
Fic. 65, Fic. 66.
Xenobalonus qlobicipitis. Diagram of the reduced “wall” of Xeno-
B, the reduced “wall”: Dp; balanus. Cy, carina; CLL+D, carino-lateral
penis. (From Gruvel’s Mono- fused with lateral; R.L, rostro-lateral ; R,
yraphie.) rostrum. (From Gruvel’s Monographie.)

the host and gives off minute ramifying filaments which no doubt
serve for the absorption of nutriment.

The body, enclosed within the mantle, consists of a cephalic
region (“prosoma” of Darwin), followed by a “thoracic” region
corresponding to the somites bearing the six pairs of cirri. These
somites are usually indistinctly defined in the membranous integu-
ment and the first is always coalesced with the head. There is no
distinct “abdomen” in the adult except in so far as it is repre-
sented by the caudal furca which is present in most Pedunculata
and afew Operculata. The furcal rami are usually small, unjointed
or with few segments. Exceptionally they may be long and multi-
articulate.

Appendages.—The antennules, which serve for attachment in the
larva, usually persist in a functionless condition imbedded in the
cement which fastens the end of the peduncle or the base of the

§

II4 DAE NCGS RAGBA

shell to the substratum (Fig. 64, ant, Fig. 67, 4’). They appear,
however, to be absent in the Acrothoracica.

The antennae disappear in the adult in all normal Cirripedia.
Their possible persistence in the Ascothoracica will be referred to
later.

The mouth-parts consist of simply formed mandibles, maxillulae,
and mazillae, the last united at the base to form a lower lip. The
upper lip is large, often bullate, and at the sides, between it and
the mandibles, are a pair of setose
lobes which have been sometimes in-
terpreted as lateral lobes of the labrum,
but which seem undoubtedly to be the
mandibular palps.

The appendages of the ‘“ thoracic ”
region, of which there are normally
six pairs, form the characteristic ‘‘cirri”
from which the name of the order is
derived (Fig. 67, Cf). Each consists of
a two-segmented protopodite bearing
two long multiarticulate rami, the seg-
ments of which are fringed with long
hairs forming, when the cirri are pro-
truded from the orifice of the shell, a
“casting-net ” for the capture of prey.
The cirri increase in length and in the
number of segments in the rami from
before backwards, and the number of
segments also increases with the age
of the animal. The first pair are com-

Weetey monly, at least in the Pedunculata,
Dissection of Lepas from the side. Separated by a little space from the
A sepionnulesj7) caune | oa comen followane pairs,. and) more) iclosely

gland and duet; Cf, cirri (thoracic

appendages); L, hepatic caeca; M, associated with the mouth- parts.
adductor muscle; Od, oviduct; Ov,

ovary; P, penis; Sc, scutum; T, Further, the first two or the first
(CLA tenon deferens. three pairs are distinguished from

the posterior pairs by being shorter
and by having the segments beset with stiff spines which prob-
ably aid in the prehension of food. In the parasitic Anelasma the
cirri are short, obscurely segmented, and quite devoid of setae
(Fig. 68).

In the Acrothoracica the cirri are reduced in number by the
disappearance of the second and sometimes also of the third pair,
and the first is separated by a wide space from the remaining pairs,
which are crowded together at the posterior end of the body. The
first pair are reduced to small papillae in Cryptophialus, but in the

remaining genera they are closely approximated to the mouth-parts,

THE CIRRIPEDIA 115

and have two unsegmented rami. In Alcippe the last three pairs
of cirri are uniramous.

In many Pedunculata a membranous process (“ filamentary
appendage,” Darwin) grows out from the side of the body just
below the origin of the first cirrus. In Conchoderma similar
appendages are also attached to the peduncles of some of the
cirri, and in that genus and in Pollicipes others spring from the
sides of the prosoma. These processes may be occupied internally
by diverticula of the testes. In many Balanidae a setose plate is
produced from the outer side of the peduncle of the third pair of
cirri, and projects half-way across the dorsal surface of the body.
In Cryptophialus two pairs of filamentary processes spring from the
dorsal surface of the body. It seems possible
that some of those appendages which are attached
to the peduncles of the cirri or in the neigh-
bourhood of their articulation to the body may
be of the nature of epipodites. In many Cirri-
pedia a fold of the integument projecting into
the mantle-cavity originates on each side of the
cephalic region at the point where the mantle
joins the body. In the Pedunculata these folds,
the “ovigerous frena” of Darwin, usually serve
for the attachment of the egg-masses, and are
equipped for that purpose with knobbed spines.
In the Verrucidae they are absent, but in the
other Operculata they are represented by large
plicated membranes no doubt branchial in function.

Alimentary System.—The stomodaeum appears, Fran Ou
as a rule, to form only the narrow oesophagus, — Anetasina squalicola.
the large stomach being without a cuticular lining, One-halt of mantle re-

moved to show the
In some Acrothoracica (Cryptophialus), however, body and the reduced
b] b]

a triturating apparatus is developed from the Monaghan) Ys
inner end of the oesophagus, where it enters the

stomach, consisting of two opposed horny dises carrying teeth and
several rows of setae. The anterior part of the stomach generally
gives off a number of large “hepatic” caeca (Fig. 67, LZ), while
ramifying tubules forming the so-called “pancreatic glands” clothe
the posterior part and open into it by numerous small apertures.

In Alcippe, among the Acrothoracica, the rectum and anus are
absent, and the ramified hepatic caeca radiate from the stomach
into all parts of the body.

Circulatory System.—No heart is present in any Cirripede, and
the lacunar channels in which the blood circulates are, for the most
part, ill-defined. The most important and constant is the “rostral
sinus” (Fig. 64, so) lying on the rostral side of the adductor
scutorum muscle. It has a pair of valves at its lower end where

116 THE CROSDACEA

it communicates, in the Pedunculata, with a canal traversing
the length of the peduncle.

Excretory System.—The excretory organs of the Cirripedia have
been the subject of much discussion, and it is only recently that
their structure has been clearly ascertained. Darwin described as
“olfactory ” organs a pair of minute orifices, sometimes elevated on
tubular papillae, on the outer side of the maxillae. These were
shown by Hoek to be the openings of a pair of fine canals, which
he regarded as “segmental organs” and described as opening into
the body-cavity. This cavity has been shown by Bruntz to be the
greatly enlarged “labyrinth” of the maxillary gland, the end-sac of
which, discovered by Nussbaum, communicates with the labyrinth
by a minute aperture. ‘The end-sac is of considerable size, and
may be divided by internal partitions. In addition to these
maxillary glands, an excretory function is discharged by the hepatic
caeca and by scattered ‘‘nephrocytes,” the most important of which
are aggregated in two masses at the sides of the cephalic region.

Glands.—A very peculiar and characteristic feature in the
organisation of the normal Cirripedia is the cement apparatus by
means of which the attachment of the animals is effected. This
consists of a pair of much-ramified follicular glands connected with
a pair of ducts which open, in the later larval stages at least, on
the antennules. In the Pedunculata these glands are lodged in
the peduncle (Fig. 67, Cd), and in the Operculata in the thickness
of the basal plate (Fig. 64, gl.ce). In many Pedunculata (Lepas,
Conchoderma, etc.) the openings of the ducts on the antennules
serve throughout life for the escape of the cement, but in others
(Scalpellum, Pollicipes) numerous additional apertures are formed
on the surface of attachment. In the Operculata the glands and
their ducts ramify in a complex way over the broad base and
discharge the secretion through numerous pores. In one species
of Lepas (L. fascicularis) the cement forms, at the end of the
peduncle, a vesicular mass, serving to increase the buoyancy of the
floating colony.

In the Acrothoracica, which bore into the shells of Mollusca
and into corals, the cement-glands are much reduced and are prob-
ably functional only in early life.

Muscular System.—In the great majority of the Pedunculata
and in the Operculata a strong adductor muscle (Fig. 64, m.a.s,
Fig. 67, JZ) connects the two scuta dorsal to and in front (on the
rostral side) of the alimentary canal. When the scuta are absent
the muscle is attached on each side to the cuticle of the mantle.
In the genus Jbla an adductor scutorum is also present, but as it
crosses the body on the ventral side of the alimentary canal
between the oesophagus and the ventral nerve-mass it cannot be
regarded as homologous with the similarly named muscle of the

THE CIRRIPEDIA 117

other Pedunculata and Operculata. In the Acrothoracica (Alcippe)
also the adductor is ventral in position.

The peduncle of the Pedunculata is provided with longitudinal
and oblique muscular fibres, and some of these may extend into the
mantle, but no definite muscles other than the adductor scutorum are
connected with the valves of the shell. In the Operculata Symmetrica,
however (not in the Asymmetrica), a pair of depressor muscles are
connected with the terga and two pairs with the scuta (Fig. 64,
m.d.t, m.d.s).

Nervous System.—The ventral nerve-chain is concentrated into
a single mass, within which, however, the outlines of five pairs of
ganglia may be made out. In the Pedunculata a pair of large
nerves originating from the anterior part of the cerebral ganglia
pass down the peduncle, and may perhaps represent the antennular
nerves.

Sense-Organs.—Apart from the setae, supposed to have a sensory
function, on various parts of the external surface, and from such
doubtfully sensory structures as “ Koehler’s organ” in the pedun-
cular seales of Pollicipes, the chief organ of special sense persisting
in the adult is the nauplius-eye. This is deeply buried in the
tissues of the body, on the dorsal surface of the stomach, and may
be single (Pedunculata), or divided into two parts (Operculata).
In Lepas it consists of two pigment-cups, each containing a single (7)
cell, the inner surface of which bears a series of rodlets imbedded
in the pigment. The structure of the paired eyes in the Operculata
is not fully known, but it seems probable that they correspond to
the two halves of the Lepadid eye separated, and not to the
paired compound eyes of the Cypris larva.

veproductive System.—The great majority of the Cirripedia are
hermaphrodite, and cross fertilisation is rendered possible by their
gregarious habits.

The ovaries in the Pedunculata are lodged in the peduncle
(Fig. 67, Ov), sometimes invading the mantle (Conchoderma), and in
the Operculata they occupy the basal and, when fully developed,
also the parietal portions of the mantle (Fig. 64, ov). The paired
oviducts traverse the prosoma and open to the exterior at or near
the base of the first pair of cirri. Just before reaching the exterior
each oviduct expands to form a genital atrium (described by
Darwin as an “acoustic organ”), with glandular walls within
which is secreted a sac or sheath for the reception of the eggs.
The extruded eggs contained in these sacs form the “ovigerous
lamellae” frequently found within the mantle-cavity, where they
are retained until hatching takes place.

The festes lie for the most part in the prosoma (Fig. 64, ct,
Fig. 67, 7’), extending, however, into the thoracic region and even
into the filamentary appendages and the bases of the cirri.

118 THE CRUSTACEA

Each vas deferens expands in the thoracic region to form a seminal
vesicle (Fig. 64, v.s). The two vasa deferentia unite after entering
the long thread-like penis (Figs. 64, p, and 67, P) which arises at
the posterior end of the body on the ventral side of the anus. The
penis can he protruded from the opening of the shell to deposit
spermatozoa within the mantle-cavity of an adjacent individual,
but probably self-fertilisation may occur in isolated individuals.
The spermatozoa are filiform and motile.

Dwarf Males.—In the Operculata and in the great majority of
the Pedunculata all the individuals of a species are similar and
hermaphrodite, but in two genera of Pedunculata, Scalpellum and

Fic. 69.
Dwarf males of—A, Scalpelluwm peronii; B, S. gigas; C, S. velutinum. Cn, vestige of mantle-

cavity ; E, stomach; Gil.c, cement-gland; S, scutum; 7, tergum; Te testis Vs seminal
vesicle. (From Gruvel’s Monographie.)

Ibla, dwarf male individuals occur. These are attached within the
mantle-cavity of the large individuals, which may be either herma-
phrodites of the usual type, or, in some cases, purely females. In
the former case the males which are paired with hermaphrodite
individuals present a type of sexual relations not definitely known
to occur elsewhere in the animal kingdom except among the
Myzostomida, and were termed by Darwin “ complemental males.”

As regards their structure, the dwarf males show great differ-
ences even in closely allied species of the same genus. In one
group of species, including Scalpellum peronii, S. villosum, etc., the
male is an almost perfect miniature of the large hermaphrodite
to which it is attached (Fig. 69, A). The peduncle is distinct,
though short, and the capitular plates are well developed. The

THE CIRRIPEDIA 119

mouth-parts are normal, and the cirri are all present, but are composed
of a restricted number of segments. The alimentary canal is com-
plete, and in some cases even vestiges of the ovaries have been
found. Ina second group, comprising S. vulgare, S. gigas, ete., the
peduncle and capitulum are no
longer distinct, and the capitular
plates are vestigial (Fig. 69, B).
The mantle-cavity is greatly
reduced, and the cirri are re-
presented by six pairs of unseg-
mented processes each carrying
two or three long setae. The
gut ends blindly. In a third
group of species, represented by
S. stromiu, S. velutinwm, ete., the
capitular plates have entirely
disappeared and the structure is
still further degenerate (Fig. 69,
C). ‘It is among the species of
the third group that complete
separation of the sexes occurs,
the large individuals being quite
devoid of male organs.

The degree of degeneration
exhibited by the males appears
to be correlated, to some extent,
with their place of attachment to
the female or hermaphrodite in-
dividuals. | The less - modified
males are lodged in fossettes in
the margin of the mantle, while
in those species where the modi-
fication is more profound the
males are attached within the
mantle-cavity below or behind
the adductor muscle. 3 : A, dwarf male of Ibla quadrivalvis. Ce

In Jhbla the male (Fig. 70) IS duct of cement-gland ; C./, terminal part of
modified in a manner somewhat stomachs Go rainy On ony ale
different from that observed in ©,*®: Sub-oesophageal ganglion; 0, eye ;

z (i, oesophagus; R, rectum; Te, testis; V.s,
Scalpellum. The peduncle is long seminal vesicle; ¢, cirrus of last pair. B,
a ‘, posterior end of body with caudal furea.
and the mantle is greatly reduced (From Gruvel’s Monographie.)
and does not enclose the body.
The mouth-parts are normal, but there are only two pairs of uni-
ramous cirri. The alimentary canal is complete. The penis is
short, in correlation probably with the length and flexibility of the

peduncle and also with the place of attachment of the males,

Fig. 70.

120 THE CRUSTACEA

which are lodged quite inside the pallial cavity, on the dorsal side
of the body. Of the two species composing the
genus Jbla, one, I. quadrwvaivis, has hermaphrodite
individuals (Fig. 71) with complemental males,
while the other, J. cwmingit, has the sexes separate.
The males of the Acrothoracica (Fig. 72) are
still further modified. The appendages and _ali-
mentary canal are quite wanting and the mantle
forms merely a sheath for the greatly developed
penis, which, in <Alcippe, can extend to three or
four times the length of the body. These an-
enterous males must of necessity be short-lived,
and in addition to the two to fourteen males which
are attached to the mantle margin of a single
female, there will often be found the remains of
Fic. 71. the adhering antennules of several others which
Thlaiquadrivalvis. have attached themselves and died since the last
(From Gruvel’s
Monographie.) moult of the female.
There can be but little doubt that herma-
phroditism is the primitive condition among the Cirripedia, though

Fic. 72.

Dwarf male of Alcippe lampas. An, antennules ; C.def, vas deferens ; C.p, canal of the penis
(vestige of mantle-cavity); G,, Go, nerve-ganglia ; mus, retractor muscles of the penis; p,
penis ; pi, pigment; Tes, testis; t.c, connective tissue; V.s, seminal vesicle. (After Berndt,
from Gruvel’s Monographie.)

THE CERRIPEDIA 121

the reverse is probably the case with regard to the class Crustacea
as a whole. It has been held by some authorities that the dioecious
state is the more primitive in the Cirripedia also, and the attempt
has been made to show that the more degraded types of the dwarf
males resemble in their structure the Cypris larva, which is supposed
to represent the ancestral form of the Cirripedes before the assump-
tion of the sedentary habit. As a matter of fact, however, the
points of resemblance between these males and the Cypris larva
are very slight. Such characters as the incomplete alimentary
canal and the reduced cirri show that these males are not primitive
but degenerate forms, and that a phylogenetically older stage is
represented by species like S. peronii, in which the males resemble
the hermaphrodite individuals. It is very probable that the differ-
entiation of the sexes began among species in which, on account
of their deep-sea habitat (as in most species of Scalpellum) or
burrowing habits (as in the Acrothoracica), cross-fertilisation
between hermaphrodites was difficult. It is common, in many
species of Pedunculata, to find young individuals attached to the
peduncle of older ones, and it is but a step further to find these
younger individuals, attached in the most favourable position for
fertilisation to the mantle-margin of the others, performing only
the function of males. It is more difficult, perhaps, to imagine
why in so few cases is the separation of the sexes complete, but
possibly the retention of male organs by the large individuals may
be regarded as a precaution against a failure in the succession of
short-lived males.

DEVELOPMENT.

With a very few exceptions, the Cirripedia are hatched from
the egg in the nauplius stage, and all pass through a later larval
form, known, from the superficial likeness of its bivalved shell to
that of an Ostracod, as the Cypris stage. The nauplius (Fig. 73) has a
somewhat peculiar and characteristic structure, subject, for the most
part, to but slight modification in the different groups. The dorsal
shield is produced at the antero-lateral corners into a pair of tubular
horns, sometimes of great length. Each horn has, at its base, a
pair of unicellular glands (Fig. 73, dr) which discharge their secretion
through its open tip. The posterior end of the shield is rounded, at
least in the earlier stages, but immediately beneath it arises a long
spine directed backwards. A large process projecting downwards
and backwards from the ventral surface contains, in the later stages
of development, the rudiments of the trunk and its appendages. It
must therefore be regarded as the posterior end of the body, and
the fork which terminates it must be compared with the “caudal
furea,” although the anal opening (4) is well in front of it on the
dorsal side. The usual three pairs of limbs present the character-

122 THE CRUSTACEA

‘as ez J
f NS Silt Ly

Fig. 73.

Larval stages of Balanus. a, late nauplius stage ; 6, metanauplius, just about to pass into
the Cypris stage; A, anus; A’, antennule; A”, antenna; D, intestine; Dr, fronto-lateral
gland ; Fi-Fv, the six thoracic appendages of the Cypris stage beneath the cuticle of the meta-
nauplius; Ff, frontal filament; H, fronto-lateral horn; Mdf, mandible; Ma, maxillula; 0,
pelted Py of Cypris stage ; O’, nauplius-eye; Ol upper lip, turned forward ina, (From Claus’s
Textbook.

LHE CIRRIPEDIA 123

istic nauplius structure. In the second and third pairs the exopodite
is multiarticulate and beset with natatory setae, and the proto-
podite has masticatory hooks. The mouth is overhung by a
labrum (0/) which in its great size recalls the corresponding organ of
the Branchiopod nauplius. It contains a group of gland-cells which
open at its tip. The unpaired eye (0’) is always well developed,
and after the first stage a pair of sensory “ frontal filaments ” appear.
The later nauplius stages are characterised, especially in the Pedun-
culata, by the development of spine-like processes from the dorsal
shield and by the elongation of the caudal and posterior dorsal
spinous processes of the body. A spine which develops from
the middle of the dorsal shield was regarded by Dohrn as repre-
senting the mid-dorsal spine of the Brachyuran zoéa. Six pairs of
movable spinules are commonly developed in the later stages on
the ventral surface of the caudal process, and these have been
regarded as corresponding to the rudiments of the six pairs of
thoracic limbs. However this may be, the series of nauplius stages
is closed with a definite metanauplius stage (Fig. 73, ), in which a
rudiment of the fourth pair of appendages (maxillulae) is present.
In this stage a downward flexure of the lateral portions of the dorsal
shield is observed foreshadowing the development of a bivalve shell
which encloses the body in the succeeding Cypris stage. The six
pairs of thoracic limbs (/", /'”) can be seen developing under the
cuticle, as can also the adhesive disc of the antennules and the paired
compound eyes.

At the next moult the larva passes at once into what is known
as the Cypris stage (Fig. 74). The presence of a large bivalve shell
gives it a general resemblance to one of the Ostracoda, but it must
be noted that this resemblance does not extend to the number or
structure of the limbs nor to the internal anatomy. All the appen-
dages of the adult are present, and the larva is now essentially a
free-swimming Cirripede. The mouth is closed, and the stage was
styled by Darwin a “locomotive pupa.” The two valves of the
shell are continuous in the mid-dorsal line, and the free ventral
margins show a certain asymmetry as in many Ostracoda. An
adductor muscle in the same position as in the adult serves to bring
the valves together. Near the anterior end on the ventral margin
of each valve is a minute aperture which in some cases (Lepas
pectinata) is elevated on a blunt horn-like process. In connection
with this opening is a gland which is probably to be identified with
the gland of the fronto-lateral horn in the nauplius stage. The
antennules (Fig. 74, 1) are protruded between the valves of the
shell anteriorly. The third segment is expanded into a sucker-like
disc, on which opens the duct of the cement-gland, and which serves
for the occasional temporary attachment of the larva. The terminal
segment is attached to the side of the third, and bears besides

124 THE WCRU SLA GEA

several setae a large olfactory filament or ‘‘aesthetasc.” The
antennae are reduced to shapeless vestiges and soon disappear
entirely. The labrum becomes greatly reduced in size. The
mandibles are represented only by the gnathobasic portion, the rest
of the limb being reduced to a papilliform “palp.” The maxillulae
and maxillae are closely crowded together in nearly the position
which they occupy in the adult, and form, with the mandibles and
labrum, a prominent buccal mass. At this stage all the mouth-
parts are devoid of setae and are not functional. The six pairs of
thoracic limbs are now well developed. Each consists of a proto-
podite of two segments and two rami, each also bi-segmented,
carrying long natatory setae. The “thoracic” region of the body
is indistinctly segmented, and is followed by a small lmbless

““Pupa”’ (late Cypris stage) of Lepas pectinata. ea, carina; cd, cement-gland ; d, alimentary
canal; L, hepatic diverticulum; 0, mouth; pa, paired eye; rf, thoracic limbs, with the cirri
of the adult developing inside; sc, scutum; sm, adductor muscle; t, tergum; wa, nauplius-
eye; 1, antennule, with adhesive sucker. (After Claus, from Korschelt and Heider’s
Embryology.)

abdomen of four segments terminating in a short setose caudal
fork.

As regards the internal anatomy, the unpaired eye (wa) persists
and is accompanied by a pair of large compound eyes (pa) which
were already visible in the last metanauplius stage. Paired
diverticula from the anterior portion of the alimentary canal form the
rudiments of the digestive gland, and a rudiment of the ovary is also
visible in the anterior region. Finally, the Cypris larva becomes
permanently attached by means of the antennules, and considerable
changes go on under the cuticle in preparation for the next moult.

The most important of these changes (Fig. 75, A, B) are the
development of the long cirriform thoracic limbs of the adult, and
a concomitant change in the position of the thoracic region of the
body which comes to lie at right angles to the long axis of the

THE CIRRIPEDIA 125

shell. A deep fold of the integument (y) is formed on the ventral
surface of the preoral region. At the next moult this fold becomes
opened out, and the ventral surface posterior to it, which was at
first in contact with the surface of attachment, becomes erected at
right angles to this surface (Fig. 75, C). In this way the peculiar
form of body characteristic of the adult Cirripede is attained. In
the Pedunculata the stalk is developed by the elongation of the
preoral region of the head. The compound eyes are cast off with
the Cypris cuticle, and the rudiments of the five primary valves of
the shell (scuta, terga, and carina) are developed.

Fic. 75.

Diagram illustrating the metamorphosis of Lepas. A, Cypris stage. B, attached larva. C,
young Lepas, still surrounded by the loosened Cypris shell (s). a’, antennule; wb, abdomen ;
c, carina ; d, alimentary canal; m, mouth; 0, nauplius-eye ; pa, paired eye; rf, thoracic limbs;
8, Cypris shell; sc, seutum; t, tergum; 2, dorsal fold; y, ventral fold. (From Korschelt and
Heider’s Embryology.)

«

MORPHOLOGY OF ASCOTHORACICA.

In the Ascothoracica, all of which are parasitic in Zoantharia
or Echinoderma, the mantle may have a bivalved form (Synagoga
and Petrarca), or it may form a capacious sac (Laura, Fig. 76)
much larger than the body, with which it is connected by a
narrow neck, and having only a small opening to the exterior.
In Dendrogaster (Fig. 78) the mantle is still more developed, and
is produced into branched lobes. In Laura the mantle is covered
with stellate papillae penetrating the tissues of the host, and pre-
sumably absorptive. In all cases the mantle contains ramifications
of the enteric diverticula and portions of the gonads. The body

126 THE CRUSTACEA

in Laura (Fig. 77) is distinctly segmented into six “thoracic” and
three limbless ‘‘abdominal” somites, and ends in a caudal furea.
In Petrarca and Dendrogaster the body is unsegmented.

In the three genera just named a pair of preoral appendages are
present (Fig. 77, ant) and, except in Lawra, are armed with hooked
spines suggesting that they are organs of fixation, They differ from
the adhering antennules of the Thoracica and Acrothoracica in being
inserted, at least in Laura, at the sides of the buccal region and
more or less enveloped by the mantle. It is possible that they are
in reality the antennae, but there seems to be no definite evidence

B

Fic. 76.

Laura gerardiae. A, external view of the animal attached to a branch of the coral Gerardia
(soft tissues of coral removed). B, the mantle-sac split open showing the body in the middle.
The ramified hepatic diverticula, which are accompanied by branches of the ovary, are seen in
the mantle on each side. (After Lacaze-Duthiers, from Encycl. Brit.)

on the point. The cement-glands, so characteristic of other Cirri-
pedia, appear to be absent.

The mouth-parts are more or less reduced, but appear to be
adapted for piercing.

The thoracic appendages are biramous and articulated only in
Synagoga. In Laura they are uniramous and indistinctly segmented,
and the first pair differs from the others, being long and slender,
A similar difference is observed in Petrarca, where, however, they
are still further reduced, and in Dendrogaster they are represented
only by some indistinct papillae,

In all three genera the gut ends blindly, and the hepatic
diverticula (Fig. 76, B; Fig. 77, F), which are large, extend into
the mantle. A digastric “adductor” muscle is present on the

THE CIRRIPEDIA 127

ventral side of the alimentary canal. The nervous system is
reduced. An eye is stated to be present in Synagoga. In Lawra
the oviducts open at the base of the first pair of cirri, In the
other genera they have not been traced. Petrurca is hermaphrodite,
and the vasa deferentia open on a large penis which terminates
the body. In Laura the testes are described as lodged in the
bases of the second, third, fourth, and fifth cirri, opening to the
exterior by numerous fine ducts, but this account is open to doubt.
Dwarf males have recently been described in Dendrogaster.

Fig. 77.

Lawra gerardiae. A, body exposed by removal of one-half of the mantle. anf, antenna ;
F, hepatic diverticula; f, caudal furca; g.s, cerebral ganglion; 7, intestine; 0, opening of
mantle ; ov, ovary ; 0.2, opening of oviduct; 0. g, opening of male ducts; sac, wall of mantle.
B, one of the papillae of the mantle. fi, vascular filaments ; v, blood-vessel. (After Lacaze-
Duthiers, from Gruvel’s Monographie.) .

A nauplius larva peculiar among the Cirripedia in lacking the
fronto-lateral horns of the carapace has been observed in Laura.
In Dendrogaster the nauplius stage is suppressed and the larva
hatches as a peculiar Cypris larva (Fig. 78, C), with only five
pairs of biramous thoracic limbs, a long abdomen of five somites,
stout antennules with hooks, and a very large olfactory filament
(aesthetasc). There are no eyes, and the gut already sends a
diverticulum into each valve of the shell.

128 THE CRUSTACEA

MorpPHOLOGY OF APODA.

This order was established by Darwin for the reception of a
single species, Proteolepas bivincta, of which he found a. solitary
specimen parasitic within the mantle-cavity of a pedunculate
Cirripede, Alepas cornuta, from the West Indies. No further
specimens have been seen by later investigators.

Proteolepus (Fig. 79) is referred to the Cirripedia mainly because
it possesses adhering antennules which agree minutely with those of

SUN
OAS V
AN J\ ‘

Rie. 78.

Dendrogaster astericola. A, young specimen; B, older specimen; C, Cypris larva. a’,
antennule; ae, aesthetase; abd, abdomen; Ur, supra-oesophageal ganglion; f, caudal furea ;
m.c, mouth-cone ; p, rudiment of penis; st, stomach, sending a diverticulum into the shell-
valve ; v.2, ventral nerve-mass. (After Knipowitsch.)

normal Cirripedes. It differs most conspicuously in the absence of
any trace of a mantle and of thoracic limbs.

The body is elongated and maggot-like. It is divided into
eleven segments, but as one of the segments is in front of that
bearing the antennules, it seems clear that this segmentation does
not express the number of true somites present. The mouth-parts,
borne on the first “segment,” seem to be adapted for piercing and
sucking. ‘The labrum partly ensheathes the gnathites, of which
there appear to be two pairs, turned outwards, and serrated on the
outer margin. From the dorsal surface of the second segment

THE CIRRIPEDIA 129

proceed two ribbon-like filaments (Fig. 79, A, ant), bearing at the
tip the larval antennules, which agree in structure, as already
noticed, with the type usual among normal Cirripedes. The six
following “segments” were regarded by Darwin as thoracic and
the three remaining as abdominal. All of them are devoid of
any trace of appendages.

The alimentary canal is greatly reduced. According to Darwin,
only the oesophagus is present, and there is no trace of stomach,
rectum, or anus. The ovaries lie at the sides of the anterior part
of the body and the testes posteriorly. The vasa deferentia unite
to open at the tip of the abdomen. There is no penis.

md.

rns
SD

Sins al

Fia. 79.

Proteolepus bivincta. A, the entire animal; ant, antennules; B, buccal cone; gl.ce, cement-
gland; p.p, penial papilla; tes, testis; v.s, seminal vesicle. B, diagrammatic plan of mouth-
parts ; /.s, upper lip; md, mandible ; mz, maxillula; mz’, maxilla. C, mandible and maxillula
separated ; m, muscle. (After Darwin, from Gruvel’s Monographie.)

While Darwin was unable to investigate the development of
the species, Hansen has recently conjecturally referred to the
Apoda certain nauplius larvae obtained in various parts of the
Atlantic Ocean and the Baltic, while more recently similar larvae
have been found in the Adriatic Sea. In late nauplius stages of
this type rudiments of paired compound eyes and of six pairs of
thoracic limbs are visible, so that it can hardly be doubted that
they belong to some form of Cirripede. On the other hand, they
differ markedly in the absence of antero-lateral horns and of frontal
filaments, in the shape of the body, and especially of the strongly
developed dorsal shield, and in other characters from the known
Cirripede larvae, which, as already indicated, show great uniformity

9

130 THE CRUSTACEA

of structure throughout the group. After a careful discussion of
all their characters, Hansen considers that they must in all’ proba-
bility belong to the Apoda, and he considers that the material
examined by him includes at least ten species.

MorRPHOLOGY OF RHIZOCEPHALA.

The Rhizocephala are an exclusively parasitic group, nearly
all infesting Decapod Crustacea, and are distinguished from the
normal Cirripedes by the complete loss in the adult state of all

Fie. 80.

A, Saceulina carcini in position on the detached abdomen of the crab ; one side of the mantle
has been removed. int, intestine of the host, surrounded by the roots of the parasite; m,
mantle ; mes, mesentery ; 0, opening of mantle-cavity ; ov, egg-masses in mantle-cavity ; p}
peduncle; v.m, visceral mass; ?, opening of genital atrium; the outline of the colleteric
gland is seen surrounding it. The outline of the testis is seen above, a little to the left of the
peduncle. B, vertical section of Sacculina at right angles to the plane of the mesentery
(semi-diagrammatic) ; at, genital atrium; g, nerve-ganglion ; gl, colleteric gland opening into
genital atrium ; ovy, ovary ; 7, absorptive roots ; t, testis ; other letters asin A. (After Delage.)

traces of segmentation and of appendages, and (excluding for the
present the doubtful Sphaerothylacus) by the absence at all stages of
life of an alimentary canal.

The body (Fig. 80, A) has the form of a simple sac attached
by a short peduncle, from which root-like processes ramify through-
out the body of the host. These absorptive roots appear to be
absent in the aberrant genus Duplorbis. The visceral mass, or body
proper, is completely enveloped by the mantle, which has a narrow
aperture (0) capable of being closed by a sphincter muscle. In
Sylon the opening is double, and in Clistosaccus and Duplorbis the
mantle-cavity is completely closed. The mantle is attached to the

—

THE CIRRIPEDIA 131

visceral mass by a narrow mesentery (72s), near to which on each
side are the paired (more rarely unpaired) openings of the male
and female generative organs. In the different genera the external
form varies considerably, and with it the position of the mesentery
and of the genital apertures. In Peltogaster (Fig. 81, B), which
may be regarded as the most primitive form, the body has an
elongated sausage-shape, with the mantle-opening at one end, and
is attached by the peduncle about the middle of its length. The
mesentery is longitudinal on the proximal side (next the peduncle).
The genital apertures are placed on each side close to the mesentery,
the female openings being nearer the end where the opening of the
mantle is situated. Comparison with a normal Cirripede (Fig. 81,
A), especially as regards the position of the genital apertures,
suggests that the mesentery is on the dorsal side, and the mantle-

Fic. Sl.

Diagram to illustrate comparison of Rhizocephala with normal Cirripede. A, Lepas; B,
Peltogaster ; C, Saceulina. m, mantle; mes, mesentery ; n, nerve-ganglion ; 0, opening of mantle-
cavity. 6, male generative aperture; 9, female generative aperture.

opening at the anterior (or rostral) end. In Sacculina (Fig. 81, C),
which is parasitic on Brachyura, the whole body is flattened
in the plane of the mesentery, and has assumed a secondary and
superficial bilateral symmetry about a plane at right angles to
this and coinciding with the median plane of the host. The
mantle-aperture is in the middle of the distal edge, and the
mesentery has suffered a corresponding displacement, extending
from the mantle-opening to the point of attachment of the peduncle
on the side which, in the natural position, is turned towards the
right side of the host. The genital openings, except that they are
more widely separated from each other, occupy the same relative
positions as in Pellogaster. In other genera, such as Lernaeodiscus
and Triangulus, the symmetry becomes still more complicated, and
in Clistosaccus and Sylon the genital organs are unpaired.

The peduncle perforates the integument of the host and gives

132 LHe CRUSTACEA

off on the inside the absorptive roots which, in the case of Sacculina,
penetrate into all the organs of the host, with exception of the gills
and the heart, and extend to the terminal segments of the legs and
into the antennules and eye-stalks. The roots are covered by a
very delicate cuticle, beneath which is a layer of hypodermic cells,
and the interior is occupied by reticular connective tissue, only the
larger trunks having a central cavity. At the tips of the rootlets
in Sacculina the outer layers are invaginated to form a cavity known
as the “lagena.” In the genus Duplorbis, where the root-system
appears to be absent, the peduncle is hollow, its cavity communicat-
ing with the closed mantle-cavity and opening at the other end into
the body-cavity (haemocoel) of the host.

Internal Anatomy.—Apart from a single nervous ganglion (Fig.
80, B, 7) which lies close to the mesentery near the female genital
openings, the only organs present are those of the generative
system. The ovary (ovy) is divided into two much-lobed masses
united by a median portion and giving off on each side a short
oviduct, which widens into a “genital atrium” (wt) before opening
into the mantle-cavity. The walls of this atrium, as in the normal
Cirripedes, are glandular, often growing out into branched tubular
glands (gl) (“colleteric” glands) supplying the material of the
envelopes within which the eggs are packed in the mantle-cavity.
In Sacculina the egg-masses are retained in position by barbed
spines (“retinacula”) grouped on papillae on the lining membrane
of the mantle.

The testes (¢) have each the form of an elongated sac narrowing
towards a short vas deferens. The spermatozoa are filiform and
actively motile.

F. Miiller was the first to suggest that the Cypris larvae, which,
as Lilljeborg had previously observed, are often found attached
near the mantle-opening of young specimens of Peltogaster, might be
complemental males. Delage accepted this interpretation for the
larvae which he observed in the same position in Sacculina, but he
was unable to obtain them alive or to observe any trace of male
organs. At this stage the mantle-opening is still closed by a plug
of chitin, and it is difficult to see how fertilisation could be effected.
G. Smith, who has recently investigated the subject, finds that the
larvae die very soon after they become attached, without developing
further. In only one instance did he find evidence of what seemed
to be an abortive attempt of the cellular contents of the larva to
pass into the tissues of the mantle in the way in which the contents
of the larvae pass into the host in the ordinary course of develop-
ment. G. Smith believes the attachment of these larvae to be an
atavistic phenomenon; that the larvae are, in fact, vestigial male
individuals. The same observer has found in the mantle-cavity of

THE CIRRIPEDIA 133

Duplorbis what appear to be extremely degraded, but still functional
male individuals. In this genus the usual testes are absent, as they
are also in Sylon, but in the latter no male individuals have been
found, and parthenogenesis may perhaps occur.

DEVELOPMENT OF RHIZOCEPHALA.

The development has been most fully worked out in the case
of Sacculina by Delage, whose results have been confirmed and
extended by G. Smith. The larva is hatched in the form of a
nauplius (Fig. 82, A) showing a general resemblance to that of
the normal Cirripedes, but differing in having no alimentary canal.
The fronto-lateral horns are well developed and each contains a
pair of gland-cells (gl). A process on the ventral side, called by
Delage the rostrum, appears to represent the labrum, but there is
no mouth. Posteriorly the body terminates in a caudal furea,
The three pairs of limbs have the usual form, but the second and
third pairs are without the masticatory hooks found in the normal
Cirripedes. Frontal filaments (fs) are present, as is also the un-
paired eye (wa) resting on a cerebral ganglion. In the later stages
the thoracic somites and their appendages become differentiated
within the posterior part of the body, not forming a postero-
ventral process as in the normal Cirripedes.

The Cypris-stage (Fig. 82, B) agrees in all essentials with that
of the normal Cirripedes except for the absence of a mouth and
alimentary canal, and the vestigial condition of the mouth-parts.
The fronto-lateral glands (gl) open in the usual position near the
margin of the valves of the shell. The antennules consist of three
segments only, and are without any adhesive disc; the terminal
segment bears two appendages which are probably sensory and
a backwardly curved filamentous process which is stated to be the
organ of attachment. The six pairs of thoracic limbs have the
protopodite not distinctly segmented and the exopodite and en-
dopodite each composed of two segments. The abdomen (ab)
is unsegmented and terminates in a pair of furcal appendages.
The unpaired eye persists, but beyond the muscles for moving
the body and appendages no other internal organs are differentiated.
It is worthy of note that there appear to be no cement-glands in
connection with the antennules.

After a free-swimming life of three or four days, the Cypris
larva becomes attached to the host. In the case of Peltogaster,
which infests hermit-crabs, it is probable that the larva settles at or
near the spot where the adult afterwards appears on the host’s
abdomen. In Sacculina, which attacks Brachyurous crabs, however,
the place of attachment of the larva has no relation to the place of
emergence of the adult parasite, the latter being always found under

134 THE CRUSTACEA

the crab’s abdomen in a position inaccessible to the larva. As a
rule, the crab is attacked when the integument is still soft after
ecdysis, and the larvae may attach themselves at any point on the
dorsal surface of the carapace or on the limbs, at the base of one of
the large setae where the articular ring of uncalcified cuticle allows

Fig. $2.

Larval stages of Succulina carcini. A, nauplius after the first moult. B, free-swimming
Cypris-stage. C, Cypris-stage after attachment to a seta (bb) of the host. D, formation of the
Kentrogon larva. H, Kentrogon-stage, after the Cypris shell has been cast off and the ‘‘ dart”
lias been formed. F, penetration of the dart through the cuticle of the host. 1, 2, 3, the three
pairs of nauplius-limbs. I-VI, thoracic limbs. ab, abdomen; bb, seta of the host; f,fat-
globules ; f.s, frontal sense-organ ; gl, glands of the antero-lateral horns ; ov, mass of mesoderm
cells regarded by Delage as the rudiment of the ovary ; pf, ‘‘dart’”’; wa, nauplius-eye. ‘(After
Delage, from Korschelt and Heider’s Pmbryolegy.)

more easy penetration (Fig. 82, C). Only one of the antennules
is used for attachment, the filamentous process of the terminal
segment clasping the base of the hair. The whole of the thoracic
region of the larva, with its appendages and muscles, now becomes
detached and is thrown off, and later the bivalve shell is also
shed, while the contents of the anterior region of the body become

THE CIRRIPEDIA 135

retracted and enclosed in a new cuticle, remaining connected only
with the antennule which is fixed to the host (Fig. 82, D). Within
the sac thus formed, a tubular chitinous organ known as the “ dart”
becomes differentiated. At first the dart is invaginated into itself,
and in connection with it a second cuticular sac becomes separated
within the first. The larva at this stage was designated by Delage
the “Kentrogon” (Fig. 82, E). The point of the dart les within

Sections through successive stages in development of the ‘‘nucleus” of the Suaceulina
interna. am, outer layer of mantle; im, inner layer of mantle; m, mesoderm cells; 0,
aperture of invagination of perisomatic cavity, not shown in B; ov, rudiment of ovary; p,
perisomatic cavity. (After Delage, from Korschelt and Heider’s Hmbryology.) According
to G. Smith, the mantle-cavity is already established when the invagination to form the peri-
somatic cavity takes place as in A.

the fixed antennule, and when fully formed it becomes evaginated
and forces its way through the cuticle of the host (Fig. 82, F).
Through it the contents of the sac, consisting of a mass of
undifferentiated cells surrounded by an ectodermal layer, pass into
the body-cavity (haemocoel) of the crab, and become what Delage
called the Sacculina interna. Probably the mass of cells is at
first carried passively by the blood-currents of the host, but it
ultimately becomes attached to the lower surface of the intestine

136 THE CRUSTACEA

immediately behind the stomach. It now begins to send out
processes which branch to form the absorptive roots, while the
main part of the embryo grows backwards along the intestine
towards. the point at which emergence of the adult Sacculinu
takes place. A thickening near the growing border forms

Fic. 84.

Later stages in the development of Sacculina. A, Saceulina interna fully formed. B,
Sacculina externa just after emergence from the body of the host. a, genital atrium; ain,
outer layer of mantle; B, basal plate; 6, mantle-cavity ; C, central tumour; cl, opening of
mantle-cavity ; D, intestinal wall of host; dr, colleteric gland; f, opening of perisomatic
cavity ; g, nerve-ganglion ; im, inner layer of mantle; L, integument of host; ov, ovary; p,
perisomatic cavity ; pe, ectoderm of visceral mass ; £2, root-processes ; t, testis. (After Delage,
from Korschelt and Heider’s Embryology.)

the first rudiment of the organs of the adult, and is known as
the “nucleus” (Fig. 83). Within this the mantle-cavity arises by
delamination, and an outer cavity concentric with it, the ‘ peri-
somatic” cavity (p), is formed (according to G. Smith) by an in-
yagination of ectoderm. When the young Swcculina is completely
formed (Fig. 84, A) it has been carried by its backward growth
into the abdomen of the host, where it lies very close to the ventral

LE CLA PISDLA 137

integument. Its presence causes a degeneration of the muscular
and hypodermic tissues between it and the external cuticle, and
at the next moult of the crab a hole is left through which the body
of the parasite, protruding from the perisomatic sac, emerges on
the surface (Fig. 84, B). The mantle-opening is at first closed by
a plug of chitin, but in other respects the young Sacculina extern
has already the essential structure of the adult.

The development. of Peltogaster seems to follow much the same
course as that of Sacculina, except that no perisomatic cavity is
formed. In this genus also the parasite penetrates the cuticle and
reaches the exterior without any moult of the host. Very little is
known of the development in other genera of Rhizocephala. In
the genus Thompsonia the larvae are stated to reach the Cypris-
stage while still within the mantle-cavity of the parent.

APPENDIX TO RHIZOCEPHALA.

The genus Sphaerothylacus, described by Sluiter, is parasitic on
a simple Ascidian (Polycarpa), living attached by ramifying roots to
the inner wall of the branchial sac. The globular body is enclosed
in a mantle which has a small opening. There are no appendages,
but there is a complete alimentary canal with mouth and anus, the
latter near the mantle-opening. The two ovaries each consist of
two long caeca which unite to open, with those of the opposite side,
into a common atrium near the mouth, surrounded by a mass of
glandular tissue, no doubt representing the colleteric glands. The
testes are paired simple tubes, opening close to the anus. The
nauplius larvae differ from those of the true Rhizocephala in the
absence of fronto-lateral horns.

The genus Sarcotaces, Olsson, comprises two species which live
embedded in the muscles of fish. Their structure is very imper-
fectly known, but an alimentary canal is said to be present and
there are no “roots.” The nauplius larva is without fronto-lateral
horns.

The systematic position of both genera is quite obscure, and
only further investigation can determine what relation, if any, they
bear to the true Rhizocephala.

REMARKS ON Habits, ETC., OF CIRRIPEDIA.

The Cirripedia are exclusively marine, only a very few
species penetrating into brackish water. In correlation with
their sedentary habits the non-parasitic Cirripedia have
developed a peculiar method of feeding by sweeping the water
for floating particles of nutriment, with a net formed by
the tendril-like branches of the thoracic limbs. Most species

138 THE CRUSTACEA

are attached to rocks, seaweeds, etc., at the bottom, but the species
of Lepas and other genera are found on floating timber and ships’
bottoms, while in JL. fascicularis, the colonies of which gather
round small floating objects such as dead Velellae or Spirula
shells, additional buoyancy is gained by a vesicular mass of secretion
from the cement-glands. Many Operculata are found attached to
or embedded in corals, while the pedunculate Lithotrya and the
Acrothoracica burrow into corals and the shells of Mollusca.
Various species of Pedunculata and Operculata are constantly found
attached to large marine animals such as whales, turtles, and sea-
snakes, or to the limbs and gills of large Decapod Crustacea. In
the case of the operculate 7uhicinella, found on whales, the shell
becomes deeply embedded in the epidermis of the host. The
line dividing commensalism from parasitism is definitely crossed by
the pedunculate Anelasma, in which the mouth-parts and limbs are
reduced, and the peduncle, embedded in the flesh of a shark,
absorbs nourishment by ramified “roots.” From this it is but a
step to the parasitic and degenerate Rhizocephala, of which the
habits have already been indicated.

The smallest Cirripedia are found among the Acrothoracica, some
species of which are only two or three millimetres in length. Most
of the Thoracica are much larger, the bulkiest being Balanus
psittacus, of which the shell is stated to reach nine inches in height
by two or three inches in diameter. The peduncle of Lepas
anatifera may grow to 16 or 18 inches long.

PALAEONTOLOGY.

The characters and phylogenetic importance of some of the
Palaeozoic Cirripedia have already been alluded to. It may be
added that, like Pollicipes, the still existing genus Scalpellum dates
back to the Silurian, and that both are well represented in the later
Secondary rocks. Of the extinct genera, the Palaeozoic Turrilepas
and the Cretaceous Loricula, already mentioned, are the most
important. The earliest undoubted Operculate is Verruca (Asym-
metrica) from the Upper Cretaceous. Many of the existing genera
of Pedunculata and Operculata are found fossil in Tertiary
deposits.

AFFINITIES AND CLASSIFICATION.

The great structural differences separating the Cirripedia from
the other Crustacea show that they must have diverged very early
from the main line of Crustacean descent. The simple biramous
form of the trunk-limbs and their number have been regarded as
indicating an affinity with the Copepoda, but there is little else to

THE CIRRIPEDIA 139

support this view. ‘The resemblance of the bivalved shell of the
Cypris larva to that of an Ostracod extends to such characters
as the asymmetry of the valves and the presence of fronto-lateral
glands near the margins of the shell; but the rest of the organisa-
tion differs widely from that of the Ostracoda. Among the
characters which are probably significant of the isolated position
of the Cirripedia are the difference in position of the genital
apertures in the two sexes and the fact that the female openings are
placed farther forward than in any other Crustacea. The nature of
the larval development, especially the sudden transition between
the sharply contrasted nauplius and Cypris stages, indicates a
high degree of specialisation, and the structure of the adult animals
is in many respects so clearly correlated with the sessile habit and
the mode of obtaining food as to afford little help in deciphering
their phylogeny. It may be noted here that, like other groups
of sedentary organisms, the Cirripedia show a tendency to the
assumption of a superficial: radial symmetry, which becomes very
marked in the Operculata.

The Cirripedia were divided by Darwin into three orders,
Thoracica, Abdominalia, and Apoda. The order Abdominalia
contained the single genus Cryptophialus, which Darwin, misled by
a superficial segmentation of the body, supposed to possess ap-
pendages on the abdominal region. It has been shown, however,
that the appendages in question are really thoracic, and that
Cryptophialus does not differ in this respect from <Alcippe, which
Darwin (although recognising the resemblance between the two
genera) placed among “the Thoracica. In the classification of
Gruvel, adopted here, these two genera and some allied forms are
grouped together as Acrothoracica, but it is to be noted that the
differences separating this order from the Thoracica are probably
less important than those distinguishing the other orders, and
that the recently: described Koleolepas of Stebbing helps to ‘unite
the two.

The genus Proteolepas, the sole representative of the order
Apoda, is still known only from Darwin’s description of a single
specimen and its affinities are obscure. In the absence of a mantle
it differs widely from all other Cirripedia.

The Rhizocephala are plainly characterised as Cirripedia by
their larval stages, but much remains to be done in elucidating the
relationships of some of the genera at present referred provisionally
to this order. The Ascothoracica form another order, established
since the date of Darwin’s work, but many points in their morpho-
logy and development are still too imperfectly known to allow of
their systematic relations being precisely defined.

140 THE CRUSTACEA

SuB-CLASS CIRRIPEDIA.

ORDER 1. Thoracica.

A mantle present. Six pairs of cirriform trunk-appendages.

Sup-OrpER 1. Pedunculata.

Peduncle and capitulum distinct. Outer plates of shell, when present,
not forming a ‘‘ wall.”

Family Lepapmpar, Lepas, Linn. (Fig. 57, A); Dichelaspis, Darwin ;
Pollicipes, Leach (Fig. 60); Scalpellum, Leach (Fig. 61); Ibla, Leach (Fig.
71); Lithotrya, Sowerby ; Conchoderma, Olfers ; Alepas, Rang ; Anelasma,
Darwin (Fig. 68); Koleolepas, Stebbing.

SuB-ORDER 2. Operculata.

No peduncle. Scuta and terga forming a movable operculum. Outer
plates of shell coalesced to form a “ wall.”

TrIBpe 1. ASYMMETRICA.

Scutum and tergum of one side movable, without depressor muscles.
Family VeERRUCIDAE. Verruca, Schum.

TRIBE 2. SYMMETRICA.

Scuta and terga of both sides movable, with depressor muscles.

Family BatanipaE. Balanus, Lister (Fig. 57, B); Coronula,
Lamarck; 7’wbicinella, Lamarck; NXenobalanus, Steenstrup (Fig. 65) ;
Elminius, Leach; Pyrogoma, Leach. Family CHTHaMaLipan. Chtha-
malus, Ranzani; Catophragmus, Sowerby (Fig. 62); Octomeris, Sowerby.

OrpdER 2. Acrothoracica.

A mantle present. Trunk-appendages reduced in number, the
posterior pairs widely separated from the first pair.

Family Atctppipan. Aleippe, Hancock (Trypetesa, Norman) (Fig. 72).
Family KocHnoriInipak. Sochlorine, Noll. Family CRYPTOPHIALIDAE.
Cryptophialus, Darwin.

OrpDER 3. Ascothoracica.

Mantle containing diverticula of alimentary canal. Trunk-append-
ages more or less reduced.

Family Lavuriparn. Laura, Lacaze-Duthiers (Fig. 76). Family
SyNaGoGIDAE. Synagoga, Norman. Family Prerrarcipar. Petrarca,
Fowler. Family DrenproGastRipar. Dendrogaster, Knipowitsch (Fig.
78).

OrpER 4. Apoda.

Mantle absent. No trunk-appendages.
Family PROTEOLEPADIDAE. Proteolepas, Darwin (Fig. 79).

THE CIRRIPEDIA 141

OrveR 5. Rhizocephala.

Mantle present. No appendages nor alimentary canal. A system

of absorptive roots nearly always present.

Families not defined. Probably several should be recognised. _Pelto-

gaster, Rathke ; Sacculina, Thompson (Fig. 80) ; Sylon, Kroyer ; Clostosac-
cus, Lilljeborg ; Lernaeodiscus, F. Miller ; Triangulus, Smith ; Duplorbis,
Smith; Thompsonia, Kossmann.

bo

“TIT

(oe)

LITERATURE.

. Aurivillius, C. W. S. Ueber einige ober-silurische Cirripedien aus Got-

land. Bih. Svenska Vet. Akad. Handl. xviii. Afd. iv. No. 3, 24 pp. 1 pl.,
1892.

. —— Studien iiber Cirripedien. K. Svenska Vet. Akad. Hand]. (n.f.) xxvii.

(7), 107 pp. 9 pls., 1895.

. Berndt, W. Zur Biologie und Anatomie von Alecippe lampas. Zeitschr.

wiss. Zool. xxiv. pp. 896-457, pls. xix.-xxil., 1903.

Studien an bohrenden Cirripedien (Ordnung Acrothoracica, Gruvel,
Abdominalia, Darwin). Arch. f. Biontologie, i. (2) pp. 165-210, pls. xiv.-
xvii., 1906.

. Claus, C. Die Cypris-iihnliche Larve (Puppe) der Cirripedien. . . . Schr.

Ges. Naturw. Marburg, Suppl. Heft v. 17 pp. 2 pls., 1869.

. Darwin, C. A Monograph of the Sub-Class Cirripedia, 2 vols. 8vo. Ray

Soe. London, 1851-1854.

A Monograph of the Fossil Lepadidae . . . 1851. A Monograph of
the Fossil Balanidae and Verrucidae, 1854. Palaeontographical Soc.

Delage, Y. Evolution de la Sacculine. Arch. Zool. expér. (2), ii. pp. 417-
736, pls, Xxli.-xxx., 1884.

. Fowler, G. H. A Remarkable Crustacean Parasite [Petrarca]. Quart. J.

Micr. Sci. (n.s.) xxx. pp. 107-120, pl. viii., 1889.

. Groom, T. T. Onthe Early Development of Cirripedia. Phil. Trans. clxxxv.

pp. 119-232, pls. xiv.-xxviii., 1895.
— On the Mouth-Parts of the Cypris-Stage of Balanus. Quart. J. Micr.
Sci. (n.s.) xxxvii. pp. 269-276, pl. xxix., 1895.

. Gruvel, A. Monographie des Cirrhipédes ou Thécostracés. 8vo. Paris,

1905 [1904].

. Hansen, H. J. Die Cladoceren und Cirripedien der Plankton-Expedition.

Ergeb. Plankton-Exp. ii. 58 pp. 4 pls., 1899.

. Hock, P. P. C. Report on the Cirripedia. Rep. Voy. ‘‘Challenger,”’ Zool.

viii. 169 pp. 13 pls., 1883 ; and x. 47 pp. 6 pls., 1884.

5. Krohn, Aug. Beob. ii. d. Cementapparat u. d. weiblichen Zeugungsorgane

einiger Cirripedien. Arch. f. Naturgesch. xxv. pp. 855-364, 1859.

. Lacaze-Duthiers, H. de. Histoire de la Laura Gerardiae. Mém. Acad. Sci.

France, xlii. (2), 160 pp. 8 pls., 1883.

. Lilljeborg, W. Liriope et Peltogaster, H. Rathke. Nova Acta Soc. Sci.

Upsalensis, (3), iii. pp. 1-35, pls. i.-iii., and pp. 73-102, pls. vi.-ix., 1859-
1860.

. Miller, Fr. Die Rhizocephalen, eine neue Gruppe schmarotzender Krebse.

Arch. Naturgesch. xxviii. pp. 1-9, pl. i., 1862.
Die zweite Entwickelungsstufe der Wurzelkrebse. Arch, Naturgesch.
xxix. pp. 24-33, pl. ili., 1863.

142 THE CRUSTACEA

20. le Rot, Otto. Dendrogaster arborescens und Dendrogaster ludiwigi, zwei
entoparasitische Ascothoraciden. Zeitschr. wiss. Zool. Ixxxvi. pp. 100-
133, pls. vil.-viil., 1907.

21. Smith, G. Rhizocephala. Fauna und Flora des Golfes von Neapel.
Monogr. xxix. 123 pp. 8 pls., 1906.

22. Thompson, J. Vaughan. Zoological Researches, vol. i. 8vo, Cork, 1830.
Memoir IV. On the Cirripedes or Barnacles, pp. 69-88, pls. 9 and 10.

23. —— Discovery of the Metamorphosis in the Second Type of the Cirripedes,
viz. the Lepades. .. . Phil. Trans, 1835, Pt. ii. pp. 355-358, pl. vi.
24. Natural History and Metamorphosis of . . . Sacculina carcint.

Entom. Mag. iii. pp. 452-456, 6 figs., 1836.

25. Weltner, W. Verzeichniss der bisher beschriebenen recenten Cirripedien-
arten. Arch. Naturgesch. ixiii. Bd. i. pp. 227-280, 1898.

26. Willemoés-Suhm, R. v. On the Development of Lepas fascicularis and the
“‘ Aychizoéa” of Cirripedia. Phil. Trans. elxvi. pp. 131-154, pls. x.-xv.,
1876.

Pe 5

CHAPTER VI
THE MALACOSTRACA

Sup-Ciass MAacostraca, Latreille (1806).
SERIES I. LEPTOSTRACA.

DIVISION PHYLLOCARIDA.
Order Nebaliacea.

SERIES IJ. EUMALACOSTRACA.

DIvIsIon 1. SYNCARIDA.
Order Anaspidacea.

DIVISION 2. PERACARIDA.

Order 1. Mysidacea.
Cumacea.
Tanaidacea.
Isopoda.
Amphipoda.

Or me Ww Lo

DIVISION 3. EUCARIDA.
Order 1

?

Euphausiacea.
Decapoda. (9,

Lo

Division 4. HopLocARIDA.
Order Stomatopoda.

Definition.—Crustacea in which the carapace is variously
developed or may be vestigial; there are typically fourteen (rarely
fifteen) trunk-somites, all of which (except the fifteenth) bear
appendages ; the telson rarely has a caudal furca ; antennules often
biramous ; the mandibles may have a palp; the trunk-limbs are
differentiated into two tagmata, a thoracic of eight and an
abdominal of six pairs; female genital apertures on the sixth,

143

aA THE CRUSTACEA

male apertures on the eighth trunk-somite ; paired eyes usually
present ; development usually with metamorphosis, young rarely
hatched in nauplius stage.

The sub-class Malacostraca includes such a diversity of forms
that it will be necessary to deal more fully than in the case of the
other sub-classes with the separate orders composing it. Before
doing so a brief account must be given of the general type of
organisation found throughout the sub-class.

Apart from the fixed number of somites, to which the Leptostraca
offer the only exception, the most characteristic feature of the
Malacostraca is the separation of the trunk-limbs into sharply
defined thoracic and abdominal tagmata. This, together with the
constancy in position of the genital apertures, on different somites
in the two sexes, is sufficient to demonstrate the unity of the
sub-class,

Leaving the Leptostraca aside for the present, the more primi-
tive members of each of the “ divisions” in the scheme of classi-
fication here adopted approximate to a common type of structure
from which the more specialised members of each group diverge
very widely. Thus, the possession of a carapace enveloping the
thoracic region, movably stalked eyes, biramous antennules, a
scale-like exopodite on the antenna, natatory exopodites on the
thoracic limbs, an elongated and ventrally flexed abdomen, and a
“tail-fan” formed by the lamellar rami of the last pair of append-
ages spread out on either side of the telson, are characters common
to the Mysidacea, Euphausiacea, and the lower Decapoda, and,
with some modifications, to the Anaspidacea and Stomatopoda. It
seems reasonable to suppose that this combination of characters,
making up what has been called the “caridoid facies,” must be
attributed to the hypothetical common stock of the Malacostraca.
At all events, it is possible to represent, in diagrammatic fashion,
a generalised Malacostracan which serves as a convenient summary
of the morphology of the group (Fig. 85). Some of the characters
of this type require to be considered in more detail.

The antennule, as already stated, is biramous, having two
flagella springing from a peduncle of three segments. Since the
antennules in the other sub-classes are always uniramous, as they
are in the nauplius, it seems probable that the two flagella do not
represent the endopodite and exopodite. When only one flagellum
is present in the Malacostraca it is the outer which persists, and
it alone, as is shown by the sensory filaments which it carries,
corresponds to the single ramus of the other sub-classes. In certain
Decapoda (Caridea) and in Stomatopoda there are three flagella,
the outer flagellum being divided into two.

The protopodite of the antenna is composed of two or of three

THE MALACOSTRACA 145

segments. According to Hansen the latter number is, here as
elsewhere, the more primitive. The endopodite is flagelliform, and
the expodite has the form of a plate, the so-called “scale” or
“squama,” probably of use in swimming. As a rule the first three
segments of the endopodite are enlarged and are counted with the
two (or three) segments of the protopodite as forming a five- (or six-)
segmented peduncle.

_ The mandible has a “palp” of three segments, never biramous.
The oral edge of the mandible is more or less distinctly divided into
a “molar process” and an “incisor process,” and between them is
armed with bristles or spines. An accessory blade, the lacinia mobilis,
lying close to the cutting edge of the incisor process and apparently

auer. SRR ie
Co ieee) Ee (Ia

ie ) |) eet ere

ia 2 i \\ \ mx 4
“i 7 I NY) NILE waste ae”
pip. AN # a PA
“urop. a a
Magee
Fic. 85.

”

Diagram of a generalised type of Malacostraca showing the ‘“‘ caridoid facies.’”’ a’, antennule ;
a’, antenna ; abd.som, abdominal somites ; c, carapace ; e, eye; er, exopodite of antenna; md,
mandible ; ma’, maxillula; ma’, maxilla; plp, pleopods ; 7, rostrum ; ¢, telson; th.app, thoracic
appendages ; wrop, uropods; ¢ and @ indicate the positions of the genital apertures in the
male and female sex respectively.

formed by the enlargement of one of these spines, is found in some
of the orders, and is perhaps also a primitive character.

The mazillulae have two endites and a “palp” of several
segments. According to Hansen, whose investigations on the
skeletal framework of the mouth-parts will be often referred to,
the two endites belong to the first and third segments of the
appendage, a small sclerite which Hansen supposes to represent
the second segment having no endite in connection with it. An
exite, in the form of a rounded plate, may be present; according
to Hansen it belongs to the first segment. The mazillae are more
complex in form and the primitive plan of their structure is not
quite clear. Apparently there are two endites, each of which is
bifid, corresponding to the second and third segments, and a palp
of one or two segments.

The thoracic appendages (Fig. 86) are all similar, none of them, in
the primitive type, being differentiated as maxillipeds. Each has a
protopodite of two segments, the coxopodite and basipodite, with,

10

146 LIFE CRUSTACEA

according to Hansen, a pre-coxal segment (pleuropodite of Coutiere)
which is distinct only in the Leptostraca and Stomatopoda. The ,
axis of the limb is continued by the endopodite which forms an
ambulatory leg, while the flagelliform exopodite is used for
swimming. There are five segments in the endopodite, termed
by Milne-Edwards respectively the ischiopodite, meropodite,
carpopodite, propodite, and dactylopodite (often abbreviated to
ischium, merus, carpus, propodus, and dactylus). | Hansen con-
siders that the terminal claw which is sometimes distinct from the
dactylopodite represents an additional segment, making, with the
pre-coxa, nine segments in the axis of the limb instead of the
seven usually recognised. It seems
probable, however, that this claw
(termed stylopodite by Coutiére) is
simply an enlarged spine and not
one of the segments of the limb.

At the bases of the thoracic
limbs on the outer side are a series
of epipodial appendages (exites)
probably originally branchial in
function. It is not quite clear how
many of these appendages must be
attributed to each thoracic limb of
the primitive type, but probably at

jaate least two are to be recognised, an
Diagram of a Malacostracan thoracic eprpodite attached to the coxopodite
appendage. bs, basipodite; carp, carpo- and a proepipodite to the pre-coxal
podite; cx, coxopodite; dact, dactylopodite; ci
en, endopodite ; ep, epipodites ; ex, exopo. Segment. The oostegites, or brood-
ane Sa es tins eA plates, attached to the inner side of
the coxopodite in the female sex in
some of the orders, and forming a pouch for the protection of the
eggs and young, may possibly be derived from some of these epi-
podial structures, as Claus suggests. The terminology applied to the
thoracic limbs in systematic works differs greatly in the various orders
of Malacostraca. From one to three of the anterior pairs may be
called mawillipeds, the second and third pairs are in some cases known
as gnathopods, and the last five pairs are often termed peracopods. |

The abdominal appendages are all biramous and are used in
swimming, but the sixth pair differ in form and function from the
others. The first five pairs are known as pleopods. 'They have the
protopodite composed of two segments (occasionally there are
traces of a third), and the rami are fringed with long setae and
assist the thoracic exopodites in the ordinary swimming move-
ments of the animal. The appendages of each pair are coupled
together by a group of hooked spines (retinacula) either on the
inner edge of the protopodite or on a special process of the

THE MALACOSTRACA 147

endopodite known as the appendix interna. The sixth pair of
abdominal appendages, known as the wropods, are larger than the
others, with a short, unsegmented protopodite and broad lamellar
rami which lie at the sides of the telson and form with it the
“tailfan” which is used in swimming, or rather springing, back-
wards by sudden flexion of the whole abdomen.

The Leptostraca alone among the more primitive orders of
existing Malacostraca stand apart from the scheme outlined above,
and seem to have diverged from the main line of Malacostracan
descent before the assumption of the caridoid. form. Their
systematic relations will be discussed more fully later.

CLASSIFICATION OF THE MALACOSTRACA.

The group Malacostraca, established by Latreille in 1806, has
been accepted as a natural division by nearly all subsequent
writers. Almost the only divergences of opinion as to its limits
have had reference to the Leptostraca, which many zoologists
following Milne-Edwards have referred to the Branchiopoda or
have regarded as occupying an intermediate place between
Malacostraca and “‘ Entomostraca.” Claus’s investigations on the
structure of Nelalia, however, have been generally accepted as
demonstrating its Malacostracan affinities. In the arrangement
here adopted (following Grobben) the order Nebaliacea is included
within the sub-class Malacostraca, but its distinctness from the
other orders is marked by placing it in a separate division
(Leptostraca) opposed to the other orders grouped together as
Eumalacostraca.

In the arrangement of the Eumalacostraca most carcinologists
hitherto have followed the lines laid down by Leach, who, in 1815,
divided the group into two legions—the Podophthalma and the
Edriophthalma—according to the condition of the eyes, movably
pedunculate in the one and sessile in the other. As originally
defined, the two groups were also distinguished from each other
by the presence in the Podophthalma of a carapace which was
absent in the Edriophthalma, this character giving occasion for the
names Thoracostraca and Arthrostraca applied to the same groups
by Burmeister in 1834. The progress of research, however,
rendered it increasingly difficult to frame satisfactory definitions
of the two divisions. Thus, the sessile-eyed Tanaidacea were
found to possess a true, though reduced, carapace, while the
Cumacea were still more plainly intermediate between the two
groups. The recent discovery of the very remarkable genus Anaspides,
which has stalked eyes but no carapace, and the closely allied
Koonunga with sessile eyes, makes the retention of the old arrange-
ment quite impossible.

148 THE CRUSTACEA

An important departure from the line of classification generally
followed was made in 1883 by Boas, who showed that the order
“Schizopoda” as then understood comprised two very different
groups, which he separated as distinct orders, the Euphausiacea and
Mysidacea. Boas discarded the old divisions Podophthalma and
Edriophthalma, and divided the Malacostraca into seven orders,
Euphausiacea, Mysidacea, Cumacea, Isopoda, Amphipoda, Decapoda,
and Squillacea (or Stomatopoda). Hansen, in 1893, carried the
reform of the classification a step further. Setting apart (as
Huxley had previously done) the aberrant Stomatopoda, as well
as the Leptostraca, he showed that the remaining Malacostraca
fell into two well-defined groups, the line of division passing
through the old order Schizopoda ; on the one side he placed the
Euphausiacea with the Decapoda, and on the other the Mysidacea
with the Cumacea and the Edriophthalmate orders Tanaidacea,
Isopoda, and Amphipoda. The classification adopted here is
essentially that of Hansen, as modified and extended by the
present writer in 1904.

It will be convenient to give here definitions of the main
groups into which the Malacostraca are divided. The orders will
be considered in greater detail in the subsequent chapters.

SuB-CLASS MALACOSTRAGCA.
Series I. Leptostraca, Claus (1880).

Abdomen of seven somites, the last of which is without appendages, —
and a telson bearing a pair of movably articulated furcal rami; an
adductor muscle runs between the two valves of the carapace ; thoracic
limbs all similar, more or less foliaceous, with protopodite of three
segments.

Serigs II. Eumalacostraca, Grobben (1892).

Abdomen of six somites (the number may be reduced by coalescence),
the last of which typically bears a pair of appendages, and a telson which
never bears movable fureal rami; no adductor muscle of the carapace ;
thoracic limbs rarely all similar (Euphausiacea), typically pediform,
protopodite of two segments except in Stomatopoda.

Diviston 1. SyncaripA, Packard (1886).

Carapace absent ; first thoracic somite fused with the head or defined
therefrom by a groove; protopodite of antenna of two segments ; mandible
without lacinia mobilis; thoracic legs flexed between fifth and sixth
segments ; no oostegites; no appendix interna on pleopods; hepatic
caeca numerous ; heart much elongated, tubular. -

THE MALACOSTRACA 149

Division 2. PERACARIDA, Calman (1904).

Carapace, when present, leaving at least four of the thoracic somites
distinct ; first thoracic somite always fused with the head ; protopodite
of antenna typically of three segments; mandible with lacinia mobilis
(except in parasitic and other modified forms); thoracic legs flexed
between fifth and sixth segments ; oostegites attached to some or all of
the thoracic limbs in female, forming a brood-pouch ; no appendix in-
terna on pleopods; hepatic caeca few and simple; heart generally
elongated, extending through the greater part of thoracic region, or
displaced into abdomen ; spermatozoa generally filiform; development
taking place within the brood-pouch, young set free at a late stage.

Division 3. Evcarrpa, Calman (1904).

Carapace coalescing dorsally with all the thoracic somites ; eyes
pedunculate ; protopodite of antenna with, at most, two distinct seg-
ments ; mandible without lacinia mobilis in adult ; thoracic legs flexed
between fourth and fifth segments; no oostegites; an appendix interna
sometimes present on pleopods; hepatic caeca much ramified; heart
abbreviated, thoracic; spermatozoa spherical or vesicular, often with
radiating appendages ; development as a rule with metamorphosis, a free-
swimming nauplius stage in the more primitive forms.

Division 4. Hopiocaripa, Calman (1904).

Carapace leaving at least four of the thoracic somites distinct ; two
movable segments are separated from the anterior part of the head, bear-
ing respectively the pedunculate eyes and the antennules; protopodite of
antenna of two segments ; mandible without lacinia mobilis ; posterior
thoracic limbs with protopodite of three segments (the relation of the
segments of the anterior thoracic limbs to those of the limbs in the other
divisions is doubtful) ; an appendix interna on pleopods; hepatic caeca
much ramified ; heart much elongated, extending through thoracic and
abdominal regions ; spermatozoa spherical; development with meta-
morphosis, a free-swimming nauplius stage is not certainly known.

LITERATURE.
(General Morphology and Classification of Malacostraca. )

1. Boas, J. E. V. Studien iiber die Verwandtschaftsbeziehungen der Mala-
kostraken. Morphol. Jahrb. viii. pp. 485-579, pls. xxi.-xxiv., 1883.

2. Calman, W. T. On the Classification of the Crustacea Malacostraca. Ann.
Mag. Nat. Hist. (7) xiii. pp. 144-158, 1904.

3. Claus, C. Neue Beitriige zur Morphologie der Crustaceen. Arb. zool. Inst.
Wien, vi. pp. 1-108, pls. i.-vii., 1885.

4. Hansen, H. J. Oversigt over de paa Dijmphna-Togtet indsamlede Krebsdyr.
Dijmphna-Togtets zool.-bot. Udbytte, pp. 185-286, pls. xx.-xxiv., and
Résumé, pp. 508-511, 1887.

150 THE CRUSTACEA

5. Hansen, H. J. Zur Morphologie der Gliedmassen und Mundtheile bei
Crustaceen und Insecten. Zool. Anz. xvi. pp. 1938-198 and 201-212.
Translated in Ann. Mag. Nat. Hist. (6) xii. pp. 417-434, 1893.

6. Sars, G. O. Histoire naturelle des Crustacés d’eau douce de Norvége,
1 Livr. Les Malacostracés, pp. 1i+145, 10 pls. 4to. Christiania, 1867.

7. Stebbing, T. k. kR. A History of Crustacea. Recent Malacostraca. Internat.
Sci. Ser. London, 1893.

CHAPTER VII
THE LEPTOSTRACA

SERIES LEProsTRAca, Claus (1880).
DrvistoN PHYLLOCARIDA, Packard (1879).

Order Nebaliacea.

Definition.—To the characters mentioned on p. 148 as distinctive
of the series the following may be added: Carapace present ; all
the thoracic somites distinct; eyes pedunculate ; mandible with-
out lacinia mobilis; no oostegites ; first four pairs of abdominal
appendages biramous, with appendix interna, last two pairs reduced ;
hepatic caeca few ; heart elongated ; development embryonic, young
set free at a late stage.

Historical.—The first-known member of the Leptostraca was
the Cancer bipes of O. Fabricius, described from Greenland. Leach,
who in 1815 established the genus Nebalia, placed it among the
Macrura, but H. Milne-Edwards, while admitting its affinities with
Mysis, ranked it as a Phyllopod, and this view was long and widely
held. Metschnikoff in 1865, from a study of its development,
replaced the genus among the Malacostraca as a “ phyllopodiform
decapod.” Claus, in a series of memoirs ending with his exhaustive
monograph of 1889, vindicated the title of Nebalia to rank as a
Malacostracan, and placed it in a group Leptostraca, alongside the
Arthrostraca and Thoracostraca. The resemblance of certain fossil
Crustacea to Nebalia had long been recognised, and Packard in
1879 proposed the name Phyllocarida for the group, including the
living and fossil genera. Sars has called attention to the similarity
in general form between Nelalia and certain Copepoda, but Claus
showed this resemblance to be merely superficial.

MorpPHOLOGY.

The carapace (Fig. 87) is compressed laterally so as to form a
bivalved shell (though without any definite hinge-line), loosely
enveloping the thorax and more or less of the abdomen, and quite

151

152 THE CROSTACEA

concealing, in most cases, the thoracic hmbs. The two halves of the
shell can be approximated by the action of an adductor muscle
traversing the body in the region of the maxillae. Anteriorly, the
carapace is produced into a movably articulated rostral plate (7),
not provided with special muscles but elevated or depressed by the
movements of the underlying parts. The carapace is not attached
to the body behind the maxillary region, and the eight thoracic
somites which, except in Nebaliopsis, are very short and crowded
together, are all distinctly marked off by grooves on the delicate
integument. Of the abdominal somites the fourth alone may have
distinct pleural plates, or these may be altogether absent. The
telson (¢) bears the two styliform or lamellar furcal rami (/)

Fic. 87.

Nebalia bipes, 9, from the side. a’, antennule; w’, antenna; abl, ab®6, first and sixth
abdominal appendages ; ad, adductor muscle of carapace ; f, caudal furca ; p, palp of maxillula ;
r, rostral plate ; t, telson; 1, 7, first and seventh abdominal somites. (After Claus.)

articulated with it and moved by special muscles ; the anus opens
between the rami towards the ventral side.

Appendages.—The antennules (Fig. 88, A) have a peduncle of
four segments bearing a flagellum of varying length and, external
to it, a movable scale. It seems probable that this scale represents
the outer ramus of the antennule of other Malacostraca, and the
occurrence of four (instead of three) segments in the peduncle is
paralleled in certain species of Tanaidacea.

The peduncle of the antenna (Fig. 87, w”) is apparently com-
posed of four segments, of which the last two are coalesced in
Nebalia and Paranebalia. Hansen recognises, in addition, a short
basal segment and another, very short, between the second and
third of the larger segments. The exopodite is absent. The
distal part of the endopodite forms a flagellum which, in the adult
male, may be nearly as long as the body. .

The mandible (Fig. 88, B) has a strong molar process; the

ee ee

}
j
A
}
;

THE LEPTOSTRACA 153

incisor process is small and simple in Nebalia and Paranebalia,
large and toothed in Nebaliclla, and absent in Nebaliopsis. The
palp is large and has three segments.

The mavillula (Fig. 88, C) has the usual two endites. The palp
is vestigial in Nebaliopsis; in the other genera it is attached to
the distal margin but curves outwards and backwards so that the

ai

Fic. 8s.

Cephalic appendages of Nebalia. A, antennule; B, mandible; C, maxillula ;
D, maxilla. (After Claus.)

very long, slender, and indistinctly segmented flagellum in which it
terminates is directed obliquely upwards along the side of the
thorax underneath the carapace (Fig. 87, p).

The mazillae (Fig. 88, D) approximate in general form to the
thoracic limbs, except for the absence of an epipodite. There are
generally four endites, but the distal one is much reduced in
Nebalia and Paranebalia. The endopodite is divided into two
segments in Nebalia and, like the exopodite, is generally elongated.

154 THE CROESTACEA

In Nebaliopsis, however, the endopodite is a short lobe and the
exopodite is hardly indicated.

The eight pairs of thoracic limbs are all similar, except in
Nebaliopsis, and they present considerable differences of structure
in the four genera.

In Nebalia (Fig. 89) the whole limb is much flattened. The
broad coxopodite and basipodite are distinctly separated, and on
the proximal side of the former Hansen has detected a small
pre-coxal segment. To the outer margin of the coxopodite is
attached the broad lamellar epipodite (ep), obscurely divided into

Ye

Fia. 89.

First thoracic limb of Nebalia. en, endopodite ; ep, epipodite ; ex, exopodite. (After Claus.)

a proximal and a distal lobe by a slight notch on the outer margin
opposite the poit of attachment. The basipodite bears externally
the oval flattened exopodite (ex) and is continued without any
distinct line of articulation into the narrower endopodite (en).
From the distal end of the endopodite three, or, in the case of
the eighth pair, four segments are marked off, so that, except
for the absence of an articulation between the basipodite and
ischiopodite, all the segments of the typical malacostracan leg can
be distinguished. In Nebaliella (Fig. 90, B) the epipodite is absent,
the exopodite has more numerous marginal setae, and the articula-
tion between the basipodite and ischiopodite is more distinctly

BHE LEPTFOSTRACA 155

marked. In Paranebalia (Fig. 90, A) the endopodite is long and
slender, projecting beyond the edges of the carapace in the natural

/ :
V/ Pe
(Ki Va ne ays

Wh

itis
5, FY aye
EAE?

Sips

f eH

Fig. 90.

Thoracic limbs of Leptostraca. A, Puranebalia longipes, fifth limb. B, Nebaliella antaretica,
fourthlimb. C, Nebaliopsis typica, tirst limb. D, the same, second limb. en, endopodite ; ep,
epipodite ; ex, exopodite. (A after Sars; B, C, D after Thiele.)

position. The exopodite is also long and narrow, and is provided,
on its outer edge, with numerous long plumose setae which suggest
a natatory function. The epipodite is very small. The ischio-

156 THE CRUSTACEA

podite is defined from the basipodite, at least in the last pair,
and Hansen recognises a minute terminal segment as well as a
pre-coxal, making altogether nine segments in the axis of the limb.
In Nebuliopsis the thoracic limbs are very different from those of
the other genera. Except the first and last pairs, they are unseg-
mented lanceolate lamellae (Fig. 90, D), having a slight lobe on
the outer edge to represent the exopodite, and a more distinctly
marked bilobed epipodite; the inner edge is beset with setae
along its whole length. In the last pair, which are almost without
setae, a terminal segment is marked off, and in the first pair
(Fig. 90, C) this part, although not distinctly segmented off, is
produced into a finger-shaped distal lobe (en).

In Nebulia the tip of each of the thoracic limbs carries, in the
breeding female, a fan of long plumose setae turned inwards to
form the floor of a basket-like brood-chamber which is closed
behind by rows of long setae on the inner edges of the last pair.

The first four pairs of abdominal appendages are biramous and
are used in swimming ; the last two pairs are small and uniramous.
The former (Fig. 91) have a stout protopodite of two segments and
long indistinctly segmented rami fringed with spines and plumose
setae. From the inner edge of the endopodite close to its base
there springs a short appendix interna (a.i) bearing a group of
hooked spines at its tip.

Alimentary System.—The masticatory stomach, in Nebalia, is of
a comparatively simple type. It is divided into a “cardiac” and a
“pyloric” portion, the former with masticatory ridges moved by
muscles, and the latter with two pairs of lateral setose lobes and a
dorsal groove which is continued as a delicate chitinous funnel,
open below, some distance into the mid-gut. The mid-gut extends
back to the penultimate segment of the body. Four pairs of
hepatic caeca open near its anterior end and a pair of short caeca
open separately on the ventral side in the same region. Near its
junction with the proctodaeum the mid-gut gives off an unpaired
dorsal caecum, bifid at the tip.

Circulatory System.— The heart, in Nebalia, extends from the
cephalic region to the fourth abdominal somite. It has seven pairs
of ostia, and the last pair, which are larger than the others, are
situated in the region of the sixth thoracic somite. The exopodites
and epipodites of the thoracic limbs are traversed by a close net-
work of blood-channels and no doubt serve as respiratory organs.
The valves of the carapace probably also assist in respiration, and
the blood circulating in them is returned to the pericardial sinus by
a definite venous channel on each side.

Heeretory System.—Both the antennal and the mazaillary glands
are present in a vestigial condition, the former lying in the
proximal segment of the antennal peduncle, while the latter is

THE LEPTOSTRACA 157

placed close to the adductor muscle of the carapace at the base of
the maxilla. The gland in each case consists of a minute saccule
giving off a short duct, but the external openings have not been
detected.

Hight pairs of glands lying at the bases of the thoracic limbs
are also believed to be excretory. Each consists of a thickening of

Pleopod of second pair of Nebalia. a.i, appendix interna ; en, endopodite ;
ex, exopodite. (After Claus.)

the hypodermis partly surrounding the efferent blood-channel from
the epipodite. These glands alone become coloured by intra vitam
treatment with indigo-carmine, while the antennal and maxillary
glands excrete particles of carmine when the animal has been fed
with that substance.

Muscular System.—The adductor muscle (Fig. 87, ad) of the
carapace has two muscular heads attached to.the valves and con-

158 THE CRLUSTACEA

nected by a median tendinous part which passes under the stomach
in the region of the maxillae. The muscle is innervated from the
maxillary ganglion.

Nervous System.— The brain is complex, admitting of close
comparison with that of other Malacostraca. The oesophageal
connectives are short and are united by the commissure of the
antennal ganglia behind the oesophagus. In the ventral chain the
ganglia of the mandibular, maxillular, and maxillary somites are
distinct, though, like the eight thoracic ganglia, they are closely
crowded together. Six abdominal ganglia are present, the seventh
somite, like the telson, having no ganglion in the adult. In the
embryo, however, a transitory seventh abdominal ganglion has been
found.

Sense-Organs.—The eyes are stated to resemble, in their intimate
structure, those of the Mysidacea. In Nebaliella and Nebaliopsis
and in one species of Nebalia (N. typhlops) the eyes are vestigial,
though the peduncles persist. On the upper and inner surfaces of
the ocular peduncle, in Nebalia, there are two small tubercles,
supposed to be sensory organs. Olfactory filaments of the usual
type are present on the antennules and, in the male, also on the
antennae.

Reproductive System.—The most conspicuous external difference
between the sexes consists in the much greater length of the
antennal flagellum in the male. The gonads have the form of
paired tubes extending, when mature, through nearly the whole
length of the body. ‘The short vasa deferentia open on papillae on
the coxopodites of the last thoracic limbs. The oviducts are hard
to detect, but they appear to open on the sixth thoracic somite.
The spermatozoa are spherical and are aggregated into globular
spermatophores. The eggs are carried, as already stated, between
the thoracic feet of the female.

Development.—The development of Nebalia takes place within
the brood-chamber of the parent without any free-swimming larval
stages, and presents many- points of resemblance to that of the
Mysidacea. The first three pairs of appendages appear simul-
taneously, giving a well-marked nauplius stage. The remaining
appendages develop in order from before backwards. ‘The embryo
becomes free from the egg-membrane at a stage when all the
thoracic appendages, and sometimes also those of the abdomen, are
marked off (Fig. 92). The carapace at this stage does not extend
beyond the second thoracic somite. When the young leave the
maternal brood-chamber they have attained, in all essential respects,
the structure of the adult.

THE LEPTOSTRACA 159

REMARKS ON Hapits, ETC.

All the Leptostraca are marine. Most of the species occur in
shallow water or at moderate depths, but Nebaliopsis belongs to the
“bathypelagic”” fauna at
depths exceeding 1000
fathoms. Many have an
extremely wide distribution,
the common European Nebalia
bipes, for instance, ranging °
from Greenland to Chile and
Japan. The species named
appears to be very resistant
to unfavourable conditions,

Cale : : : Embryo of Nebalia, just hatched. a’, antennule ;
thriving in water which Sq’, antenna; f, caudal furea; md, mandible; ma’,
foul with decaying matter. misliua; ma’, maxilla; nl fst pleopod ; le
Locomotion is effected by (After Claus.)
powerful strokes of the an-
terior four pairs of pleopods. ‘The thoracic limbs serve the purpose
of respiration, and by their rhythmic movements produce a current
of water which brings food-particles to the mouth. ‘The water is
drawn in from behind and expelled in a stream below the rostral
plate.

The largest of existing Leptostraca is Nebaliopsis typica, Sars,
which reaches a length of about 40 mm. The other species are
from 4 to 12 mm. in length.

‘ A ‘
fa ‘ ! ’
3. md. mx! mx" thi

Fic. 92.

PALAEONTOLOGY

Certain fossil Crustacea, generally grouped together as a family,
Ceratiocaridae, are believed to be more or less. closely allied to
the existing Leptostraca. The various genera, ranging from the
Cambrian to the Triassic epochs, differ considerably among them-
selves, but the more typical forms, such as Ceratiocaris (Fig. 93) and
Hymenocaris, resemble Nebalia in general form, having a bivalve
carapace, sometimes with an articulated rostral plate, and an ex-
tended abdomen. Nothing is definitely known of the appendages.
A pair of serrated plates observed within se outline of the shell
in some instances have been described as “gastric teeth,” but
may possibly be the mandibles (m). Some of the fossils are of
great size, Ceratiocaris, from Ordovician and Silurian rocks, reaching
a length of two feet.

The chief difference which can be observed between the fossils
and the living representatives of the Leptostraca is that, in the
former, the terminal appendages of the abdomen are always more

F

160 THE CRUSTACEA

numerous. In most cases there are three such appendages, the
telson being produced as a median style between the furcal rami.

AFFINITIES AND CLASSIFICATION.

The alliance of the Leptostraca with the other Malacostraca is
amply justified by the agreement in the number of the appendages,
by the sharp distinction between the thoracic and abdominal series,
and by the position of the genital apertures. Other characters,
probably of less importance, are the biramous form of the anten-
nules, the possession of a masticatory stomach, and the complex
structure of the brain. The most important differences from the
Eumalacostraca are the presence of an additional somite in the
abdomen, of a caudal furca, and of an adductor muscle of the carapace.

Fic. 93.

Ceratiocaris papilio, «a, traces of antennules (?); m, toothed plates, possibly
the mandibles ; 7, rostal plate. (After H. Woodward.)

These are no doubt primitive features and indicate that the Lepto-
straca diverged from the Malacostracan stock before the assumption
of the typical caridoid form. It may be suggested that the
development of the uropods to form a tail-fan in the primitive
Eumalacostraca was associated with the loss of the caudal furea.
The resemblance of the lamellar thoracic limbs of Nebalia to
those of the Branchiopoda, which has led to the Leptostraca being
associated in many classifications with that group, is doubtless
significant, and it becomes still more striking in the case of
Nebaliopsis. The absence of endites in the Leptostracan limb,
however, is an important difference. According to the view,
already mentioned (p. 42), that the exopodite is represented, in
the appendages of Apus, for example, not by the flabellum but by
the sixth endite, it would seem impossible to draw a close com-
parison with the appendages of Nebalia. Without going so far
as this, however, it may be suggested as a possibility that the

THE LEPTOSTRACA 161

“phyllopod” form of the thoracic limbs in the Leptostraca may
be to some extent secondary, having arisen by suppression of the
locomotor function in limbs of the more typical Malacostracan
form. In this case Paranebalia, in which the phyllopod character
of the thoracic appendages is very little marked, would be more
primitive than Nebalia and Nebaliopsis.

It is difficult to decide how much importance should be given
to the presence of an adductor muscle as indicating an affinity
between the Leptostraca and the Conchostraca, but the possession
by the former of a mandibular palp and well-developed maxillae
forbid their being derived directly from any of the existing
Branchiopoda.

As regards the relation of the Leptostraca to the various groups
of Eumalacostraca, there seems to be a general agreement that
their nearest allies are to be sought among the Mysidacea, which
they resemble especially in their mode of development. It may
be necessary to mention that, apart from a vague similarity in
general form, perhaps the result of a similarity in habits, there
is no ground for the supposition that they have any direct affinity
with the Cumacea.

The four existing genera of Leptostraca may, for the present,
be referred to a single family. In the absence of information as
to the structure of the limbs in the fossil Ceratiocaridae, it is not
possible to assign them to a definite systematic position in relation
to the living forms.

Orver Nebaliacea, Calman (1904).

Family Nepatipar. Nebalia, Leach; Paranebalia, Claus ; Nebaliopsis,
G. O. Sars; Nebaliella, Thiele.

LITERATURE.

1. Claus, C. Ueber den Bau und die systematische Stellung yon Nebalia.
Zeitschr. wiss. Zool. xxii. pp. 323-330, pl. xxv., 1872.

Ueber den Organismus der Nebaliden und die systematische Stellung
der Leptostraken. Arb. zool. Inst. Wien, viii. pp. 1-148, pls. i.-xv.,
1888.

3. Metschnikof, E. Development of Nebalia [Russian]. Zapiski Imp. Akad.
Nauk. St. Petersburg (8vo series), xili. 48 pp. 2 pls., 1868.

4, Robinson, Margaret. On the Development of Nebalia. Quart. J. Mier.
Sci. 1. pp. 383-433, pls. xvi.-xxi., 1906.

5. Sars, G. O. Report on the Phyllocarida. Rep. Voy. ‘‘ Challenger,” Zool.
xix. 38 pp. 3 pls., 1887.

Fauna Norvegiae. Vol. I. Phyllocarida and Phyllopoda, 4to, pp.
vi+140, 20 pls. Christiania, 1896.

7. Thiele, Joh. Die Leptostraken. Wiss. Ergeb. deutschen Tiefsee-Expedi-
tion ‘‘ Valdivia,” viii. 26 pp. 4 pls., 1904.

Ueber die Leptostraken. Deutsche Siidpolar-Expedition, 1901-1903,

Bd. ix. Zool. i. pp. 61-68, pl. ii., 1905.

Way

CHAPTER VIII
THE SYNCARIDA :

DIVISION SYNCARIDA, Packard (1886).

Order Anaspidacea.

Definition.—To the characters mentioned on p. 148 as distinctive
of the Division, the following may be added: Thoracic limbs
with exopodites (except the last, or the last two pairs), and with
a double series of lamellar epipodites attached to the outer side
of the coxopodites (except the last pair); the first pair may have
enathobasic endites on the coxopodite ; pleopoda with the endo-
podite reduced or absent except in the first two pairs in the male
sex; uropods lamellar, forming, with the telson, a tail-fan; a
statocyst is present in the basal segment of the antennules.

Historical.A naspides tasmaniae was first described by G. M.
Thomson in 1892, and more fully in 1894. He placed it among
the “Schizopoda,” establishing for it the family Anaspidae. In
1897 the present writer discussed some points in its morphology
and called attention to its resemblance to certain fossil Crustacea
for which Packard had established the group Syncarida. In 1904
Grobben (in his edition of Claus’s Lehrbuch der Zoologie) referred
Anaspides to a new subdivision of the Malacostraca which he
termed Anomostraca, and in the same year the system of classifica-
tion adopted here was published. Quite recently a new and very
remarkable representative of the Syncarida has been discovered
and described by Mr. O. A. Sayce under the name Koonunga cursor.
It has been suggested that Bathynella natans, described by Vejdovsky
in 1882, also belongs to this group, but our knowledge of the
structure of this minute form is still very imperfect.

MorPHOLOGY.

The body, in the living Synearida, is elongated and sub-
cylindrical, with all the trunk-somites distinct from each other.
In Anaspides (Fig. 94) the anterior limit of the first thoracic

162

THE SYNCARIDA 163

somite appears to be marked by a transverse “ cervical groove ” (¢.g7)
which crosses the dorsal surface and runs obliquely forwards on
each side to end just behind the mandible. In Koonunga (Fig. 95)
this groove is obliterated dorsally, but a short portion persists on
each side running upwards from the lower margin of the head.

Fic. 94.

Anaspides tusmaniae, 6, 3. e.gr, ‘cervical groove”; II, VIII, second and eighth thoracic
somites ; 1, 6, first and sixth abdominal somites. (Drawn by Miss G. M. Woodward.)

It has been suggested that this groove indicates the limit between
the mandibular and maxillular somites and corresponds to the
“cervical sulcus” of the Mysidacea, and perhaps to the transverse
groove of the head in many Branchiopoda. On the other hand,
a forward displacement of the lateral plates of the anterior thoracic

Fie. 95.

Koonunga cursor, 6, X 11. (From an original drawing by
Mr. O. A. Sayce, slightly modified.)

somites is observed in some other Malacostraca, and it is quite
probable that this groove in Anaspides has undergone a similar
displacement and that it really does define the first thoracic somite
from the head. Running backwards from this groove on each side in
Anaspides is a horizontal line marking off inferiorly a quadrilateral area.

'

164 THE CRUSTACEA

The front of the head is produced, in Anaspides, into a short
rostrum. On the dorsal surface, in front of the cervical groove,
is a pigmented area with a circular central spot surrounded by four
minute pits. The significance of this structure is quite unknown,
but it may be comparable to an obscure “dorsal organ” apparently
glandular in nature, occupying a similar position in certain other
Malacostraca. It has not been observed in Koonunga.

The thoracic somites have no pleural plates and those of the
abdominal somites are slightly developed. The telson, in Anaspides
and Koonunga, is short, of simple form, with a fringe of spinules
on the posterior margin.

Appendages.—The antennules are biramous, with long flagella.
The first of the three segments of the peduncle contains a statocyst,
opening by a narrow slit on the dorsal surface. In the male
Anaspides the basal part of the inner flagellum is enlarged and armed
with serrated spines. It appears probable that it may be used as
a clasping-organ. In Koonunga, the antennule of the male has a
curious globular organ attached to the first segment of the outer
flagellum. The surface of the organ is covered with minute cup-
like structures which are possibly sensory.

The antenna has a scale-like exopodite in Anaspides, but in
Koonunga this is absent. The protopodite consists of two segments,
and the first two segments of the endopodite are enlarged, so that
the peduncle consists of four segments only.

The mandibles (Fig. 96, A) have a large palp of three segments.
The serrated incisor process 1s separated from the molar process in
Anaspides by a rounded lobe (s) fringed with setae. The lower lip
is large and deeply cleft.

The mazillula (Fig. 96, B) has two endites and a vestigial palp. A
small exite, not projecting beyond the outer edge, can be recognised>

The mazilla (Fig. 96, C) has three endites directed distally
and crowded together, and a short, unsegmented palp. There is
no exopodite.

The thoracic limbs are all alike in general structure. In
Anaspides (Fig. 3, E, p. 8) the endopodite is composed of six
segments (instead of the usual five) in the anterior pairs, but the
articulation between the basipodite and ischiopodite becomes indis-
tinct in passing backwards along the series, and in the last three
pairs these segments have completely coalesced. In Anaspides the
main flexure of the limb is between the fifth and sixth segments,
but in Koonunga it appears to be between the fourth and fifth.
This difference, however, is due to the fact that in all the thoracic
legs of Koonunga, as in the posterior pairs of Anaspides, the
basipodite and ischiopodite have coalesced. The terminal segment
is small, and bears from three to five stout curved claws, one of
which on the posterior legs is larger than the others.

bas

THE SYNCARIDA 165

In all except the last pair of thoracic limbs the coxopodite
bears externally two ovate epipodial lamellae, each attached by a
narrow base and having a small proximal segment marked off by a

B. “Ny

transverse line. These epipodites
have a very thin cuticle and no
doubt act as gills,

Exopodites are present on all
but the last (Anaspides) or the
last two (Koonunga) pairs of tho-
racic appendages. On the first
pair they are short, unsegmented
rods, but on the other limbs they
are many-jointed and fringed with
plumose setae. According to G.
Smith they are not used in swim-
ming, but serve to keep a current
of water flowing over the branchial
plates.

The first pair of thoracic limbs

Mouth-parts of Anaspides. A, man- in Anaspides (Fig. 3, D, P- 8) i oy

dible ; B, maxillula; C, maxilla. er, differentiated from the others by
exite ; 4, Ineisor process ; m, molar pro- =
cess ; p, palp; s, setose lobe. the presence on the inner face
of the coxopodite of two movably
articulated gnathobasic lobes (yn). In Koonunga these lobes are
wanting, but the limb differs from those which follow it in being
much more stoutly built.

The pleopods have the exopodite long, many-jointed, and fringed
with setae, forming a powerful swimming-organ. The endopodite
(except in the first two pairs of the male) is small and composed
of two segments in Anaspides, and entirely absent in Koonunga.

Fic. 96.

166 THE (CROUSTACEA

Sometimes, but not always, it is absent from the last pair also in
Anaspides. In the males of both genera the first two pairs have
the endopodites modified as copulatory organs. In the first pair
of Anaspides the endopodite is a thick lobe, curved inwards and
having a group of retinacula on a short process (perhaps a vestigial
appendix interna) near the distal end of its inner edge. The endo-
podite of the second pair is composed of two segments, the first
elongated, bearing some spines and a group of retinacula near the
distal end, and the second curved and spoon-shaped. In the
natural position these appendages are turned forwards, the endo-
podites of the second pair lying within the trough formed by the
apposition of those of the first pair, and between the latter and the
sternal surface of the thorax.

The uropods in Anaspides are large, with lamellar rami, fringed
with spines and setae, and form, with the telson, a tail-fan of the
usual type. The exopodite is crossed by an incomplete suture or
line of articulation near the distal end. In Koonunga the protopo-
dite is relatively longer and the rami are not so broad, so that the
fan-like arrangement is not quite so typical. The exopodite is
undivided.

As regards the internal anatomy, our information is as yet very
restricted, and refers only to Anaspides.

Alimentary System.—The masticatory stomach appears to be of
very simple type, its armature consisting of longitudinal chitinous
ridges beset with setae. The extent of the mid-gut has not been
ascertained. The hepatic caeca are numerous, very long slender
tubes. There are two median dorsal caeca—one in the region of
the first and the other in the fifth abdominal somite.

Circulatory System.—The heart is a long tube extending
through a great part of the length of the body. The number of
the ostia has not been ascertained. There is stated to be an
unpaired descending artery originating from the under-surface of
the heart between the last two thoracic somites.

Excretory System.—On each side of the head, posterior to the
mandibles, is a glandular mass of considerable size, showing in
sections a convoluted tubular structure. No duct has yet been
traced from it, but its position suggests that it may be the maxillary
gland.

Sense-Organs.—The paired eyes of Anaspides are set on short
movable peduncles; those of Koonunga are very small and are
sessile on the sides of the head.

In both genera a saccular invagination of the integument, sup-
posed to be an otocyst (or statocyst), is found in the basal segment
of the antennular peduncle. It opens by a small slit on the dorsal
surface of the segment. Internally, on the upper side, is a row of
peculiarly modified setae. Each is divided into two segments, the

THE SYNCARIDA 167

distal one swollen and pyriform. While resembling in its position
the otocyst of Decapods, this organ differs strikingly from it in the
nature of the setae.

Reproductive System.—The ovaries form an elongated lobed mass
on each side, extending through the posterior part of the thorax
and into the abdomen. ‘The oviducts open on the inner face of the
coxopodites of the sixth pair of thoracic limbs. Between the bases
of the last pair of legs on the sternal surface of the thorax is a
rounded prominence directed forwards. At its tip a slit-like
aperture gives entrance to a blind sac, with thick and apparently
muscular walls. At the base of the sac on each side is a racemose
gland, apparently opening by a short duct into its cavity. It seems
probable that this structure (originally described as the opening of
the oviducts) is a receptaculum seminis. A similar organ is present
in Koonunga.

The testes are a pair of very long slender tubes, convoluted
anteriorly, lying above the alimentary canal. The vasa deferentia
terminate in a pair of oblique slit-like apertures on the sternal
surface of the last thoracic somite.

The development, unfortunately, is still entirely unknown.

REMARKS ON HABITS, ETC.

Anaspides occurs in rocky pools at an elevation of about 4000
feet in the mountains of Tasmania. It reaches a length of about
38 mm. Koonunga is found in freshwater pools near Melbourne,
and does not exceed 9 mm. in length.

“PALAEONTOLOGY.

A group of fossil Crustacea found in Carboniferous and Permian
rocks in Europe and America, for which the name Syncarida was
proposed by Packard, appear to be closely allied to the living
- Anaspides and Koonunga. The structure is best known in the case
of Uronectes (Gampsonyx) (Fig. 97), described by Jordan and von
Meyer from the Lower Permian of Saarbriicken. The exact
number of free somites is doubtful, but there appear to be eight
in the thoracic region, and there are indications that the sixth
abdominal somite was divided in a manner recalling the condition
found in certain Mysidacea. The eyes are pedunculated. The
antennules are biramous, and the antennae have a rounded scale-
like exopodite. One of the anterior pairs of thoracic limbs is
enlarged and armed with stout spines. The presence of exopodites
on the thoracic limbs is probable, although denied by Fritsch, but
the structure of the appendages is very obscure. The uropods are
lamellar, forming a tail-fan with the telson; the exopodites are

168 THE CRUSTACEA

divided by a suture. In Praeanaspides (Fig. 98), recently described
by Dr. H. Woodward from the English Coal-measures, the seg-
mentation of the body agrees with that of Anaspides, and exopodites
are certainly present on some of the thoracic limbs. Other genera
are Palacocaris, Acanthotelson, and Casocaris.

Fig. 97.
Uronectes [=Gampsonyx] fimbriatus. a’, antennule; e, supposed eye ; en, traces of exopodites
on thoracic limbs; /, enlarged thoracic limb, probably the second ; J, first thoracic somite.
(After Jordan and von Meyer.)

AFFINITIES AND CLASSIFICATION.

The existing genera of Syncarida present characters which
indicate for them a very isolated place among living Malacostraca,
while suggesting more or less remote affinities with widely divergent

Fic. 98.

Praeanaspides praecursor, from the Coal-measures of Derbyshire.
(From H. Woodward in Geol. Mug.)

groups. They have retained characters of the primitive caridoid
type in the tail-fan, the biramous antennules, the scale-like exopodite
of the antenna (in Anaspides), and the natatory thoracic exopodites.
With the loss of the carapace, however, the segmentation of the
body comes to resemble that of the Isopoda and Amphipoda, though
the demarcation of the first thoracic somite from the head (if this

THE SYNCARIDA 169

be indeed the significance of the ‘cervical groove ”) is not so distinct
in any other Eumalacostraca. The homologies of the segments of
the endopodite in the thoracic limbs are not quite clear, but the
fact that the main flexure of the limb is between the fifth and sixth
segments in Anaspides is a point of agreement with the Peracarida,
to which group some slight resemblance may be traced in the
structure of the maxillae. The possession of a statocyst in the basal
segment of the antennule is only paralleled among the Decapoda, and
the presence of a receptaculum seminis on the last thoracic sternite
of the female and the modification of the first two pairs of pleopods
in the male may also point to an affinity with that group. On the
other hand, the double series of epipodial lamellae on the thoracic
appendages of both genera, and the double gnathobasic lobes on the
coxopodite of the first pair in Anuspides, are important features not
found in any other Malacostraca.

The fossil genera mentioned above show that already in
Palaeozoic times a group of Malacostraca existed which, while
retaining caridoid features in tail-fan, antennules, antennae, and
pedunculated eyes, had a completely segmented body and no
carapace. <Anaspides alone among living Crustacea agrees with
them in this combination of characters, and there appears to be no
reason to doubt that it and Koonunga are really descendants of the
Syncarida of Carboniferous and Permian times.

Bathynella natans, to which allusion has been made, is a minute
Crustacean (1°0 mm. in length), described in 1882 by Vejdovsky
from two specimens found in a well in Prague. It has not since
been rediscovered. It appears to possess eight free thoracic somites.
There are no eyes. The antennules are uniramous, and the antennae
have a small exopodite. The first seven pairs of thoracic limbs are
biramous, and each has a single vesicular epipodite. The last pair
are vestigial. Only the first and last abdominal somites bear
appendages. If its structure has been correctly interpreted, Bathy-
nella would seem to be a degenerate member of the Syncarida, but
only the discovery of further specimens will enable its systematic
position to be definitely fixed.

OrpER Anaspidacea, Calman (1904).

Family ANaAspIDIDAE. Anaspides, G. M. Thomson. Family
Koonuneipar. Koonunga, Sayce.

LITERATURE.

1. Calman, W. T. On the Genus Anaspides and its Affinities with certain Fossil
Crustacea. Trans. Roy. Soc. Edinburgh, xxxviii. (4), pp. 787-802, 2 pls.,
1896.

On the Characters of the Crustacean Genus Bathynella, Vejdovsky.

Journ. Linn. Soc, Zool. xxvii. pp. 338-344, pl. xx., 1899.

2.

170 THE CRUSTACEA

3. Fritsch, A. Fauna der Gaskohle und der Kalksteine der Permformation
Bohmens. Bd. iv. Heft 3, Crustacea, ete., 1901.

4, Jordan, H., and von Meyer, H. Ueber die Crustaceen der Steinkohlenforma-
tion von Saarbriicken. Palaeontographica, iv. pp. 1-16, pls. i-ii., 1854.

5. Packard, A. S. On the Synearida, ete. Mem. Nat. Acad. Sci. Washington,
ili. Pt. 2, Mem. 15, pp. 123-189, 4 pls., 1886.

6. Sayce, O. A. Description of a new remarkable Crustacean with Primitive
Malacostracan Characters. Victorian Naturalist, xxiv. No. 7, pp. 117-120,
1907 ; reprinted in Ann. Mag. Nat. Hist. (8), i. pp. 350-355, 1908.

Thomson, G. M. Ona Freshwater Schizopod from Tasmania. Trans. Linn.
Soe. (2), Zool. vi. (3), pp. 285-303, pls. xxiv.-xxvi., 1894.

8. Vejdovsky, F. Thierische Organismen der Brunnenwiisser von Prag. Prag,

1882.
9. Woodward H. Some Coal-measure Crustaceans with Modern Representatives
[Praeanaspides}]. Geol. Mag. (n.s.) Dec. 5, vol. v. pp. 385-396, 1908.

“I

ADDENDUM.

Since this chapter was in type G. Smith has described a third living
representative of the Syncarida, Pwranaspides lacustris, from the Great
Lake of Tasmania, and has given further details as to the habits and
internal anatomy of Anaspides (‘‘ Preliminary Account of the Habits and
Structure of the Anaspididae .. .,” Proc. Royal Soc. (B) lxxx. pp.
465-473, pl. xiii, 1908).

|
.

CHAPTER IX
THE MYSIDACEA
Order Mysidacea, Boas (1883).

Definition.—Peracarida which retain more or less completely the
primitive caridoid facies; the carapace extends over the greater
part of the thoracic region, but does not coalesce dorsally with more
than three of the thoracic somites; the eyes, when present, are
movably pedunculate ; the antennules are biramous ; the antennae
have usually a large scale-like exopodite ; the thoracic limbs (except
sometimes the first and second pairs) have natatory exopodites ; the
first and sometimes also the second pair are modified as maxillipeds ;
a lamellar epipodite is present on the first pair; ramified branchiae
may be attached to the body-wall close to the bases of the thoracic
limbs ; the pleopods are often reduced ; the uropods are lamellar,
forming a tail-fan ; the young leave the brood-pouch provided with
all the appendages of the adult.

Historical—The group Schizopoda, established by Latreille in
1817, and long approximated to the Stomatopoda on the authority
of H. Milne-Edwards, finds a place in most modern systems of
classification, as comprising, after exclusion of many larval Decapods
formerly referred to it, the forms here treated of together with the
Euphausiidae. Boas, in 1883, however, discarded this grouping,
and established the two orders Mysidacea and Euphausiacea, point-
ing out that they were by no means closely related, and this view
has been also advocated by Hansen. Our present knowledge of the
structure and classification of the Mysidacea is very largely due to
the work of G. O. Sars.

MoRPHOLOGY.

From five to seven of the thoracic somites are distinct, and the
last two or three of these may be left uncovered by the carapace
on the dorsal side. The carapace may be produced in front as a
short rostrum, and there is usually a transverse groove or “cervical
sulcus” (Fig. 99, ¢.s) on the dorsal surface in the region of the

171

172 LLUE SCRAPS AG)

mandibles. The possible homology of this groove with the
cervical groove of Anaspides has been already mentioned. The
abdominal somites have the pleural plates generally reduced or
absent ; but in Gastrosaccus the pleura of the first somite are greatly
enlarged in the female to help in forming the brood-pouch. The

Mysis relicta, female. c¢.s, cervical sulcus ; m, brood-pouch. (After Sars.)

sixth somite is generally longer than any of the others, and in
Gnathophausia it is divided by a transverse groove (Fig. 100, gr)
about the middle of its length. Itis possible that we have here
two somites in process of coalescence, and that seven somites are
represented in the abdomen of the Mysidacea as in that of the

Fie. 100.
Gnathophausia willemoesti, Sars. (According to Ortmann this is the fully adult form of G.
zoea, W. Suhm.) x 3. gr, groove partially dividing the last somite. (After Sars.)

Leptostraca. It is important, however, to note that the last somite
in this case bears appendages (uropods) and that the penultimate
does not, while in the Leptostraca the reverse is the case. The
indications of a similar division of the sixth abdominal somite in
certain fossil Syncarida have already been alluded to.
Appendages.—The ocular peduncles are peculiarly modified in
many deep-sea forms in which the eyes are imperfect or absent.
In Dactylerythrops the peduncle is produced as a finger-like process

THE MYSIDACEA 173

beyond the eye ; in Boreomysis scyphops the distal end of the peduncle
is expanded and excavated in a cup-like form and is without
pigment or any trace of ocular structure, but in other species of
the same genus the eyes are normally developed ; in some Petal-
ophthalmidae the peduncles are leaf-like or spiniform; while in
Pseudomma, Amblyops, and some allied genera, they are repre-
sented by broad plates extended
horizontally in front of the carapace.

In the Mysidae the three-seg-
mented peduncle of the anftennules
carries in the male sex, in addition
to the two flagella, a conical process
beset with numerous sensory fila-
ments.

The antennae have the protopodite
distinctly composed of three segments
(Fig. 101, 1, 2, 3). A lamellar ex-
opodite or “scale” (sc) is always
present except in Arachnomysis and
allied genera, where it is represented
by a spine. In many Mysidae it is
divided into two segments by a trans-
verse suture near the tip.

The mandibles have generally a
well-developed lacinia mobilis (Fig.
102, /.m), differing in form on the
two sides, and a row of spines (s) in- mosint
terposed between the incisor and _ Cephalothoracic region of Mysis relicta,
molar processes. The row of spines young female, from below. Most of the

thoracic appendages have been removed.

is absent in the Lophogastridae and ™;: external flagellum of antennule; a”,
5 flagellum of antenna; ex, exopodites of

Eucopiidae and some Mysidae, and _ thoracic appendages ; 1, labrum ; md, palp

; | Tecan Balas. as of mandible ; 0, oostegites, not yet fully

In some cases the lacinia mobpills 1s pees sc, scale or exopodite of an-
c eye 1 ! enna ; th 1-th 3, first, second, and third

wanting. The molar process is smiall “fioracie appendages a°s, the fies

or absent in a few Mysidae. p\ palp segments of the protopodite of the an-

: tenna. (After Sars.)

is always present, and becomes greatly

enlarged in the aberrant Petalophthalmus, where it appears to have

a prehensile function.

The mavzillulae (Fig. 103, A) have two endites arising, according
to Hansen, from the first and third segments, and a slightly
developed laminar exite, which Hansen states belongs to the first
segment. In the genus Gnathophausia (Fig. 104) a palp of two
segments is present, directed backwards beneath the carapace like
that of the Leptostraca.

The mazillae (Fig. 103, B) have a complex structure. There
are two endites corresponding to the second and third segments

(Hansen), the first of which is incompletely and the second com-

174 THE CRUSTACEA

pletely divided into two. A plate-like lobe on the outer side (/)
is regarded as the exopodite and springs from the third segment
(Hansen). The palp is composed of two segments. In Gnatho-
phausia a pigmented papilla on the outer side close to the base
bears the opening of a gland producing a luminous secretion.

The thoracic appendages have
the coxopodite very small, and

0-8 have usually an exopodite con-

aa sisting of a peduncle and a
iain 38 multi-articulate setose flagellum
$<" attached near the proximal end
ma - - -- | of the basipodite. The ex-

opodites of the first pair may
be reduced (Lophogastridae,
Eucopiidae) or absent (some
species of Gnathophausia, Petal-
Bre 02: ophthalmidae), and those of the

A, mandible of Mysis. B, oral edge of same, oie ? :
further enlarged. 7, incisor process ; /.im, lacinia second pair are absent in Petal-

eae ; m, molar process ; s, Spine-row. (A after ophthalmus.

The first pair of thoracic
limbs are always specialised as maxillipeds. In the Lophogastridae
and Eucopiidae they are without distinct endites. In the Mysidae
(Fig. 105, A) an endite is generally borne by the basipodite, and
sometimes also by each of the two following segments. In Petal-
ophthalmus the first and second thoracic limbs (in the other genera
of Petalophthalmidae only the
second) have a large lamellar
endite developed from the
meropodite.

In the Lophogastridae
(Fig. 106) the last seven pairs
of thoracic limbs are all
similar, and exhibit the usual
number of seven segments, Fic. 103,
the dactylus being large and A, maxillula, B, maxilla, of Mysis oculata, 1-6,

f 4 segments of the appendages ; 11-14, endites of the
having generally a claw-like respective segments according to Hansen’s earlier

. interpretation (in his later papers the endites here
spine at the apex. In the numbered 3 and 4 in the maxilla are regarded as
y Oc resulting from the division of a single endite cor-
Eucopiidae the second to the responding to the third segment, and the segments
fifth pairs are subchelate, and here numbered 5 and 6 become 4 and 5 respectively) ;
5 : os ee f, flabellum or exopodite. (After Hansen.)

the next three pairs, which
are exceedingly long and slender, have also the dactylopodite flexed
against the propodite to form a prehensile organ. In the Mysidae
there is, as a rule, a distinction between the second and the follow-
ing limbs. The former, sometimes called second maxillipeds or
“onathopoda,” are bent inwards towards the mouth, with the
normal number of segments and with a rounded dactylopodite

THE MYSIDACEA

175

without a claw. The remaining pairs (Fig. 105, B) have the
propodite (except in most Petalophthalmidae and some species of

Striclla) divided into secondary segments
from two (Loreomysis, Siriella) to eight or
nine in number. The dactylopodite is
usually small, and terminates in a claw-like
spine. In Heteromysis the third pair are
enlarged and prehensile.

In all Mysidacea the first pair of thoracic
limbs have a simple lamellar epipodite (Fig.
105, A, ep) directed backwards beneath
the carapace. In the Lophogastridae and
Eucopiidae a series of ramified gills (Fig.
106, br) are developed in connection with
the last seven thoracic limbs. Each consists
of three or four main branches, which are
again bipinnately or tripinnately divided.
The largest branch is bent round on the
sternal surface of the thorax between the
insertion of the limbs, a point of some
interest In connection with the position of

Fic. 104.
Maxillula of Gnathophausia
longispina. p, palp. (After
Sars.)

the gills in the Amphipoda. Although the gills of the Lopho-

Fia. 105.

A, first thoracic appendage (maxilliped) of Mysis. B, third thoracic appendage of same.
The minute coxopodite is omitted in each case. bs, basipodite ; d, dactylopodite ; ep, epipodite ;
ex, exopodite ; 1, masticatory lobes or endites of basipodite, ischiopodite, and meropodite ; prp,

propodite, divided into seven segments in B. (After Sars.)

176 THE CRUSTACEA

gastridae and Eucopiidae are attached to the body-wall or to the
articular membrane rather than to the coxopodites of the limbs, it
is probable that they are really of the nature of epipodites. In

Gnathophausia a short finger-like
) process bearing long setae is
s\~ found on the outer side of the

presents a reduced distal epi-
podite (Fig. 106, ep). In the
Mysidae and Petalophthalmidae
there are no epipodites on the
limbs posterior to the first
thoracic pair, apart from some
vestiges described in Huchae-
fomera and allied genera. Seven
pairs of oostegites are found
attached to the coxopodites of
all except the first pair of
thoracic appendages in the

Second thoracic appendage of Gnathophausia females of the Lophogastridae,
longispina. br, branchia; ep, epipodial process; Eucoplidae, and Petalophthal-
be,exopadive: s(ATer BES) midae, and in the genus Boreo-
mysis among the Mysidae. In the other Mysidae the number does
not exceed three pairs, and it is often reduced to two, corre-
sponding to the last two thoracic somites (Fig. 101, 0).

The pleopods are well developed in both sexes in the Lopho-
gastridae and Eucopiidae, where they have multiarticulate rami
fringed with setae, and no special modifications are found in either
sex. In the Petalophthalmidae and Mysidae the pleopods are
vestigial in the female (except in the little-known <dArchaeomysis),
but are often well developed in the male. When they are reduced
in the latter sex some of the pairs, most commonly the fourth, are
specially modified. In the males of some Mysidae the peduncle
bears distally, in addition to the two rami, a lobe or process of
varying form, to which a branchial function has been attributed.

The wropods have the exopodite divided into two segments by
a transverse suture in the Lophogastridae, Eucopiidae, and Petaloph-
thalmidae, and, less distinctly, in certain Mysidae. A statocyst is
present near the base of the endopodite in most Mysidae, but it
is absent or vestigial in Boreomysis and in the other families.

Alimentary System.—The stomach in Mysis (Fig. 107, st) is
divided into a globular cardiac portion occupying the greater part
of the cavity of the head in front of the cervical sulcus and a much
smaller pyloric portion. The interior of both chambers has
numerous ridges and prominences armed with spines and setae.
In particular, a tongue-shaped process directed backwards on the

Fic. 106,

coxopodite, and apparently re

- |

THE MYSIDACEA P77

floor of the pyloric division, and bearing on each side anteriorly a
double comb-like row of iridescent setae, can be identified with a
similar process found in Amphipoda and Isopoda. The extent of
the mid-gut does not seem to have been
determined. Five pairs of hepatic caeca
(Fig. 107, hep) are found in Mysis, opening
Hy a common duct on each side just behind
the tongue-shaped process on the floor of the
pyloric chamber. Two pairs are very short
and directed forwards; of the three pairs
directed backwards, the upper and lower
extend through the greater part of the
thorax while the middle pair are much
shorter. In Striella there are only three
pairs, one turned forwards and two longer
pairs turned backwards. An unpaired dorsal
diverticulum (d) is given off at the junction
of stomach and intestine. Fic. 107,
Circulatory System.—The heart of the ajimentary canal of Mysis.
Mysidae is elongated, fusiform, extending (oo sere c an testing
the whole or the greater part of the length Here ase ie
of the thoracic region. There are only two ~ %
pairs of ostia, one dorsal to and slightly in advance of the other.
Anteriorly and posteriorly the heart is continued into median aortic
vessels each flanked at its origin by a pair of lateral vessels. From
the under-side of the heart a number of median vessels are given
off to the underlying viscera, and near the posterior end there
originates an unpaired descending artery which passes on one side
of the intestine. On approaching the sternal surface it divides in
the median plane into three branches which pass between the con-
nectives of the nerve-chain in the fifth, sixth, and seventh thoracic
somites. The anterior branch is continued forwards as a subneural
artery through the anterior thoracic somites ; the middle branch
supplies the sixth and the posterior the seventh and eighth somites
and their limbs. The abdominal aorta gives off in each somite,
besides paired vessels which terminate in the pleopods, a median
branch which passes on one side of the intestine and runs for a
little way alongside the ventral nerve-cord, sometimes anastomosing
with its neighbours in front and behind. The interest of this dis-
position of the arterial trunks lies in the fact that the descending
artery given off from the posterior end of the heart, which is clearly
homologous with the similar vessel found in the Decapoda, is here
seen to’ be one of a series of median vessels originating from the
under-side of the heart and of the abdominal aorta, and contribut-
ing to the formation of a discontinuous sternal or subneural vessel
on the ventral side of the body.

I2

178 LHE CROSTACEA

Fine capillary networks surround and penetrate the optic
ganglia and those of the thoracic region. Converging venous
channels on the sides of the thorax convey the blood from the
limbs to the pericardium. Small papilliform elevations of the
integument on the course of these channels in Mysis have been
credited with a branchial function. The chief seat of respiration
in the Mysidae, however, appears to be the carapace, in which is a
rich network of blood-channels receiving blood from the sinuses of
the anterior part of the body and returning it to the pericardium.
The epipodite of the maxilliped may also have a branchial function,
and at all events serves, by its movements, to maintain a current
of water under the wings of the carapace. The branchiae of the
Lophogastridae and Eucopiidae have already been described.

Excretory System. —The antennal gland is well developed in
Mysis. The canal is much convoluted and expands into a small
bladder before opening to the exterior on the second segment of
the antennal peduncle. Groups of excretory cells are present also
at the bases of the thoracic limbs.

Nervous System.—The oesophageal connectives are elongated
and a post-oesophageal (antennal) commissure appears to be present.
In Loreomysis the full number of eleven pairs of ganglia can be
distinguished in the cephalothoracic part of the ventral chain, but
in Mysis all are coalesced into a continuous mass within which only
ten pairs of ganglia can be made out. In Gnathophausia the first
three pairs are completely coalesced and the fourth is closely
approximated to them, but the remaining seven pairs are distinct.
In all cases six abdominal ganglia are present.

Sense-Organs.—The eyes have the cornea slightly faceted ex-
ternally. The crystalline cone is bipartite and the elongated
rhabdome is quadripartite. In certain bathypelagic Mysidae the
ommatidia are divided into two groups differing in structure. In
Gnathophausia there is, on the upper surface of the ocular peduncle,
a small prominence which probably corresponds to the sensory
papillae found in the Leptostraca.

The statocyst, which is found in the endopodite of the uropods
in nearly all Mysidae (Fig. 108), consists of a spacious vesicle
originating as an invagination of the integument and remaining in
communication with the exterior (in some species at least) by a
narrow fissure. It contains a single large discoidal statolith (sf),
consisting of an organic nucleus surrounded by a thick shell of
calcium fluoride and resting on a group of setae springing from
the floor of the cavity. The tips of the setae are imbedded in
the substance of the statolith. Each statocyst is supplied by a
large nerve (7) from the last pair of abdominal ganglia.

Holt and Tattersall have observed in Hansenomysis a pit on the
upper surface of the proximal segment of the antennule. Although

———

THE MYSIDACEA 179

no sensory setae could be discovered, it seems possible that this
pit may represent the antennular statocyst of Syncarida and
Decapoda.

Reproductive System.—The two tubular ovaries are connected
with each other by a narrow bridge. The oviducts proceed from
their hinder ends and probably open in the usual position at the
base of the sixth thoracic limbs. The testes are closely approximated
in the middle line and consist each of a number of pyriform follicles
opening into the vas deferens, which is dilated near the front of
each testis to form a seminal vesicle. The external openings are
situated on papilliform elevations at the bases of the last pair of
thoracic limbs. The spermatozoa have the form of slender rods
each with a filiform tail attached at an acute angle at one end.

Fria. 108,

A, telson and one uropod of Mysis, from above. The marginal setae of the uropod are
omitted. B, the statocyst, seen in optical section from the side, further enlarged. en, endo-
podite of uropod, containing the statocyst near its base ; ex, exopodite of uropod ; 7, nerve
supplying sensory setae of statocyst; st, statolith; t, telson. (After Sars.)

Development.—The whole course of development takes place
within the brood-pouch. In the Mysidae segmentation is of the
discoidal type. ‘The embryo becomes freed from the egg-membrane
after the appearance of the first three pairs of appendages, at which
stage, corresponding to the nauplius, the first larval cuticle is
formed (Fig. 109). The caudal region, which within the egg was
flexed ventrally, becomes extended and the body acquires a slight
dorsal curvature. An important feature is the presence of two
immovable setose styles (f) terminating the abdomen and _ re-
presenting the caudal furca of the Leptostraca. Under the cuticle
of this maggot-like nauplius stage the remaining cephalic and
thoracic appendages (th) appear simultaneously, followed by the
uropods and, after an interval, by the pleopods. The elongation of
the body in the post-naupliar region is effected by successive divisions
of a series of teloblastic cells as in Isopoda. A pair of lateral

180 DLE VCR SLACEOA

thickenings of epiblast appear very early and, approaching ‘each
other on the dorsal side, fuse to form an invaginated “dorsal
organ” (d). The young animal leaves the brood-pouch with all the <
appendages developed.

Advanced embryos closely similar to those of the Mysidae have
been observed in Lophogaster and Eucopia.

REMARKS ON HABITS, ETC.

The great majority of Mysidacea are marine, but a few Mysidae
occur in fresh water either as apparently recent immigrants from
the sea, or as “relict” forms like the J/ysis
relicta (Fig. 99) found in lakes in Northern
Europe, Ireland, and North America. A
few Mysidae are members of the surface
plankton, and a number of peculiarly
modified genera of that family, like all
the members of the other families, are
bathypelagic at great depths.

TNDero, OF Masts (Macnonyes. Most of the Mysidae are of small size,
oe eae ie ee few approaching Boreomysis scyphops, which
mandible; i, thoracic limbs. reaches 85 mm. in length; on the other
aii banana hand, Anchialus pusillus is only 3 mm.

hand, S pus y
long. Among the Lophogastridae many species are of considerable
dimensions, and Ginathophausia ingens, the largest member of the
order, reaches a length of 157 mm.

Fia. 109.

PALAEONTOLOGY.

The genus Pygocephalus was established by Huxley in 1857
for a species occurring in the Coal-measures of Scotland which he
compared with the existing genus Mysis. Dr. H. Woodward has
recently made the highly important discovery that Pygocephalus
possessed a brood-pouch formed by six or seven pairs of imbricating
oostegites (Fig. 110), thus showing that it must be classed with
the Peracarida. Pygocephalus has a broad and apparently flattened
body, with a carapace covering the thoracic region. The antennules
are biramous and the antennae have a broad scale-like exopodite.
Seven pairs of thoracic limbs are visible in the fossils (the first pair
were probably folded inwards as maxillipeds and are therefore
invisible), carrying each a multiarticulate exopodite. The uropods
and telson form a broad tail-fan. This combination of caridoid and
Peracaridan characters justifies us in assigning Pygocephalus a place
among the Mysidacea, although it is impossible at present to define
more precisely its relation to the existing families of the order.
It is not known whether the tergal portions of any of the thoracic

|
I

THE MYSIDACEA 181

somites were distinct beneath the carapace in Pygocephalus, but in
the genus Crangopsis of Salter, from the Lower Carboniferous,
Ortmann has shown that at least four somites are distinct. It
is probable that other fossil genera, such as the Carboniferous
Anthrapalaemon, may he found to possess Mysidacean characters.

AFFINITIES AND CLASSIFICATION ;

The removal of the Mysidacea from their old association with
the Euphausiidae in the group “ Schizopoda” is
justified by the fact that the two groups do not
have in common any characters except those of
the primitive caridoid facies which they share
with the lower Decapoda and, in part, with the
Stomatopoda. On the other hand, the con-
nection of the Mysidacea, through the Cumacea
and Tanaidacea, with the Isopoda and Amphi-
poda is shown not only by the characters given
in the definition of the division Peracarida, but
also by many connecting characters which link
together the individual orders. For example,
the retroverted palp of the maxillula in Gnatho-
phausia is repeated inthe Cumacea and Tanaidacea,
and the branchial epipodite of the first thoracic Pygocephalus Coopert,
limb in these two orders may be derived from ee

. . 7 ale specimen, from
the simpler appendage found in the Mysidacea. _ velow,showing the imbri-

The families mentioned below are those Wom eer
accepted by G. O. Sars, with the addition of
the Petalophthalmidae, established by Holt and Tattersall (following
Czerniavsky). The sub-families of the Mysidae as adopted here
have been regarded by Norman as distinct families.

Fie. 110.

ORDER Mysidacea, Boas (1883).

Family Lopnocasrripar. Lophogaster, M. Sars; Gnathophausia,
Willemoés-Suhm (Fig. 100), Family Evcoprmpar. Eucopia, Dana.
Family PeraLopHTHALMIDAE. Petalophthalmus, Willemoés-Suhm ; Han-
senomysis, Stebbing. Family Mystpar. Sub-Family ARCHAEOMYSINAE.
Archaeomysis, Czerniavsky. Sub-Family Lepromystnar. Leptomysis,
G. O. Sars; Erythrops, G. O. Sars ; Dactylerythrops, Holt and Tattersall ;
Euchaetomera, G. O. Sars; Amblyops, G. O. Sars ; Pseudomma, G. O. Sars.
Sub-Family AracHNomysINar. Arachnomysis, Chun. Sub-Family
Mysmpetinar. Mysidetes, Holt and Tattersall. Sub-Family Mysrnar,
Mysis, Latreille (Fig. 99) ; Macromysis, White (= Praunus, Leach). Sub-
Family Srrtomystnar. Sti/omysis, Norman. Sub-Family Herrromysinar.
Heteromysis, S. I. Smith. Sub-Family Mysipeninar. Mysidella, G, O.

182

LHE ORO SAAC EA

Sars. Sub-Family Srrieviiar. Szrielia, Dana. Sub-Family Gasrro-
SACCINAE. Gastrosaccus, Norman; Anchialus, Kroyer (= Anchialina,
Norman and Scott). Sub-Family Borromystnaxr. Boreomysis, G. O. Sars.

“I

10.

11.

14.

15.

iv

LITERATURE.

. Beneden, EH. van. Recherches sur Jlembryogénie des Crustacés: II.

Développement des Mysis. Bull. Acad. Belgique (2), xxviii. pp. 232-
249, 1 pl., 1869.

. Bergh, R. S. Beitrige zur Embryologie der Crustaceen: I. Zur Bildungs-
geschichte des Keimstreifens von J/ysis. Zool. Jahrb. Anat. vi.

pp. 491-528, pls. xxvi.-xxix., 1893.

. Chun, C. Atlantis. Biologische Studien tiber pelagische Organismen :

V. Ueber pelagische Tiefsee-Schizopoden. Bibliotheca Zoologica, vii.
Heft 19, pp. 137-190, pls. viil.-xv., 1896.

. Claus, C. Zar Kenntniss der Kreislaufsorgane der Schizopoden und

Decapoden. Arb. zool. Inst. Wien, v. pp. 271-318, pls. xxi.-xxix.,
1884.

. Czerniarsky (Chernyavskii), V. I. Monographia Mysidarum imprimis

imperii Rossici. Trudui St. Peterburg. Obshchest. Estest. xii. (2), xiii.
(1), and xvili., 1882-83.

. Delage, Y. Circulation et Respiration chez les Crustacés Schizopodes

(Mysis, Latr.). Arch. Zool. expér. (2), i. pp. 105-180, pl. x., 1883.

. Holt, E. W. L., and Tattersail, W. M. Schizopodous Crustacea from the

North-East Atlantic Slope. Rep. Fisheries, Ireland, 1902-1903, pt. ii.
App. iv. pp. 99-152, pls. xv.-xxv., 1905; and Supplement, Fisheries,
Ireland, Sci. Invest., 1904, v. 50 pp. 5 pls., 1906.

. Norman, A. M. British Schizopoda of the Families Lophogastridae and

Euphausiidae. Ann. Mag. Nat. Hist. (6), ix. pp. 454-464, 1892.

On British Mysidae, a Family of Crustacea Schizopoda. Op. cit. (6),
X. pp. 143-166 and 242-263, pls. ix. and x., 1892.

Nushawm, J. WUembryologie de JMMysis chameleo (Thompson). Arch.
Zool. expér. (2), v. pp. 123-202, pls. v.-xii., 1887.

Sars, M. Beskrivelse over Lophogaster typicus, en maerkvaerdig Form
af de lavere tifoddede Krebsdyr. Pp. iv+37, 3 pls. 4to. Christiania,
1862.

. Sars, G. O. Histoire naturelle des Crustacés d’eau douce de Norvége. 1 Livr.

Les Malacostracés. Pp. iii+145, 10 pls. 4to. Christiania, 1867.

Carcinologiske Bidrag til Norges Fauna: I. Monographi over
de ved Norges Kyster forekommende Mysider. 3 pts. 42 pls. 4to.
Christiania, 1870-79.

— Nye Bidrag til Kundskaben om Middelhavets Invertebratfauna: I.
Middelhavets Mysider. Arch. Math. Naturvid. ii. pp. 10-119, 36 pls.,
1876.

Report on the Schizopoda. Rep. Voy. “‘ Challenger,” Zool. xiii, 228
pp. 38 pls., 1885.

Willemoés-Suhin, 2. von. On some Atlantic Crustacea from the
“Challenger” Expedition. Trans. Linn. Soc. (2), Zool. i. pp. 23-59,
pls. vi-xili, 1875.

Woodward. H. On Pygocephalus, a Primitive Schizopod Crustacean.
Geol. Mag. (n.s.) Dec. 5, vol. iv. pp. 400-407, pl. xviii., 1907.

CHAPTER X
THE CUMACEA
Order Cumacea, Kroyer (1846).

Definition.—Peracarida in which the carapace coalesces dorsally
with the first three or four thoracic somites, overhangs on each
side to enclose a branchial cavity, and is produced in front into two
plates which usually meet each other above in front of the head to
form a pseudorostrum ; the telson may be coalesced with the last
somite ; the eyes are generally coalesced into a single organ set on
an immovable process of the head; the antennules may be
biramous ; the antennae have no exopodite ; some of the thoracic
limbs have natatory exopodites ; the first three pairs are modified
as maxillipeds; the first pair have an epipodite generally pro-
vided with branchial lobules and an exopodite forming a respiratory
siphon ; the pleopods are absent in the female and often reduced
in the male ; the uropods are styliform ; the young leave the brood-
pouch before the appearance of the last pair of thoracic limbs.

Historical.—The first described Cumacean was the Oniscus
scorpioides of Lepechin (1779), and other species were described by
Montagu (1804), Say (1818), and H. Milne-Edwards (1828). The
last-named author established the genus Cuma, from which the
name of the order is derived, but he later regarded this as being a
larval decapod, and he maintained his opinion of the larval nature
of the group as late as 1858, although Kréyer had described
ovigerous females in 1841 and his discovery had been confirmed
by H. Goodsir and others. While Spence Bate, Norman, Lilljeborg,
Hansen, Dohrn, and others have contributed descriptions of species
and observations on structure and development, by far the greater
part of our present knowledge of the group is based on the elaborate
and beantiful memoirs of G. O. Sars.

MorRPHOLOGY.

The general shape of the Cumacea is usually very characteristic,
owing to the sharp distinction between the inflated cephalothoracic
183

134 THE CRUSTACEA

region and the slender and very mobile abdomen carrying at its tip
the styliform uropods (Fig. 111). The extreme specialisation of
the respiratory system, with the concomitant modification of the
anterior part of the carapace, are the most striking features
differentiating this from the neighbouring orders. As in the
Mysidacea and Tanaidacea the first thoracic limb (maxilliped)
carries a backwardly directed membranous epipodite lying in a
cavity between the carapace and the side wall of the body; but in
the Cumacea this epipodite is of relatively great size, and is
usually (though not always) furnished with respiratory processes or
lamellae (Fig. 112, br), which may be very numerous and are often
better developed in the more active males than in the females.
Anteriorly, the branchial cavity is continued as a narrow channel
covered by a forward extension of the lateral plate of the carapace,

Fig. 111.

Diastylis Goodsiri, 2, from the side. x 4. a’, antennule; 71, 75, first and fifth legs (fourth
and eighth thoracic appendages) ; m, brood-pouch ; ps, pseudorostrum ; t, telson; wr, uropod.
(After Sars.)

the two lateral plates generally meeting each other above in front
of the head and forming a more or less prominent psewdorostrum (ps)
divided ‘by a Y-shaped fissure (Fig. 112, fr). Within this channel
lies the exopodite of the same appendage in the form of a narrow
stalk bearing distally a membranous expansion, which jis rolled
upon itself to form a tube, or unites with its fellow of the opposite
side in a single tube (ev) capable of protrusion from the front of
the head below the pseudorostrum. Sometimes the pseudorostral
plates do not quite meet in front of the head, and in certain genera
(Zygosiphon) these plates, and the respiratory channels which they
cover, are placed wide apart at the sides of the broadly expanded
frontal region, while the exopodal tubes project as long transparent
siphons.

Eyes are altogether deficient in many genera. When present
they are usually coalesced to form a single median organ (Fig.
112, e) borne on the front of the head, which is produced into an
oculiferous lobe lying between the two plates of the pseudorostrum.

THE CUMACEA

185

When the lateral plates are removed, the conformation of the head
and the position of the eye show some similarity to the arrange-

ment met with in the Oedicerotidae
among the Amphipoda. The two eyes
are distinct in the embryo, and in one
genus (Vannastacus) also in the adult.

Appendages. —The antennules rarely |

have both flagella well developed, the
inner being usually reduced or absent.
The antennae differ remarkably in the
two sexes. In the female (Fig. 112, a’
they are vestigial, while in the male they
consist of a stout peduncle of five seg-
ments, of which the last two are enlarged
and clothed with a brush of long setae,
while the flagellum is filiform and may
exceed the length of the body (Fig. 113).
In life this long flagellum is usually
carried folded close to the side of the
body, protected by the lower edge of the
carapace and by the pleural plates of the
abdomen, or in a special groove which
runs along the sides of the abdominal
somites. In the genus Lamprops the
antennal flagella of the male are short
and stout, and are used as clasping-organs
to hold the female.

The mandibles never carry a palp, but
in other respects conform to the type
characteristic of the Peracarida. In the
Leuconidae and in the genus Diastyloides
the body of the mandible is short and

triangular and the row of spines is reduced.

molar process is styliform.

Fic. 112.

Diagram of anterior part of
body of Diastylis, 2, from above,

showing the internal organs. a’,
antennule; «@’, antenna; Or,

branchial epipodite of first maxil-
liped enclosed in branchial cavity
at side of carapace ; e, eyes, coal-
esced into one; ex, exopodite of
first maxilliped, forming the re-
spiratory siphon; fr, lateral
branch of ‘‘frontal fissure’ be-
tween the head and the lateral
plate of pseudorostrum ; h, heart;
hep, hepatic caeca; 11, first pair
of legs; ov, ovary; ps, pseudo-
rostrum. (After Sars.)

In Campylaspis the

Fic. 113.
Pterocuma pectinatum, , from the Caspian Sea.

(After Sars, from Ency. Brit.)

The mazillulae (Fig. 114, A), except in Platyaspis and Para-
lamprops, carry a retroverted palp as in Tanaidacea and Lopho-
gastridae.

The mazillae (Fig. 114, B) with their two terminal

186

THE CRUSTACEA

endites present a close approximation to those of Tanaidacea and

Isopoda.

Fic, 114.

A, maxillula, B, maxilla, of Diastylis Goodsiri.
1-4, segments of the appendages; / 1-14, endites
of the respective segments; f, flabellum (ex-
opodite); p, palp. According to Hansen’s later
interpretation, the chitinous piece here numbered
4 in the maxilla does not represent a distinct
segment, and the endites 73 and /4 result from
the division of a single endite belonging to the
third segment. (After Hansen.)

In Campylaspis the endites are suppressed.

The first thoracic appendages
with their respiratory epipodites
(Fig. 115) have a close resem-
blance to those of the Tanaidacea,

_in which group, however, there

is no exopodite. The basipodite
has an endite directed distally,
and carries on its inner edge
two or three hooked spines
(‘‘coupling-hooks”) which inter-
lock with those of the other side.
The second and third thoracic
limbs, though less specialised,
may also be reckoned as maxilli-
peds, since they are turned for-
wards and applied to the oral

region with their basipodites flattened and meeting in the middle

line, while the terminal segments are relatively
weak and carried in a folded position. The
second pair are without exopodites, but in the
female a small scale bearing a fan-like fringe
of setae is attached behind to the base of the
limb, projecting backwards into the marsupial
chamber and serving to keep in motion the
eggs or embryos contained therein. This scale
is doubtless homologous with the oostegites,
which are well developed on the four succeed-
ing pairs of limbs, where they are firmly
attached to the small coxal segments. The
third pair are only rarely devoid of exopodites.
The fourth pair of thoracic limbs are long
raptorial or prehensile legs (Fig. 111, 7),
though their broad basipodites, sometimes
meeting in the middle line, are not dissimilar
to those of the preceding pair. The fifth pair
(2nd legs) often have a reduced number of
joints and differ in details from the succeed-
ing three pairs, which are all similar and appear
to be fossorial in function. The small terminal
segment in these limbs is tipped with a com-
paratively weak spine, which only in the
Nannastacidae becomes a stout curved claw.

Fie. 115.
First maxilliped of Dia-

stylis stygia. bs, basipodite ;
br, branchial lamellae on
epipodite ; en, endopodite ;
ep, epipodite ; ex, exopodite,
forming the respiratory
siphon. (After Sars.)

Natatory exopodites

are always present on the fourth pair (1st legs), and usually on

one or more of the succeeding pairs in the

female sex; in the

THE CUMACEA 187

males (Fig. 113) they are generally present on all save the last
pair of legs.

The pleopods are always absent in the female and sometimes in
the male, but more usually in the latter sex from one to five pairs
are well developed and biramous. The wropods are always con-
spicuous, their slender rami furnished with comb-like rows of spines
apparently used in cleaning the anterior appendages, for which
purpose the abdomen can be flexed ventrally and sometimes also
dorsally.

Internal Anatomy.—The masticatory stomach is stated to
resemble closely that of the Tanaidacea. There are from one to
four pairs of hepatic caeca (Fig. 112, hep). In one genus (Platycuma)
the anterior part of the intestine is coiled, forming a spiral of
two and a half turns within the carapace, but it has not been
ascertained whether the coiled part belongs to the mesenteron or
to the proctodaeum. In this genus also the hepatic caeca appear
to be absent. The heart (h) is usually somewhat elongated, but
in Platycuma it is subglobular. There are three pairs of ostia.
Besides anterior and posterior median arteries, the heart gives off
a pair of antero-lateral vessels and an unpaired descending artery.
A well-developed muzillary gland is present, which, according to
Claus, resembles closely that of Apseudes (Tanaidacea). The
ventral nerve-chain consists of ten thoracic and six abdominal
ganglia.

The simple tubular paired ovaries are connected, at least in the
young, by a narrow transverse bridge. _The openings of the
oviducts have not been seen. The festes are separate, tubular, with
four small caeca anteriorly. The short vasa deferentia open on
the sternal surface of the last thoracic somite.

DEVELOPMENT.

The development appears to resemble, in its main features,
that of the Isopoda. In the earlier stages the embryo is curved
dorsally. As in the Tanaidacea and Isopoda, the young leave the
brood-pouch with the last pair of legs still undeveloped. In certain
species this deficiency persists very late, and possibly in some
cases throughout life.

REMARKS ON HABITS, ETC.

The Cumacea are exclusively marine (including under this term
the group of peculiar species inhabiting the Caspian Sea), and are
generally found burrowing in sand or mud. No species appears to
be truly pelagic, although the actively swimming males of some
species, and less commonly the females, are found in the plankton

188 THE CRUSTACEA

of inshore waters. In Arctic seas the Cumacea are conspicuous by
their abundance and relatively large size, but they are also common
in suitable localities in tropical waters. Many species, often also
of considerable size, occur in the deep sea.

The thirteen species known from the Caspian Sea all belong
to the family Pseudocumidae, and were originally referred to the
single genus Psewdocuma, which comprises only three truly marine
species. It is interesting to note that several of the Caspian
species ‘‘mimic” in their general aspect widely different genera of
other families, and have on this account received such specific
names as diastyloides, eudorelloides, and campylaspoides.

The largest known Cumacean is the Arctic Diastylis Goodsiri
(Fig. 111), which reaches a length of 35 mm. Some deep-sea
species are not much inferior to this, but the average size is much
less, and some species do not exceed 1°5 mm. in length.

No fossil Cumacea are known.

AFFINITIES AND CLASSIFICATION.

The systematic position of the Cumacea has been somewhat
obscured by the customary classification of the Malacostraca into
Edriophthalma and Podophthalma, since they unite the sessile eyes
of the former group with the carapace of the latter. As a matter
of fact, apart from characters of specialisation which seem to have
arisen within the order, they clearly stand midway between the
Mysidacea and the Tanaidacea, just as they combine, to some
extent, the swimming powers of the one with the burrowing habits
of the other.

OrpeR Cumacea, Kroyer (1846).

Family Bopotrimpar. JBodotria, Goodsir (= Cuma, H. Milne-
Edwards) ; Cyclaspis, G. O. Sars ; Zygostphon, Calman. Family Vaun-
TOMPSONIIDAE. Vauntompsonia, Spence Bate. Family Lruconrpa®.
Leucon, Kroyer ; Eudorella, Norman. Family Nannastacipan. Nan-
nastacus, Spence Bate; Campylaspis, G. O. Sars; Platycwma, Calman.
Family CeratocuMIDAE. Ceratocuma, Calman. Family PsrupOCUMIDAE.
Pseudocuma, G. O. Sars; Pterocuma, G. O. Sars (Fig. 113). Family
LAMPROPIDAE. Lamprops, G. O. Sars; Paralamprops, G. O. Sars. Family
PLATYASPIDAE. Platyaspis, G.O. Sars. Family Diastytrpap. Dviastylis,
Say (Fig. 111); Dzastyloides, G O. Sars,

LITERATURE.

1. Calman, W. T. On the Cumacea. Rep. Pearl Fisheries Ceylon. Roy. Soe.
il, pp. 159-180, 5 pls., 1904.

The Marine Fauna of the West Coast of Ireland: Part IV. Cumacea.

Fisheries, Ireland, Sci. Invest., 1904, i. 52 pp. 5 pls., 1905.

2.

THE CUMACEA 189

3. Calman. W. T. The Cumacea of the ‘‘Siboga” Expedition. Uitkomsten
. . H.M. ‘‘Siboga,” Monogr. xxxvi. 23 pp. 2 pls., 1905.

On New or Rare Crustacea of the Order Cumacea from the Collection
of the Copenhagen Museum: Part I. Trans. Zool. Soc. London, xviii.
pp. 1-58, pls. i.-x., 1907.

5. Dohrn, A. Untersuchungen iiber Bau und Entwickelung der Arthropoden:
1. Ueber den Bau und die Entwickelung der Cumaceen. Jenaische
Zeitschr. v. pp. 54-81, pls. ii, and iii., 1870.

6. Sars, G. O. Om den aberrante Krebsdyrgruppe Cumacea og dens nordiske
Arter. Forh. Vidensk. Selsk. Christiania, 1864, pp. 128-208.

Beskrivelse af de paa Fregatten Josephines Expedition fundne
Cumaceer. Kgl. Svenska Vet.-Akad. Handl. ix. No. 13, 57 pp.
PlSn dee eS Le

8. — Nye Bidrag til Kundskaben om Middelhavets Invertebratfauna:
II. Middelhavets Cumaceer. Arch. Math. Naturvid. iii. pp. 461-512,
pls. i.-xxi., 1878; and op. cit. iv. pp. 1-144, pls. xxii.-lx., 1879.

9. —— Report on the Cumacea. Rep. Voy. ‘Challenger,’ Zool. xix.
73 pp. 11 pls., 1887.

if

10. Crustacea caspia: Part II. Cumacea. Bull. Acad. Sci. St. Péters-
bourg, Nouv. Sér. iv. (xxxvi.), pp. 297-338, 12 pls., 1894.
ilile An Account of the Crustacea of Norway: III. Cumacea, 115 pp.

72 pls., 1899-1900.

CHAPTER xt
THE TANAIDACEA
Order Tanaidacea, Hansen (1895).

Definition.—Peracarida in which the carapace coalesces dorsally
with the first two thoracic somites, and overhangs on each side to
enclose a branchial cavity ; the telson is not defined from the last
somite; the eyes, when present, are usually set on short, im-
movable peduncles ; the antennules may be biramous ; the antennae
may have a small exopodite; vestigial exopodites are sometimes
present on the second and third pairs of thoracic limbs; the first
pair of thoracic appendages are modified as maxillipeds ; they have
an epipodite lying in the branchial cavity, but no exopodite ; the
second pair are chelate; the pleopods are usually present and
biramous ; the uropods are slender; the young leave the brood-
pouch before the appearance of the last pair of thoracic limbs.

Historical.—The first known member of this order was that
described by Montagu in 1808 as Cancer gammarus talpa, now placed
in the genus Apseudes. Leach, Latreille, and others ranked the
species known to them among the Amphipoda, while H. Milne-
Edwards placed them among the Isopoda, remarking, however, that
they established a transition to the Amphipoda. Dana (1852)
united them with certain parasitic and other Isopoda in a group
Anisopoda interposed between Isopoda and Amphipoda, and Spence
Bate in 1868 combined them with the Isopod Anthuridae and
Anceidae (Gnathiidae) in a no less heterogeneous group of “ Isopoda
aberrantia.” Van Beneden (1861) called attention to the im-
portance of the carapace of Tanais as a systematic character, and
approximated that genus to Cuma and Mysis. F. Miiller (1864)
also attached great weight to the same character. Gerstaecker
(1886) once more included the Tanaidacea among the Amphipoda ;
but this retrograde step has met with little support, and most
modern writers follow Sars in ranking them as one of the tribes of
Isopoda (Chelifera). Claus, however, in 1888 placed them in an
independent order, for which he adopted Dana’s name Anisopoda,

190

THE TANAIDACEA 19I

and which he placed between Isopoda and Cumacea. Hansen
adopts the same view of their affinities, and suggests for the order
the name which is here used. Claus’s monograph on Apseudes is
the most important source of information on the anatomy of the
group, and the works of G. O. Sars are no less important as
regards the description and classification of genera and species.

MoRPHOLOGY.

The general form of the body (Fig. 116) resembles that typical
of the Isopoda, being depressed or sub-cylindrical, with a compara-
tively short abdominal region and with the telson coalesced with
the last somite. The homology of the reduced carapace with that
of the Cumacea and Mysidacea is indicated by the small cavity
which it overhangs on each side and within which lies the epipodite
of.the first thoracic appendage. Only the first and second thoracic

~
Ar
aes Bo {\ 43
te 7 aN |
Arf \ N_4 =
Fic. 116.
Apseudes spinosus, female. ex, vestigial exopodites of second and third thoracic limbs ; oc,
ocular lobe or peduncle ; sc, scale (exopodite) of antenna ; wr, flagelliform uropod. (After Sars.)

somites are coalesced with the carapace, but in Sphyrapus the third
somite is firmly attached to the head-region, although, according
to Sars, it is not completely fused with it.

The eyes are often absent, but when present they are usually
set on fronto-lateral processes of the head (Fig. 116, oc), which in
many species are defined by grooves and, although not movable,
appear to correspond to the ocular peduncles of the podophthalmate
groups.

A ppendages.—The antennules are biramous in the Apseudidae.
In some species the two flagella are stated to arise from a common
basal segment, so that the peduncle consists of four segments. The
antennae have, in the Apseudidae, a small exopodite (Fig. 116, sc),
and the protopodite consists of two segments, not, as is usual in
the Peracarida, of three. The mandible carries a palp in the Ap-
seudidae, but not in the Tanaidae. The mazillulae, in the former
family (Fig. 117, B), have two endites and a palp of two segments,
but in the Tanaidae the proximal endite is wanting and the palp
is unsegmented. The mavillae of the Apseudidae “Fig. Lio)

192 THE CRUSTACEA

have asmall palp. In the Tanaidae the whole appendage is vestigial.
The lower lip of the Apseudidae (Fig. 117, A) is peculiar in having
each of the lobes terminating in a movably articulated lappet.

The first pair of thoracic appendages are muzillipeds (Fig. 117, D),
agreeing with those of the Cumacea and Isopoda in having coupling-
hooks on the endite of the basipodite. The epipodite (ep) projecting
backwards into the branchial chamber is most fully developed in the
Apseudidae, where it consists of a peduncle bearing a spoon-shaped
membranous plate which terminates posteriorly in a filiform pro-
cess and is produced anteriorly as a rounded lappet fringed with
setae. The resemblance of this apparatus to the branchial
epipodite of the Cumacea is unmistakable, and the filiform
termination may be compared with the inflected apex generally
found in that group. A small lobule found in some Tanaidae may
perhaps represent the exopodite. In the Tanaidae the maxillipeds

A.

= —

Fic. 117.

Mouth-parts of Apseudes spinosus. : A, lower lip with movable lobes. B, maxillula; p, palp.
Sauer? _D, maxilliped ; en, terminal lobe or endite of basipodite; ep, epipodite. (After
are more or less united at the base, the coxopodites, and some-
times also (as in the Amphipoda) the basipodites, being coalesced.

The second pair of thoracic limbs are in nearly all cases com-
pletely chelate and are usually much stronger than the succeeding
pairs. The third pair in the Apseudidae are flattened and apparently
fossorial in function. The minute exopodites (Fig. 116, ez) with
which these two pairs are provided in many Apseudidae are placed
close to the exhalent and inhalent openings of the branchial cavity
respectively, and by their vibratory motion assist in producing the
respiratory current. In all the thoracic limbs the coxopodite is
very small, and in the posterior five or six pairs the limb ends
in a curved claw.

In the Apseudidae there are five pairs of oostegites (the first
pair very small) attached to the thoracic limbs, from the second to
the sixth pair. In some, perhaps all, Tanaidae only one pair of
oostegites is present, on the sixth thoracic limbs.

The pleopods may be fully developed in both sexes, but some-
times they are reduced in number or altogether absent in the

}

THE TANAIDACEA 193

female. The wropods are nearly terminal on the last segment of
the body. In Apseudes the two rami are long, multiarticulate,
and flagelliform. In other cases the rami may be much reduced
and the exopodite is sometimes wanting.

Internal Anatomy.—In Apseudes, the alimentary canal has three
pairs of hepatic caeca. The heart is elongated, extending through
the six free somites of the thorax, giving off a median aortic vessel
anteriorly and a pair of diverging abdominal arteries (but no
median vessel) posteriorly. In Leptochelia and in the young of
Apseudes it has two pairs of ostia, but in the adult Apseudes the
right anterior ostium disappears and those of the posterior pair
become asymmetrically placed. In Yanais only one pair persists.
The anterior aorta, after dividing to encircle the brain in the
median plane, forms a circumoesophageal ring, but there is no
subneural sternal artery. The lateral folds of the carapace are
traversed by a network of blood-channels supplied by branches
from the anterior aorta, and no doubt form the chief organs of
respiration, possibly assisted by the epipodites of the maxillipeds.

Considerable importance has been attached to the thoracic
position of the heart in the Tanaidacea as differentiating them
from the Isopoda and indicating affinity with the Amphipoda. As
a matter of fact, however, in certain Isopoda (Jaera) the anterior
end of the heart extends as far forward as it does in Apseudes,
and the suppression of the abdominal portion, leaving intact the
paired abdominal arteries, would produce a disposition of parts
essentially similar to that of the Tanaidacea.

The maxillary gland is well developed in Apseudes, and a vestige
of the antennal gland has been described. Dermal glands are
commonly found on the body and limbs, and in some Tanaidae the
secretion appears to be utilised in forming the tubes of mud in
which the animals live. In Heferofanais groups of gland-cells are
described situated on each side of the anterior thoracic somites and
opening by long ducts on the terminal segments of the correspond-
ing legs, an arrangement which recalls that found in certain
Amphipoda. The nerve-chain in Apseudes has all the ganglia of the
post-oral somites distinct.

It was stated by F. Miiller that a species of Zanais possessed an
open statocyst-cavity containing a statolith in the basal segment of
the antennule, but the observation has not been confirmed. .

The reproductive organs of both sexes are of a simple type.
The vasa deferentia, in Apseudes, open close together on a median
process of the last thoracic sternum. <A seminal vesicle is formed
in Tanais and in Leptochelia by fusion of the two vasa deferentia,
but here also the external opening is paired.

Sexual differences are often strongly marked. The olfactory
filaments of antennules and antennae are, as usual, more numerous

13

194 THE CRUSTACEA

in the male; the chelae are often much stronger and differently
shaped ; and the pleopods are always well developed in that sex
even when they are reduced or absent in the female. In several
genera of Tanaidae the oral appendages, with the exception of the
maxillipeds, are entirely lost by the sexually mature male. Fritz
Miiller described a remarkable dimorphism of the males in a species
of Leptochelia. One form of male was distinguished by the great
development of the olfactory filaments on the antennules, and had
chelae very similar to those of the female. In the other form the
olfactory filaments were less numerous, but the chelae were greatly
elongated and slender. These observations have been doubted by
subsequent writers, but they have recently received partial con-
firmation from the work of G. Smith.

Development.—The embryo shows at first a dorsal curvature as
in the Isopoda. A paired ‘dorsal organ” is present. The larvae
leave the brood-pouch with the last pair of thoracic limbs and the
pleopods undeveloped. In Apseudes, according to Claus, the lateral
plates of the carapace are at first extended as wing-like processes,
becoming afterwards bent downwards over the branchial epipodites
of the maxillipeds and fixed in position by peg-like outgrowths of
the sternum on each side.

REMARKS ON HABITS, ETC.

The Tanaidacea are exclusively marine and occur from between
tide-marks to depths of over 2000 fathoms. Many burrow in
mud, some inhabit tubes of mud agglutinated by the secretion of
the dermal glands, and several species of Tanaidae are recorded as
living in rock-crevices among a felt-like mass of filaments, pre-
sumably also secreted by the animals.

Most Tanaidacea are minute. Many species do not much
exceed one millimetre in length, but some Apseudidae reach
13 mm. or more.

No fossil Tanaidacea are known.

AFFINITIES AND CLASSIFICATION.

Mention has been made above of the very varied opinions
which have been held regarding the systematic position of the
members of this order. Among recent writers, however, there is
general agreement that the Tanaidacea must either stand as a
distinct order or be merged in the Isopoda as the most primitive
sub-order of that group. While their resemblance to the Isopoda
in general form is considerable, their marked divergence in such
characters as the possession of a distinct carapace, with its branchial
chambers, and the form of the epipodites of the maxillipeds, fully
justifies their separation.

|

THE TANAIDACEA 195

The two families into which the order is divided are dis-
tinguished by many important characters, and it may prove
necessary in the future to rank them as sub-orders.

OrpveR Tanaidacea, Hansen (1895).

Family ApsruDIDAE. Apseudes, Leach; Sphyrapus, Norman and
Stebbing. Family Tanatpan. Tanais, Audouin and Milne-Edwards ;
Heterotanais, G. O. Sars ; Leptochelia, Dana.

LITERATURE.

1. Boas, J. E. V. Wleinere carcinologische Mittheilungen: 1, Eine neue Art
der Gattung Apseudes. Zool. Jahrb. ii. pp. 109-116, 1886.

. Claus, C. Ueber Apseudes Latreillei, Edw., und die Tanaiden. Arb. zool.
Inst. Wien, v. pp. 319-332, 2 pls., 1884; op. cit. vii. pp. 189-220, 7 pls.,
1887.

3. Dohrn, A. Untersuchungen iiber Bau und Entwicklung der Arthropoden :
7. Zur Kenntniss vom Bau und der Entwicklung von Zanais. Jenaische

Zeitschr. v. pp. 293-306, pls. xi. and xii., 1870.

4. Sars, G. O. Revision af Gruppen Isopoda chelifera, med charakteristik of
nye herhen horende Arter og Slaegter. Arch. Math. Naturvid. vii.
pp. 1-54, 1882.

5. —— Nye Bidrag til Kundskaben om Middelhavets Invertebratfauna : III.
Middelhavets Saxisopoder (Isopoda chelifera). Arch. Math. Naturvid.
Xl. pp. 268-368, 15 pls., 1886.

6. Smith, G. High and Low Dimorphism; with an account of certain
Tanaidae of the Bay of Naples. Mitth. zool. Stat. Neapel, xvii. pp.
312-340, pls. xx.-xxi., 1905.

bo

Many of the works quoted in the list at the end of the next chapter deal, in
part, with the Tanaidacea. See especially those of Beddard, Delage, Hansen
(Plankton Expedition), Norman and Stebbing, Richardson, Sars, and Spence
sate and Westwood.

CHAP IE et
THE ISOPODA

Order Isopoda, Latreille (1817).
Sub-Order 1. Asellota.

4. 2. Phreatoicidea.
z 3. Flabellifera.
Bs 4. Valvifera.

- 5. Oniscoidea.

“ 6. Epicaridea.

Definition. —Peracarida in which there is no distinct carapace,
but the first thoracic somite (rarely also the second) is coalesced
with the head; the telson is rarely defined from the last somite ;
eyes sessile or set on immovable processes of the head ; antennules
uniramous (except in bathynomus); antennae sometimes with a
minute exopodite; thoracic limbs without exopodites; first pair
modified as maxillipeds, the epipodite, when present, not enclosed
in a branchial cavity ; remaining pairs all similar or variously
modified, coxopodite always short, often fused with the body and
expanded laterally ; pleopods typically biramous, with lamellar,
branchial rami, generally the second and sometimes also the first
pair modified in the male ; heart lying wholly or partly in abdomen ;
the young leave the brood-pouch before the appearance of the last
pair of thoracic limbs.

Historical.—The terrestrial habits of the more familiar members
of this order, and the close resemblance which some of them bear to
certain Diplopoda (Oniscomorpha), led to their being widely separated
from the other Crustacea in many of the earlier systems of classifi-
cation. Even Latreille, to whom the name Isopoda is due, placed
them at first among the Insecta. Leach ranked them along with
the Amphipoda in his group Edriophthalma, thus giving them the
position which they occupy in most modern systems. Our know-
ledge of the morphology and classification of the Isopoda is largely
due to the work of Scandinavian naturalists, especially to the
monographs of Schiddte, Meinert, G. O. Sars, Bovallius, Budde-

196

THE ISOPODA 197

Lund, and Hansen. The remarkable group of the Epicaridea has
attracted many investigators, but it is especially to the memoirs of
Giard and Bonnier that the student must turn for a clear account
of their structure and complicated life-
histories. As regards the internal anatomy
of the Isopoda, the literature is scattered
and fragmentary, but Delage’s study of
the circulatory system must not be passed
without mention. Bullar’s discovery of
hermaphroditism among the Cymothoidae
is also noteworthy.

MoRPHOLOGY.

In the majority of the free-living
Isopoda the body (Fig. 118) is more or
less flattened, with an oval outline as seen
from above and with a short abdominal Fig. 118.
region, In the Arcturidae and Anthuridae, ibaa itt ere rat
however, it is elongated and subcylindrical,
and in some of the latter family it is almost vermiform. In Phrea-
toicus (Fig. 119) the body is laterally compressed and the aspect is
that of an Amphipod. In the parasitic Epicaridea the adult female

Fic. 119.
Phreatoicus assimilis, 9, from the side. x S. (After Chilton.)

becomes more or less distorted and deformed and may even lose all
trace of segmentation. In addition to the first, the second thoracic
somite becomes united with the head in the Gnathiidae and Serolidae,
in the genus Sfenasellus among the Asellota, and in a few Valvifera.
The last thoracic somite occasionally remains of small size and
without appendages in the adult, as it nearly always is in the

198 THE CRUSTACEA

young. Very often some or all of the abdominal somites are fused
together, and the last somite is always coalesced with the telson
except in certain Anthuridae. The abbreviation of the abdomen
is least in the Phreatoicidae ; in the other families the anterior
somites are short and crowded together, though the telsonic seg-
ment is often of large size. The abdominal somites are usually
expanded laterally into pleural plates, and the thoracic somites
may be similarly produced over the bases of the legs, but in these
the pleural plates are often supplemented or replaced by the
expanded coxopodites which here form the coal plates or so-called
“‘ epimera.”

Appendages. —'The antennules are usually short, and in the
Oniscoidea they are almost or quite vestigial. They are never
biramous except in athynomus, where a minute vestige of the
inner flagellum is present, and in the cryptoniscan larvae of some
Epicaridea.

The antennae vary much in length, being several times as long
as the body in some Asellota, while in the Epicaridea they are
hardly more than vestiges. The peduncle usually consists of five
segments, but in the Asellota and in Bathynomus and Cirolana it
has six. In the Asellota a minute movably articulated scale repre-
senting the exopodite is sometimes present on the third segment.
In all other Isopoda the exopodite is absent. In the Arcturidae the
antennae are very large and strong and are used in seizing prey.

The mouth-parts of the Isopoda show great diversity of struc-
ture, many modifications being correlated with the parasitic or
semi-parasitic habits of certain groups. In the more typical forms
(e.g. Asellus) the mandible carries a palp of three segments, and has
a serrated incisor process, with a lacinia mobilis, at least on the
left side of the body, a row of spines, and a strong molar process.
The molar process is movably articulated with the body of the
mandible in the Cirolaninae (Fig. 120, A). The mazillula (Fig.
120, B) has two endites (corresponding, according to Hansen, to
the first and third segments) directed distally and bearing strong
setae or spines. There is no trace of a palp such as exists in the
Tanaidacea. The maxilla (Fig. 120, C) has three endites, the
proximal one directly continuous with the basal part and directed
obliquely inwards; the two others are directed distally, over-
lapping each other and movably articulated with the basal part ;
Hansen regards these as resulting from the division of a single
endite corresponding to the third segment.

The first thoracic limb is always specialised as a mazzilliped
(Fig. 120, D) and closely associated with the other mouth-parts.
It has a short but distinct coxopodite bearing externally a lamellar
epipodite (ep) generally more or less indurated, and not, apparently,
branchial in function as it is in the Tanaidacea, but serving as an

THE ITSOPODA 199

operculum to cover the lateral parts of the other oral appendages.
The basipodite is produced distally into a large endite (/*) which is
sometimes movably articulated (Bathynomus, Cirolana, Chiridotea),
and which bears one or more coupling-hooks (c) interlocking with
those of the opposite side. The endopodite or palp consists, in
the typical case, of five more or less lamellar segments, but the
number is often reduced. In the ovigerous females of Asel/us and
of certain genera of Valvifera the coxopodite bears a small lappet,
fringed with setae, projecting backwards into the marsupium and

Cy
i. 9)

Fae

Fic. 120.

Mouth-parts of various Isopoda. A, mandible of Cirolana borealis. B, maxillula of Chiridotea
entomon. C,maxillaofsame. D, maxilliped of same. E, maxilliped of adult female of Rocinela
danmoniensis. F, maxilliped of adult maleofsame. c, coupling-spine ; ep, epipodite ; 7, incisor
process ; /1, 12, 13, 14, endites of successive segments of the appendages (according to Hansen’s
later interpretation the endites /3, /4 of the maxillula result from the division of a single endite) ;
lam1-2, laminar outgrowths of first and second segments of maxilliped ; m, molar process ; ~,
palp ; s, lacinia mobilis and spine-row of mandible, which in this case are closely associated
together ; 1, 2, 3, successive segments of the appendages. (After Hansen.)

resembling the coxal appendage of the second thoracic limb in the
females of Cumacea. A similar plate, more largely developed, is
found in the females of Cymothoidae (Fig. 120, E) and Epicaridea
and of some genera of Sphaeromidae, where it is associated with
an expansion of the basipodite and with the epipodite, giving a
lamellar character to the whole appendage. In all these cases the
vibratory motions of the maxilliped cause a current of water to
pass through the marsupium for the aeration of the developing
embryos. A similar expansion of the basipodite united with the
epipodite occurs also in Serolis, where, however, the coxal lobe is
not developed. The position of this coxal lobe and its occurrence

200 THE CRUSTACEA

only in the adult female suggest its possible homology with the
oostegites of the following somites.

As an example of extreme modification of the mouth-parts and
of exceptionally marked changes taking place during development,

Fic. 121.

Gnathia mawillaris. A, late larval form (Praniza-stage). B, head of same, from below,
further enlarged. OC, adult female. D, second thoracic appendage of same, further enlarged.
E, adult male. F, maxilliped (first thoracic appendage) of same, further enlarged. G, second
thoracic appendage of same. m, mandible of male ; map, maxilliped of larva; II, III, VII,
second, third, and seventh thoracic appendages (the eighth is undeveloped in adults of this
family). (After Sars; B partly after G. Smith.)

the oral apparatus of the very aberrant Gnathia may be here
described. In the larval state (Fig. 121, A), Gnathia is parasitic
on fish, and the suctorial mouth-parts form a short conical
proboscis (Fig. 121, B). The mandibles are styliform, finely
serrate on the inner edge, without palp, molar process, lacinia
mobilis, or spines. The maxillulae and maxillae are simple, slender

THE ISOPODA 201

styles. The maxillipeds (mrp), which close the oral cone below,
have an elongated basipodite produced distally into a slender
endite, with many coupling-hooks; the next segment is also pro-
duced distally as an acute, serrate point, and the remaining
segments of the endopodite are coalesced into a short palp. The
appendages of the second thoracic segment (II), which in this
family is coalesced with the head, lie on either side of the oral cone
and end in strong curved claws which no doubt assist in pene-
trating the skin of the host. The adult animals are free-living
and have the mouth-parts very differently developed in the two
sexes. In the male (Fig. 121, E) a pair of relatively enormous
mandibles (im) are articulated at the outer corners of the front
margin of the head and are apparently used only as defensive
weapons. The small aperture of the mouth is placed much further
back on the lower surface of the head. The maxillulae and
maxillae are entirely lost. The maxillipeds (Fig. 121, I) are broad
and flattened, composed of six segments tapering gradually to the
apex ; the endite of the basipodite is small and the other segments
are fringed externally with long plumose hairs. The appendages
of the second segment (Fig. 121, G) have lost the pediform
character which they have in the larva and in all other Isopoda,
and form a pair of overlapping valves closing over the oral area.
Each consists of a large oval plate showing traces of three segments
and bearing distally one or two minute terminal segments. In
feeding, these valves are opened out and the vibratory movements
of the maxillipeds produce a current of water which is supposed
to carry food-particles towards the mouth. In the female (Fig.
121, C) the mandibles have disappeared and the maxillipeds are
similar to but smaller than those of the male. The second
thoracic limbs (Fig. 121, D) are, however, very different, consisting
of a small leg-like appendage of three segments, having at its base
a large oval plate which probably represents an oostegite, although,
in this genus, distinct oostegites are not found on any of the
other limbs.

In the Epicaridea the styliform mandibles are enclosed in a
suctorial “oral cone” formed by the upper and lower lips. The
maxillulae and maxillae are vestigial or absent, and the lamellar
maxillipeds serve, as already mentioned, to keep a current of water
flowing through the brood-pouch. In the ovigerous females of many
Cymothoidae the mouth-parts are covered by the anterior oostegites,
so that the animal is incapable of feeding, and in some genera of
Sphaeromidae the mouth-parts of the adult females (with the
exception of the maxillipeds) are reduced and functionless.

The last seven pairs of thoracic appendages in the Isopoda are
typically developed as walking-legs which may, as in the Oniscoidea,
present a uniformity of size and shape justifying the name Isopoda,

202 THE CROSTACEA

but which in other cases undergo many modifications for prehensile,
natatory, and other functions. The coxopodite has the form of a
complete segment movably articulated with the body only in the
Asellota (Fig. 122, cx). In all
other Isopoda it is more or less
completely fused with the body
and is often expanded into a coval
plate overhanging the attachment
of the limb and replacing the
Fic, 122. pleural expansion of the somite
Thoracic somite of Jaera marina, separated to which it belongs. An interest-
and seen fromin front. bs, basipodite of tho- = : : . : .
racic leg ; cx, coxopodite; pl, pleural plate. Ing series illustrating this substitu-
tion can be traced within the
family Idoteidae. In Jdotea hecticu (Fig. 123, A), the pleural plates
(pl) of the thoracic somites are well developed and completely
cover the coxopodites (c.), of which the outline can be traced on the

By on

CxX>-

pl- =

Fic. 123.
Margin of thoracic somites of, A, Idotew hectiew ; B, I. ochotensis; C, Chiridotea sabini. The

upper figures show the under surface, the lower the upper surface. cx, coxal plate (dotted) ;
pl, pleural plate ; 0, radiment of oostegite.

under-side of the plates near the outer edge. In other species of
the same genus (Fig. 123, B) the coxal plate projects beyond the
outer margin of the pleuron for a part of its length so as to be
visible on the upper surface. In yet other species of the genus
and in the allied Chiridotea (Fig. 123, C), the pleura are no longer
to be distinguished, and their place is taken by the greatly de-
veloped coxal plates, which are marked off, on the dorsal surface,
by distinct sutures, generally allowing a slight amount of move-

THE ISOPODA 203

ment. This condition is found in the Cymothoidae, Serolidae,
some Sphaeromidae, and in the Tylidae among the Oniscoidea.
When the suture line disappears, as in most Oniscoidea (Fig.
118), it is impossible to distinguish the coxal plate from a true
pleuron. In all Isopoda, however, with the single exception
of the genus Plakarthrium (Sphaeromidae), the coxopodites of
the second thoracic somite (the first free somite) are completely
coalesced with the body.

The ischiopodite of the thoracic legs is generally more or less
elongated, not very short as it
is in Tanaidacea and Amphi-
poda. The dactylopodite gener-
ally ends in a stout claw which
may be completely coalesced
with the segment or defined
from it by a suture. In Janiru
and some other Asellota, how-
ever, there are several stout
claw-like spines.

Very commonly one or
more of the anterior pairs of
thoracic legs assume a_ pre-
hensile function and become
more or less completely sub-
chelate, through never forming
a perfect chela such as is
found among the Tanaidacea.
The most perfect natatory legs
are found in Munnopsis and
related genera, where the last
three pairs have the carpus and Fic, 124.
propodus expanded into oval Gyge branchialis (Bopyridae). a, female, seen

e 5 from ventral side; Bri, oostegite ; K, abdominal
paddles fringed with long setae. appendages. , abdomen of same with adheritig

In Amesopous (Valvifera) Pincd? hom Claus's Tevbook) onat# ane
the fourth and fifth pairs of
thoracic appendages (first and second peraeopods) are unrepresented,
except by the oostegites in the female, a condition curiously repeat-
ing that found in the Caprellidea among Amphipoda.

The oostegites (Fig. 124, Bri), which, in the great majority of
Isopoda as in other Peracarida, form the brood-chamber of the
female, are clearly seen in the Asellota to be attached to the
coxopodites of certain of the thoracic legs. In the other tribes
the coxopodites are more or less completely coalesced with the
corresponding somites and the oostegites appear to spring from
the ventral surface of the body close to the bases of the legs. In
certain Cymothoidae and Epicaridea a pair of oostegites is present

204 THE CRUSTACEA

on each of the seven free thoracic somites, the last two pairs,
however, being very small. If, as has been suggested above, the
coxal lobe of the maxillipeds is homologous with the oostegites,
we have the possibility of these structures being developed on all
the thoracic appendages. More usually, however, only the first
five free somites bear oostegites, and the number may be still
further reduced, certain genera of Arcturidae possessing only one
pair attached to the fourth free somite.

Though the development of the oostegites has been traced in
only a few cases, it is known that important differences occur in
this respect. In Asellus they appear as small buds from the
coxopodites, increasing in size at successive moults until maturity
is reached. In the Oniscoidea, on the other hand, no trace of
oostegites is visible externally up to the moult which immediately
precedes oviposition. Just before this moult they are developed
underneath the cuticle, and when this is cast off they at once
expand to their full size. Special structures aiding or replacing
the oostegites in containing the brood will be described later in
connection with the reproductive system, but it may be noted here
that in a few Isopoda (Cassidina and a few allied genera among the
Sphaeromidae, and some Epicaridea) the oostegites appear to be
entirely wanting.

The pleopods are almost always biramous, with a short proto-
podite in which three segments can be recognised in Bathynomus,
and with lamellar rami generally overlapping each other with the
exopodite in front. One or both of the rami may be crossed by a
suture-line dividing it into two segments. In the simpler cases all
the pleopods are similar (except for the sexual modifications to be
described below), both rami serving as respiratory and in many
cases also as natatory organs. The latter function is indicated by
a marginal fringe of long setae and by the presence of a group of
coupling-hooks on the inner side of the peduncle. Pleopoda of
this type are found with comparatively slight modifications in the
Phreatoicidae, Gnathiidae, and Cymothoidae, but in some members
of the last two families the natatory setae, present in the young,
are lost in the adult. This is the case also in the Epicaridea, where
the pleopoda of the adult may become much reduced or altogether
suppressed, or may, on the other hand, develop into arborescent
branchiae. In the aberrant Cymothoid Lathynomus the endo-
podites bear tufts of ramified branchial filaments. Even in the
Cymothoidae, however, the uniformity of the pleopods is slightly
qualified by the fact that the endopodite of the fifth pair is always
devoid of marginal setae. This leads to the specialisation of
functions found in Sphaeromidae and Serolidae, where the anterior
pairs (the first three in Serolidae and many Sphaeromidae) are
exclusively natatory and the posterior pairs exclusively branchial.

THE ISOPODA 205

In many Sphaeromidae one or both rami of the last two pairs are
transversely plicated so as to increase the respiratory surface. In
some members of these families the exopodite of the fifth pair is
more or less indurated and forms a kind of operculum protecting
the more delicate appendages behind it. Opercular structures
having a similar function are formed in different ways in other
families. In some Anthuridae the first pair of pleopods are
enlarged and cover the remaining pairs. In the Asellidae and
Stenetriidae the exopodite of the third
pair performs the same function. In
the Parasellidae an unpaired plate
formed by the coalescence of the first
pair forms the operculum in the female,
the male having a tripartite operculum
formed by the first and second pairs.
In the Valvifera (Fig. 125), finally,
the pleopods are covered in by the
valve-like uropods. A very special
line of modification has been followed
in the case of the Oniscoidea. In the
Ligiidae, which are in many ways the
most primitive family, the pleopods are

Fic. 125.

Under-side of abdomen of male

all similar, with the exopodites stouter
than the endopodites but sharing in
the respiratory function. In many
genera of the remaining families, how-

Idotea baltica, with one of the uropods
removed to show the pleopods. 1, 2,
3, first three somites of abdomen; ¢,
telsonic segment comprising the last
three abdominal somites coalesced
with the telson; plp, pleopods; wr,

uropod ; p, penes, attached to sternum
of last thoracic somite. (After Sars.)

ever, the exopodites of the first and
second, and sometimes of all five, pairs
are specially adapted for aerial respiration by the development
within them of small cavities opening to the exterior by slit-like
apertures and giving rise internally to a system of ramifying
tubules filled with air (Fig. 126). These tubules, which are lined
with a delicate chitinous cuticle, are known as pseudo-tracheae (tr).
In certain cases (Oniscus) in which pseudo-tracheae are absent, their
place is taken by a system of air-filled spaces immediately under
the cuticle of the exopodite. These spaces do not communicate
with the exterior, and appear to become filled with air by diffusion
through the cuticle.

In the majority of Isopoda the second, and sometimes also the
first, pair of pleopods present special modifications in the male sex,
the only exceptions being the Epicaridea and the small and
aberrant family of the Gnathiidae, among the Flabellifera, where
no such modification is found. In the remaining families of the
Flabellifera and in the Phreatoicidea and Valvifera, the lamellar
endopodite of the second pair bears, in the male sex, a rod-like
process (appendix masculina) (Fig. 127, m) articulated with its inner

206 THE CRUSTACEA

edge and grooved for the reception of the bundles of spermatozoa
which it is its function to transfer to the female. This rod appears

an TAS
Woe
xX i

Sagar orem ao ooh omera yar Is
a eee:
Se a

Fic. 126.

A, exopodite of first pleopod of Porcellio scaber ; the tuft of pseudo-tracheae is seen through
the transparent cuticle. B, vertical transverse section through same. C, part of section further
enlarged. art, point of articulation of exopodite with peduncle ; c, cuticle ; gr, ‘grooved area”
of cuticle; hy, hypodermis; 7, nucleus of hypodermis of pseudo-tracheal tube; 0, external open-
ing of pseudo-tracheae ; tr, pseudo-tracheae. (After Stoller.)

to be the distal segment of the endopodite. In the groups just
mentioned the pleopods of the first pair are similar or present
but slight differences in the two
sexes, but in the majority of the
Oniscoidea and in the Asellota the
first pair are also modified in the
male sex. In the males of the
Oniscoidea the inner ramus of the
second pair is styliform and com-
posed of two segments, of which
the proximal corresponds to the
main part of the endopodite in
groups above mentioned. In the
family Ligiidae this is the only
modification of the pleopods in the
male sex, but in all the other
Oniscoidea the first pair have the
endopodites also styliform, though

Fic. 127. d
Second pleopod of an ovigerous female unsegmente : ‘
of Nerocila maculata, showing persistence In the Asellota the sexual modi-

of the appendix masculina (m). en, endo- E
podite ; ex, exopodite; e, laminar expan- fications of the pleopods are more

sion from outer edge of protopodite. complex and differ from those of all
other Isopoda. The second pair are always absent in the female.
In the females of Asellidae the first pair are small, uniramous, and
separate ; in the Stenetriidae and Parasellidae they are coalesced,

THE ISOPODA 207

forming, in the latter family, a large operculum which completely
covers the following pairs. In the male sex the Asellidae have the
first pair not greatly different from those of the female ; the second
pair are small, with a short protopodite and two rami, each of two
segments, the endopodite having a cavity in the distal segment. In
the Stenetriidae the first pair are partly fused together and the second
pair are to some extent intermediate in structure between those of
the other two families. In the Parasellidae the first pair are fused
together, their enlarged protopodites each with a small immovable
terminal ramus forming the middle plate of a tripartite operculum,
of which the lateral parts are the enlarged protopodites of the
second pair. The rami of the latter pair are borne on the inner
margin of the protopodite ; the exopodite of two segments is hook-
shaped and serves to fasten the lateral to the middle plate of the
operculum ; the endopodite forms a geniculate copulatory organ of
two, sometimes of three segments, with a cavity in its distal part
communicating with the exterior by a narrow canal.

In most Isopoda the wropods differ widely in form and position
from the pleopods. In the adult females of some Epicaridea,
however, the uropods do not differ, except in size, from the
appendages in front of them, and this is also the case in the
Cymothoid genera Anuropus and Branchuropus, where they resemble
the pleopods in structure and position and appear to share their -
branchial function. Although the uropods are usually biramous,
one or other of the rami may disappear in many <Asellota, some
Sphaeromidae, Valvifera, and Oniscoidea. ~The uropods are entirely
wanting in the Sphaeromid Vireia and in some Epicaridea. The
rami are never composed of more than one segment except in the
Asellotan Acanthocope, where the uniramous uropods present three
or five segments, including the peduncle. In’ the Valvifera
the uropods are curiously modified in form and position (Fig. 125),
They are attached far forwards at the sides of the greatly enlarged
telsonic segment, and are folded inwards so as to cover completely
the branchial pleopods. Each consists of a large plate formed by
the expanded protopodite with the small endopodite at its tip,
while the exopodite! is vestigial or absent. In many Anthuridae
the exopodite is attached near the base and the endopodite at the
tip of the elongated peduncle (leading to the erroneous statement
that the endopodite has two segments), and the exopodite is
usually folded backwards over the dorsal surface of the telson.

Alimentary System.—The stomodaeum forms, in the majority of
Isopoda, a masticatory stomach, which is comparatively simple in

1 What is here called the exopodite is usually regarded as the endopodite, and
vice versa. The interpretation given above depends on the assumption that the
uropods have reached their present position by a movement of rotation, not of simple
translation.

208 LHEV CRUSTACEA

Asellus and Chiridotea and more complicated in the Oniscoidea.
The number of types in which its structure has been studied is,
however, too small to admit of profitable comparisons between
them. In parasitic forms with suctorial mouth-parts the fore-gut
is probably always more or less modified, but little is known of the
details except in some Epicaridea. In the Entoniscidae the short
and narrow oesophagus leads into a spherical or bilobed chamber,
the cephalogaster, lined with villi and rhythmically contractile.
This is followed by a second chamber, of which the lumen is
reduced to a crescentic section by a
strong ridge or typhlosole on the
dorsal side clothed with setae which
constitute an effective strainer. A
third chamber with. muscular walls,
contracting alternately with the cepha-
logaster, is known as Rathke’s organ.
In the Bopyridae the cephalogaster
alone has been recognised.

Three pairs of hepatic caeca are
present in Idoteidae and Cymothoidae
(Fig. 128, hep); two pairs in Asellus,
Serolis, and the Oniscoidea (except
Ligia, which has three); and only
one pair in Gnathia, Paranthwra, and
the Epicaridea, in which group the

Fic. 128. caeca may give off diverticula. It
Aega psora, g, dissected from the has been stated that, apart from the
dorsal side to show the alimentary and hepatic caeca, the mid- gut of the

reproductive systems. 1, stomodaeal
region of the alimentary canal ; 2, thick- embryo gives rise to only a very

walled, suctorial part; 3, thin-walled < :

reservoir; 4, intestine; hep, hepatic short region of the alimentary canal ;
He Ee ae ee ger an, but this has been disputed, and it
seems not unlikely that considerable differences may exist in this
respect between the members of the order. In the blood-sucking
Acga (Fig. 128) the stomodaeum (1) is very short, so that the
point of attachment of the hepatic caeca is near the anterior end
of the gut. It is followed by a thick-walled part (2) which
may possibly have a suctorial function. At about the fourth
thoracic somite this suddenly dilates into a thin-walled chamber
(3) of relatively enormous size, completely filling and distending
the posterior thoracic somites when filled with blood. If this
reservoir be really of proctodaeal origin it seems difficult to suppose
that it does not exercise an absorptive function.

In some Epicaridea (Entoniscidae, Hemioniscus) the proctodaeal
invagination fails to unite with the anterior part of the gut and
either ends blindly or disappears altogether in the adult.

Circulatory System.—The most striking features of the circulatory

THE ISOPODA 209

system in the Isopoda are the great development and minute rami-
fication of the arterial vessels in the more specialised types and the
posterior situation of the heart, the latter feature being correlated
with the localisation of respiration in the abdominal appendages.

The heart lies at the junction of thorax and abdomen, extending
for varying distances into each. When elongated and tubular it
may lie for the greater part of its length in the thorax (Jaera) or
be produced backwards into the abdomen. When shortened and
saccular it lies mainly in the abdomen, only extending into the
last thoracic somite. It communicates with the well-defined peri-
cardium by one or two pairs of ostia.

Anteriorly the heart gives off the median aorta and seven pairs
of lateral thoracic arteries. Of these the three posterior usually
originate separately from the heart, the remaining four arising
from a common trunk on each side. Rarely all seven pairs spring
laterally from the aorta. Anteriorly the aorta passes behind and
below the brain to form, except in certain degraded or parasitic
forms, an oesophageal ring encircling the gullet in front of or below
the oesophageal nerve-ring. Posteriorly this ring is connected
with a ventral system of vessels which vary considerably in their
arrangement. In the more typical cases (Cymothoidae, Sphaero-
midae) a large median subnewral artery runs backwards from the
oesophageal ring along the sternal surface of thorax and abdomen,
giving off numerous lateral branches. The lateral thoracic
arteries mentioned above also contribute to the ventral system,
each one bifurcating as it reaches the lateral part of the
corresponding somite, one branch passing into the limb and
the other ramifying towards the middle line. Between the
ultimate ramifications of these two sets of vessels, those, namely,
of the subneural and of the ventro-lateral arteries respectively,
anastomoses frequently oceur, and in this way a communication
is established in each somite between the dorsal and the ventral
‘arterial systems. But, in addition, in one or other of the thoracic
somites it is found that the ventro-lateral artery on each side passes
directly into the subneural vessel, thus establishing a complete
arterial circle. In certain forms (Jdotea, Ligia) the subneural
artery is for the most part absent, and the ventral system is
formed almost entirely by the ramifications of the ventro-lateral
arteries. Vestiges of the subneural artery, however, persist
anteriorly where a short trunk runs backwards for a little way
from the oesophageal ring, and posteriorly where an abdominal
trunk is formed by anastomosis of branches from the last pair of
ventro-lateral arteries, while in the thorax similar anastomoses give
rise to a succession of short vessels in the middle line as though the
subneural vessel had become disintegrated into sections.

The posterior end of the heart always ends blindly and,is never

14

210 THEOCROSTACE A

continued into a posterior median aorta. In place of this, however,
a pair of abdominal arteries (which may unite into one immediately
after their origin), springing from the ventral surface of the heart
(or, exceptionally, from the last pair of thoracic arteries), run
backwards and send off numerous branches. In certain forms with
natatory pleopods (Conilera) where the muscles of the abdomen are
greatly developed, these vascular ramifications attain a remarkable
degree of complexity. The minute subdivision of the ultimate
arterial branches is also well shown by the vessels supplying the
hepatic caeca.

From the lacunae of the haemocoel the blood is carried to the
branchial pleopods by sinuses which vary somewhat in their
arrangement in the different types. A median ventral abdominal
sinus is nearly always present from which afferent branchial vessels
are given off. Sometimes there are also two great sinuses running
along the lateral margins of the thorax. From the pleopods the
blood is returned by efferent branchial vessels to the pericardium.
In addition to the arterial blood thus received, it appears that a
small amount of venous blood may also enter the pericardium by
some small apertures in its anterior part communicating with the
general lacunar system of the body. The existence of these apertures
is important as a starting-point for comparison with the very
different circulatory system of the Amphipoda.

Excretory System.—The antennal gland of the Isopoda, unlike
that of the Amphipoda, appears to persist only in a vestigial
condition. In Asellus and some Oniscoidea it has been recognised
as a small vesicle or a solid mass of cells without communication
with the exterior. A well-developed maxillary gland of the usual
type has been found in <Asellus, and in Ligidiwm and some other
Oniscoidea. In the Oniscidae it is reduced in size, and appears in
some cases to have no external opening. It has been suggested that
in some of the terrestrial species it may have a salivary function.

It seems probable that in many Isopoda the excretory products
are got rid of by being stored in the so-called “ fat-bodies.” An
excretory function has also been attributed to certain glands opening
on the ventral surface of the posterior thoracic and abdominal
somites.

Nervous System.—The ventral nerve-clhain presents various
degrees of concentration and coalescence of the ganglia, not always
in correspondence with the degree of fusion of the somites. In
Chiridotea and Sphaeroma seventeen distinct ganglia are found,
corresponding to all the post-oral appendages, and in Sphaeroma
an additional ganglion is found in the telson which is not repre-
sented in any other Eumalacostracan. In most cases, however, the
-ganglia in front of the second thoracic form a single mass, and not
more than four ganglia are generally distinct in the abdomen. |

'

THE ISOPODA 211

Sense-Organs.—In Munna and some allied Asellota the eyes are
set on prominent lateral lobes of the head, but there is no evidence
that these represent the movable ocular peduncles of the primitive
Malacostraca. The number of ommatidia in each eye varies from
four in Asellus to about 3000 in Bathynomus. The crystalline body
is generally bipartite, but in one of the ommatidia in each eye of
Asellus it is tripartite. The number of retinular cells and of
rhabdomeres may be 4, 5, or 7 in different genera.

The only Isopoda in which statocysts have been observed are
Anthura gracilis) and another species of Anthuridae, where they
have recently been described by Thienemann. A pair of them are
situated in the anterior part of the telson. Each communicates
with the exterior by a fine canal and contains a single statolith.
Muscles are attached to the wall of each statocyst. In view of the
sluggish movements and burrowing habits of the Anthuridae, their
possession of these organs is somewhat remarkable.

Leproductive System—The ovaries vary in form, but are generally

elongate and tubular and are not connected with each other in

the middle line. In some Epicaridea they give off segmentally
arranged diverticula. The oviducts are short and simple, occasion-
ally (Asellus) dilating to form a sperm receptacle. <A peculiarity
which is quite unique among Crustacea is presented by certain
Epicaridea (Hemioniscidae, Liriopsidae) which have two pairs of
oviducts. As the oviducts, or at least their external apertures, are
not developed until the segmentation of the body has disappeared
in the adult females, it is not possible to determine whether both
pairs belong to one somite.

A remarkable cycle of changes takes place in the female repro-
ductive organs of the Oniscoidea. When sexual maturity is reached,
but before the oostegites have developed, the generative apertures
are present in the usual position, but instead of communicating
with the oviducts, each leads into a blind invagination of the integu-
ment, which functions as a receptaculum seminis. After this has
been filled with sperm in copulation, it acquires a communication
with the oviduct and the sperms pass up into the ovary. At the
next ecdysis the receptacula disappear and the oviducts no longer
communicate with the exterior. The fertilised eggs are stated to
pass into the body-cavity and from thence to the marsupium by
way of a slit-like unpaired aperture between the last two thoracic
somites. This statement, however, can hardly be accepted without
further confirmation, as the existence of a free opening from the
body-cavity (haemocoel) to the exterior would be quite unparalleled
among Arthropoda. A second lot of eggs are fertilised by sperms
remaining in the oviducts and pass into, the marsupium after the
first brood have left it. After liberation of the second brood,

1 According to Gurney, the species is really Cyathura carinata (Kroyer).

212 THLE ACROSS PACE A

ecdysis takes place, the oostegites are cast off and receptacula are
again developed, the animal reverting to the condition in which
it was before impregnation.

The arrangement of the oostegites which form the marsupial
chamber in all normal Isopoda has already been described. In
certain cases, however, brood-pouches are formed in other ways.
In the section Cryptoniscina among the Epicaridea a series can be
traced in which the oostegites diminish in size and finally disappear,
their place being taken by lateral folds of the body. The term of
the series is given by Hemoniscus, in which the brood-cavity is
from the first completely closed, arismg by delamination in a
thickening of the ventral ectoderm.

A remarkably varied series of adaptations for carrying the
eggs and young have recently been made known in the family
Sphaeromidae. In some members of this family the marsupium is
formed by the oostegites in the usual manner, but in others special
brood-pouches are formed by invaginations of the ventral integument,
and in some cases here also oostegites are quite wanting.

In addition to their protective function in sheltering the eggs
and young, it has been suggested that the oostegites may in some
cases supply nourishment to the developing embryos. In certain
Oniscoidea papilliform projections from the sternal surface of the
thoracic somites have also been credited with this function.

The testes, in the majority of Isopoda, consist each of three
follicles (Fig. 128, ¢s) opening into a common vas deferens (v.d).
Only in a few cases is the number of follicles reduced to one on
each side. The external openings are generally set on papilliform
or tubular processes (penes) (Fig. 125, »), which may be fused into
one (Oniscoidea, except Ligiidae, Arcturidae). In the Epicaridea
the penes are commonly absent and the aperture may be paired or
single, but in Priapion a bifurcated penis of great size is present.

The position of the penes sometimes departs a little from the
general rule among Malacostraca in so far as they may spring, not
from the last thoracic sternum, but from the articular membrane
between it and the first abdominal somite, and may even be
attached to the sternum of the latter. It is very improbable,
however, that the vasa deferentia ever perforate the copulatory
appendages of the second pleopods as they have been stated to do
in the Tylidae (Oniscoidea).

The occurrence of protandrous hermaphroditism has been
demonstrated in certain genera of the sub-family Cymothoinae
among the Cymothoidae, and of the tribe Cryptoniscina among
the Epicaridea. It is not known to occur in the other sub-families
of the Cymothoidae; and though its limits within the group
Epicaridea are not exactly known, it is certain that many of the
families, probably the whole of the tribe Bopyrina, are definitely

THE ISOPODA 213

of separate sexes. In certain Cymothoinae the external characters
of the male sex do not completely disappear when the individual
passes into the female phase, the copulatory appendage of the
second pleopods sometimes remaining of conspicuous size even in
specimens which have the marsupium filled with eggs (Fig. 127).
As in many other Crustacea, traces of hermaphroditism probably
exist normally in the young of many Isopoda. In Sphaeroma,
vestiges corresponding to the three testicular follicles are found at
the anterior end of the ovary in young specimens, and what may
be a vestige of the oviduct is found in the male.

Mention may be made here of the supposed occurrence of
“hypodermic impregnation” in the Asellotan Jaera. It is stated
that a spermatophore is inserted by the male between the thoracic
terga of the female, and that it. penetrates the articular membrane
and passes into the body-cavity, discharging its contents into the
oviduct, while the empty capsule is expelled by the oviducal
aperture. The account of this extraordinary process cannot,
however, be accepted without further investigation.

DEVELOPMENT.

The eggs are usually large, with superficial segmentation. In
Hemioniscus, however, which, from the peculiar formation of the
marsupium, is practically viviparous, the eggs are minute, without
yolk, and undergo complete and equal segmentation, giving rise to
a hollow blastosphere. It is characteristic of the Isopoda, as con-
trasted with the Amphipoda, that the developing embryo is curved
towards the dorsal side. A “dorsal organ” is present in many
Isopod embryos, and assumes very diverse forms. In Cymothoidae
it arises as a thickened plate of cells which becomes invaginated,
forming a small cavity opening to the exterior by a narrow neck.
In Oniscus, on the other hand, the thickening is stated to become
constricted off from the dorsal surface and to form a saddle-shaped
plate partly enveloping the embryo and connected with it only by
a narrow stalk, but the accuracy of this account has been denied.
In Asellus a pair of trilobed hollow processes grow out from the
sides of the thoracic region. These have been regarded as repre-
senting the dorsal organ, but Claus has compared them with the
lateral wings of the carapace in the larva of Apseudes. A distinet
carapace-fold has been described in the embryo of Jaera, extending,
at first, over the region of the second thoracic somite, but afterwards
becoming reduced. ‘Transitory rudiments of exopodites are stated
to be present on the thoracic limbs in early embryos of Ligia.

In all Isopoda the young leave the brood-pouch with the last
pair of thoracic limbs undeveloped (as in Tanaidacea and Cumacea),
but otherwise in most free-living species the young are very similar

214 THE CRUSTACEA

to the adults. In many parasites, however, a certain amount of
metamorphosis occurs. In the Cymothoinae, for instance, the
young are free-swimming, but the adults lose the natatory setae of
the pleopods and undergo considerable changes of shape in becoming
permanently attached to the host. In this case the life-history is
complicated by the fact that each individual passes through stages
in which it presents the characters, first of the male, and afterwards
of the female sex. The remarkable changes in the structure of the
mouth-parts, which are accompanied by considerable changes of
general shape, in the Gnathiidae have already been described.

It is in the Epicaridea, however, that the changes during
development are most profound. In spite of the great diversity of
structure among the adults, the natural character of this group is
rendered evident by the uniformity of the larval stages throughout
all the families. In the first or epicarid stage (‘“stade épicaridien,”
Bonnier) (Fig. 129, B) the body is short and broad and strongly
convex dorsally, with seven thoracic and six abdominal somites
distinct ; the antennules are very short, the antennae longer and
used in swimming, and both are sparingly provided with sensory
filaments ; six pairs of thoracic legs are present, all, except some-
times the posterior pairs, strongly subchelate ; the pleopods are uni-
or biramous, with natatory setae ; the uropods are usually biramous
and styliform ; the telsonic segment is generally produced into an
‘anal tube”; eyes are usually present but imperfectly developed.
In the last larval or cryptoniscan stage (“stade cryptoniscien,”
Giard and Bonnier) the body is elongated ; the antennules are often
biramous, with numerous sensory filaments ; seven pairs of thoracic
legs are present, with coxal plates, and at least the anterior pairs are
subchelate; there is no anal tube; the eyes are well developed, some-
times very large. According to Sars, whose views have recently
received support from some experiments by Caullery, a third larval
stage intervenes, in some if not in all cases, between the two just
described. In this stage, formerly described as a distinct genus
under the name J/icroniscus, F. Miiller, the larva is temporarily
parasitic on pelagic Copepoda (Gymnoplea). A certain amount of
retrogressive metamorphosis takes place, the appendages are imper-
fectly segmented, the muscles appear to degenerate, and the pleopods
lose their natatory setae. Later, the larva assumes the cryptoniscan
form and leaves the Copepod to seek a second host. In those
families of the Epicaridea grouped together in the tribe Crypto-
niscina, the male becomes sexually mature in the eryptoniscan stage,
while the adult female, which, in some if not in all cases, is the
same individual in a later stage of development, becomes variously
degenerate and may lose all appendages and even all traces of
segmentation. In the tribe Bopyrina, where the occurrence of
hermaphroditism is doubtful, both sexes pass beyond the crypto-

hd

THE ISOPODA 215

niscan stage before sexual maturity is reached. The male (Fig.
129, A) develops to the bopyroid stage (“stade bopyrien,” Bonnier),
characterised by the reduction in size of most of the appendages ;
antennules and antennae lose their sensory filaments and become
almost vestigial, the thoracic legs are shorter and without coxal
plates, the pleopods are greatly reduced, without natatory setae,
and the eyes are lost or persist only as pigment-spots. The young

Fic. 129.

A, male of Cancrion miser (Entoniscidae). B, larva of Portunion maenadis (Entoniscidae) in
epicarid stage. a, antennule; dg, antenna; ab, abdomen; au, eye; h, testis; he, heart ; 1,
hepatic caeca ; ply-plg, the six pairs of abdominal appendages; 7, oral cone; to-t7, second to
seventh pairs of thoracic appendages (the eighth pair are undeveloped at this stage); th, thorax.
(After Giard and Bonnier, from Korschelt and Heider’s Embryology.)

post-larval female is generally similar to the male, so that we may
speak of a bopyroid stage in both sexes, but the adult female is
usually much modified, often asymmetrical and distorted by the
great development of ovaries and brood-pouch (Fig. 130). The

Male is often found attached, like a parasite, to the body of the

much larger female (Fig. 124, B).

216 THE CRUSTACEA

REMARKS ON HABITS, ETC.

The great majority of Isopoda are marine, but the large group
of Oniscoidea are terrestrial in their habits, and many of them
have developed special organs for aerial respiration, as already
described. The Asellidae and Phreatoicidea inhabit fresh water.
A very remarkable assemblage of forms .have recently been
described from subterranean waters in many parts of the world.
These include not only freshwater types like Asellidae and

Fic. 130.

Adult female of.Portunion maenudis (Entoniscidae). A, the brood-chamber partly opened
and the oostegites spread out; the abdomen is turned to show the ventral surface. B, the
brood-chamber unopened, showing dorsal surface of abdomen. Iv, the three lobes of the first
oostegite on the right side; I/, the same on the left side; II r, II7, second oostegites, right and
left ; Ill 7, IIL/, third oostegites, right and left ; IV, fourth oostegite ; V7, V/, fifth oostegites,
right and left ; ab, abdomen; ae, vestige of antenna; ai, vestige of antennule ; ex, exopodite
of second pleopod ; eng, eudopodite of third pleopod ; cg, head, dilated into a bilobed form by
the ‘‘ cephalogaster” ; h, cardiac prominence; mf, maxilliped ; ov, ovary ; pl, pleural lamella
of first abdominal somite ; th, thorax. (After Giard and Bonnier, from Korschelt and Heider’s
Embryology.)

Phreatoicidea, but also members of the Cirolaninae, Anthuridae, ,
and Sphaeromidae, which are otherwise characteristically or ex-
clusively marine in habitat. The number of parasitic forms is
very large, including many of the Cymothoidae and the whole of
the Epicaridea, the former infesting chiefly fishes and the latter
exclusively Crustacea (Ostracoda, Cirripedia, Mysidacea, Isopoda,

THE ISOPODA 217

including members of the same sub-order, Amphipoda, Euphausiacea,
Decapoda). In both groups the parasitic habit is associated with
the occurrence of hermaphroditism. The Cymothoidae present a
series leading from the predatory, actively swimming Cirolaninae,
with mouth-parts adapted for biting, to the sedentary Cymothoinae,
with suctorial mouth-parts. Some of the Epicaridea (Entoniscidae)
become practically endoparasitic, penetrating into the body of the
host, although remaining enveloped by an invagination of the

Fic. 131.

Bathynomus giganteus, dorsal view, about three-sevenths of natural size.
(After Milne-Edwards and Bouvier.)

integument. The mode of absorbing nutriment by root -like
processes penetrating the body of the host, which is found in
the Rhizocephala and some Copepoda, appears to be adopted by
some of the Liriopsidae.

Some of the smallest Isopoda are found among the Asellota,
certain species of which do not exceed 14 mm. in length when
adult. A length of three inches is exceptional in the Order, and
Lathynomus giganteus (Fig. 131), which reaches nearly eleven inches

218 THE CROSTACEA

in length by five in breadth (270 x 118 mm.), is by far the largest
known Isopod.

PALAEONTOLOGY.

Fossil remains which may be definitely referred to the Isopoda
are comparatively rare, and the little that is known of their
morphology leaves their systematic position in most cases doubtful
and throws no light on the phylogenetic history of the group. No
palaeozoic forms can be referred, with any certainty, to this Order,!
but several genera are known from Secondary rocks. The genus
Urda, Miinster, from the Jurassic of Solenhofen, if it be an Isopod,
presents very peculiar characters, having large mandibles projecting
in front of the head as in the male Gnathia, which it seems to
approach also in the number and relative sizes of the body-somites,
although differing in the large size of the eyes. Cyclosphaeroma
(Jurassic) and Palaega (Chalk) strongly resemble in general shape
the recent Sphaeromidae and Aeginae respectively. Several genera
of Sphaeromidae and Oniscoidea are described from Tertiary deposits.
A deformation of the carapace of the Brachyuran Palaeocorystes from
the Greensand has been supposed to indicate the presence of an
Epicaridean parasite.

AFFINITIES AND CLASSIFICATION.

The close affinity of the Isopoda with the Tanaidacea, and
through them with the more primitive members of the Peracaridan
division, is clear; they represent the termination of one of the
lines of divergence from the caridoid type. The most primitive
characters, on the whole, have been retained by the Asellota, which
have small and complete coxopodites on the thoracic legs, six
distinct segments in the peduncle of the antennule, and sometimes
a vestigial exopodite on the same appendage. The Cirolaninae,
however, have retained, in Lathynomus, a vestige of the inner
flagellum on the antennule, and have, in some cases, six segments in
the antennal peduncle, while in the more completely segmented
abdomen, and probably in the structure of the pleopods, they may
claim to be more primitive than the Asellota.

The structure of the Isopoda is so diversified, and the number of
forms included in the Order is so large, that their classification is a
matter of some difficulty. The system now most generally adopted
is that of Prof. G. O. Sars, which is given below with some slight
modifications. The tribes (here regarded as sub-orders) into which
he divides the Order are for the most part natural groups, but they
are of very unequal value. Hansen has pointed out that the

' 1 The Devonian Ozxyuropoda, recently described from Ireland by Carpenter and

Swain, is, however, regarded, with considerable probability, as an Isopod.

THE ISOPODA 219

Asellota stand somewhat apart from the rest, especially as regards
the structure of the pleopods. On the other hand, the Epicaridea
are closely related to some of the Flabellifera, the systematic value
of the modifications due to parasitism having been here as elsewhere
somewhat overestimated. The Gnathiidae, again, are an aberrant
family whose relation to the more normal Flabellifera is not clear,
and the same may perhaps be said of the Anthuridae.

ORDER Isopoda, Latreille (1817).
Sub-Orper 1. Asellota, Latreille (1806).

All the abdominal somites coalesced (except in Stenasellus) ; antennal
peduncle of six segments; mouth-parts never suctorial ; coxopodites of
thoracic legs small, the last six pairs freely movable ; first pair of pleopods
differing in the two sexes, second pair absent in female ; uropods sub-
terminal, often biramous, styliform.

Family Asetimpar. Asellus, Geoffroy; Stenasellus, Dollfus. Family
STENETRUDAE. Stenetriwm, Haswell. Family ParasELiuipan. Janira,
Leach ; Jaera, Leach; Munna, Boeck ; Desmosoma, G. O. Sars ; Nanno-
niscus, G. O. Sars; Munnopsis, M. Sars ; Ewurycope, G. O. Sars ; Acantho-
cope, Beddard.

SuB-ORDER 2. Phreatoicidea, Stebbing (1893).

Abdominal somites all free; antennal peduncle of five segments ;
mouth-parts normal ; coxopodites of thoracic legs small, the last six pairs
movable ; first pair of pleopods similar in the two sexes, second pair
present in female ; uropods sub-terminal, biramous, styliform ; body more
or less laterally compressed, amphipod-like.

Family Parearoicipan. Phreatoicus, Chilton (Fig. 119); Phreatoi-
copsis, Spencer and Hall ; Phreatoicoides, Sayce.

Sus-ORDER 3. Flabellifera, G. O. Sars (1882).

Abdominal somites free or more or less coalesced ; antennal peduncle
rarely with six segments; mouth-parts often suctorial ; coxopodites of
thoracic legs more or less expanded into coxal plates, partially or com-
pletely fused with body ; first pair of pleopods similar in the two sexes,
second pair present in female; uropods lateral, generally biramous,
lamellar, forming a caudal fan.

Family Gyatuipar. Gnathia, Leach (Fig. 121) (= Anceus, Risso)
(3), and Praniza, Latreille(Q and yg.) Family ANTHURIDAE. Anthura,
Leach ; Cyathura, Norman and Stebbing ; Paranthura, Bate and West-
wood ; Cruregens, Chilton. Family Cymornompar. (The following
sub-families are often ranked as families.) Sub-Family CrrobaNInaE
(Evryprcrnak). Cirolana, Leach; Eurydice, Leach; Conilera, Leach ;
Bathynomus, A. Milne-Edwards (Fig. 131), Sub-Family AnuRoPopINAE.
Anuropus, Beddard; Branchuropus, Moore. Sub-Family EXcoRALLANINAE.
Excorallana, Stebbing. Sub-Family Coratnaninan. Corallana, Dana;

THE CRUSTACEA

iS)
iS)
ie)

Alcirona, Hansen; Tachaea, Schiddte and Meinert. Sub-Family ArGa-
THONINAE. Argathona, Stebbing. Sub-Family BARyBRoTINAE. Barybrotes,
Schiddte and Meinert. Sub-Family Ancrnarn. Aega, Leach ; Rocinela,
Leach. Sub-Family Cymornornar. Cymothoa, Fabricius; Ceratothoa,
Dana; Meinertia, Stebbing; Nerocila, Leach. Family SEROLIDAr.
Serolis, Leach. Family SpHAEROMIDAB. Sub-Family Limnorrnae.
Limnoria, Leach. Sub-Family SpHAEROMINAE. Sphacroma, Latreille ;
Cymodoce, Leach ; Dynamene, Leach ; Campecopea, Leach ; Monolistra,
Gerstaecker ; Vireia, Dollfus ; Cassidina, H. Milne-Edwards; Ancinus,
H. Milne-Edwards. Sub-Family PraKkarrariunar. Plakarthrium,
Chilton.

Sus-Orper 4. Valvifera, G. O. Sars (1882).

Abdominal somites more or less coalesced ; antennal peduncle of five
segments ; mouth-parts normal ; coxopodites of thoracic legs expanded
into coxal plates, rarely quite concealed beneath pleural plates ; first pair
of pleopods similar in the two sexes (except in Pseudidothea), second pair
present in female; uropods lateral, opercular, folded inwards over pleo-
pods, exopodite vestigial or absent.

Family Ipornipas. Idotea, Fabricius; Chiridotea, Harger ; Glyptonotus,
Eights. Family Caarrinmpan. Chaetilia, Dana. Family Psruprpo-
THEIDAE. Pseudidothea, Ohlin. Family Honocnatuipar. Holognathus,
G. M. Thomson. Family AMESOPODIDAE. Amesopous, Stebbing. Family
ARCTURIDAE (ASTACILLIDAE), Arcturus, Latreille ; Astacilla, Cordiner ;
Anarcturus, zur Strassen.

Sus-OrRDER 5. Oniscoidea, G. O. Sars (1882).

Abdominal somites rarely coalesced; antennules minute ; antennal
peduncle of five segments ; mouth-parts not suctorial, mandibles without
palp, maxillae reduced ; coxopodites of thoracic legs expanded into coxal
plates, usually completely coalesced with body, rarely defined by sutures ;
first pair of pleopods usually differing in the two sexes, sometimes absent,
second pair present in female ; uropods sub-terminal, generally biramous and
styliform ; terrestrial in habits, often with pseudo-tracheae in pleopods.

Family Licirpan. Ligia, Fabricius ; Ligidiwm, Brandt. Family
TRICHONISCIDAE. Trichoniscus, Brandt; Haplophthalmus, Schiddte. Family
TytipakE. Tylos, Audouin ; Helleria, von Ebner. Family ONIscipar,
Sub-Family ScypHactnan. Scyphaz, Dana. Sub-Family ONIScINAE.
Oniscus, Linnaeus ; Porcellio, Latreille (Fig. 118). Sub-Family ARMADIL-
LIDINAE. <Armadillidium, Brandt; Cubaris, Brandt (= Armadillo,
Latreille).

Sus-OrDER 6. Epicaridea, Latreille (1831).

Parasitic forms in which the adult females are greatly modified, often
asymmetrical, sometimes without appendages and without segmentation of
the body ; mouth-parts suctorial, with simple piercing mandibles, max-
illulae and maxillae vestigial or absent ; pleopods, when present, without
sexual modification ; uropods uniramous, very small, often absent; late

DHE ISOPODA 221

larval (cryptoniscan) stage with abdominal somites distinct, with coxal plates
on thoracic somites, with uni- or biramous pleopods, and with terminal,
biramous, styliform uropods ; parasitic on Crustacea.

TRIBE 1. CRYPTONISCINA.

Male becomes mature in cryptoniscan stage ; protandrous hermaphro-
ditism probably universal ; brood-pouch not formed by oostegites ; first
larval stage with biramous pleopods.

Family Hemroniscrpar. Hemioniscus, Buchholz (on Cirripedia).
Family Cyproniscipar. Cyproniscus, Kossmann (on Ostracoda). Family
LiriorpsipAr. Liriopsis, Schultze ; Danalia, Giard (on Rhizocephala).
Family AsconisciDAr. Asconiscus, G. O. Sars (on Mysidacea). Family
CRINONISCIDAE. Crinoniscus, Pérez (on Cirripedia). Family Popasconipar.
Podascon, Giard and Bonnier (on Amphipoda). Family Caprropsipar.
Cabirops, Kossmann ; Clypeoniscus, Giard and Bonnier (on Isopoda).

TRIBE 2. BopyRIna.

Male becomes mature in bopyroid stage ; sexes probably always distinct ;
brood-pouch formed by oostegites; first larval stage with uniramous
pleopods.

Family Dastpar. Dajus, Kroyer; Notophryxus, G. O. Sars (on
Mysidacea and Euphausiacea). Family Bopyripaz (including ParyxIDAE
of Bonnier). Bopyrus, Latreille ; Gyge, Cornalia and Panceri (Fig. 124) ;
Phryxus, Rathke (on Decapoda). Family Enroniscrpar. Entoniscus,
F. Miller ; Portwnion, Giard and Bonnier (Fig. 130); Priapion, Giard
and Bonnier ; Cancrion, Giard and Bonnier (on Brachyura).

LITERATURE.

1. Beddard, F. FE. Report on the Isopoda. Rep. Voy. ‘‘Challenger,” Zool.
xi. pp. 85, 10 pls., 1885 ; and xvii. pp. 178, 25 pls., 1886.

2. Bobretzky, N. Zur Embryologie des Oniscus murarius. Zeitschr. wiss.
Zool. xxiv. pp. 179-203, pls. xxi.-xxii., 1874.

3. Bonnier, J. Contribution & l'étude des Epicarides: Les Bopyridae. Tray.
Stat. zool. Wimereux, viii. pp. 396, 41 pls., 1900.

4. Budde-Lund, G. Crustacea Isopoda Terrestria. Pp. 319. 8vo. Hauniae,
1885.

5. —— A Revision of ‘‘Crustacea Isopoda Terrestria,” with additions and
illustrations. 1. Hubelum. Entom. Meddel. (2), i. pp. 67-97, 4 pls., 1901
(published separately, 1899). 2. Spherilloninae. ‘3. Armadillo (only
published separately), pp. 33-144, 5 pls. Copenhagen, 1904.

6. Bullar, J. F. The Generative Organs of the Parasitic Isopoda. Journ.

Anat. Physiol. xi. pp. 118-128, pl. iv., 1876.
- —— On the Development of the Parasitic Isopoda. Trans. Roy. Soc.
London, clxix. (2), pp. 505-521, pls. xlv.-xlvii., 1878.

8. Caullery, M. Recherches sur les Liriopsidae. Mitth. zool. Stat. Neapel,

Xvill. pp. 583-643, pl. xxvi., 1908.

“I

THE CRUSTACEA

Ne)

10.

ial

12.

13.

18.

NG)

20.

21.

. Caullery, M., and Mesnil, F. Recherches sur | Hemioniscus balani, Buch-

holz. Bull. Sci. France et Belgique, xxxiv. pp. 316-362, pls. xvii. and
Xvill., 1901.

Chilton, C. On a New and Peculiar Freshwater Isopod from Mount
Kosciusko [Phreatoicus]. Rec. Australian Mus. i. pp. 149-171, pls.
XXil1.-xxvl., 1891.

The Subterranean Crustacea of New Zealand. Trans. Linn. Soc.
London (2), Zool. vi. pp. 163-284, pls. xvi.-xxiii., 1894.

Delage, Y. Contribution a Vétude de l'appareil circulatoire des Crustacés
édriophthalmes marins. Arch. Zool. expér. ix. pp. 1-173, pls. i.-xii.,
1881.

Dohrn, A. Die embryonale Entwicklung des Asel/us aquaticus. Zeitschr.
wiss. Zool. xvii. pp. 221-278, pls. xiv.-xv., 1867.

Entw. und Organ. von Praniza (Ancews) maxillaris. Zeitschr.

wiss. Zool. xx. pp. 55-80, pls. vi.-vill., 1869.

. Giard, A., and Bonnier, J. Contributions 4 l'étude des Bopyriens. Trav.

Inst. zool. Lille et. . . Wimereux, v. pp. 252, 10 pls., 1887.

. Hansen, H. J. Cirolanidae et familiae nonnullae propinquae Musei Hau-

niensis. K. Danske Vidensk. Selsk. Skr., 6 Raekke, naturvid. og math.
Afd., v. (3) pp. 239-426, 10 pls., 1890.

. —— Isopoden, Cumaceen und Stomatopoden der Plankton-Expedition.

Ergebn. Plankton-Exp. ii. pp. 105, 8 pls., 1895.

The Deep-Sea Isopod Anuropus branchiatus, Bedd., and some

Remarks on Bathynomus giganteus, A. M.-Edw. Journ. Linn. Soe.

London, Zool. xxix. pp. 12-25, pl. iv., 1903.

On the Morphology and Classification of the Asellota-Group of
Crustaceans, with Descriptions of the Genus Stenetriwm, Hasw., and its
Species. Proc. Zool. Soc. London, 1904, ii. pp. 802-331, pls. xix.-xxi., 1905.

— On the Propagation, Structure, and Classification of the Family
Sphaeromidae. Quart. Journ. Microsc. Sci. (n.s.), xlix. pp. 69-135, pl.
vil., 1905.

Lloyd, Rk. HE. The Internal Anatomy of Bathynomus giganteus, with a
Description of the Sexually Mature Forms. Mem. Indian Museum, i. (2),
pp. 81-102, pls. ix.-xii., 1908.

. M‘Murrich, J. P. Embryology of the Isopod Crustacea. Journ. Mor-

phology, xi. pp. 63-154, pls. v.-ix., 1895.

. Mayer, P. Carcinologische Mittheilungen: VI. Ueber den Hermaphrodi-

tismus bei einigen Isopoden. Mitth. zool. Stat. Neapel, i. pp. 166-179,
1s Woy USO;

. Miers, E. J. Revision of the Idoteidae. Journ. Linn. Soc. London, xvi.

pp- 1-88, pls. i.-ii1., 1883.

. Milne-Edwards, A., and Bouvier, Z. L. Les Bathynomes. Mem. Mus.

Comp. Zool. Harvard, xxvii. No. 2, pp. 133-175, 8 pls., 1902.

. Norman, A. M., and Stebbing, T. k. RK. On the Crustacea Isopoda of the

”

‘‘Lightning,” ‘‘ Porcupine,” and ‘‘ Valorous’” Expeditions: Part I.
Apseudidae, Tanaidae, Anthuridae. Trans. Zool. Soc. xii. pp. 77-141,
pls. xvi.-xxvil., 1886.

. Richardson, Harriet. A Monograph on the Isopods of North America.

Bull. U.S. Nat. Mus. No. liv. pp. liii+727, 740 text-figures, 1905.

. Roule, L. Etudes sur le développement des Crustacés. Le développement

du Porcellio scaber. Ann. Sci. Nat. Zool. (7), xviii. pp. 1-156, 10 pls.,
1894.

29.
30.
31.

32.

33.

‘

THE ISOPODA 223

Sars, G. O. Histoire naturelle des Crustacés d’eau douce de Norvége.
lLivr. Les Malacostrac¢s, pp. iii+145, 10 pls. 4to. Christiania, 1867.

— An Account of the Crustacea of Norway: Vol. II. Isopoda [including
Tanaidacea], pp. x +270, 104 pls. Bergen, 1896-1899.

Schiddte, J.C. Krebsdyrenes Sugemund. Naturhist. Tidsskr. (3), iv. pp.
169-206, pls. x.-xi., 1866 ; and x. pp. 211-252, 1875-76.

Schiddte, J. C., and Meinert, Fr. Symbolae ad Monographiam Cymothoarum,
Crustaceorum Isopodum familiae. Naturhist. Tidsskr. (3), xii., xiii.,
xiv., 1879-1885.

Spence Bate, C., and Westwood, J. O. A History of the British Sessile-
Eyed Crustacea. 2 vols., 1863 and 1868. Issued in parts, 1861-1868.
The Isopoda (including Tanaidacea) occupy the greater part of vol. ii.

. Stebbing, T. Rk. Rk. Isopoda. Gardiner’s Fauna... Maldive and Lacca-
dive Archipelagoes, ii. pt. 8, pp. 699-721, pls. 49-53, 1904.

. — Report on the Isopoda. Rep. Pearl Fisheries Ceylon, Roy. Soc. iv.
pp. 1-64, pls. i.-xil., 1905.

. — South African Crustacea. 4 pts. Marine Invest. S. Africa, 1900,
1902, 1905, 1908.

. Thienemann, A. Statocysten bei Anthwra gracilis, Leach. Zool. Anz.

Xxvi. pp. 406-410, 2 figs., 1903.

CHAPTER XIII

THE AMPHIPODA

Order Amphipoda, Latreille (1816).

Sub-Order 1. Gammaridea.
2. Hyperiidea.
3. Caprellidea.
4. Ingolfiellidea.

9
9?

oP)

Definition.—Peracarida in which there is no distinct carapace,
but the first thoracic somite (more rarely also the second) is
coalesced with the head; the telson is usually distinct from the
last somite ; eyes sessile; antennules often biramous; antennae
without exopodite, the peduncle typically of five segments ;
thoracic limbs without exopodites ; first pair modified as maxil-
lipeds, coalesced at the base, without epipodite ; remaining pairs
variously modified, the second and third commonly prehensile,
coxopodites always short, usually expanded as coxal plates,
movably connected with the body; branchial appendages on inner
side of coxopodites of some of the thoracic limbs ; pleopods, when
fully developed, divided into two sets, the first three pairs with
multiarticulate rami, the last two pairs generally similar to the
uropods, with unsegmented rami; no sexual modification of pleo-
pods ; the young leave the brood-pouch provided with all the
appendages of the adult.

Historical. —In establishing the order Amphipoda (1816)
Latreille excluded from it the genus Cyamus, which he referred to
the Isopoda. Later, he established a separate order, Laemodipoda,
for Caprella and Cyamus, placing it between the Amphipoda and
Isopoda. This arrangement was adopted by H. Milne-Edwards,
who further divided the Amphipoda into two families, Gammarina
and Hyperina. Kréyer, in 1843, showed very clearly that the
Laemodipoda present only an extreme modification of the Amphi-
pod type. Dana, in 1852, subdivided the Order into three groups
—Caprellidea, Gammaridea, and Hyperiidea, a classification which
has held its own to the present time. There appear to be no
sufficient grounds for establishing the additional divisions of

224

THE AMPHIPODA 225

Synopidea, Bovallius, and Subhyperini, Della Valle, and still less
reason for the inclusion of the Tanaidacea, advocated by Gerstaecker.
On the other hand, the very remarkable genus Jngo/fiella, Hansen,
may conveniently, for the present, be kept apart in the sub-order
Ingolfiellina which Hansen has established for it. Among the more
important contributions to our knowledge of the group mentioned in
the list of literature at the end of this chapter, attention may be
called to Spence Bate’s British Museum Catalogue, Spence Bate and
Westwood’s Monograph of the British species, and to the works of
Boeck, Bovallius, Claus, and Delage. As with so many other
groups of Crustacea, the memoirs by G. O. Sars are numerous and

so,

=
=
ry SNS
sao a = a ee
va

Fic. 132.

Gammarus locusta, g, from the side. x 4. a’, antennule; w’, antenna ; acc, accessory (inner)
flagellum of antennule; br, branchia; ev, coxal plate; gn, gnathopods; plp’’, pleopod of
third pair; prp’, prp”’, first and second peraeopods (fourth and fifth thoracie appendages) ;
t, telson; ur, uropod (sixth abdominal appendage); II, VIII, second and eighth thoracic
somites ; 1, 6, first and sixth abdominal somites. (After G. O. Sars.)

of the first importance. Della Valle’s Monograph is valuable for
anatomical and biological details, but the systematic part of the
work is to be used with caution. The bibliographical history of
the Order has been given at length in the admirable Introduction
to Stebbing’s Report on the “ Challenger ” collection, and the same
author has recently completed a masterly revision of the Gam-
maridea for the Tierreich. P. Mayer’s Monograph and his later
memoirs on the Caprellidea will not soon be superseded as the chief
sources of information on that sub-order.

MoRPHOLOGY.

The body of a typical Amphipod, such as Gammarus (Fig. 132),
is laterally compressed, with the abdomen of considerable size and

-

15

226 THE ‘CROSTACEA

flexed ventrally between the third and fourth somites. The large
coxal plates (cv) on the thoracic somites projecting downwards
increase the depth of the body and add to the appearance of lateral
compression. Even within the sub-order Gammaridea, however,
this typical form is sometimes departed from by attenuation of the
body or by its dorso-ventral flattening, which, in Pereionotus and
some other genera, is carried so far as to give the general appear-
ance of an Isopod. In the sub-orders Hyperiidea and Caprellidea
the range of modification is much greater. The Hyperiidea, while
departing the less widely, on the whole, from the typical form,
include such extreme types as the balloon-like Mimonectes and the
almost linear Rhabdosoma (Fig. 133). The Caprellidea differ from
both the other sub-orders in the vestigial condition of the abdomen

Fig. 133.
Rhabdosoma piratum (Hyperiidea). (After Stebbing, from Lncy. Brit.)

and the coalescence of the second thoracic somite with the head ;
they comprise two families of widely different facies, the filiform
Caprellidae (Fig. 134) and the flattened, Isopod-like whale-lice,
Cyamidae (Fig. 135). ‘

The eyes, when present, are sessile on the sides of the head.
Sometimes they coalesce in the median line, and in some Oedi-
cerotidae the fused eyes are borne on a projecting frontal lobe.
In Ingolfiella, distinct eye-lobes are present (although the eyes
are apparently deficient), defined by suture-lines from the antero-
lateral margins of the head-region. It is possible that these
lobes may represent the eye-lobes of Tanaidacea and the ocular
peduncles of more primitive Malacostraca, though the great
specialisation of Jngolfiella in other respects is rather against this
view.

Appendages.—The antennules (Fig. 132, a’) consist typically of
a peduncle of three segments carrying two flagella. The outer
flagellum is usually long and multiarticulate, while the inner (acc)

Fie. 134.

A, Phtisica marina, 9, x5. B, Caprella linearis, 9, x7 (Caprellidea). a’, antennule ;
a’, antenna; abd, vestigial abdomen, with small appendages in A; br, branchiae; gn.
enathopods (second and third thoracic appendages); m, brood-pouch; prp’, prp”, first and
second peraeopods (fourth and fifth thoracic appendages), wanting in B; IV, V, fourth and
fifth thoracic somites. (After G. O. Sars.)

=

Fia. 135.

Paracyamus boopis. A, male, dorsal view, x 4. B, maxillipeds. a’, antennule; a’, antenna ;
abd, vestigial abdomen ; br, branchiae ; gn, gnathopods (second and third thoracic appendages) ;
IV, V, fourth and fifth thoracic somites. (After G. O. Sars.)

227

228 THE CRUSTACEA

is frequently absent, and, when present, is generally inconspicuous
and composed of few segments.

The antennae (Fig. 132, a”) when fully developed have a
peduncle of five segments and a more or less elongated flagellum.
A scale or exopodite is never developed. A conspicuous conical
or spiniform tubercle on the second joint of the peduncle bears the
aperture of the antennal gland, indicating that the five segments of

A
N
fy

ts
=
=

\

—
> = Se

eS
on
é
vA
B

a Se
\ Me

=

Fic. 136.

Phronima sedentaria. a, female; b, male. A’, antennule; A’, antenna; D, intestine; Dr,
gland in chela of sixth thoracic appendage; G, genital aperture} of male; H, heart; K,
branchia ; Kf, mandible ; N, ventral nerve-chain; 0, eye; Ov, ovary. (From,Claus’s!Tezxtbook.)

the peduncle must be derived from the six-segmented condition by
a coalescence of two segments distal to the gland-opening, probably
the third and fourth. In many cases the antennules and antennae
are more strongly developed in the male than in the female sex,
and bear more numerous sensory setae. In some Hyperiidea
(Fig. 136) the antenna, though well developed in the male, is
represented in the female only by a rounded tubercle containing
the antennal gland on the front of the head. In some cases the

THE AMPHIPODA 229

antennae have almost a pediform character, the segments of the
peduncle being long and stout and the flagellum reduced, as in
the Amphithoidae and allied families and conspicuously in the
Corophiidae.

The mandibles have usually the typical Peracaridan structure
with molar process, serrated incisor process, lacinia mobilis on the
left mandible or on both, a row of spines, and a palp of three
segments, but any of these parts may be modified or absent. The
palp, in particular, may be present or absent in genera otherwise
very closely related.

The mazillulae (Fig. 137, A) are remarkable in that they
commonly exceed the maxillae in size and complexity of structure.
Two endites are present, springing, according to Hansen’s inter-
pretation, from the first and third segments, and the fourth and

Fic. 137.

A, maxillula, B, maxilla, C, maxillipeds, of Socarnes bidenticulatus (Gammaridea). The
distal segments of the left maxilliped are omitted. 1-7, segments of the appendages ; 11-13,
endites of the respective segments. (After Hansen.)

fifth segments form a “ palp” which is turned forwards and inwards,
resembling in appearance, and no doubt also in function, a third
endite. The mavillae (Fig. 137, B) are small in size and simple
in form, consisting mainly of two plates which, according to Hansen,
are the endites of the second and third segments. The lower
lip may attain to greater complexity than in most other divisions
of the Malacostraca and its modifications are of some systematic
importance. The two main lobes (paragnatha) of which it else-
where consists are in many cases supplemented by a pair of
accessory lobes lying between them, while the main lobes them-
selves may be produced at the outer corners or each divided by
incision into two as in the Amphithoidae.

The first thoracic appendages or muzwillipeds (Fig. 137, C) are
always coalesced at the base, the coxopodites fusing to form an
unpaired plate. The basipodite is pr oduced into an endite, usually
referred to as the “inner plate” (/?), which may be armed with
teeth, spines, or setae, but does not carry coupling-hooks, The

230 THE CRUSTACEA

ischiopodite also bears an endite (the “outer plate,” J), and the
remaining four segments form the “palp.” The palp is not
unfrequently abbreviated by the suppression of one or two of its
segments, and the coalescence of the proximal
Ny region may involve the basipodites partially or

:

SS

completely. Both these modifications are carried
to an extreme in the Hyperiidea (Fig. 138),
where the maxillipeds are represented by an

Fra, 138, unpaired plate carrying a pair of movable, un-

Reduced maxilli: jointed appendages, representing in all probability
peds of Hyperia galba. : . . 4 : * 6
(After G. O. Sars.) the ischiopodites with their endites, and a median

process corresponding to the coalesced inner
plates. In the Cyamidae the maxillipeds are sometimes of
normal structure, but they may be greatly reduced (Fig. 135, B),
and in Platycyamus they are represented only by an unpaired
plate without any trace of articulations. In Cyamus nodosus the
interesting observation has been made that the young animals
taken from the brood-pouch have well-developed maxillipeds with
the full number of segments, although in the adults of this species
they are reduced to a pair of unjointed appendages attached to the
common basal plate.

Of the remaining seven pairs of thoracic appendages, the first
two are commonly, though not invariably, modified for prehension,
and are distinguished as gnathopods (Figs. 132, 134, 135, gn) from
the remaining five pairs, the peracopods, which are generally organs
of locomotion. Each limb consists of the usual seven segments.
The coxopodite is always short, but is usually expanded externally
to form a coval plate (Fig. 132, cx), sometimes of great size ;
internally it bears the branchial plate (d7) and oostegite when
these are present. In the Caprellidea and Ingolfiellidea the
coxopodite remains small. In some Hyperiidea it is entirely
coalesced with the somite. The basipodite is usually more or less
elongated ; the ischiopodite, on the other hand, generally short,
contrary to the rule among the Isopoda. The terminal claw is
usually coalesced with the dactylopodite.

The lateral compression of the body in most Amphipoda has
lead to a separation of the thoracic legs into an anterior group of
four (the two gnathopods and the first two paraeopods) and a
posterior of three, which are opposed to each other in the direction
of the principal articulations. In the case of the anterior group
the limb is bent forwards at the articulation between the ischio-
podite and meropodite, and backwards at that between meropodite
and carpopodite, and the dactylopodite points backwards ; in the
posterior group these directions are reversed and the dactylopodite
points forwards except in the case of certain Gammaridea, where
the direction of the dactylopodite (but not of the other segments)

THE AMPHIPODA 231

is reversed.' The distinctness of these two groups is further
expressed by the relations of the coxal plates. Where these are
small or of moderate size they are of similar form throughout the
series, but when, as in many Gammaridea (Fig. 132), enlargement
takes place, it is mainly the first four that become expanded so
as to cover from the outside the basipodites, or even the whole
limb; the last three coxal plates in this case generally remain
small and their place in protecting the gills within is taken by
the expanded basipodites. The two pairs of legs following the
gnathopods (the fourth and fifth of the thoracic series) are, among
the Gammaridea (Fig. 132, prp’, prp”), not unfrequently more or
less different from the succeeding pairs. In the Caprellidea, these
two pairs are vestigial or absent except in the genus Phtisicu (Proto)
(Fig. 154, A) and its immediate allies.

In the gnathopods of the Gammaridea every gradation may be
traced from the simple, non-prehensile leg to the well-formed,
sub-chelate, or perfectly chelate type, and even to more complex
forms, as in Leucothoé and Aora. The gnathopods of Ingolfiella
have a very unusual structure, the propodite and dactylopodite
together forming the movable finger which is opposed to the
expanded carpopodite. Some of the peraeopods may show modifi-
cation for prehensile purposes in Gammaridea, and in Polycheria
all of them are sub-chelate. In the Hyperiidea much greater
variety occurs, and any of the peraeopods except the last pair may
be transformed into a chela, sometimes of large size (Fig. 136).
The gnathopods, in this group, are always small. In the Caprellidae
(Fig. 134) the gnathopods are sub-chelate and the last three pairs
of peraeopods are also fitted for grasping. A point of interest
with regard to these peraeopods is the existence in the basipodite
of a definite “fracture-plane” at which the limb breaks off in
autotomy. <A similar fracture-plane is found in the legs of many
Decapoda, where the habit of autotomy is highly developed.

The branchiae (Figs. 132, 134, 135, br; Fig. 136, K) are
attached to the inner surfaces of the coxopodites, near the
posterior border. They are generally vesicular or lamellar in
form, and in some Gammaridea the respiratory surface is in-
creased by numerous transverse ridges or folds. In some species
of Cyamidae (Cyamus physeteris) the branchiae are ramified.
Accessory branchiae occur in certain Gammaridae and Talitridae
on some of the thoracic limbs and also on the first abdominal
somite. The greatest number of branchiae is six pairs, occurring
on the last six thoracic limbs in many Gammaridea. The number

1 The correlation between the lateral compression of the body and this grouping
of the legs is well illustrated by comparison with Phreatoicus, the only Isopod where
the body is laterally compressed and where the legs are divided into two groups
exactly as in Amphipods.

232 LHE -(CROSTACGEA

in this sub-order, however, is not unfrequently reduced to five,
four, or even three pairs. In Hyperiidea the last pair of thoracic
legs never carry branchiae and the number may vary from five
to two pairs. In Caprellidea as a rule only two pairs of branchiae
are present, on the fourth and fifth thoracic somites, but in some
genera of Caprellidae there is an additional pair on the third somite
(that of the second gnathopods).

The oostegites spring from the inner surface of the coxopodites
on the proximal side of the branchial plates. Four pairs are
commonly present, on the third to the sixth thoracic somites, but
the number may be reduced. In the Caprellidea (Fig. 134, m)
two pairs only exist,-on the fourth and fifth somites, but in
addition a pair of small valvular appendages covering the external
apertures of the oviducts on the sixth somite are probably to be
regarded as vestiges of a third pair. Vestigial oostegites are
stated to occur normally in the male sex in a few cases (e.g.
Cyamus globicipitis and Synurella polonica).

It is very characteristic of the Amphipoda that the abdominal
appendages are sharply divided into two groups differmg in
structure. In the majority of Gammaridea (Fig. 132) and
Hyperiidea (Fig. 136) all the six pairs are present, the first three
pairs are turned forwards and consist of a peduncle carrying two
subequal rami, each of which is multiarticulate and fringed with
long setae ; the inner side of the peduncle bears distally a number
of retinacula, and the first joint of the endopodite has internally
one or two peculiar ‘cleft spines” which no doubt serve the same
purpose of coupling together the pair of appendages. These limbs
are the chief natatory organs among Amphipoda, and they also
serve when the animal is at rest to maintain a current of water
over the gills. The last three pairs of abdominal appendages are
directed backwards and are generally similar to each other, so that
the name wropods is commonly used to include them all, though
in not a few cases the last pair retain, in details of form and
size, some mark of that differentiation from the preceding append-
ages which they show in other orders of the Malacostraca. As a
rule, the three pairs are biramous ; not unfrequently the exopodite
of the last pair consists of two segments, but except for this the
rami of all are unjointed. Sexual differences not unfrequently
occur in the size and structure of the last pair, but in no
Amphipoda are any of the pleopods modified as copulatory organs.
The abdomen of most Caprellidea is unsegmented and may bear
vestigial appendages to the number of three pairs (Fig. 134, abd).
An interesting link with the normal Amphipoda is constituted by
the genus Cercops, where five distinct somites and a terminal piece
(perhaps the telson) are present. The first and second somites
bear, in the male sex only, minute filiform appendages of two

THE AMPHIPODA 233

segments which appear to correspond to the first and second
pleopods of the normal type, while the fourth and fifth somites
carry in both sexes stout two-segmented limbs answering to the
first and second uropods. In most other Caprellidae the rudimentary
appendages are more fully developed in the male than in the female
sex, but in a few the abdomen is quite without appendages. In
the male Cyamidae a median appendage is present which seems to
result from the fusion of a pair of uropods. In Jngolfiella the first
three pairs of abdominal limbs are represented by small triangular
plates, sometimes with a minute basal segment, without any trace
of rami. The last pair is vestigial.

Alimentary System.—The alimentary canal of the Amphipoda
appears to differ from that of most Isopoda in the much greater
development of the mid-gut region, which forms the greater part of
its length. The stomodaeum forms a masticatory or triturating
stomach, the structure of which appears to be fairly uniform
throughout the Gammaridea and Caprellidea, and to be more or
less simplified in the Hyperiidea. When fully developed it presents
anteriorly two lateral ridges projecting into the cavity, armed with
spines and stiff setae. These ridges are moved by powerful muscles
passing outwards to the body-wall on either side, and appear to be
the most important instruments of trituration. Posterior to these
are two pairs of setose ridges running more or less transversely,
while in the floor of the cavity is a strong ridge ending behind in a
free tongue-like process and carrying anteriorly four comb-lke
rows of iridescent setae. The chitinous lining of the stomodaeum
projects backwards into the beginning of the mid-gut as a cuticular
funnel. In Phronima, where the apparatus appears to be adapted
for straining rather than for masticating the food, the whole stomach
is telescoped for a little way into the capacious mid-gut. The
hepatic caeca are generally four in number and of considerable
length, but in a few genera of Gammaridea and in most Hyperiidea
only one pair is present, while in the Caprellidea the ventral pair
and in Phronima both pairs remain rudimentary. Just above the
point where the hepatic caeca communicate with the gut by a
common aperture on each side, a short dorsal, forwardly directed
caecum, unpaired in Gammaridea, paired in Hyperiidea and
Caprellidea, arises from the anterior end of the mid-gut. At the
posterior end of the mid-gut, at its junction with the proctodaeum,
a second pair of caeca of very varying size is commonly present in
the Gammaridea. In a few cases only a single unpaired caecum is
present (Melita), and in Synurella, though two tubes are present in
the young, that on the right side atrophies and only that on the
left persists. Similar paired caeca are only exceptionally present
in Hyperiidea (/%bilia) and Caprellidea (Cuprella). To these
posterior caeca of the mid-gut an excretory function has been

234 THE CRUSTACEA

attributed, mainly on the ground that they sometimes contain
calcareous concretions ; as they are outgrowths of the mesenteron,
it is impossible to regard them as homologous with the Malpighian
vessels of insects. In the Hyperiidea the anterior part of the
mid-gut may be dilated while the posterior part remains narrow.
It is stated to be lined by a very delicate cuticle of non-chitinous
nature. The proctodaeum is short, rarely reaching forward to
the posterior limit of the thorax, or, in the Caprellidea, into the
penultimate thoracic somite. An “anal gland” in the form of a
small diverticulum is described in Synurella.

Circulatory System.—The circulatory system of Amphipoda is
remarkable for the imperfect development of the arterial vessels
and the consequent lacunar character of the greater part of the
circulation ; as compared with that of the Isopoda it differs also in
the position of the tubular heart, which extends through the greater
part of the thoracic somites but does not reach the abdomen. It
lies in a spacious pericardium which may extend backwards into
the abdomen. Three pairs of ostia are present in most Gammaridea,
but Corophium has only one pair; the Caprellidea have three pairs ;
in the Hyperiidea only two pairs are present as a rule, but in
Phronima, although the male has only two, the female has three
pairs. The heart is continued at either end into the anterior and
posterior aortae, which are defined by valves. In addition, a pair
of arteries supplying the eyes and adjacent parts may arise from
its anterior end, but only in the Hyperiidea are there two or three
pairs of lateral arteries arising from the heart in the thorax and
comparable to the thoracic arteries of the Isopoda. The anterior
aorta is stated to divide in the median plane to encircle the brain
in a ‘pericerebral vascular ring” very characteristic of the order,
with which is connected (except in Caprellidae) an oesophageal
ring similar to that of the Isopoda. It seems probable, however,
that these rings are rather lacunar spaces than well-defined vessels.
There is no trace of the subneural artery commonly developed in
Isopods, the oesophageal ring opening posteriorly into the great
ventral sinus which extends through the whole length of the body,
and into which the posterior aorta also empties its contents at
or near the end of the abdomen. Except perhaps in those forms
(Hyperiidea) which possess lateral thoracic arteries, the appendages ,
of the thorax and abdomen receive their blood-supply from this
ventral sinus. Within the appendages the afferent blood-streams
are contained in well-marked vessels which send branches to the
gills. The efferent vessels of the appendages unite to form in each
somite (except sometimes in the abdomen) a pair of pericardial
vessels by which the blood is returned to the heart.

In comparing the circulatory system with that of the Isopods,
it is clear that the course followed by the blood in the abdominal

THE AMPHIPODA 235

region is similar in both cases, the ventral sinus sending blood into
the appendages, from which it is returned to the pericardium by
the centripetal sinuses ; the ventral sinus in Amphipoda receiving,
however, arterial blood directly from the posterior aorta. In the
thorax the course of the circulation is very different.

In the Isopoda the appendages receive blood directly from the
heart by means of the lateral thoracic arteries and return it to the
ventral or lateral thoracic sinuses ; in the Amphipoda, on the other
hand, the limbs with their branchial plates receive blood from the
ventral sinus and return it directly to the pericardium by the peri-
cardial vessels. The ventral sinus of the Amphipoda, however,
does not wholly correspond to the ventral or lateral sinuses of the
Isopoda, but, since it receives arterial blood both anteriorly and
posteriorly from the aorta, represents in part also the sternal
system of arteries in the last-named group, while the homologues of
the thoracic afferent pericardial vessels of the Amphipoda are to
be found in the blood-stream which enters the pericardium of the
Isopoda through the minute apertures at its anterior end.

Exeretory System.—No trace of a maxillary gland has been
recognised in any Amphipod. The antennal gland, on the other
hand, is rarely, if ever, wanting. It has been most fully studied
in certain freshwater Gammaridae, where it presents the usual
divisions of end-sac, convoluted tube, and duct, the latter being some-
times dilated into a vesicle. The gland is usually contained within
the first segment of the antenna, and its external aperture is at
the tip of a conical or spiniform process of the second segment.
““Coxal glands” are described as present in all the thoracic and the
first three abdominal appendages of Gammarus. They consist of
small groups of cells, without duct or opening to the exterior,
rendered visible in the living animal by feeding with carmine.

Dermal Glands.—In many Amphipoda there are found groups
of unicellular glands lying in the thoracie appendages and opening
by fine ducts at or near the extremity of the limb. Among the
Gammaridea such glands are well developed in the Photidae,
Aoridae, Amphithoidae, Jassidae, Corophiidae, and some of the
allied families, where they are confined to the fourth and fifth
thoracic appendages, lying mainly in the basipodite and connected
with a duct which opens on the tip of the claw. In the Ampelis-
cidae similar glands occur but are more widely distributed on the
other appendages of the body. In all the families named the
glands secrete a cementing material which is used in building up
with particles of mud or sand or fragments of weed the cases or
tubes in which the animals live. In the Talitridae, which burrow
in sand, glands of similar structure are scattered over the surface
of the body and appear to secrete a mucinous substance which lines
the burrows. Glands of very similar structure to those just

236 TELE CRG STAC

described, but apparently with different functions, occur in many
Hyperiidea. In the Phronimidae, where they have been most
carefully studied, they occur in all the thoracic legs, and the
ducts open at the end of the limb or, in the case of the ante-
penultimate pair, on teeth of the palmar edge of the chela. It is
supposed that in this case they act as poison-glands. In many
Caprellidae groups of gland-cells also supposed to secrete a poison
are present in the hand of the second gnathopods, their ducts
opening on a prominent tooth of the palmar edge. Finally, glands
of similar structure may be found, as in many other Crustacea, in
the oral appendages and on the oesophageal walls, and are supposed
to be salivary in function.

Nervous System.—The ventral nerve-chain presents, in the
majority of the Gammaridea, twelve pairs of ganglia connected by
double longitudinal commissures, the sub-oesophageal supplying the
mouth-parts, followed by seven corresponding to the free thoracic
somites and four abdominal ganglia; but the number may be
reduced, especially among the Hyperiidea, by the coalescence of
one or two of the anterior thoracic with the sub-oesophageal
ganglia, the fusion of the last two thoracic, and the restriction of
the abdominal ganglia to three pairs. In the. Caprellidea, though
four pairs of abdominal ganglia may be distinct in the young, they
become in the adult fused into a single mass approximated to the
last thoracic ganglion and lying in the penultimate thoracic somite.
In Phronima the nerves to the mouth-parts arise from the oeso-
phageal commissures close to the under-side of the brain. A post-oral
antennal commissure such as exists in the Isopoda is perhaps in-
dicated by the presence (in Gammaridea and Caprellidae) of a
median foramen piercing the sub-oesophageal ganglionic complex
near its anterior margin and giving passage to an unpaired strand
of muscle running between the lower surface of the stomach and
the lower lip.

Sense-Organs.—The paired eyes of the Gammaridea show great
diversity of size and disposition. They are rarely so large as to
occupy the greater part of the.surface of the head (Tvrischizostoma),
while on the other hand they are in not a few cases quite vestigial
or apparently absent. In the Oedicerotidae, as already mentioned,
they are coalesced to form a single organ which is advanced to the
front of the rostral process, and in a few cases (Tiron, Synopia) a
pair of small accessory eyes are placed below the main eyes.. This
leads to the very remarkable condition found in the Ampeliscidae,
which possess two pairs of eyes, each of which is made up of numerous
ommatidia differing only in details from those forming the eyes of
other Amphipoda, underlying a single lenticular thickening of the
cuticle.

In the Caprellidea the eyes are always small, but in the

THE AMPHIPODA 237

majority of the Hyperiidea (Fig. 136, 0) they are enormously
enlarged, occupying nearly the whole surface of the head. In this
case each eye is commonly divided into two parts, the dorsal
differing in the great elongation of the crystalline cones and in
other details from the lateral division. Apart from the Am-
peliscidae, the eyes of the Amphipoda are characterised by the
fact that the corneal covering is not faceted, or, in other words,
that corneal lenses are not formed.

In addition to “sensory filaments” of the usual type borne
by the main flagellum of the antennule, and sometimes particularly
numerous on the enlarged proximal segment of the flagellum
(Lysianassidae, Hyperiidea), many Gammaridea have on the
antennae, and sometimes on the antennules, peculiar organs known
as calceoli. These are, in the simplest cases, little flattened vesicles
attached by a narrow stalk, but in some the structure is more
complex. They are often, but not always, confined to the male
sex, and have been variously interpreted as olfactory or auditory
organs, as adhesive suckers, and even as sexual ornaments.

A pair of statocysts have been described in connection with the
anterior part of the brain in Oxycephalidae.

Reproductive System.—The paired ovaries and testes are of
simple tubular form and lie in the thoracic region. The testes
are continued posteriorly into short vasa deferentia which may be
slightly dilated into seminal vesicles and open on short papillae
on the sternum of the last thoracic somite. The oviduct leaves
the ovary at about the middle of its length and opens on the inner
surface of the fifth coxal plate (sixth thoracic somite). It is stated
that an actual opening does not exist until the moment when the
eggs are extruded. The spermatozoa consist of a slender, rod-like
head, to which a filiform tail, stated to exhibit vermiform move-
ments in some cases, is attached at an acute angle. Definite
spermatophores are not formed, at least in the majority of Amphi-
poda. The spermatozoa are deposited on the ventral surface of the
body of the female immediately before the eggs are extruded, and
fertilisation is external. The occurrence of ova within the testis
has been observed in species of Orchestia, where it is perhaps
universal in young individuals.

DEVELOPMENT.

Segmentation is at first total, later becoming superficial, with
early differentiation of the blastoderm on the ventral side. The
teloblastic mode of growth in the post-naupliar region of the
embryo which occurs in many Isopoda and Mysidacea does not
present itself.

A “dorsal organ” is early developed as a median thickening

238 THE CRUSTACEA

of the ectoderm, the cells of which become pyriform, projecting
inwards and connected with the exterior by a narrow neck. The
larval cuticle, which is formed soon after the differentiation of
appendages has begun, remains adherent to the dorsal organ after
separating from the rest of the ectoderm. Later, the cells lose
their apparently glandular character and become invaginated as a
thin-walled vesicle, which persists after the embryo is freed from
the egg-membrane.

The dorsal curvature of the blastoderm as it lies upon the
spherical surface of the yolk is early exchanged for a ventral
curvature as the abdominal region of the developing embryo
becomes folded downwards and forwards. The embryo is not
liberated from the egg-membrane until the body and appendages
have assumed more or less their final form. |The young, however,
remain within the marsupium for some time longer, leaving it
finally only at the ecdysis which precedes the next act of oviposi-
tion. ‘The accounts of some older writers, according to which the
young after leaving the marsupium of the parent returned to it for
shelter when alarmed, have not been confirmed by any modern
observer.

The post-embryonic development in most Amphipoda consists
mainly in the gradual assumption of secondary sexual characters
and other features of subordinate importance. Only in the
Hyperiidea, and notably in the Platyscelidae, do the changes of
form occurring after the young leave the brood-pouch deserve the
name of metamorphosis.

REMARKS ON HABITS, ETC.

The Hyperiidea and Caprellidea are exclusively marine (the
reported occurrence of a Caprellid in the Lake of Geneva rests .
on insufficient evidence), as are also the great majority of the
Gammaridea. The Hyperiidea are pelagic in habitat, sometimes
ranging from the surface to great depths, and having often an
exceedingly wide horizontal distribution, The Caprellidea, though
for the most part inhabiting shallow water and almost or quite
without the power of swimming, include some species of almost
cosmopolitan range. The Ingolfiellidea have also a very wide
distribution, for the two species which at present compose the
sub-order come from Davis Straits and from the Gulf of Siam, at
depths of 1870 fathoms and of 1 fathom respectively.

The marine Gammaridea are rarely pelagic ; they are abundant
in the littoral region and penetrate to great depths. The vast
abundance of individuals and species in Arctic and Antarctic seas
is especially noteworthy. As regards the freshwater species, the
predominance of the genus Gammarus and its nearest allies must

THE AMPHIPODA 239

be noticed ; the occurrence of species from genera otherwise marine
in the “relict” faunas of lakes in Northern Europe and America
and in the Caspian Sea; the peculiar blind subterranean species
(Niphargus, etc.) which come to the surface in wells and penetrate
into the abyssal waters of deep lakes; and the radiation of single
genera into numerous species in a limited area in the Gammari of
Lake Baikal and the Hyalellae of Lake Titicaca. The only terres-
trial Amphipoda occur among the Talitridae, which in northern
latitudes live, for the most part, just above tide-marks, but in the
warmer regions of the globe penetrate inland to great distances.

Perhaps no Amphipoda except the whale-lice (Cyamidae) (Fig.
135) are truly parasitic, though some forms with suctorial mouth-
parts seem to be semi-parasitic on fish (7ischizostoma). Many
species, however, are commensal with sponges and other organisms.
The pelagic Phronima (Fig. 136) lives in a transparent barrel-shaped
case fashioned from the swimming-bell of a Siphonophore or from
a test of a pelagic Tunicate.

The Gammaridea probably include the smallest as well as the
largest Amphipoda, for many species do not exceed two or three
millimetres in length. The largest is Alicella gigantea, Chevreux,
which reaches a length of 140 mm.

PALAEONTOLOGY.

Fossil remains of Amphipoda are exceedingly rare, and although
various problematical fossils from Palaeozoic rocks have been
referred to this group, it is only in the Tertiary and Post-Tertiary
deposits that undoubted Amphipoda have.been found. All belong
to the Gammaridea, and though a genus Palaeogammarus has been
established for a species found in Baltic amber, its generic and even
specific distinctness from some of the living forms of Gammarus is
uncertain.

AFFINITIES AND CLASSIFICATION.

Although the Amphipoda plainly belong to the Peracaridan
division of the Malacostraca, their relation to the other Orders of
the division is by no means so clear as in the case of the Isopoda.
It seems very likely that their affinity to the Isopoda is not so close
as has been supposed. Apart from the sessile eyes and the
segmentation of the body, characters which, there is reason to
suppose, have originated independently in at least one other case
(Koonunga), almost the only point of agreement between the two
Orders is found in the possession of coxal plates on the thoracic
somites. But coxal plates are not developed in the most primitive
Isopoda, the Asellota, and if their appearance in that Order was
later than the acquisition of the typical Isopodan characters, the

240 THE CRUSTACEA

coxal plates of the Amphipoda must have had an independent
origin. The possession, by the typical Amphipoda, of a well-
developed inner ramus on the antennule and of a palp on the
maxillula are also among the characters which suggest that they
diverged from the common stock before the origin of the Isopoda.
It is quite probable, however, that their origin must be sought for
still further back. They do not show the late appearance of the
last thoracic limbs and the tendency to coalescence of the telson
with the last somite—characters which are common to Cumacea,
Tanaidacea, and Isopoda—while they possess a well-developed
antennal gland, which is never more than vestigial in these
Orders. Further, if the branchiae of the Amphipoda be, as Claus
suggests, epipodites which have become shifted from the outer to
the inner surface of the thoracic coxopodites, it follows that the
Amphipoda must be supposed to have diverged, not later than the
origin of the Mysidacea, from the primitive caridoid stock of the
Peracarida.

A regards the four sub-orders recognised in the classification
given below, it must be admitted that the differences separating the
Gammaridea from the Caprellidea are not very profound. <A
Caprellid which should unite the abdomen of Cercops with the
thoracic limbs of P/tisica would be very hard to exclude from the
Gammaridea. The Hyperiidea hardly depart more widely from
the Gammaridea, but the retention of the three divisions is at
least convenient. The sub-order Ingolfiellidea, established by
Hansen for the two species of the genus Jngolfiella, is not admitted
by Stebbing, who places the genus among the Gammaridea, but
there seems to be force in Hansen’s contention that its inclusion in
that sub-order would logically require the absorption of the
Caprellidea also.

The difficulties in the way of classifying the Amphipoda are of
a different order from those met with among the Isopoda. We
have to deal with a vast diversity of forms within a comparatively
small range of morphological variation, with the consequence that
genera and even families have to be established on trivial characters,
and their limits are often hard to define.

OrDER Amphipoda, Latreille (1816).
Sus-Orper 1. Gammaridea, Dana (1852).

Head not coalesced with second thoracic somite ; palp of maxillipeds
with two to four segments; all the thoracic legs present, usually with
well-developed coxal plates; abdominal somites generally distinct, with
well-developed appendages ; eyes rarely very large.

Family Lystanassipan, Lystanassa, H. Milne-Edwards; Alicella,

THE AMPHIPODA 241

Chevreux ; Socarnes, Boeck ; Trischizostoma, Boeck. Family Srxco-
CEPHALIDAR, Stegocephalus, Kroyer. Family AMPELISCcIDAE. Ampelisca,
Kroyer. Family Havustormpar. Haustorius,S. Miller ; Urothoe, Dana.
Family PHOXOCEPHALIDAE. Phoxocephalus, Stebbing. Family Ampui-
LOCHIDAE. Amplilochus, Spence Bate. Family LevucorHoipar. Leucothoe,
Leach. Family ANAMIXIDAE. Anamizis, Stebbing. Family Mrroripar.
Metopa, Boeck. Family Cressipan. Cressa, Boeck. Family Sreno-
THOIDAE. Stenothoe, Dana. Family PHutantipAr. Phlias, Guérin ;
Pereionotus, Spence Bate and Westwood. Family CoLoMAsTIGIDA®.
Colomastix, Grube. Family Larystiupar. Lafystius, Kroyer. Family
LAPHYSTIOPSIDAE. Laphystiopsis, G. O. Sars. Family AcANTHONOTO-
ZOMATIDAE. Acanthonotozoma, Boeck. Family PARDALIScIDAE. Parda-
liset, Kroyer. Family Lituseporaipar. © Lilljeborgia, Spence Bate.
Family O®kDICEROTIDAE. Oediceros, Kroyer. Family SyNopripar.
Synopia, Dana. Family TrRONIDAE. Tiron, Lilljeborg. Family
CaLLiopupAk. Calliopius, Lilljeborg. Family PLeustipan. Pleustes,
Spence Bate. Family ParampuirHompar. Paramphithoe, Bruzelius.
Family Aryiipar. Atylus, Leach. Family Metrurpipripan. Mel-
phidippa, Boeck, Family Evstripar, Lusirus, Kroyer. Family
Barerak. Batea, F. Miller. Family Ponrocenetmpar. Pontogeneia,
Boeck. Family GammariparE. Gammarus, Fabricius (Fig. 132) ;
Niphargus, Schiddte; Synurella, Wrzesniowski; Melita, Leach. Family
DEXAMINIDAE. Dexamine, Leach ; Polycherta, Haswell. Family TanirripaE
(ORCHESTHDAE). Talitrus, Latreille ; Orchestia, Leach ; Hyalella, S. Smith.
Family Aortmar. Aora, Kroyer. Family PHoripar. Photis, Kroyer.
Family Isarmpar. Isaea, H. Milne-Edwards. Family AMpHITHOIDAE.
Amplhithoe, Leach. Family JAsstpar (PopoceRIDAE auctt.). Jassa, Leach
(Podocerus auctt.). Family CoropHupar. Corophium, Latreille. Family
CHELURIDAE. Chelura, Philippi. Family Popocrertpar. Podocerus, Leach
(= Platophium, Dana). Family Hyperiopstipar. Hyperiopsis, G. O. Sars.

Sus-OrDER 2. Hyperiidea, Dana (1852).

Head not coalesced with second thoracic somite ; palp of maxillipeds
absent ; all the thoracic legs present, coxopodites small or coalesced with
the body ; abdominal somites generally distinct, with well-developed
appendages ; eyes generally very large.

Family Scrnipar. Scina, Prestandrea. Family Visritpar. Vibilia,
H. Milne-Edwards. Family Cytiopopipar. Cyllopus, Dana. Family
LANCEOLIDAE. Lanceola, Say. Family CysrisomaTIpAE. Cystisoma,
Guérin. Family PararHrRonimipar. Paraphronima, Claus. Family
PHRONIMIDAE. Phronima, Latreille (Fig 136). Family Mimonecripar.
Mimonectes, Bovallius. Family Hyrertpar. Hyperia, Latreille ; Phroni-
mopsis, Claus; Euthemisto, Bovallius. Family PHrosintpar. Phrosina,
Risso. Family PHorcorrHAPHIDAE. Phorcorrhaphis, Stebbing. Family
PLATYSCELIDAE. Platyscelus, Spence Bate. Family Scettpagn. Thyropus,
Dana. Family Pronormar. Pronoe, Guérin. Family TrypHANIDAE.
Tryphana, Boeck. Family OxycrPHALIDArE. Ozxycephalus, H. Milne-
Edwards ; Rhabdosoma, White (Fig. 133).

16

iS)
as
is)

THE CHU S ACTA

Sus-Orper 3. Caprellidea, Dana (1852).

Head coalesced with second thoracic somite ; palp of maxillipeds with
from one to four segments (rarely absent); rarely all the thoracic legs
well developed, fourth and fifth pairs usually vestigial or absent, coxo-
podites small or coalesced with the body ; abdominal somites generally
all fused, appendages vestigial ; eyes small.

Family CApRELLIDAE. Cercops, Kroyer ; Phtisica, Slabber (Proto,
Leach) (Fig. 134, A); Caprella, Lamarck (Fig. 134, B). Family CyamMIpAr.
Cyamus, Latreille; Platycyamus, Liitken ; Paracyamus, G. O. Sars (Fig.
135).

Sup-Orper 4. Ingolfiellidea, Hansen (1903).

Head not coalesced with second thoracic somite ; palp of maxillipeds
with four segments; all the thoracic legs present, coxopodites small ;
abdominal somites distinct, first three and last pairs of abdominal
appendages vestigial ; eyes wanting but articulated eye-lobes are present.

Family INGOLFIELLIDAE. Ingolfiella, Hansen.

LITERATURE.

1. Bate, C. Spence. Catalogue of the . . . Amphipodous Crustacea in .
the British Museum, pp. iv+399, 58 pls. 8vo, 1862.

2. Bate, C. Spence, and Westwood, J. O. A History of the British Sessile-Eyed
Crustacea, 2 vols., 1863 and 1868. Issued in parts, 1861-1868.

3. Boeck, A. De Skandinaviske og Arktiske Amphipoder. Pp. 711, 32 pls.
4to. Christiania, 1872-1876.

4. Bovallius, C. Mimonectes, a Remarkable Genus of Amphipoda Hyperiidea.
Nova Acta R. Soc. Sci. Upsal. (8), xiii. No. 4, pp. 15, 3 pls., 1885.

5. Contributions to a Monograph of the Amphipoda Hyperiidea. Kgl.
Svenska Vet.-Akad. Handl., Ny Foljd. xxi. No. 5, pp. 72, 10 pls., 1887 ;
and xxii. No. 7, pp. 434, 18 pls., 1889.

6. The Oxycephalids. Nova Acta R. Soc. Sci. Upsal. (3), xiv. No. 4,

pp. 141, 7 pls., 1890.
7. Chevreux, E. Amphipodes provenant des Campagnes de |’Hirondelle, 1885-
1888. Résultats des Campagnes scientifiques . . . Monaco, xvi., 1900.
8. Claus, C. Zur Naturgeschichte der Phronima sedentaria, Forsk. Zeitschr.
wiss. Zool. xxii. pp. 331-338, pls. xxvi.-xxvil., 1872.

9. —— Der Organismus der Phronimiden. Arb. zool. Inst. Wien, ii. pp. 59-
146, pls. ili.-x., 1879.
10. —— Die Platysceliden, pp. 77, 26 pls. 4to. Wien, 1887.

11. Delage, Y. Contribution a l'étude de l’appareil circulatoire des Crustacés
édriophthalmes marins. Arch. zool. expér. ix. pp. 1-173, pls. i.-xii., 1881.

12. Della Valle, A. Gammarini del Golfo di Napoli, Fauna und Flora des
Golfes von Neapel, Monogr. xx. 1 vol. and atlas, 1893.

13. Dybowsky, B. N. Beitr. z. naiheren Kenntniss der in dem Baikal-See vor-
kommenden . . . Gammariden. Horae Soc. Entom. Rossicae, x., Beiheft.
pp- 190, 14 pls. 4to, 1874.

14. Hansen, H. J. The Ingolfiellidae, fam. n., a New Type of Amphipoda.
Journ. Linn. Soc. London, Zool. xxix. pp. 117-133, pls. xiv.-xv., 1903.

15.

- THE AMPHIPODA 243

Liitken, C. F. Bidrag til Kundskab om Arterne af Slaegten Cyamus, Latr.,
eller Hvallusene. K. Danske Vidensk. Selsk. Skr. (5), Naturvid. Afd. x.
(3), pp. 2381-284+3 pp. resumé, pls. i.-iv., 1873; op. cit. (6), iv. (4), pp.
315-322, 1 pl., 1887 ; op. cit. (6), vii. (9), pp. 419-484, 1 pl., 1893.

16. Mayer, P. Caprelliden. Fauna und Flora des Golfes von Neapel, Monogr.
vi., 1882; and Nachtrag zu den Caprelliden, Monogr. xvii., 1890.

17. —— Die Caprelliden der ‘‘Siboga”-Expedition. Uitkomsten ... H.M.
**Siboga,” Monogr. xxxiv. pp. 160, 10 pls., 1903.

18. Nebeski, O. Beitriige zur Kenntniss der Amphipoden der Adria. Arb. zool.
Inst. Wien, iii. pp. 111-162, 4 pls., 1880.

19. Sars, G. O. Histoire naturelle des Crustacés d’eau douce de Norvége.
1 Livr. Les Malacostracés, pp. iii+ 145,10 pls. 4to. Christiania, 1867.
20 An Account of the Crustacea of Norway: Vol. I. Amphipoda. Pp.

viii+711, 248 pls. Christiania and Copenhagen, 1890-1895.
21. Stebbing, T. R. R. Report on the Amphipoda. Rep. Voy. ‘‘ Challenger,”

22.

Zool. xxix. 2 vols. and atlas, 1888.
Amphipoda: I. Gammaridea. Das Tierreich, Lief. xxi. pp. xxxix +
806, 127 text-figs., 1906.

CHAPTER XIV
THE EUPHAUSIACEA

Order Euphausiacea, Boas (1883).

Definition.—Eucarida which retain the primitive caridoid facies ;
the exopodite of the maxilla is small; none of the thoracic limbs
are specialised as maxillipeds ; branchiae in a single series, attached
to the coxopodites of the thoracic limbs (podobranchiae) ; young
hatched in the nauplius-stage.

Historical.—The genus Thysanopoda was placed by H. Milne-
Edwards in his tribe of “ Mysiens,” and most subsequent writers
have retained the association of Euphausiacea and Mysidacea in the
group ‘“Schizopoda.” As already mentioned, Boas was the first to
separate the two orders. Some of the later larval stages were
described as distinct genera by Dana before their true nature was
pointed out by Claus. Metschnikoff’s discovery of the nauplius-
stage of Huphausia (1869) drew special attention to the larval his-
tory of the group. The most complete account of the structure,
development, and classification of the Order is that given by G. O.
Sars in his “Challenger” Report. The phosphorescence of certain
Euphausians was first observed by J. V. Thompson; the light-pro-
ducing organs have been investigated by several zoologists, the
most detailed account being that given by Chun.

MorPHOLOGY.

The general form of the body (Fig. 139) is completely caridoid.
The carapace coalesces dorsally with all the thoracic somites, and
is produced in front as a rostrum which is never of great length.

The telson (Fig. 142, C) has a pair of large movably articulated
spines (s) near the tip. Sars has shown that these are formed by
enlargement of one out of several pairs of marginal setae which are
present in the larvae, and it is therefore impossible to regard them
as representing the caudal furca of the Leptostraca.

Appendages.—The antennules are always biramous, and some-

244

THE EUPHAUSIACEA 245

times show sexual modifications in the male. The antennae have a
protopodite of two segments, a large lamellar scale or exopodite,
and an endopodite with three peduncular segments and a long

Fic. 139.
Meganyctiphanes norvegica, 8, x 2.

flagellum. The mandibles (Fig. 140, A) generally have a palp;
the incisor process is directly connected with the molar process,
there being no lacinia mobilis or row of spines in the adult,

Fia. 140.

Mouth-parts of Meganyctiphanes norvegica. A, mandible; B, maxillula; C, maxilla. e;
exite of first segment of maxillula; ex, exopodite of maxilla; 7, incisor process ; m, molar
process ; p, palp.

although some spines are present in the - larval stages. The
maxillulae (Fig. 140, B) have the usual two endites and a palp
which is generally unsegmented, but has three segments in Bentheu-
phausia and two in some larvae. An exite of the third segment
(exopodite) is present in the larva, but is replaced in the adult.
by an exite (¢) of the first segment, sometimes erroneously called

New

246 THLE sont CO, See Leet

the exopodite. The mazillae (Fig. 140, C) generally consist of
four segments; the second and third have each two endites and
the third a slightly developed flabelliform exite (exopodite) ; the
fourth segment generally forms the palp, but in Dentheuphausia the
palp consists of three segments. :
None of the thoracic limbs (Fig. 141) are specialised as maxilli-
peds, the first pair being similar in general structure to the
succeeding pairs. The coxopodite is distinct and of considerable
size ; the main. flexure of the limb is between the meropodite and
carpopodite ; the terminal segment is blunt and is without a
distinct claw, bearing, as a rule, only a group of setae and

Thoracic appendages of Meganyctiphanes norvegica: A, first; B, second; C, seventh; D,
eighth. br, branchia (epipodite) ; en, endopodite ; ex, exopodite ; p, luminous organ.

spines ; the exopodite is flattened and fringed with long natatory
setae.

On the outer side of the coxopodite is attached an epipodite (dr),
which is small and simple in form on the first pair, but ramified in
a complex fashion on the other pairs of thoracic limbs. These
branchiae, which are apparently quite homologous with the podo-
branchiae of Decapoda, are not covered by the carapace, but hang
out freely at the sides of the body.

The last pair or the last two pairs of thoracic appendages are
commonly much reduced or quite vestigial, though the branchiae
connected with them are of large size (Fig. 141, D). The coxopodite
of the first pair is usually shghtly produced inwards, but only in
Bentheuphausia does this so-called “masticatory lobe” differ very
perceptibly from that of the succeeding pairs. A more important
exception to the uniformity of the thoracic limbs is found in the
genera forming the sub-family Nematoscelinae. In these, one of
the pairs, the second or the third, has the endopodite greatly
enlarged and modified as a raptorial weapon. In Nematoscelis, the

THE EUPHAUSIACEA 247
ee ED oh EE ee

second pair is modified and the terminal segments bear a group of
long serrated “harpoon-like” spines. In Nematobrachion, the details
of the raptorial limbs are very similar to those of Nemutoscelis, but
it is the third pair that is modified. In Stylocheiron, the enlarged
third pair has a prehensile form, the terminal segment being, in
most cases, opposed to a strong spine or a group of spines on the
penultimate segment. In S. abbreviatum, G. O. Sars (=S. chelifer,
Chun), the spines are replaced by a process of the segment, form-
ing a perfect chela.

The pleopods (Fig. 142, A) are strongly developed in both
sexes; the rami are flattened and fringed with long setae; the
endopodite has an appendix interna (i) on its inner edge. The

Fic. 142.

Abdominal appendages of Meganyctiphanes norvegica (the marginal setae of the rami are
omitted). A, pleopod of third pair. B, endopodite of first pair of male, with the copulatory
apparatus unfolded. C, telson and uropod. en, endopodite ; ex, exopodite; i, appendix
interna ; s, movable sub-terminal spines of telson ; ¢, telson.

first and second pairs are modified as copulatory organs in the
male sex, the endopodite having on its inner edge a secondary
lobe, which in the first pair (Fig. 142, B) is very large and armed
with a complex apparatus of hooks and spines. The uropods
(Fig. 142, C) have the exopodite divided by a suture only in
Bentheuphausia.

Internal Anatomy.—The details of the internal structure of
Euphausiacea are still very imperfectly known. The hepatic caeca
appear to resemble those of Decapoda, being generally much rami:
fied and forming a large mass lying on each side of the thoracic
region. The heart is short, polygonal in outline, with three pairs
of ostia. The disposition of the main arterial trunks appears to
be similar to that in the lower Decapoda. An antennal gland is
present, opening on the proximal segment of the antennal peduncle.
In the thoracic portion of the ventral nerve-chain the full number

248 THE CRUSTACEA

of eleven pairs of ganglia can be distinguished, all of them, however,
united in a common sheath of connective tissue. The paired eyes
are each divided into two parts in the sub-family Nematoscelinae,
the fronto-dorsal division having elongated ommatidia of a structure
supposed to be adapted for perception of very faint light. The
nauplius-eye persists in the adult, lying between the paired eyes
beneath the rostrum.

No. statocysts have been found in any Euphausiacea. A
system of very remarkable organs, formerly regarded as ‘‘ accessory

S eyes” but now known to be lumin-
\ ous organs (photospheres), is found
in all EKuphausiacea except benth-
euphausia. As a rule, two pairs
of these organs are situated in the
coxopodites of the second and
seventh pairs of thoracic append-
ages respectively (Fig. 141, p), an
unpaired series on the sternal sur-
face of the abdomen between the
bases of each of the first four pairs
of pleopods, and a pair, differing
in structure from the others, on
the upper surfaces of the ocular
Section through one of the thoracic peduncles. In Stylocheiron, only
phosphorescent organs of Nematoscelis. c¢, the posterior thoracic palr, the first
cuticle ; h, hypodermis ; 1, lens; /.7, ring of :
lamellae surrounding the lens; n, nerve; abdominal organ, and those on the
eng ean reflector ; str, striated body. ocylar peduncles are present. Each
of the thoracic and abdominal photo-
spheres (Fig. 143) is globular in form, lying beneath and detached
from the hypodermis, and, in some cases at least, moved by special
muscles. The centre of the organ is occupied by a “striated
body ” (str) composed of radiating lamellae, which seems to be the
actual source of light, and in which the fibrils of a special nerve
appear to terminate. On the inner side of the photosphere is a
concave reflector (7) composed of concentric lamellae, and on the
outer side is a lens (/), the whole surrounded, except on the outer
side, by a sheath of pigment (yg). The organs on the ocular
peduncles differ in the absence of a lens, in their incomplete separa-
tion from the hypodermis, and in other details of structure.

The spermatozoa are simple round or oval nucleated cells.
They are transferred to the female in lageniform spermatophores,
which are formed within the widened terminal parts of the vasa
deferentia.

The ova are small in size and are sometimes carried, probably
only for a short time, “loose among the thoracic legs, which, with
their setae, form a sort of basket” (Holt and Tattersall, Huphausia).

Fia. 143.

J
1

THE EUPHAUSIACEA 249

In other cases the ova are agglutinated together in a paired or
unpaired mass, which is carried attached to the sternal surface of
the thorax, close to the bases of the posterior thoracic legs. These
egg-packets are formed by some cementing material apparently
extruded along with the eggs, and bear no sort of morphological
resemblance to the brood-sac of the Mysidacea which is formed by
the oostegites.

DEVELOPMENT.

With the possible exception of the genus Stylocheiron, where the
relatively large size of the eggs suggests an abbreviated meta-
morphosis, the Euphausiacea leave the egg in the form of a typical
nauplius, and reach the adult stage by a series of changes closely
parallel to those occurring in the metamorphosis of the Penaeidea
among the Decapoda. Claus was the first to show that the forms
described by Dana as distinct genera under the names Calyptopis,
Furcilia, and Cyrtopia are successive stages in the development of
Euphausiacea, and Sars has been able to fill in, with considerable
detail for several species, the outline thus furnished.

The newly hatched nauplius, as described by Metschnikoff and
by Sars, has an oval unsegmented body, without shell-fold, and with
the three pairs of nauplius appendages in their typical form, the
first uniramous, the second and third biramous ; the median eye is
not developed till the next stage. The mouth is not at first open,
and there is no masticatory process on the base of the antenna
such as exists in Copepoda and Cirripedia.

In the next stage the larva assumes the form of a metanauplius
(Fig. 144, A), showing rudiments of three additional pairs of ap-
pendages, maxillulae, maxillae, and first thoracic limbs; the shell-
fold is defined posteriorly and partly envelops the hinder end of
the body. In later metanauplius-stages the third pair of appendages
{mandibles) lose their natatory character and become reduced to
the basal masticatory part, with only a very small rudiment to
represent the palp ; the shell-fold now projects in front as well as
behind and overhangs the head in a hood-like form.

The metanauplius is succeeded by a series of Calyptopis-
stages (Fig. 144, B, C) characterised by the elongation of the trunk-
region and the differentiation of its somites in regular order from
before backwards. The thoracic somites are very short and crowded
together. The appendages already present become more fully
developed, and, later, the rudiments of the last pair of abdominal
appendages appear. The paired eyes develop but are covered at
this stage by the frontal hood of the carapace.

In the next succeeding Furcilia-stages the paired eyes become
free and movable. The pleopods develop from before backwards
and, later, the anterior thoracic limbs. The Cyrtopia-stage is

250 THE CRUSTACEA

characterised chiefly by changes in the antennules and antennae.
The former, which have become biramous already in the Calyptopis-
stage, now elongate, while the latter lose their natatory function, and
their rami, at first similar, become differentiated into “scale” and
flagellum respectively. The Cyrtopia gradually assumes the form

Fic. 144,

Larval stages of Huphausia. A, metanauplius. B, calyptopis. C, later calyptopis-stage.
1, antennule ; 2, antenna; 3, mandible; 4, maxillula ; 5, maxilla; I, first thoracic appendage ;
th, thoracic somites ; ab, abdomen; (@)-(a5), first five abdominal somites ; @g, uropod ; an, anus,§
f.s, frontal sense-organs. (A after Metschnikoff; B and C after Claus; from Korschelt and
Heider’s Embryology.)

of the adult by the successive development of the remaining
thoracic limbs.

The development of the various appendages, which has been
traced in detail by Sars, offers many features of interest. The palp
of the mandible only begins to redevelop in the Cyrtopia-stage.
The maxillula has at first a small lobe on its outer edge which
appears to represent the exopod and is quite independent of the

ut
I

THE EVPHAUSIACEA 2

plate which in the adult has been regarded as the exopod, but which
is in reality a process of the first segment of the limb. A very
remarkable feature in the development of the paired eyes has been
found by Sars in the case of Nematoscelis. Here, a transitory larval
eye consisting of seven ommatidia is formed at the apex of the eye-
stalk and is later pushed to the outer side by the development of
the permanent visual organ. Though this transitory organ is stated
to disappear in the adult, it seems possible that it may really persist
as the luminous organ of the eye-stalk, especially since in other
genera (Nuyctiphanes, Huphausia) the luminous organ appears before
the eye itself. The heart is visible already in the later metanauplius-
stages. The liver at first consists of three caecal tubes on each side.

REMARKS ON HABiTs, ETC.

The Euphausiacea are characteristically pelagic animals, forming
part of the surface-plankton of the ocean and descending to con-
siderable depths. They are generally remarkably transparent, but
Bentheuphausia, which appears to be a true deep-sea form (1000-
1800 fathoms), is said to be “‘ quite opaque and of a similar vivid
red colour to that of most other true deep-sea crustaceans.” The
adult size of most Euphausiacea lies between 10 and 40 mm.; a
species of Zhysanopoda reaches 55 mm. in length.

No fossil Euphausiacea are known.

AFFINITIES AND CLASSIFICATION.

The differences in structure which justify the separation of the
Euphausiacea from the Mysidacea have already been insisted on.
A certain degree of resemblance in general facies is sufficiently
accounted for, on the one hand, by the approximation of the basal
members of the Peracaridan and Eucaridan lines of descent to the
common caridoid stock of the Eumalacostraca ; and on the other, by
the similarity in habitat between the Euphausiacea and many of
Mysidacea. The resemblances between the members of the present
Order and some of the lower Decapods, especially the Penaeidea,
are of much greater importance. The complex copulatory armature
of the first pleopods has a general resemblance to that of the
Penaeidea, the larval development of the two groups is closely
parallel, and the presence in some Sergestidae of phosphorescent
organs resembling, though differing in details from, those of the
Euphausiacea may also be an indication of affinity.

At present, the Euphausiacea are regarded as constituting only
a single family.

tN

TA E AMOROUS TACEA

Ww
ul

OrpeER Euphausiacea, Boas (1883).

Family EupHavusiipar. Sub-Family EvupHausunar. Huphausia,
Dana; Thysanopoda, Milne-Edwards; Nyctiphanes,G. O. Sars; Meganycti-
phanes, Holt and Tattersall (Fig. 139). Sub-Family NemaTOSCELINAE.
Nematoscelis, G. O. Sars; Nematobrachion, Calman ; Stylochetron, G. O.
Sars. Sub-Family BenrHEevPHaAusIINAE. Bentheuphausia, G. O, Sars.

LITERATURE.

1. Chun, C. Atlantis. Biologische Studien tiber pelagische Organismen. 5.
Ueber pelagische Tiefsee-Schizopoden. Bibliotheca Zoologica, Bd. vii.
(Heft 19), pp. 137-190, pls. viii.-xv. 6. Leuchtorgane und Facettenaugen,
tom. cit. pp. 191-262, pls. xvi.-xx., 1896.

2. Claus, C. Ueber einige Schizopoden und niedere Malacostraken Messina’s.
Zeitschr. wiss. Zool. xiii. pp. 422-454, pls. xxv.-xxix., 1863.

3. Hansen, H. J. Preliminary Report on the Schizopoda. . . . Bull. Mus.
Océanogr. Monaco, No. 30, pp. 32; and Further Notes on the Schizopoda,
op. cit. No. 42, pp. 32, 1905.

4. Holt, E. W. L., and Tattersall, W. M. Schizopodous Crustacea from the
North-East Atlantic Slope. Rep. Fisheries, Ireland, 1902-1903, pt. ii. App.
iv. pp. 99-152, pls. xv.-xxv., 1905; and Supplement, Fisheries, Ireland,
Sci. Invest., 1904, v. 50 pp. 5 pls., 1906.

Metschnikof, E. Ueber ein Larvenstadium von Huphausia. Zeitschr. wiss.
Zool. xix. pp. 479-482, pl. xxxvi., 1869.

en

6. Ueber den Naupliuszustand von Luphausia. Op. cit. xxi. pp.397-401,
pl. xxxiv., 1871.
7. Sars, G. O. Report on the Schizopoda. Rep. Voy. ‘‘Challenger,” Zool.

xill. pp. 228, 38 pls., 1885.

CHAPTER XV
THE DECAPODA

Order Decapoda, Latreille (1802).
Sub-Order 1. Natantia.
Tribe 1. PENAEIDEA.

» 2. CARIDEA.
» & STENOPIDEA.

Sub-Order 2. Reptantia.
Section {. PALINURA.
Tribe 1. ERYONIDEA.
i) te. OCVRLARTD RA:

Section 2. ASTACURA.
Tribe NEPHROPSIDEA.

Section 3. ANOMURA.
Tribe 1. GALATHEIDEA.
» 2. LHALASSINIDEA.
» o. PAGURIDEA.
» 4. HIPPIDEA.

— Section 4. BRACHYURA.
Tribe 1. DROMIACEA.
Sub-Tribe 1. DRomImDEA.
. 2. HOMOLIDEA.

‘ Tribe 2. OXYSTOMATA.
» & BRACHYGNATHA.
Sub-Tribe 1. BRACHYRHYNCHA. -
5 2. OXYRHYNCHA.

Definition. —Eucarida in which the caridoid facies may be
retained or may be greatly modified ; the exopodite of the maxilla
is very large (scaphognathite) ; the first three pairs of thoracic
limbs are specialised as maxillipeds ; branchiae typically in several
series, attached to the coxopodites of the thoracic limbs (podo-
‘ branchiae), to the articular membranes (arthrobranchiae), and to the
} 253

254 THE CRUSTACEA

lateral walls of the thoracic somites (pleurobranchiae), very rarely
absent ; young rarely hatched in nauplius-stage.

Historical—The great majority of the larger and more familiar
Crustacea belong to the Decapoda, and this Order received far more
attention from the older naturalists than any of the others. A
considerable number of species are mentioned by Aristotle, who
describes various points of their anatomy and habits with accuracy,
and sometimes with surprising detail. A long series of purely
descriptive writers who have added to the number of known forms
without contributing much to a scientific knowledge of them begins
with Belon and Rondelet in the sixteenth century, and perhaps
does not altogether come to an end with Herbst’s Naturgeschichte
der Krabben und Krebse (1782-1804). Among the most noteworthy
of early contributions to anatomy are Swammerdam’s memoir on
the Hermit-Crab (1737), and that of Roesel von Rosenhof on the
Crayfish (1755). Réaumur’s observations on the phenomena of
ecdysis and the regeneration of lost parts in the Crayfish (1712-
1718) have become classical. The foundations of classification were
laid by J. C. Fabricius (1793), who divided the Linnean genus Cancer
into a large number of genera, the majority of which are still
recognised. Latreille, to whom the name of the Order is due (1802),
also began its subdivision into sub-orders and families. In this
more than in any other group of Crustacea the works of H. Milne-
Edwards, and especially his Histoire Naturelle des Crustacés, may be
taken as marking the beginning of the modern period, and his
classification of the Decapoda has been that most generally accepted
until very recently. Almost contemporaneous with Milne-Edwards’s
great work, and often surpassing it in morphological detail and
systematic insight, was de Haan’s volume on the Crustacea of Japan
(1833-1849). The first important departure from the general plan
of classification laid down by these authors was made by Boas in
1880, and his system has been further elaborated by Ortmann and
by Borradaile. J. Vaughan 'Thompson’s discovery of the larval
metamorphosis of Decapoda (1828-1831), confirming the earlier
observations of Slabber and Cavolini in the eighteenth century,
gave rise to a curious controversy in which Westwood and others
denied the possibility of such a metamorphosis, basing their argu-
ments chiefly on Rathke’s memoir on the development of the
Crayfish (1829). F. Miiller in 1863 made the highly important
discovery that Penaeus is hatched from the egg in the form of a
nauplius, and the clue thus given to the interpretation of the other
larval stages was followed up especially by Claus. The development
of deep-sea exploration within the last thirty years has resulted in
the discovery of a large number of important new types of Decapoda,
which have been described by Spence Bate, Miers, Henderson, A.
Milne-Edwards, Bouvier, Faxon, Alcock, and others. The numerous

THE DECAPODA 255

species of fossil Decapoda have been little studied from the point of
view of phylogeny, but reference may be made to Bouvier’s essay
on the origin of the Brachyura as an example of the results which
may be obtained in this department. Among other papers which
have been fruitful in suggesting lines of research for later workers
may be mentioned Huxley’s memoir on the classification and distri-
bution of the Crayfishes (1878); A. Milne-Edwards’s note on the
transformation of the ocular peduncle into an antenna-like organ in
a Palinurid (1864), the forerunner of much recent work on regenera-
tion and abnormalities ; Giard’s papers on parasitic castration ; and
Faxon’s discovery of the alternating dimorphism in the males of
Cambarus.

MoRPHOLOGY.

Amid the great diversity of general shape exhibited by the
Decapoda, two chief types may be distinguished. In the first or
Macrurous type the general caridoid facies is retained, the body is
elongated and subcylindrical, the abdomen is long and terminates in
a tail-fan. In the Brachyurous type (which is not confined to the
Brachyura, but recurs in several groups of Anomura) the cephalo-
thorax is greatly expanded laterally and more or less depressed,
while the abdomen is reduced and folded underneath the cephalo-
thorax. A very peculiar modification is found in most Paguridea,
where the abdomen is markedly asymmetrical and spirally coiled,
in correlation with the habit of living in the empty shells of
Gasteropod Molluscs.

The carapace coalesces dorsally with all the thoracic somites
and overhangs on each side as a branchiostegite, enclosing the
branchial chamber within which the gills are concealed. Anteriorly
it may be produced into a rostrum, which in a few genera of Caridea
(Rhynchocinetes, ete.) is movably articulated. In most Brachyura
the rostrum is reduced to a short but broad frontal plate, of which
the relations to the adjacent parts will be described below. In
some Macrura (Scyllaridae) and in many Anomura and Brachyura,
where the cephalothorax is flattened from above downwards, the
lateral portions of the carapace are abruptly bent inwards towards
the bases of the legs. The lateral margin thus produced is
commonly toothed or otherwise armed.

The surface of the carapace is commonly marked by depressions
and grooves corresponding in part to the insertions of various muscles,
but in part independent of these. In this way several regions
of the carapace are defined which, especially in the Brachyura,
may be still further divided into sub-regions. For convenience
of systematic description these various areas are denominated ac-
cording to a scheme of terminology introduced for the most part
by H. Milne-Edwards (1851). More recently the furrows of the

256 THE CRUSLACT A

carapace have been studied by Boas and by Bouvier. Only a few
points can be mentioned here. In the lobsters and crayfish a con-
spicuous groove (Fig. 145, c) crosses the dorsal surface of the
carapace transversely about
the middle of its length
and curves forwards on
either side. This groove,
named the “cervical groove”
by Milne-Edwards (¢ in
Boas’s terminology, the
“branchial groove ” of Bou-

Carapace of the Norway Lobster (Nephrops nor- vier), ae supposed by him

vegicus) trom the side. (After Boas.) The letters refer- to indicate the line of
ring to the grooves of the carapace are those used by Becks

Boas. @,¢’, the ‘‘cervical groove” of Bouvier, ‘‘anterior division between the por-
cervical groove” of Borradaile ; ¢, ‘‘ branchial groove” 47 S
of Bouvier, ‘posterior cervical groove” of Borradaile. tions of the carapace aris-

ing from the antennal and
mandibular somites respectively. Other writers, for instance,
Huxley, regarded it as marking the limits of the cephalic and
thoracic regions. There appears to be no ground, however, for
regarding this groove as of greater importance than some of the
other grooves of the carapace. In some cases an equally con-
spicuous transverse groove (e¢ of Boas, “cervical groove” of Bouvier)
(Fig. 145, ¢, ¢) crosses the
carapace a little in front of the
cervical, and as this is the only
transverse groove, apparently,
to be found in any of the lower
Macrura (Stenopidea, Caridea),
it seems at least as likely to
afford an important morpho-

Fia. 145.

Fic. 146.
logical landmark. In some Carapace of Callianassa novaebritanniae (Tha-

7 ‘ ete lassinidea) from the left side. (After Borradaile.)’
cases por tions of the cat apace c, e, the grooves so lettered by Boas (see Fig. 144) ;
may be separated by a lonogi- 1.0, linea anomurica (perhaps also the linea dromii-

‘ pete) dica), the front part of which is the line b of
tudinal groove or uncalcified Boas; 1.1, linea thalassiniea (perhaps also the

linea homolica), the front part of which is the line’

line, which may ‘even’ form: 2° gor Boss: 7, rostrm,

movable hinge. Of this nature

are the linea thalassinica (Fig. 146, 1.4) of the Thalassinidea, with
which the J. homolica of the Homolidae may perhaps be identical,
and the l. anomurica (l.a) of many Anomura, identified with the
1. dromiidicw of Dromiidae and the unfortunately named “ epimeral
suture” of other Brachyura.

The sternal surface of the cephalothorax is very narrow in
many Macrura, but is often broad in those which have a depressed
form. It is broad in many Anomura and in all Brachyura, with
the exception of Raninidae. The thoracic sterna are usually clearly
distinguishable, and, in the lower forms, seem to preserve a certain

THE DECAPODA 257

degree of mobility. In the higher forms they become firmly united,
with the exception of the last thoracic sternum, which may be
movable (Astacidae, Parastacidae, and Anomura).

In front of the mouth, regions representing the sterna of the
three preoral “somites” can be distinguished, but on account of
the ‘cephalic flexure” the ophthalmic and antennular sterna are
directed forwards, or even upwards. The antennal sternum is
mainly represented by the epistume, a plate of varying shape lying
between the labrum and the bases of the antennae. In the
Natantia the epistome is comparatively narrow, and on each side is
separated from the lateral portions of the carapace by the exhalent
branchial channels. In most of the Reptantia the epistome (Fig.
147, A, ep) is broad and comes in contact with the carapace on each
side, and in the Brachyura it becomes firmly united with it. In
this way there is defined more or less distinctly a buccal frame
within which lie the mouth-parts, and which in most Brachyura is
closed by the operculiform third maxillipeds. The sides of this
buccal frame are formed by the free antero-lateral margins of
the carapace (Fig. 147, B, /.m), while in front it is more or less
distinctly delimited by the epistome itself, or by a transverse ridge
(Fig. 147, B, a.m) which divides the epistome into two parts, the
epistome proper and the endostome or palate (end). In most
Brachyura also (except the Dromiacea) the proximal segments of
the antennae are fused with the epistome. In the Macrura the
anterior margin of the carapace forms on each side of the base of
the rostrum a more or less distinct ‘orbital notch,” within which
the eye rests when it is turned outwards. In the Brachyura this
transverse direction of the eye-stalks is permanent, and the orbit
is usually (except in Dromiacae) completed by the downgrowth
of a process (/.p) from the front, external to the antennules, which
unites either directly or, more usually, by intervention of the second
segment of the antenna, with the sub-orbital lobe (s.0) of the cara-
pace. Further, in all the Brachyura the rostrum or frontal plate
sends downwards in the middle line a process (m.p) which unites
in front of the ophthalmic and antennular sterna with the epistome,
and separates from one another the basal segments of the antennules.
The greater part of the ophthalmic peduncle is in this way con-
cealed in a kind of sheath, and only the terminal segment appears
and is movable within the orbit.

In the Dromiacea the second segment of the antennal peduncle
is free and there is no corresponding process of the front, so that
the orbits are incompletely or not at all defined. The arrange-
ment is hardly more complete in certain Oxyrhyncha (JJacrocheira)
(Fig. 147, B), but in most Brachyura the antennal peduncle joins
with the front to form a partition separating completely the
orbits from the ‘“antennular fossae,” into which the antennules

17

258 THE CRUSTACEA

may be withdrawn. There is, however, great diversity in the de-
tails of structure of the “facial” region among the Brachyura, and
these are of considerable value as systematic characters.

In the Seyllaridae among the Macrurous groups the cephalic

Fic. 147.

Head and anterior part of body from below. A, Nephrops norvegicus. B, Macrocheira
Kaempferi. C, Carpilius convexus. (Drawn by Miss G. M. Woodward.) a’, antennule; «”,
antenna ; a.m, ridge forming anterior margin of the mouth-frame and dividing the epistomial
area into epistome proper and endostome; c, point where the lateral wing of the carapace
touches, or, in B and ©, fuses with, the epistome; e, eye, in C retracted into, and partly
concealed by, the orbit; end, endostome ; ep, epistome; ex, exopodite ; l.m, lateral margin
of buccal frame ; U.p, lateral process of rostral plate, which in C comes in contact with the basal
segment (2+8) of the antenna ; md, mandible; mp, median process of the front (in B and C)
uniting with anterior process of epistome; mxp?, third maxilliped; 7, rostrum or (in C)
frontal plate ; s.o, suborbital lobe forming floor of orbit; ¢, in A, tubercle bearing opening of
antennal gland, in B and C, operculum covering the opening and probably representing the
reduced first segment of the antenna; 1-5, the segments of the antennal peduncle.

region is modified in a way that at first sight suggests the Brachy-
urous type, the eyes being widely separated and lodged in complete
orbits. In this case, however, the front unites in the middle line
not with the epistome but with the greatly enlarged antennular
somite.

In the Alpheidae (Caridea) the anterior margin of the carapace

THE DECAPODA 259

is modified in a very peculiar manner, growing over and, in most
cases, completely enclosing the eyes.

The differences in the development of the abdominal region are
no less conspicuous than in the case of the cephalothorax, and
have been utilised as affording characters for the primary sub-
divisions of the Order. In the Natantia the abdomen is large and,
with its appendages, forms the chief organ of swimming. It is
generally more or less compressed and its somites have well-
developed pleura. It is dorsally humped or bent between the
third and fourth somites in many Caridea (Eukyphotes, Boas) (Fig.
148), but the character is not so constant as to justify great

Fic, 148.
Heterocarpus Alphonsi (Caridea, Pandalidae), showing the ‘‘ humped” form of the abdomen
and the multiarticulate meropodite and carpopodite of the second leg. (From Alcock,

Naturalist in Indian Seas.)

systematic importance being attached to it. In the Palinura and
Astacura the importance of the abdominal appendages as natatory
organs is generally reduced, and the abdomen itself is not humped.

Among the Anomura, the Thalassinidea (Fig. 149) have retained
the extended abdomen of the Macrurous groups, but the pleura
are more or less reduced; the Galatheidea (Fig. 150) have the
abdomen more or less closely flexed under the cephalothorax but
not greatly modified; the Paguridea, with the exception of some
interesting transitional forms (Pylochelidae) (Fig. 151), have the
abdomen and its appendages more or less unsymmetrically developed
and its somites imperfectly indicated. In the hermit-crabs (Pagu-
ridae and Coenobitidae) the abdomen is soft-skinned and spirally

260 LAE CROSBACH A

Fia. 149.

Iconaxiopsis andamanensis (Thalassinidea). (From Alcock, Naturalist in Indian Seas.)

Fria. 150.

Munida andamanica (Galatheidae), abdomen extended.
(From Alcock, Naturalist in Indian Seas.)

THE DECAPODA 261

coiled to fit into the Gasteropod shells inhabited by the animals.
Only the sixth somite and the telson are fully calcified, the tergal
portions of the other somites being merely indicated by widely

Fig. 151.

Pylocheles Miersit (Paguvidea). «, end view of the animal lodged in a tube of water-logged

mangrove or bamboo, its chelipeds closing the opening. The lower figure shows the animal

ina hein attitude after removal from its refuge. (From Alcock, Naturalist in Indian
; . Seas.

| separated chitinous plates in the membranous investment of the
dorsal surface. In the coco-nut crab Birgus (Coenobitidae) (Fig.
; 152), which has abandoned the use of a covering for the hinder
} part of the body, the abdomen, though short, is symmetrical
and its terga are well calcified. In the Lithodidae (Fig. 153),

262 THE CKO S LACE A

Fic. 152.

Birgus latro, g, about 4th natural size. The last pair of thoracic legs are folded out
of sight in the branchial chambers. (From Aleock, Naturalist in Indian Seas.y

Fia. 153.

Neolithodes grimaldii (Lithodidae). (After Milne-Edwards and Bouvier, from Eney. Brit.)

THE DECAPODA 263

which afford a remarkable instance of “convergence” in the assump-
tion of the Brachyuran facies, the relationship to the hermit-crabs
is shown by the fact that the short abdomen, which is closely bent
up under the cephalothorax, has the terga incompletely calcified,
and is, in the female, more or less unsymmetrical, bearing append-
ages only on one side.

Among the Brachyura the abdomen is always closely flexed
under the cephalothorax, and is much reduced in size. The shape
usually differs much in the two sexes, being narrow in the male
but broad and often excavated for the reception of the eggs in the
female. The terga of all the six somites, as well as the telson,
may remain distinct, but very often two or three of the somites
may become coalesced, especially in the male sex.

In the region of the thorax a system of internal skeletal structures
is developed by infoldings of the cuticle (apodemes) forming the
endophragmal system. In the Natantia, with feebly calcified integu-
ment, this system is but slightly developed, but in the Palinura and
Astacura, and especially in the Brachyura, it attains a great degree
of complexity. A “sternal canal” may be formed by the meeting
of the sternal apodemes of opposite sides above the nerve-cord, and
in the anterior part of the thorax this may give a firm plate or
“entosternite” lying between the nerve-cord and the alimentary
canal. It is not certain whether this entosternite involves any
elements other than those supplied by the ectodermal and cuticular
infoldings forming the apodemes; if it does not it can hardly be
regarded as homologous with the entosternite already mentioned
in Branchiopoda (p. 44), which appears to be of mesodermal origin.

In the Brachyura a sternal canal is not formed, the union of the
apodemes being confined to one or two of the posterior thoracic
somites, where it gives rise to a transverse bar known as the “sella
turcica.”

Appenduges.—Among the Decapoda the ocular peduncles (Fig.
154) assume more the character of limbs than they do in any
other Crustacea, since they are generally (perhaps always) divided
into two, or more rarely three, movable segments. Instances of
extreme development of the eye-stalks occur among Caridea and
Brachyura, sometimes the first (Podophthalmus, Fig. 154, C) and
sometimes the second segment (Mucrophthalmus, Fig. 154, D) being
elongated. The corneal surface is generally terminal, but may be
oblique and even lateral, the peduncle running out beyond it into
a styliform process which may equal in length the rest of the eye-
stalk (Ocypoda, Fig. 155). In certain species of Gelasimus one of
the ocular peduncles terminates in a long process of this kind while
the other does not. In cases where the eyes are atrophied, as in
abyssal or cavernicolous decapods, the peduncle often persists in a
reduced state (Figs. 161, 162).

264 THE CRUSTACEA

The antennules have the three segments of the peduncle always
distinct, and as a rule both flagella are present. In many Caridea

Fia. 154,

Ocular peduncles of Decapoda. A, Ranina scabra (Brachyura). B, Astacus fluviatilis
(Astacura). C, Podophthalmus vigil (Brachyura). D, Macrophthalinus pectinipes (Brachyura). 1,
2, 3, successive segments of the peduncle.

Fie. 155.

Ocypoda macrocera (Brachyura) in a natural attitude with the eyes elevated, showing the
styliform prolongation of the ocular peduncles. (From Alcock, Natwralist in Indian Seas.)

(Fig. 156, A) the outer flagellum is bifurcated near the base, and
in some cases the three flagella appear to arise separately from the

THE DECAPODA 265

end of the peduncle. The proximal segment of the peduncle, which
in most cases lodges the statocyst, possesses in the Natantia a very
characteristic expansion of its outer margin in the form of a rounded
lobe or spiniform process known as the_stylocerite (sty). In the
Brachyura the flagella are very short or quite vestigial ; the basal
segment is enlarged and generally firmly fixed in the antennular
fossa, and the other two segments fold up beside it.

Certain special modifications of the antennules may be men-
tioned here. In the Sergestidae the outer flagellum of the male
is bifurcated and forms apparently a prehensile organ. In Hymeno-
cera (Caridea) the inner flagellum is broadly foliaceous. In
Solenocera (Penaeidae) the same flagellum is in the form of a

Fig. 156,

A, antennule, B, antenna, of Athanas nitescens. (After Sars.) 1-5, segments of the peduncle
(the fourth segment in the peduncle of the antenna is not visible from above); ex, ‘‘ scale”
or exopodite of antenna; 7, inner flagellum; o, outer flagellum of antennule with its inner
branch bearing olfactory filments; st, statocyst in basal segment of antennule; sty, stylo-
cerite ; ¢, tubercle bearing aperture of antennal gland.

half-tube ensheathing the outer flagellum and forming with its
fellow of the other side a long siphon supposed to have a respira-
tory function. In Albunea (Hippidea), where by a rare exception
only one flagellum is present, a respiratory siphon is formed by the
apposition of the two antennules, which bear each a double longi-
tudinal row of setae.

In the lower Decapoda the peduncle of the antenna has five
segments, the two segments of the protopodite and the first three
of the endopodite, but the segments are usually more or less
displaced so as to articulate with each other in a zigzag manner
(Fig. 156, B). The exopodite (vx) forms a large foliaceous “scale ”
(squama) in the Natantia. In most Reptantia the number of
peduncular segments is reduced by the fusion of the second and

266 THE CRUSTACEA

third, and the exopodite, when present, is often reduced to a spine-
like ‘“‘acicle.” In the Scyllaridea the number of free segments is
further reduced by the coalescence of the proximal segment with
the epistome. In the Brachyura, the proximal segment is only
distinct in the Dromiacea; in the other groups it is either fused
with the epistome or, perhaps, represented by a small operculum
(Fig. 147, B and C, ¢) which covers the external opening of the
antennal gland. ‘The exopodite is absent in all the Brachyura ex-
cept possibly in certain Dromiacea (Homolodromiidae), where an
immovable spiniform process is supposed to represent it. The
flagellum is very short in most Brachyura and may disappear
altogether. In some Corystidae the two flagella form a long
respiratory siphon in much the same way as the antennules do in
Albunea. In the Palinuridae not only the peduncle but also the
flagellum is very stout, and in the Scyllaridae the whole appendage
is expanded and flattened, and the flagellum is represented by a
broad, shovel-like plate..

The mandibles never have a distinct lacinia mobilis, although,
in some of the lower types (Atyidae), they may have a group of
setae or spines on the inner edge. ‘The incisor is widely separated
from the molar process in many Caridea (Fig. 157, A), but in the
other groups the two cannot be distinguished or are separated only
by a groove. In some Caridea the incisor process is wanting. A
palp of three segments is usually present, but the number of seg-
ments is sometimes reduced, and among the Caridea the palp is not
unfrequently entirely absent either in isolated genera (Hippolyte,
Palaemonetes) or throughout whole families (Crangonidae, Atyidae).
In the Penaeidae the palp is expanded and lamellar, and apparently
takes part in enclosing the respiratory passages.

The mavillulae (Fig. 157, B, and Fig. 9, B, p. 13) have two in-
wardly turned endites, and a palp which is sometimes divided into
two, and even, in some species of Penaens (Fig. 158, A), into three or
four, segments. An outwardly turned plate (ex) directly connected
with the proximal endite, and having the same relations as the
large external plate of the maxillula of Euphausiacea, can some-
times be observed, but only exceptionally (e.g. Curidina) is it of
considerable size. The chief difference from the maxillulae of the
Euphausiacea consists in the absence of a distinct second segment,
which here appears to be fused with the first.

The mazillae are closely comparable to those of Euphausiacea,
though the relative proportions of the parts are very different. In
the typical form such as we find in the Crayfish (Fig. 9, C, p. 13)
the two endites are each divided into two by a deep incision, there
is an unsegmented palp, and a very large lamellar expansion on the
outer side to which the name scaphognathite is given. According
to Hansen, the two bifid endites arise here, as in the Euphausiacea,

THE DECAPODA 267

<

from the second and third segments of the limb. Coutiére, how-
ever, states that in some primitive Caridea the double proximal

Bie. 157

Mouth-parts of Pandalus borealis (Caridea). (After Sars.) A. mandible; B, maxillula; C,
maxilla; D, first maxilliped ; E, second maxilliped. ¢, proximal endite of maxilla (accord-
ing to Boas, the small distal lobe alone represents the endite and the large proximal lobe does
not represent the proximal division of the endite in other Decapoda) ; en, endopodite ; ep,
epipodite ; ex, exopodite ; 7, incisor process ; m, molar process of mandible’; mb, mastigobranchia ;
P, palp ; pb, podobranchia ; se, scaphognathite of maxilla ; *, lobe on exopodite of first maxilliped
characteristic of Caridea.

Fig. 158.
A, maxillula of Penaeus caramote ; 1-4, palp of four segments; ex, exite connected with

proximal endite. B, first maxilliped of same ; 1-5, endopodite of five segments ; ep, epipodite ;
ex, exopodite. (After Boas.)

endite can be seen to belong to the first segment, and that the
other two lobes are independent of each other, belonging respectively

268 THESCROUSLTACEA

to the second and third segments. The scaphognathite has been
variously interpreted as an epipodite or as consisting of epipodite
and exopodite together. A comparison with the maxilla of the
Euphausiacea shows, however, that it must be regarded as an
extreme development of the plate which in the latter case is
identified as the exopodite.

The modifications which this typical form undergoes within the
Order are not very striking nor do they afford much material of
systematic value. An undivided proximal endite is characteristic
of the Caridea, in which group (with some few exceptions) it is
also greatly reduced in size (Fig. 157, C). In the Pasiphaeidae
both endites disappear.

It is characteristic of the Decapoda that the first three pairs
of thoracic limbs are more or less distinctly differentiated from the
others as mazillipeds. It must be noted, however, that the line of
demarcation between the two groups of appendages is not always
sharply drawn, and that in the Penaeidea and Caridea the third
maxillipeds are often distinctly pediform.

In all Decapods, however, the jirst mazilliped (unlike the
corresponding appendage of the Euphausiacea) has completely lost
its pediform character. The endopodite is greatly reduced in size,
and the coxopodite and basipodite are produced inwards as broad
endites of which the proximal is often divided by an incision.
The most primitive condition is found in certain Penaeidae (Fig.
158, B), where the endopodite presents the full number of five
segments. In other Decapoda the number of segments is never
more than two and the endopodite is often unsegmented. The
exopodite is always present; in the Caridea (Fig. 157, D) it
presents a characteristic lamellar expansion of its outer margin
(lobe a of Boas), the narrow distal part corresponding apparently
to the flagellum, which in the higher forms is segmented off from
the peduncle and may be divided into numerous articulations.
The epipodite is rarely absent (¢g. in many Anomura) and is
especially large in the Brachyura (Fig. 159, A).

The second mazilliped departs less from the general type of the
thoracic limbs than does the first. The proximal segments are not
produced inwards as distinct endites. The endopodite is relatively
short, permanently flexed inwards, and its distal part is commonly
more or less flattened.

In the family Stylodactylidae (Caridea) the second maxillipeds
appear to present an anomalous structure, two terminal segments
articulating side by side on the end of the fifth segment. In the
great majority of the Caridea (Fig. 157, E) the terminal segment
articulates, not with the distal end but with the inwardly turned
(morphologically the outer) margin of the preceding segment. The
number of distinct joints is not infrequently reduced by the fusion

THE DECAPODA 269

of the basipodite and ischiopodite. The exopodite is rarely absent
(Sergestidae, Pasiphaeidae), and is often divided into a peduncle and
a multiarticulate flagellum.

The third mazilliped may, in the Natantia, even exceed in
length the next succeeding pair of appendages. The coxo-
podite and basipodite are almost always connected by an im-
movable articulation. In the Caridea the ischiopodite is quite
coalesced with the meropodite, and the dactylopodite is obsolete
or coalesced with the preceding segment. A serrate ridge or
“crista dentata” (Fig. 147, A, map) is commonly present on the
third segment, but no endites are developed from the first and
second segments. Among the Brachyura (Fig. 147, B, C, map?)
the third maxillipeds become greatly modified to form an oper-

Fic. 159.

A, first, B, third maxilliped of Neptunus pelagicus (Brachyura). (After de Haan.)
en, endopodite ; ep, epipodite (mastigobranchia) ; ex, exopodite.

culum to the buccal frame and entirely lose their pediform char-
acter. The ischiopodite and meropodite become broad plates and
the terminal three segments are often hidden behind the meropodite.
The peduncle of the exopodite may also be expanded and share
in forming the operculum. Its terminal flagellum is either folded
out of sight or may be entirely lost. The epipodite forms a long
curved blade in most Brachyura (Fig. 159, B, ep).

The remaining five pairs of thoracic appendages (peraeopods) are
typically ambulatory legs, composed of the usual seven segments.
Exopodites may be present on some or all of them in some Penaeidea
and Caridea (Pasiphaeidae, Fig. 160, Hoplophoridae, some Atyidae,
and Crangonidae), but elsewhere they are wanting. As a rule one
or more pairs are chelate or sub-chelate, except in the Scyllaridea
(where, however, the last pair are imperfectly chelate in the female
sex) and in some Hippidea. The first three pairs are chelate in

270 THE CRUSTACEA

most Penaeidea and in the Stenopidea and Astacura (Fig. 161), the
first four or all five pairs in the Eryonidea (Fig. 162), the first two

Via. 160.

Psathyrocaris fragilis (Pasiphaeidae), showing the greatly developed exopodites of the thoracic
legs (a ‘‘Schizopod ” character) and of the pleopods. (After Alcock.

Fic. 161.

Nephropsis Carpenteri (Nephropsidae), g. A deep-sea species in which the eyes have almost
disappeared but the vestigial eye-stalk can be seen below the rostrum. (From Alcock,
Naturalist in Indian Seas.)

in most Caridea, the first or the first two in Thalassinidea (Fig.
149, p. 260), and the first pair only in the other Anomura (Fig. 150,

THE DECAPODA 271

p- 260) and the Brachyura.

In most Anomura the last pair, and in

a few Brachyura the last or the last two pairs, are subchelate. A
very remarkable form of chela is found in the genus Psalidopus

(Caridea) (Fig. 163), in which
both fingers are movably articul-
ated with the propodite, an
arrangement resembling that
found in the second maxilliped
of Stylodactylus.

In most of the Reptantia,
where the first pair of legs are
chelate and much larger than
the others, they are commonly
referred to as the chelipeds, and
the following four pairs are
distinguished as walking-legs.
Frequently the chelipeds are
asymmetrical in size and shape
on the two sides, the larger
chela having the fingers armed
with blunt crushing -tubercles,
while the smaller has sharp
cutting-teeth. In many cases,
as, for instance, in the lobster,
the larger crushing-chela may
be on the right or the left side
indifferently, but in some Bra-
chyura it is constantly on the
same side of the body. A
curious reversal of asymmetry
sometimes occurs as a result of
the loss of the larger chela; at
the next ecdysis the remaining
chela assumes more or less com-
pletely the characters of a large
crushing-chela, while the re-
generating limb has the form
of a small cutting-chela.

A modification of some of
the legs as swimming-paddles
occurs in various groups, for in-

Fic. 162.

Pentacheles IHextii (Eryonidea). The vesti-
gial eye-stalks are fixed in notches in the front
of the carapace. (From Alcock, Naturalist in
Indian Seas.)

stance, in the Portunidae (Brachyura), where the last pair are so

modified.

pair of legs may become multiarticulate and flagelliform.

In some Natantia and in one genus of Hippidea one

This

modification occurs especially in the second pair of many Caridea
(formerly grouped together as Polycarpinea) (Fig. 148), where the

272 THE CRUSTACEA

carpopodite and sometimes also the meropodite and ischiopodite
are subdivided into small articulations.

Secs.)

r

peculiar chelae in which both fingers are

, Naturalist in Indian

gs have

(From Alcock

, the first le

Fia. 163.
cures at the side

eed fi

As shown in the enlar,
movable, while the second legs terminate in a brush of setae.

Psalidopus spiniventris (Caridea).

While in the Natantia, with few exceptions, all the seven seg-
ments of the limb are distinct and movable, among the Reptantia

inf

He

THE DECAPODA 273

this is only the case in the Eryonidea. In the Astacura the
first pair, and in the remaining Reptantia all the five pairs, of
legs have the basipodite and ischiopodite immovably united.
Perhaps correlated with this fusion is the presence of a “fracture
plane” in the basipodite, at which separation of the limb takes
place in autotomy in many Reptantia.

In a few Decapoda some of the legs become quite vestigial or
even disappear altogether. In the Sergestidae the last two pairs
are reduced, and in Acefes the last pair and in Leucifer the last two are -
quite absent. In the Pinnotheridae (Brachyura) the last pair may
be rudimentary or absent. In many Crangonidae the second pair are
smaller than the others, and in Paracrangon they disappear entirely.
This case is especially noteworthy since the suppression of members
of a meristic series rarely occurs except at one end of the series.

The epipodites and associated structures of the thoracic limbs
will be described below in connection with the branchial system.

The pleopods of the Decapoda present typically the same structure
as those of the Euphausiacea. Of the two segments composing the
protopodite the first is usually small, often apparently absent, the
second elongated and often stout. The two rami may be multi-
articulate and flagelliform, more often flattened and unsegmented,
and bear a marginal fringe of natatory setae. The endopodite may
bear on its inner margin an appendix interna tipped with a group of
coupling-hooks.

It is interesting to note that the Penaeidea and Stenopidea,
which, on the whole, take the lowest place among the Decapods,
never possess an appendix interna (except in so far as an element
derived from it may possibly share in forming the copulatory
appendage on the first pair of pleopods in the male), though the
presence of that organ in the Leptostraca, Euphausiacea, and
Stomatopoda shows that its possession must be reckoned a
primitive feature among the Malacostraca.

The pleopods are most strongly developed in the Natantia,
where they form the chief swimming-organs. In the Reptantia the
natatory function is less important and the pleopods are generally
feebler, though in some fossorial Thalassinidea they are of consider-
able size. An appendix interna is wanting except in some Thalas-
sinidea and in the Scyllaridea, where the pleopods are peculiarly
modified. In the Anomura, excluding the Thalassinidea, the
pleopods are generally feeble, often uniramous, and are sometimes
absent from the first somite, as they are also in the Scyllaridea
and Parastacidae. They are absent altogether in the males of
Hippidea, Lithodidae, and of some other Paguridea ; when present
in the Paguridea, they are, as a rule, developed only on one side
of the body and an appendix interna is sometimes present. In
the Brachyura the first and second pairs (which are specially

18

274. THE CRUSTACEA

modified, as described below) alone persist in the male, while in
the female the second to the fifth pairs are (with rare exceptions)
developed as egg-carrying appendages, with short protopodite and
long and slender rami; the first pair are absent in the female ex-
cept in the Dromiacea: In Callianidea (Thalassinidea) the rami of
the pleopods are fringed with long filaments, apparently branchial in
function ; this isolated case forms a curious parallel to the develop-
ment of branchial filaments on the pleopods in the Stomatopoda
and in Bathynomus among the Isopoda.

Sexual modifications are commonly presented by the pleopods,
most constantly by those of the first and second pairs, which in the
male assume a copulatory function. In the case of the first pair
the difference may be slight, as in most Caridea, where the endo-
podite is reduced to a small leaflet, differing more or less in shape
in the two sexes, and in the male armed with a group of coupling-
hooks. In the Penaeidea the first pair of the female have the
endopodite small or wanting ; in those of the male it is represented
by a membranous plate, often of large size and complicated struc-
ture, attached to the inner side of the peduncle, and bearing (as in
the Caridea) a group of coupling-hooks which interlock with those
of the other side. To this apparatus the name of pefasma has been
given by Spence Bate. In the Reptantia the appendages of this
pair are never biramous. In the female sex they are greatly reduced
in size or altogether absent, Occasionally they are absent in both
sexes (Parastacidae, Scyllaridea,, some Paguridea, and Hippidea),
but more commonly they are developed in the male into copulatory
appendages, usually styliform, with a spoon-shaped or tubular
terminal part. In some Thalassinidea (Upogebia), by a rare excep-
tion, these appendages are present (uniramous) in the female but
absent in the male sex.

The second pair in the female sex are almost always similar to
those which follow. In the male sex, however, this is rarely the
case (some Scyllaridea, Parastacidae, Upogebia). As a rule, they
are modified by the development of an accessory process, the
appendix masculina (Boas), from the inner edge of the endopodite.
This appendix is small in the Penaeidea and Caridea (in which latter
it may coexist with the appendix interna), but in the other groups
it increases in importance, the terminal part of the endopodite
diminishing, as does also the exopodite, until in the Brachyura
(and some Anomura) there remains only a styliform appendage of
two segments, the proximal representing the protopodite. and the
distal the endopodite together with its appendix masculina.

The wuropods retain in the Macrurous' groups the general
characters of the caridoid type, having a short protopodite and
broad lamellar rami, forming with the telson a tail-fan. As a rule
the exopodite is more or less distinctly divided by a transverse

+ ~— s
ate

THE DECAPODA 275

joint, and very rarely as in Laomedia (Thalassinidea) the endopodite
is similarly divided.

Among the Anomura the uropods are variously modified. In
the Galatheidea they retain more or less the type of structure
which they showed among the Macrura. In most Paguridea they
become modified as organs for fixing the posterior end of the body
in the shell or other “lodging carried by the animal, the rami are
stout and curved, with roughened, “file-like ” surfaces which are
pressed against the shell, and the appendages of the two sides share
in the asymmetry of the whole abdomen. In the Lithodidae alone
among Anomura the uropods are wanting. This is all but
universally the case also among the Brachyura, where only in
certain Dromiacea (Dromiidea) are there found traces of uropods in
the form of small plates intercalated on each side between the last
abdominal somite and the telson.

Branchial System.—With the single exception of the aberrant
genus Leucifer, all Decapoda possess branchiae connected with some
or all of the thoracic somites and lying in the cavities enclosed by
the branchiostegites on each side. The typical number of branchiae
which may be present on each side of a somite is four, arranged as
follows: One is attached to the lateral wall of the somite dorsal
to the articulation of the appendage (pleurobranchia), two to the
articular membrane between the coxopodite of thé appendage and the
body-wall (arthrobranchiae), and one, representing a differentiation
of part of the epipodite, is inserted on the coxopodite itself
(podobranchia).

Four series of gills corresponding to these can be traced in a
more or less incomplete form throughout the whole series of the
Decapods. They are, however, not invariably distinguished from
each other by the position of attachment in the manner just
described. In particular, the distinction between arthrobranchiae
and pleurobranchiae is often very difficult to draw in practice,
and there are some cases where an arthrobranchia in one species
is plainly homologous with a pleurobranchia in another. Claus
has shown that in the development of Penaeus three bud-like
outgrowths appear on the proximal part of most of the thoracic
limbs (Fig. 164, A). The distal one (a) gives rise to the epipodite
with its podobranchia and the two others (b, c) are the arthro-
branchiae. As development proceeds an apparent change in the
position of these last is brought about by coalescence of the proximal
part of the appendage with the body, so that the branchiae no longer
appear as outgrowths of the limb but spring from that part of the
body-wall which afterwards forms the articular membrane of the
joint. The pleurobranchia appears a little later than the other two
(Fig. 164, B, d), but its place of origin is very close to if not actually
on the basal part of the limb itself. Williamson has observed a

276 THE CRUSTACEA

similar transference of the gills from the limb to the body-wall in
the development of Crangon (Caridea), and Bouvier in Uroptychus
(Galatheidea). Claus concludes from these observations that not
only the podobranchiae but also the arthro- and pleurobranchiae
are originally appendages of the limb. The absorption of the
proximal part of the limb into the body-wall is of importance in
view of Hansen’s recognition of a pre-coxal element in the ap-
pendages of various Crustacea.

The origin of the podobranchiae by differentiation of part of
the epipodite is also clearly shown in the development of Penaéus.
The most distal of the three outgrowths mentioned above early
becomes bilobed. .The distal lobe, which lies in front of the

mxp2 MXP, :

Fic. 164.

Two stages in the development of the branchial system of Penaeus. (After Claus.) A, early
stage; B, later stage after appearance of the rudiments of pleurobranchiae. maxp1-map?,
maxillipeds ; 11-15, leg 23; @, distal series of rudiments. giving rise to mastigobranchiae and
podobranchia (on inxp?) ; b, c, rudiments of arthrobranchiae ; d, rudiments of ‘pleurobranchiae.
In B the distal rudiment on map? is dividing into podobranchia (pb) and mastigobranchia (mb).

proximal one, develops in the case of, the second maxilliped (Fig.
164, B, mzp?) into the podobranch (in the other appendages it:
disappears), while the proximal ,and: posterior lobe becomes the
sepipodite or mastigobranchia of the adult, a bilobed membranous
lamina’ which extends upwards into the branchial chamber between
the gills. On the. first pair of maxillipeds the distal lobe remains
simple and persists as the distal part of the laminar epipodite of
the adult. It is remarkable, however, that in the only cases in
which the epipodite of the first maxilliped develops branchial
filaments (in some Parastacidae), these are borne, not by the distal
part which appears to represent the podobranchia, but by the
proximal division.

In most Reptantia the podobranchiae have a similar relation to
the mastigobranchiae to that just described in Penaeus. In the

THE DECAPODA 277

Astacidae, however, the axis of the gill coalesces with the mastigo-
branchia, which has the form of a folded membranous lamina from
which the branchial filaments spring directly. In the Parastacidae
this lamina is greatly reduced or disappears.

In the Caridea, the mastigobranchiae, when present, have usually
the form of short curved rods, directed backwards, each ending in
a hooked process which grasps a tuft of long slender setae on the
coxopodite of the next succeeding appendage. ‘This tuft of setae,
which is also present in some Reptantia, springs from a small
papilla which Coutiere has compared with the setiferous epipodial
process found in Gnathophausia (Mysidacea) (Fig. 106, ep, p. 176), and
which he regards as a distinct element of the branchial system
(setobranchia of Borradaile). In a species of Liconaxius (Thalas-
sinidea) Coutiere has found that the coxopodite of the first leg
bears two podobranchiae, one attached as usual to the base of the
mastigobranchia, the other close to, if not actually inserted on, the
setobranchia. In no other Decapod is more than one podobranchia
found on any limb.

As regards their structure, each branchia consists of a stem or -
axis which is attached at or near one end and bears numerous
lateral branches. According to the form and arrangement of these
latter, three main types of gills have been distinguished, which,
however, are connected by intermediate forms. In the fricho-
branchiate type (Fig. 165, B) the branches are filamentous, and are
arranged in several series around the axis. In the phyllobranchiate
type (Fig. 165, C) the branches are flattened laminae, and as a
rule only two opposite series are present. The dendrobranchiate
type (Fig. 165, A) is characterised by the fact that the biserial
primary branches are themselves ramified, sometimes in a very
complex fashion. The dendrobranchiate type is peculiar to the
Penaeidea, but each of the other two types recurs in widely
separated groups. Thus the Caridea have phyllobranchiae, as
have also all the Brachyura, with the exception of some of the
primitive Dromiacea, which have trichobranchiae. The Stenopidea,
Palinura, and Astacura have trichobranchiae. Among the Anomura,

~phyllobranchiae are the rule, but Aeglea among the Galatheidea,

and the Pylochelidae, with several genera of Paguridae among the
Paguridea, have trichobranchiae, and the gills of some Thalassinidea
are intermediate in character. :

In the number and arrangement of the- gills very great differ:
ences exist, which afford valuable systematic characters. At the
same time, the important divergences sometimes presented by
closely allied forms render it necessary to use caution in estimating
the value of these characters (compare, ¢.g., Caridina and Limnocari-
dina, or Pandalus and Pandalina). The last thoracic somite is
invariably destitute of mastigobranchia, podobranchia, or arthro-

278 LHE CROSPACEA

branchiae, though it may carry a pleurobranchia and a setobranchia.
As a rule no gills are present on the first thoracic somite, but
in some Penaeidea, Stenopidea, Astacura, and Thalassinidea, a
minute arthrobranchia (? pleurobranchia) is present, while in some
Parastacidae the epipodite bears some branchial filaments and is, in
fact, a rudimentary podobranchia.

On the remaining somites the podobranchiae are the most
frequently suppressed. It is characteristic of the Scyllaridea and
Astacura that they possess a full series of podobranchiae, and less
complete series are found in the more primitive Penaeidea (Cerata-
spinae and Aristeinae), in the Eryonidea and some Thalassinidea,
and in the primitive Homolodromiidae among the Dromiacea. In

b.c.

Fic. 165.

Branchiae of Decapoda. The lower figures show the complete branchiae, the upper figures
transverse sections of the same. A, dendrobranchiate type (Penaeus canaliculatus). B, tricho-

branchiate type (Astacus flwviatilis). C, phyllobranchiate type (Palaemon lar). b.c, blood-
channels in axis of branchia.

all other Decapods they are absent from the legs and, except in
Brachyura, from the third, though not uncommonly present on the
second, maxillipeds. Apart from the podobranchiae, the mastigo-
branchiae and setobranchiae may persist in a more or less complete
series, especially in the Caridea. The pleurobranchiae are stated
to extend forwards to the somite of the third maxilliped in some
Caridea, and to that of the second in the Penaeidae ; but it must
be noted that the distinction between pleuro- and arthrobranchiae
in the crowded anterior part of the branchial chamber is often
obscure. They form the chief part of the gill-system in the Caridea,
where five are usually present, and, on the other hand, they are
quite wanting in most of the Thalassinidea. In the Brachyura a
formula of nine branchiae on each side is found in all the main sub-
divisions ; but while it is practically universal in the Oxyrhyncha

io >

THE DECAPODA 279

and in those families of the Brachyrhyncha formerly grouped
together as Cyclometopa, it suffers reduction in many of the Cato-
metopa, especially in terrestrial and parasitic forms, and in the
majority of the Oxystomata.

The table on p. 280 gives the branchial formulae in a series of
representative forms.

The arrangements for maintaining a current of water through
the branchial chamber and for preventing the ingress of foreign
particles are very varied and often complex. The branchial
current is caused by the vibratory movements of the scaphognathite
or exopodite of the maxilla, and as a rule it sets from behind
forwards, though it appears that in some cases, especially in
Decapods which burrow in sand or mud, the direction of the
current is periodically reversed. In the simplest cases, as in most
of the Macrurous groups, the water enters along the lower margin
of the branchial chamber, which is protected by setae, and in par-
ticular by those of the setobranchiae. The exhalent current passes
out at the sides of the oral region in front. This arrangement is
modified in the Brachyura by the free edge of the branchiostegite
fitting closely to the bases of the legs on each side, only leaving an
aperture for the ingress of water in front of the base’ of the cheliped.
This aperture is provided with an opercular valve formed by the
base of the long epipodite of the third maxilliped. These arrange-
ments may be further complicated in various ways, especially in
the case of burrowing forms. The exhalent passages, which in
some cases may by reversal of the current become inhalent, are not
unfrequently prolonged towards the front of the head by the apposi-
tion of various appendages. In many Penaeidea the lamellar
mandibular palps, the antennal scales, and the antennular peduncles
co-operate to this end; in the Brachyura and some Anomura the
flattened third maxillipeds carry the exhalent channels at least as
far as the anterior margin of the buccal frame ; the flagella of the
antennules in some Hippidea and of the antennae in the Corystidae
form a long exhalent (or inhalent) siphon; and in the Leucosiidae
among the Brachyura the inhalent as well as the exhalent channels
are carried forwards to the front of the head beneath the expanded
maxillipeds. Some special adaptations for aerial respiration will
be described below in connection with the circulatory system.

Alimentary System.—The stomodaeal “ stomach ” of the Decapods
is developed into a triturating and straining apparatus of great
complexity. The simplest form of the gastric armature appears to be
found in the Penaeid genus Cerataspis (Fig. 166), recently studied by
Bonnier. Here the chitinous lining of the stomach, although pro-
vided with numerous internally projecting ridges armed with setae
and spinules, is nowhere indurated or calcified to form distinct
sclerites such as are found in other Decapeds, and in so far it

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THE DECAPODA 281

resembles that of many of the more primitive Malacostraca. <A
deep transverse infolding of the dorsal surface, which marks the
division into the larger anterior or cardiac and the smaller posterior
pyloric chamber, is produced internally into a strong median tooth
{m.t). The floor of the cardiac chamber presents internally a median
(mr) and a pair of lateral (/.7) longitudinal ridges defined by deep fold-
ings of the cuticle and representing elements which in other forms
become calcified sclerites ; just above these on each side are series
of stout denticles (d), of which a posterior group in the vicinity of the
“median tooth” appear to correspond to the “lateral teeth” of other
Decapods. The pyloric division has its lumen greatly reduced by
infoldings of its walls, and may be regarded as being divided by a
longitudinal fold (7) on each side into a dorsal and a ventral portion,

Fic. 166.

Dissection of the stomach of Cerataspis monstruosus (semi-diagrammatic). card, cardiac
chamber ; d, lateral denticles ; 7, terminal lappets projecting into mid-gut ; /.r, lateral ridge ;
m.r, median ventral ridge of cardiac chamber; m.t, median tooth ; pyl, pyloric chamber ; 7,
longitudinal ridge separating dorsal and ventral divisions of pyloric chamber ; w, wedge-
shaped ridge with straining apparatus. (After Bonnier.)

of which the former is a direct continuation of the cardiac chamber,
while the latter is a diverticulum closed in front and communi-
cating with the dorsal chamber only by a narrow slit between the
setose margins of the longitudinal ridges. The ventral chamber
has its cavity again divided into two portions by a strong median
wedge-shaped ridge (w) which rises from its floor and is produced
posteriorly into a tongue-like process overhanging the apertures of
the hepatic ducts into the mid-gut. The lateral surfaces of this
ridge are provided with a characteristic armature which seems to
act as a straining apparatus ; it consists of numerous parallel plate-
like ridges running longitudinally and standing at right angles to
the surface, each bearing on its edge a comb-like fringe of setae
lying parallel with the surface and covering in the groove lying
between each ridge and the next. This wedge-shaped ridge and

282 LHE CRUSTACEA

straining apparatus appear to be very constant throughout the
group, and are no doubt homologous with the very similar structures
found in other orders of Malacostraca. At its posterior end the
chitinous lining of the stomodaeum terminates in four tongue-like
lappets (/) (much elongated in Penaeus) which project freely into the
cavity of the mid-gut.

In the other Penaeidea the stomodaeal armature is much more
complex than that just described. A large number of sclerites,
more or less calcified, are differentiated in the walls of both cardiac
and pyloric chambers. A dorsal and a ventral series can be dis-
tinguished, the dorsal and dorso-lateral pieces of the cardiac chamber
being in relation to the strong median and lateral teeth. From
this arrangement of the parts found in the Penaeidea, that charac-
teristic of the Reptantia may be easily derived, the chief differences
being due to the appearance of additional sclerites, and especially
of a series of intermediate pieces on the lateral walls of the two
chambers. The elements of the dorsal series are the more important,
forming as they do a system of levers moving the dorsal and lateral
teeth.

The great majority of the Caridea diverge more widely from
the Penaeid type owing to the disappearance of the whole of the
dorsal series of sclerites and of the dorsal and lateral teeth associated
with them, the roof of at least the cardiac chamber remaining quite
membranous. Only the Atyidae and one or two others among the
families of Caridea hitherto examined possess certain elements of
the dorsal series well developed, but they are differently arranged
from those of the other Decapods.

Mention must be made here of the gastroliths or “crab’s eyes,”
which are discoidal calcareous nodules in the lateral walls of the
cardiac division of the stomach in Crayfish (4stacus) and Lobsters
(Homarus). They are periodically formed shortly before ecdysis
takes place, and are shed into the cavity of the stomach, to be
broken up and dissolved, apparently providing some of the material
necessary for the calcification of the new integument. No similar
structures are definitely known to occur in any other group of
Decapods.

The mid-gut varies very much in length in different Decapoda,
but exact observations have been made only on a few types. In
the Crayfish (Astacus) it is exceedingly short, so that the dorsal
lappet which terminates the cuticular lining of the stomodaeum
extends through it into the beginning of the proctodaeum. In
most, if not all, Brachyura it is also very short. In the Lobster
(Homarus), however, it occupies five-sixths of the post-gastric part
of the alimentary canal. In species of Alpheus (Caridea) the mid-
gut extends as far as the last somite, and in Paguristes it is longer
than the proctodaeum. From the upper surface of the mid-gut

THE DECAPODA 283

there arises anteriorly in Astacura and most Thalassinidea a short
unpaired caecum. In Callianassa among the Thalassinidea and in
most Paguridea a pair of longer or shorter caeca are present, and
in most Brachyura they form two long and convoluted tubules. In
the Caridea and Galathaeidea and in Paguristes (Paguridea) no
caeca are found. Dromia possesses a single short caecum, and so
resembles the Astacura and differs from the other Brachyura.

An unpaired caecal tube of considerable length springs from
the dorsal surface of the intestine in the Brachyura, and a shorter
caecum is present in the Lobster, in the Thalassinidea, and in some
Paguridae. It is probable that in all these cases the caecum arises
from the posterior end of the mid-gut. In Alpheus, according to
Coutiere, the mid-gut is produced backwards beyond its junction
with the narrower hind-gut into a number of blind saccules.

Groups of gland-cells on the walls of the oesophagus, on upper and
lower lips, and on the maxillulae and maxillae, have been regarded
as salivary glands. Quite similar glands, however, may occur through-
out the whole length of the hind-gut also, and they are identical in
structure with the dermal glands which occur in various situations
on the surface of the body.

With the single exception of Leucifer, which possesses only two
pairs of hepatic caeca, the voluminous “liver” of the Decapods
consists of a mass of minutely ramified tubules, lying mainly in the
thorax. It communicates with the anterior part of the mid-gut by,
as a rule, a single duct on each side, but in Alpheus (Coutiere) three
ducts are present. In Paguridae the hepatic glands are displaced
backwards, and lie for the most part in the abdominal region.

Circulatory System.—The heart in all Decapods is_ short,
polygonal in outline, and situated under the posterior part of
the carapace. As a rule there are three pairs of venous ostia,
of which one, or in the Brachyura two pairs are situated on the
upper surface. Coutiére has demonstrated the existence of two
additional pairs in certain Caridea, and possibly further research
will show that these are present in other cases.

Anteriorly the heart gives off a median ophthalmic artery
which runs forward to supply the region of the eyes. On each
side of this originates an antennal artery, which, besides supplying
the antennae, sends branches also to the rostrum, eyes, and adjacent
parts. In <Astacus, Bouvier finds that terminal branches of the
antennal arteries unite in front of the brain in a median vessel
which runs backwards to anastomose on the walls of the oesophagus
with branches of the sternal (subneural) artery—an arrangement
which recalls the cireumoesophageal vascular ring of some Isopoda
and Amphipoda. A second pair—the hepatic arteries—arise from
the sides of the heart a little way behind the antennal arteries,
and are distributed to the hepatic glands and adjacent viscera.

284 TLE CISC SL Ciel

Posteriorly the heart sends off a median vessel, the superior
abdominal artery, while the unpaired descending artery (some-
times called the sternal artery) may arise separately from the
heart (Brachyura) or may branch off from the superior abdominal
artery just beyond the valves which mark its origin from the
heart.

The descending artery passes on one side (either to right or left)
of the intestine and pierces the ventral nerve-chain in nearly all
Decapods, passing between the connectives uniting the sixth and
seventh thoracic ganglia. Only in some of the Brachyura, where
the concentration of the nervous system reaches its highest point
(Oxyrhyncha and some Brachyrhyncha), this perforation of the nerve-
mass does not take place, the artery passing behind instead of
through it. On arriving at the ventral surface the artery bifurcates
in the median plane, a large branch, to which the name of sternal
artery is commonly applied, running forwards to supply the ventral
surface of the thorax and its appendages, while a smaller branch
running backwards also beneath the nerve-chain is the inferior
abdominal artery (absent only in Paguridea). These two arteries
taken together form a median longitudinal trunk quite comparable
to the subneural vessel of Isopods, and, like it, may communicate
with the dorsal system of vessels by a circumoesophageal ring.
A further communication is very often present at the posterior end
of the abdomen, where a vascular ring encircling the intestine
unites the superior and_ inferior abdominal arteries. A pair of
posterior lateral arteries arising from the superior abdominal
artery near its origin from the heart, and often unsymmetrically
developed, are of importance since they irrigate the branchiostegal
regions of the carapace which have a respiratory function.

A venous sinus in the mid-ventral line receives the blood from
the lacunar system of the body and appendages and distributes
it to the gills, whence it is returned to the pericardial sinus by
branchio-pericardial channels running in the inner wall of the
branchial cavity. A minor circuit for the blood is afforded by the
lacunar network of the branchiostegites, which, receiving blood
partly from arteries and partly from adjacent venous sinuses,
return it directly to the pericardium by special channels.

In terrestrial Decapods various modifications of the respiratory
and circulatory systems are met with. In those most completely
adapted to a terrestrial life (Birgus, Cardisoma) the lining membrane
of the branchial cavity is very vascular and covered with minute
villi. The supply of venous blood to the sinuses of the branchio-
stegal regions is more important and more definite than in
aquatic Decapods, and the apparatus no doubt functions as a
lung. In the terrestrial Hermit-crabs (Coenobita) a very peculiar
respiratory organ is found. A rich vascular network is developed

THE DECAPODA 28

uw

in the delicate skin of the abdomen, especially on the dorsal side
anteriorly. Two pairs of venous trunks running along the sides
of the abdomen return the blood to the pericardium, a pair of
rhythmically contractile vesicles at the base of the abdomen serving
to accelerate the flow.

Exeretory System.—In all Decapods the antennal gland is well
developed, and generally presents a complexity of structure not
found elsewhere among Crustacea. It has in most cases lost its
original tubular form and assumed that of a compact gland. Three
divisions are commonly distinct—the saccule, the labyrinth, and the
bladder, with its efferent duct leading to the exterior. The
saccule, which represents the end-sac of the typical antennal
gland, may retain its simple saccular form, but more commonly
it is complicated either by the development of partitions dividing
up its cavity, or by numerous branches which ramify through
the mass of the labyrinth. The labyrinth may be considered as
derived from a sac which, by the rich development of partitions
and trabeculae from its walls, has been converted into a spongy
mass traversed by a complex system of canals. In the Crayfish
(Astacus) the structure is still further complicated, mainly by the
elongation of a portion'of the labyrinth into a whitish cord of
spongy substance which is convoluted upon itself, forming the
“medullary” portion of the gland, the greenish “cortical” layer
representing the proximal portion of the labyrinth which com-
municates with the end-sac. The bladder may retain, as in the
Crayfish, the form of a simple vesicle communicating with the
exterior by a short duct. In many cases, however, it sends off
prolongations which may extend through a great part of the body.
In some Caridea this vesical system is very extensive, lobes from
the two sides uniting with each other to form an unpaired vesicle
above the stomach. In the Brachyura three main lobes are given
off from the bladder, which are very constant throughout the group,
such differences as do occur being correlated with the differences
in shape of the carapace. In the Paguridae, however, the vesical
system reaches its greatest complexity (Fig. 167). The bladder
sends off prolongations which ramify between the organs and
anastomose to form delicate networks and arborisations in the
region of the thorax, and two long diverticula, which may unite
with each other, pass backwards to traverse the whole length of
the abdomen. In Palinurus an accessory gland not found in any
other type opens into the duct of the bladder. The external
aperture is in most cases placed on a papilliform elevation on the
proximal segment of the antennal peduncle. In the Brachyura
the aperture is covered by an operculum (Fig. 147, B and ©, 2),
capable of being opened and closed by special muscles. It has
been shown that this operculum in all probability represents the

286 RAE CRUSTACEA

reduced proximal segment of the antenna, and the muscles attached
to it have been identified with those which move the proximal
antennal segment in the lower Decapods. This structure was
described by Audouin and Milne-Edwards
as a kind of auditory ossicle.

No trace of the maxillary gland is
known to persist in any adult Decapod,
though it is frequently well developed in
the larval stages.

Traces of glandular organs, presumed
to be homologous with the antennal and
maxillary glands, have been observed in
embryonic stages in certain other somites
of the trunk. In addition, certain other
structures are found in adult Decapods, the
excretory functions of which have been
demonstrated physiologically, although
their morphological significance remains
obscure. The most important of these
are the “branchial glands,” which are
masses of connective-tissue cells surround-
ing the venous channels in the axis of the
gills and are devoid of ducts. Other
glands of the dermal type also occur in

Fic. 167. connection with the gills.
tea Nervous System.—Great differences exist
abd, unpaired vesicle lying in In the number and disposition of the
abdomen ; arb, arborisations of : : :
the vesical system in thorax; 1, ganglia composing the ventral. chain.
seeteaie. CAftoe Marchal) ©? Among the lower Decapods the six ganglia
corresponding to the six abdominal somites
are distinct, but those of the cephalothorax may be more or less
coalesced. The largest number of distinct ganglia appears to be
found in the Astacura, where those of the five posterior
thoracic somites are well separated, the remaining cephalotho-
racic ganglia being more or less completely coalesced to form
a large suboesophageal ganglion. In other cases coalescence
has taken place to a greater extent, and in the Scyllaridea and
some Caridea, at least, all the cephalothoracic sternal ganglia form
a single mass. Among the Anomura the degree of coalescence
varies, and sometimes the first abdominal ganglion is approximated
to the thoracic mass. Among the Brachyura the concentration of
the nervous system reaches its highest point; the whole of the
sternal ganglia are united into a rounded mass lodged in the
thorax, from which the nerves radiate outwards. As a rule this
mass is perforated in the centre for the passage of the descending

artery. In the more primitive Dromiacea, however, the concentra-
4

i

THE DECAPODA 287

tion is somewhat less complete, the outlines of five pairs of ganglia
ean be distinguished in the central mass, while posteriorly is a
shortened chain of five pairs of ganglia corresponding to the
abdominal somites, although not extending beyond the posterior
limits of the thorax.

A system of visceral nerves is well developed in the Decapoda.
A gastric plexus is formed by anastomosis of three nerves, a median
one arising from the posterior surface of the cerebral ganglia and
a pair from the oesophageal commissures. Special nerves to the
rectum are given off by the last abdominal ganglion.

Sense-Organs.—The paired eyes are well developed in the great
majority of Decapods, although, as already mentioned, they may
be reduced or entirely absent in deep-sea and cave-dwelling forms
as well as in some parasitic and burrowing species. The cornea is
generally distinctly faceted, the facets being square or hexagonal
in outline. Sometimes they are square in the centre of the corneal
area and hexagonal towards the margin. As a rule the crystalline
cone is formed by four cells, and there are seven retinular cells
enclosing a quadripartite rhabdome. The nauplius-eye has heen
found to persist in a vestigial condition in the adult in many of
the lower Decapoda.

A pair of stutocysts lodged in the proximal segment of the anten-
nules occur in the great majority of Decapods (Fig. 156, A, st, p. 265).
Only in certain Caridea do these organs appear to be entirely
wanting (Pandalus, Hippolyte). The statocyst develops as an
invagination of the integument, and in most of the lower Decapods
it remains in communication with the exterior, sometimes by a
wide aperture (Crangon), more commonly by a narrow slit. Rarely
among the Natantia the statocyst appears to be quite closed
(Leucifer, Sergestes), and this is the case also in the Galatheidea
and Hippidea among the Anomura and in the whole of the
Brachyura. In the Brachyura, after ecdysis, the statocyst is open
to the exterior by a narrow slit, which, however, soon closes by
coalescence of the newly formed cuticle covering its edges. In this
group also the cavity assumes a complex form by the folding of
its walls. In those cases where the statocyst remains open it
contains a number of foreign particles, sand-grains, which act as
statoliths, and are in some cases agglutinated together into a mass
by an organic substance secreted by dermal glands on the inner
surface of the sac. In this mass the tips of the sensory setae
are embedded. When ecdysis takes place the chitinous cuticle
lining the statocyst is thrown off and with it the contained sand-
grains, and it has been shown that fresh grains are introduced by
the animal either burying its head in the sand or placing the
grains in position by means of its chelae. When the statocyst is
without external opening it usually contains no solid particles.

288 THE CRUSTACEA

This is the case in the Brachyura and the majority of the Anomura.
In the few Natantia, however, which have.closed statocysts, solitary
statoliths, probably of organic composition, are present, which are
no doubt formed zn situ. As with the open statocysts, the lining
membrane, and with it the statolith, is cast and renewed at each
ecdysis. In all cases the inner surface of the statocyst bears
plumose sensory setae arranged in one or more rows. In Leucifer
the tips of the sensory hairs are embedded in the substance of the
statolith.

The development of the statocysts has been traced in the
Lobster and the Shore-crab. In both cases the functional state is
assumed rather suddenly ; at the fourth larval stage in the lobster
and the first Megalopa-stage in the Crab. In the latter the statocyst
is at first open to the exterior and sand-grains are found in it.

Sensory filaments occur in most cases on the external flagellum
of the antennules, commonly in larger numbers in the male than in
the female sex. In many Caridea they are confined to a specially
thickened portion of the flagellum, and when the flagellum
bifurcates the filaments are borne by the secondary branch
(Fig. 156, B, p. 265). In some terrestrial species (Coenobita) the
filaments are very short, forming a close fur.

Phosphorescent organs are now known in a number of deep-sea
Decapoda (Sergestidae, Penaeidae, Hoplophoridae, Pandalidae,
Eryonidae), but the nature of the organs differs widely in the
different groups. In Aristews coruscans (Penaeidae) (Fig 168)
and Heterocarpus alphonsi (Pandalidae) (Fig. 148, p. 259) Alcock
observed a luminous fluid to be emitted from. the base of the
antennae, apparently from the orifices of the antennal glands.
This case may be compared with that of Gnathophausia among
the Mysidacea, where a luminous secretion is produced by a gland
on the maxilla which may possibly be the excretory maxillary gland.
Polycheles phosphorus (Eryonidae) was found by the same observer
to be “luminous at two points between the last pair of thoracic
legs, where there is a triangular glandular patch.” Numerous
phosphorescent organs have been found by Coutiere on the body
and limbs of various Hoplophoridae, but their structure has not
been examined. In Sergestes challengeri Hansen has found an
extraordinary number of luminous organs (about 150) on the
body and limbs, although they are not found in other species of
the genus. In this case the structure recalls that found in the
Euphausiacea. Each organ has, internally, a reflector, composed
apparently of concentric lamellae, enclosing a mass of cells.
There is nothing corresponding to the “striated body” of
Euphausiacea, and the “lens” is double, the outer part being
formed by a thickening of the cuticle which has no counterpart in
the Euphausiacea.

—<Y

THE DECAPODA . 289

Reproductive System.—The testes as a rule lie partly in the
thoracic region and partly in the abdomen, and, except in some
Paguridae, are connected with each other across the middle line.
In the simplest cases, as in some Caridea, they are tubular in form,
but as a rule they send off numerous caecal diverticula. In
Leucifer the two testes unite with each other to form an unpaired
mass lying below the intestine. In the Paguridae they are dis-
placed backwards so as to lie wholly in the abdominal region, where
they are unsymmetrically placed on the left side, either fused into
a single mass or entirely separated from each other, the right testis
lying in front of the left.

The vas deferens presents typically three divisions (which,
however, are not distinctly defined in many Caridea): (1) a narrow

Fic. 168.
Aristeus coruscans (Penaeidae). (From Alcock, Naturalist in Indian Seas.)

efferent duct leading from the testis; (2) a glandular part, with
wider lumen, often convoluted ; (3) a terminal ductus ejaculatorius
with muscular walls. In Brachyura (except Dromiidae) the distal
portion of the second or glandular division is provided with caecal
diverticula which in some cases are very numerous, forming a large
glandular mass. In Lewifer the structure of the vas deferens is
very complex, and there are two distinct glandular regions.

In nearly all cases the terminal portion of the vas deferens
perforates the coxopodite of the last pair of legs, or emerges on the
arthrodial membrane between the coxopodite and the body. In
the majority of cases no penes are formed, but in some genera of
Paguridae (Spiropagurus, etc.) a membranous tubular penis is present
on one side only. In all Brachyura a pair of penes are present,
the tips of which lie within the grooves of the first pair of
abdominal appendages. In those families of Brachygnatha formerly

19

290 | THE CRUSTACEA

grouped together as Catometopa these penes either lie for a short
distance from their base within grooves excavated in the last
thoracic sternum, or else they perforate the sternum directly, the
vasa deferentia in this case not entering the coxopodites of the
legs at all, as they do in most other Decapods.

In most Macrura and in the Dromiidae the spermatozoa when
discharged are enclosed by a sheath of secretion which sets to a
firm membrane, forming a continuous cord-like mass. In Scyllarus
and in the Anomura this is broken up into separate spermatophores
attached by one end in a row on a strip of membrane. In the
Brachyura (except the Dromiidae) the spermatophores are quite
separate.

The spermatozoa are remarkably varied and complex in
structure. As a rule they are provided with stiff radiating pro-
cesses which serve to attach them to the surface of the egg, and,
in some cases, an “explosive” apparatus is present which effects
penetration of the egg-membrane. :

The ovaries generally resemble the testes in shape and position.
In the Penaeidae they may extend through the whole length of
thorax and abdomen, but in most cases they are of less extent. In
Leucifer, and in most if not all Thalassinidea and Paguridea, they
lie wholly in the abdomen. They are always united across the
middle line, sometimes at more than one point. In the Crayfish
the two ovaries (like the testes) are joined together posteriorly so
that the organ has a trilobed form. Except in Leucifer and in the
Brachyura, the oviducts are simple in form and open on the
coxopodites of the sixth thoracic appendages (third legs). In
Leucifer, which is peculiar in so many points of structure, the
oviducts have receptacula seminis connected with them and unite
to open by a median aperture on the sternal surface of the thorax.
In the Brachyura, where intromittent organs are developed in the
male, the terminal part of the oviduct is of considerable length and
serves as a vagina, while a lateral pouch, sometimes double, with
glandular walls, forms a receptaculum seminis. In the Dromiacea
the receptaculum seems to be a temporary structure formed at the
time of copulation. In the Brachyura, with exception of the
primitive Dromiacea and of certain Oxystomata (Raninidae, some
Dorippidae), the oviducal apertures are removed from the coxo-
podites of the legs and open on the sternum of the corresponding
somite.

In addition to the internal receptacula seminis mentioned above,
an external organ having apparently the same function is found
in certain Decapods. It is best known in the Penaeidae, where it
has been named the thelycum and affords characters of systematic
importance. It lies on the sternal surface of the thorax and
appears to be formed by two or more outgrowths from the last

THE DECAPODA 291

thoracic somite enclosing a cavity within which may sometimes be
found the large foliaceous spermatophores deposited by the male.
In the Lobster (Homarus) (Fig. 169) a median pouch enclosed by
three processes on the sterna
of the last two thoracic
somites has the same function,
and in the Crayfishes of the
genus Cambarus (but not in
Astacus) a more complicated
organ in the same position
is known as the “annulus
ventralis.” These structures
have not hitherto been studied
from a comparative point of
view, but it seems likely that
an investigation of their mor-
phology and their relation to

the structures occupying a Fia. 169.
imilar iti i Sy- Sternal surface of posterior thoracic somites of
similar position in the Syn female Lobster (Homarus gammarus), showing the

earida would yield important receptaculum seminis. VI-VIII, bases of the last
< ] three pairs of legs; 9, external openings of ovi-
results. ducts ; l.p, lateral process on penultimate sternum ;

tiny the great miayanity: ofp, netaa pores on Le orabessteami a
Decapods the eggs after ex-
trusion are carried by the female attached to the abdominal append-
ages. Only in the Penaeidea they appear to be shed free into the
water immediately on extrusion, or carried for a short time only, as
in Leucifer, where they have been found attached to the posterior
thoracic limbs. The attachment of the eggs to the abdominal
appendages of the parent is effected by means of a cementing
material. Asa rule this material seems to be produced by dermal
glands, which are found abundantly developed on the inner faces of
the pleural plates of the abdomen and on the uropods. In some
cases (Stenopus and Thalassinidae), where the pleural plates are
slightly developed, the glands occur mainly on the pleopods, and in
the Paguridae they are distributed over the ventral integument of
the abdomen. In the Brachyura, however, such glands are absent
or only little developed, and the function of producing the cementing
material is stated to be discharged by the receptaculum seminis.

Secondary sexual characters among the Decapods are numerous
and varied. In many cases the males are distinguished from the
females by the greater size and different shape of the chelipeds and
by the narrower abdomen. JDimorphism of the males has been
noted in many cases, and Faxon discovered that in Crayfishes of the
genus Cambarus the two forms are alternating breeding and non-
breeding phases in the life-history of the same individual. A
closely similar series of changes has been found by Coutiere and by

292 LHE CRUSTACEA

G. Smith in the males of some Oxyrhyncha, and it is very probable
that it may occur also in other groups of Decapoda.

Mention may be made here of the remarkable phenomena of
‘parasitic castration,” discovered by Giard in Decapods infested by
Rhizocephala, Entoniscidae, and other parasites, and more recently
investigated by G. Smith. The latter observer finds that, in
Brachyura infected with Succulina, the females show very little
modification of external characters beyond a reduction in size of
the pleopods, although the gonad is reduced in size or even
completely eradicated. Infected males, however, assume in various
degrees the secondary sexual characters proper to the female; the
chelipeds (in species with dimorphic males) remain in the form of
the non-breeding phase and resemble those of the female; the
abdomen becomes more or less broadened and may assume com-
pletely the female form; the copulatory styles (first and second
pleopods) are greatly reduced, and small pleopods may appear on
the third to the fifth abdominal somites. In the most completely
modified specimens only the reduced copulatory styles remain to
show that they once were males. The very remarkable observation
has been made that these completely modified males, in the rare
cases when they recover sufficiently from the parasitic infection
to regenerate a gonad, become perfect hermaphrodites, the gonad
producing both spermatozoa and ova.

Observations, as yet unpublished, made by A. Wollebaek,
seem to indicate that certain deep-water Decapoda are normally
hermaphrodite.

DEVELOPMENT.

With some noteworthy exceptions to be mentioned below, the
Decapoda pass through a more or less extensive metamorphosis
after leaving the egg. The most complete series of changes occurs
among the Penaeidea, some at least of which are hatched as free-
swimming nauplii and have a larval history closely parallel to that
of the Euphausiacea.

In the Penaeidae the development was first made known
by Fritz Miller, and further elucidated by Claus, Brooks, and
Kishinouye. The Nauplius (Fig. 170, A), which has been hatched
from the egg by the last-named of these authors, has a quite typical
form. The pear-shaped or oval body is without a shell-fold and
has two terminal setae posteriorly. The median eye is present and
the three pairs of nauplius-limbs, the third pair of which are with-
out any masticatory process. In the succeeding Metanauplius-stage
four pairs of limb-rudiments are developed behind those already
present, the masticatory process appears on the third pair, the
swimming-branches of which begin to diminish, and a pair of
papillae on the anterior margin represent the “frontal organs,”

THE DECAPODA 293

which persist through several of the later stages. The next stage
observed is the Protozoea (Fig. 170, B), in which the seven pairs
of limbs already indicated are well developed ; the carapace covers
the anterior part of the body; the abdomen, which has a furcate
termination, is still unsegmented, but the six posterior thoracic
somites are defined, though very short. The mandibular palp has
quite disappeared (to reappear at a later stage), and the first and
second thoracic appendages are biramous swimming-limbs. At this
stage the rudiments of the paired eyes begin to appear beneath the

B.

A.

Fic. 170.

Early stages of Penaeus. A, nauplius; B, early
Protozoea-stage. (After F. Miiller, from ney.
Brit.)

carapace, there are three pairs of hepatic caeca, and the heart is
developed, though as yet with only one pair of ostia. In a later
Protozoea-stage (Fig. 171, A) the five anterior abdominal somites
are indicated, the sixth being not yet marked off from the telson,
and the rudiments of the third pair of thoracic limbs appear. In
the following stage, to which the name of Zoea is given, the paired
eyes become free from the carapace and are movable, the carapace
begins to grow out into a median rostral spine, the third pair of
thoracic limbs are biramous, and rudiments of the remaining five
pairs are present. The first five pairs of abdominal appendages
(Fig. 171, B) are present as very small buds, but the sixth pair

294 TE CRO S LACE

have already begun to outstrip these in order of development and
are larger and bilobed. In a later Zoea-stage (Fig. 171, C) the
sixth pair form with the furcate telson a well-marked tail-fan, but
the first five pairs of abdominal limbs are stated to be temporarily
suppressed, to reappear again at a later stage; a retrograde change
is also observed in the peduncle of the antennule, which in the
later Protozoea was divided into five segments but now becomes

LCLE,-
Py pease

is oe
waive

peuwl
(SAS AAAANE\ MRSS

an

i

joie. ihygile

Later stages of Penaeus. A, older Protozoea-stage. B, under-surface of thorax and
abdomen of somewhat later stage with rudiments of limbs. C, Zoea-stage. D, Schizopod-stage.
1, antennule ; 2, antenna; 3, mandible ; 4, maxillula; 5, maxilla; I-VIII, thoracic appendages ;

(IV-VIII), the posterior thoracic somites; 0;-05, pleopods; ag, uropods; ab, abdomen ; 7,

endopodite ; ex, exopodite ; fr, frontal sense-organ; 1, hepatic caeca; ¢, telson. (After
Claus, from Korschelt and Heider’s Embryology.)

once more unsegmented. The five posterior pairs of thoracic
limbs (legs), which in this stage are bilobed rudiments, develop in
the succeeding Schizopod-stage (Fig. 171, D) (usually called the
Mysis-stage) into biramous natatory limbs and take up the function
of locomotion hitherto fulfilled chiefly by the antennae. The
abdomen has now increased greatly in size as compared with the
cephalothorax, and the first five pairs of abdominal appendages

THE DECAPODA 295

begin to reappear. The various appendages now begin to assume
the form which they have in the adult. The antennules have a
three-segmented peduncle, with two flagella as yet unsegmented.
The endopodite and exopodite of the antenna become respectively
flagellum and scale. The palp of the mandible begins to redevelop.
In a later stage, which may be called post-larval, the exopodites of
the thoracic limbs become reduced and the abdominal appendages,
now well developed, take on the function of swimming-organs.
While it is tolerably certain that the general course of develop-
ment in the Penaeidae is as described above, it is to be observed
that as yet the complete series of larval forms has not been traced
out in the case of any one species, and it is just possible that some
of the changes stated to occur, e.g. the alleged temporary disappear-

Fic. 172.

Metanauplius-stages of Leucifer. A, just hatched; B, later stage. a’, antennule; a”,
antenna ; d, shell-fold; md, mandible; m/f’, first maxilliped ; ma’, maxillula; ma”, maxilla;
ol, labrum ; p, paragnatha. (After Brooks, from Korschelt and Heider’s Embryology.)

ance of the first five abdominal appendages in the later Zoea-stage,
may be due to confusing together in one series the larvae of
different species. In the closely related family of the Sergestidae,
however, Brooks has been able to trace out in considerable detail
the life-history of a single species, Leucifer typus. In this case the
animal leaves the egg as a metanauplius (Fig. 172, A) with four
pairs of limb-buds already visible behind the three pairs of
nauplius-limbs. This is followed by a later metanauplius (Fig. 172,
B) in which the shell-fold and the masticatory process of the
mandible appear. The Protozoea (Fig. 173, A), with seven pairs
of functional limbs, differs from that of Penaeus chiefly in the
different shape of the carapace, which has already the beginning
of a rostrum, and in having only four of the six posterior thoracic

296 THE CRUSTACEA

somites defined. The rudiments of the paired eyes appear in the
later Protozoea-stage (Fig. 173, D), when also the seventh thoracic

Hie, 173:

Protozoea and Zoea stages of Leucifer. <A, first Protozoea-stage. B, maxillula of same.
C, maxilla of same. D, later Protozoea-stage (Hrichthina, Dana). E, Zoea-stage. a’, antennule ;
uw’, antenna ; bg, uropods ; en, endopodite; ex, exite; h, heart; 1, hepatic diverticula ; md,
mandible ; mf’-mf’’, the three pairs of maxillipeds; mp'”, somite of third maxillipeds ; ma’,
maxillula ; ma’, maxilla; 0, paired eye; oc, nauplius-eye; ol, labrum; 7, rostrum ; th1-th4,
rudiments of fourth to seventh thoracic limbs (first four legs); ¢1-t4, fourth to seventh thoracic
somites ; 1-6, abdominal somites. (After Brooks, from Korschelt and Heider’s Embryology.),

somite (the eighth remains undeveloped in the adult Lewcifer) and
the first four abdominal somites appear. The Zoea-stage (Fig. 173,
E) differs from that of Penaeus in the fact that the eyes are not

r

an alll

THE DECAPODA 297

yet free from the carapace, and that the third thoracic limbs, like
the four following pairs, only appear as bilobed rudiments. The
uropods are present as rudiments, but the pleopods are not yet
indicated. A Schizopod-stage (Fig. 174, A) follows, with movable
paired eyes, with seven pairs of biramous thoracic appendages
functioning as swimming-feet, and with well-developed tail-fan.
Later stages (Fig. 174, B) show rudiments of the first five pleopods.
A Mastigopus-stage (Fig. 174, C) intervenes before the assumption
of the adult form.

The larvae of Sergestes, though differing remarkably in appear-
ance from those of Leucifer, conform closely to the same type of
development. The youngest known larvae are Protozoeae (Fig.
175, A), which differ from those of Leucifer in their compact
form and in the possession of stalked eyes and of biramous third
maxillipeds. The most characteristic feature, however, is the
armature of the carapace. A rostrum, a median dorsal, and a pair
of lateral spines are present as in Leucifer, but much stronger,
and each bearing a double row of secondary spines. The Zoea
(Elaphocaris of Dana) has this spine armature still more developed,
and an additional pair of compound spines appear on either side
of the rostrum. In the Schizopod-stage (known as Acanthosoma)
(Fig. 175, B) the armature of the carapace is very much reduced.
Before the adult stage is reached a Mastigopus-stage intervenes,
characterised by the temporary disappearance of the last two
pairs of thoracic limbs, which are present alike in the Acanthosoma
and in the adult animal. It is interesting to notice that in this
character Leucifer represents a permanent Mastigopus-form.

In the remaining groups of Decapoda no case is known where
the larva is hatched at a stage preceding the Zoea, though in some
instances a larval cuticle, moulted soon after hatching, has been
supposed to present characters of the Protozoea.

Among the Caridea the earliest larval form is a Zoea in which
the third thoracic appendages are already well developed. The
posterior thoracic region is undeveloped, though the abdominal
somites, with the exception of the last, are defined. The carapace
has a rostrum and supra-orbital and antennal spines, but no further
armature. In many cases the stage at hatching is still farther
advanced, the paired eyes are stalked and movable, and one or more
pairs of the posterior thoracic appendages are present as rudiments.
In spite of the retarded development of the last five thoracic somites,
it is noteworthy that the appendages appear in regular order from
before backwards, with the exception of the uropods, which generally
develop precociously. In the Schizopod-stage it is a very general
but not universal character of the Caridean larva that it is with-
out exopodites on the last thoracic feet. In many Caridea there
is still further abbreviation, leading to complete suppression of the

298 THE CRUSTACEA

larval stages, more especially among Arctic, abyssal, and freshwater
forms, A specially interesting case is that of Palaemonetes varians,

»

Fia. 174.

Later stages of Leucifer. A, younger Schizopod-stage. ©’ B, later Schizopod-stage (less
magnified), ©, Mastigopus-stage. a’, antennule; a’, antenna ; ab;-abs, pleopods ; abe,
uropods ; ¢, carapace ; dr, antennal gland ; ev, flagellum, ew, scale, of antenna ; md, mandible ;
mf, mf”, first and second maxillipeds ; ma’, maxillula ; ma'’, maxilla; 0, paired eye ; oc, nauplius-
eye; ol, labrum; 7, rostrum; 1-6, abdominal somites. (After Brooks, from Korschelt and
Heider’s Himbryology.)

THE DECAPODA 299

of which two races are known, the one found in Southern Europe
being exclusively freshwater in habitat ; the other, found in Britain
and Northern Europe, inhabiting brackish or salt water. The
former hatches at a stage when all the limbs except the uropods
are present, and the first two pairs of legs have exopodites. In

AX Bi Z ff
BP MY fy

ot J aitiain|
ae 7 Ol | 1
nf

‘saf!
ie

Pia. 175.
Larval stages of Sergestes. A, Protozoea-, B, Schizopod-stage (Acanthosoma). a’, antennule ;
a’, antenna; mf’-mf’’, the three pairs of maxillipeds ; ma’, maxillula ; mx’, maxilla ; ol, labrum ;
sd, maxillary gland. (After Claus, from Korschelt and Heider's Embryology.)

the northern race all the ambulatory legs are rudimentary on
hatching, and there are no abdominal limbs.

None of the Astacura are known to possess a Zoea-stage. The
Lobster (Homarus) is hatched in the Schizopod-stage (Fig. 176),
with natatory exopodites on all the thoracic limbs, but without
any abdominal appendages. In the further course of development

300 THE CRUSTACEA

the uropods are the last to appear. In Nephrops (Fig. 177) the
course of development is very similar, but the larvae are
distinguished by the long spines of the abdominal somites and
telson. The freshwater Cray-
fishes have a direct develop-
ment, the young on hatching
resembling the adult in most
points, but lacking the first
and the last pairs of abdominal
appendages.

The Scyllaridea have a
very peculiar and character-
istic series of larval forms,
which were long described as
adults under the generic name
Phyllosoma (Fig. 178). These

Fia. 176. larvae are remarkable for the

Larva of American Lobster (Homarus ameri- laroe size to which some attain
canus), in Schizopod-stage. a’, antennule; «’, c=) us Q
antenna; mf”, third maxilliped ; pi-py, the five and for their extremely flat-
Schelband Heider's Embryctogy.) Ss tened and leaf-like form and
glassy transparency. The body

is sharply divided into three regions. The first, which is covered
by the oval carapace, includes the head and the first two thoracic

somites. The remainder of the thorax forms a discoidal plate and

Fic. 177.
Late Schizopod-stage of Nephrops norvegicus. a’, antennule; a”, antenna; mf’, third

maxilliped ; pl-p®, the five pairs of legs; pl?, pl®, pleopods; r, rostrum. (After Sars, from
Korschelt and Heider’s Embryology.)

is followed by the narrow and indistinctly segmented abdomen.
The last two thoracic appendages are not developed in the newly
hatched larva, but the four pairs in front of them are long and
slender, with natatory exopodites. The first thoracic limbs are
rudimentary (Palinurus) or absent (Scyllarus), and the second pair

THE DECAPODA 301

are uniramous. It will thus be seen that the Phyllosoma represents
a modification of an early Schizopod-stage.

A point of some interest in these forms is the occurrence of
retrogressive changes in the course of development. Thus the
antenna and the maxilla undergo a certain degree of degeneration
before hatching, and the seventh and eighth thoracic and the
abdominal somites, which are well defined in the embryo, become
indistinct in the larva.

The development of Thalassinidea is interesting on account of
the points of resemblance which it shows with the Caridea. The
earliest larva is a Zoea, which in some cases (Callianassa and
Calocaris) resembles that of Caridea in having the three maxillipeds

Fic. 178.

Phyllosoma-larva of Palinurus, just before hatching. ad, abdomen ; L, hepatic caeca ; II-VI,
thoracie appendages (second and third maxillipeds and first three pairs of legs) ; 1, antennule ;
2, antenna. (After Claus, from Korschelt and Heider's Embryology.)

biramous and natatory ; but in others (Upogebia and Jazea) only the
first and second are present on hatching, the third becoming natatory
only in the following Schizopod-stage, while the endopodite is still
rudimentary, as in other Anomura. The existence of a Schizopod-
stage, in which only the last two thoracic limbs are rudimentary
and the uropods and rudiments of the pleopods are present, consti-
tutes an important distinction from the other Anomura. The larvae
of Juxea (= Calliavis) are of exceedingly peculiar form, having the
cephalic region produced into a long “neck” resembling at first
sight that of Leucifer. To this larval type the name of 7rachelifer
has been given. The remaining groups of the Anomura and the
Brachyura differ from those just described in the suppression of the
Schizopod-stage, the legs developing without exopodites in a
Metazoca-stage which follows the Zoea. In the Anomura the Zoea

302 THE CRUSTACEA

(Fig. 179, A) possesses two pairs of maxillipeds, the third pair
(Fig. 179, C) being present as rudiments. The carapace has its
posterior border produced into two lateral spines (greatly elongated
in Porcellana, Fig. 180), and a long rostrum is present. In the
next succeeding stage, the Metazoea (Fig. 179, B), the third
maxilliped becomes biramous and natatory (a point of distinction,
from the Brachyuran type), and the uniramous ambulatory limbs
and the pleopods are developed as rudiments.

The Brachyura, as a rule, are stated to hatch inthe Zoea-stage
(Fig. 181), but since rudiments of the posterior thoracic limbs are

|!
a
:
Fic. 179.
Larval stages of Eupagurus bernhardus (Paguridea). A, Zoea. B, Metazoea. C, rudiments
of third maxillipeds in Zoea-stage. D, caudal fan of Metazoea. a’, antennule; «”, antenna;

a°, fifth pleopod ; «6, uropod; k, rudiments of gills; mf’-mf’”’, the three pairs of maxillipeds ;
ol, labrum ; pi-piv, first four legs ; 7, rostrum ; ¢, mandibular palp. (After Sars, from Korschelt
and Heider’s Embryology.)

frequently present, it might be more correct to call thé larva a
Metazoea. Throughout the group a very characteristic form is
given to the Zoea by the development of long spines on the
carapace. As a rule, a rostrum, a median dorsal, and a pair of
lateral spines are present. Of these, the dorsal spine (d.s) is
the most constant; great importance was formerly attached to
it as a characteristic of the Zoea-stage. In many Brachyura the
larva when hatched is enclosed in a cuticle which is moulted shortly
after hatching, and this cuticle in many cases presents characters
difiering from those of the larva which escapes from it. In

THE DECAPODA 303

Carcinus maenas, for instance, the first larval skin lacks the spines

of the carapace, the antennae are larger
and differently formed, the shape of
the caudal fork and its spine armature
are different from those of the succeed-
ing stage, and the abdominal portion is
not distinctly segmented. These char-
acters have been supposed to indicate
that we have here the last traces of a
Protozoea-stage like that of the Pen-
aeidea.

The Metazoeal stages, which differ
from those of the Anomura in the fact
that the third maxilliped does not
assume a natatory function, are suc-
ceeded in nearly all cases by a Megalopa-
stage (Fig. 182, A, B), in which all the
appendages have assumed very much
the form which they have in the adult,
but the abdomen is large and usually
carried extended, and the five pairs of
pleopods are used for swimming. In
some cases the Megalopa-stage is sup-
pressed, the Metazoea being succeeded
by a stage in which the animal has
assumed the chief characters of the
adult.

Complete suppression of the meta-
morphosis occurs in some (perhaps all)
Potamonidae, and probably in some
other freshwater and terrestrial Brachy-
ura. In those Anomura which have
become most completely terrestrial (ir-
gus and Coenobita) Borradaile has shown
that the young are marine, and that
hatching takes place at the Zoea-stage.

REMARKS ON HABITS, ETC.

The habits and habitats of the
Decapoda are more varied, and have
been much more studied, than in the
case of any other group of Crustacea.
Space will not permit of allusion to
more than one or two of the more
salient points.

Fic. 180.

Metazoea of Porcellana longicornis
(Galatheidea). mf-mf’’, the three
pairs of maxillipeds ; p, rudiments
of legs and gills. (After Sars, from
Korschelt and Heider’s Embryology.)

304 THE CRUSTACEA

Truly freshwater Decapods (apart from estuarine or brackish-
water species which may penetrate into fresh water) are found
among the Natantia in the
family Atyidae and in several
genera of Palaemonidae ; of
the Reptantia, the Cray fishes
of the families Astacidae and
Parastacidae, the monotypic
Aegleidae among the Ano-
mura, and the Potamonidae
(Thelphusidae) and numerous
species of Grapsidae among
the Brachyura, are also dwel-
lers in fresh water. Some of
these are more or less am-
phibious in their habits, like
many Potamonidae, and some
Crayfishes are found burrow-
ing in the earth far from
streams or ponds, their bur-
Wie rows reaching down to the

() hk * | ground-water. The same is

a reported of the marine or
brackish-water Thalassina.

Fra. 181. Truly terrestrial species:

First Zoea-stage (after the first moult) of Carcinus Aare found among Paguridae

maenas. ca’,antennule ; «”’,antenna; abd, abdomen ; an Y Sa z
d.s, dorsal spine of carapace (the so-called ‘‘ Zoea ”- (Birgus and Coenobitu) and

spine) ; f, fureate telson ; md, mandible ; ma’, maxil- Brachyura (Gecarcinidae)
lula; mx’, maxilla; r, rostrum; thi, thii, first and 4

second maxillipeds, biramous and natatory ; thiii-thy, and it is interesting to note
AO NaN acs following thoracic appendages. that these are derived not

from freshwater but from
marine types, and all (except, possibly, some Gecarcinidae) pass
their early stages in the sea.

The Sergestidae belong to the plankton, occurring at the surface
and descending to great depths. A few Brachyura (Planes and
some other Grapsidae) lead a pelagic life, clinging to driftweed,
floating timber, and the like.

It is worthy of note that the deep-sea Decapods include the
more primitive members of each of the chief subdivisions: the
Aristeinae among the Penaeidea, the Hoplophoridae among the
Caridea, the Eryonidea among the Palinura, the Pylochelidae among
the Paguridea, and the Homolodromiidae among the Brachyura.

Parasitism and commensalism in varying degrees are common.
The Paguridae alone, which live in the empty shells of Gasteropod
molluscs, present a whole series of cases of commensal association
with Sponges, Coelentera (Fig. 183), and Polychaete worms ;.

THE DECAPODA 305

Spongicola, Typton, and Hiconaxius live in sponges, many Pontoniinae
and Pinnotheridae (as Aristotle knew) in the mantle-cavity of bivalve
molluses; members of the first-named family inhabit the pharyngeal
cavity of Tunicates, and some Pinnotheridae are found in the
“respiratory trees” of Holothurians and the rectum of sea-urchins.
Many Decapods are constantly found among living corals, and the
Hapalocarcinidae live in “galls” on the branches of corals. A
very peculiar habit is that of some crabs of the genus Melia, which
earry in each cheliped a living Actinian and use it as a weapon.

Fic. 182.

Later stages of Curcinus maenas. A, young Megalopa. B, older Megalopa. C, post-larval
stage. d, dorsal spine of carapace; 7, rostrum (A after Spence Bate ; B and C after Brook.
From Korschelt and Heider’s Hinbryology.)

Special interest attaches to the stridulating organs, found in
many Decapoda, since their possession is presumptive evidence that
the animals do have some power of hearing. A few Penaeidae,
some Palinuridae, and a considerable number of Brachyura are now
known to have stridulating organs in various parts of the body.
That of Ocypoda, shown in Fig. 184, is one of the few of which the
sound-producing function has been demonstrated by observation of
the living animals. It consists of a file-like series of ridges () on
the inner surface of the propodite of one of the chelipeds, which can
be rubbed up and down upon a sharp ridge (4) on the ischiopodite
of the same appendage, producing a hissing sound, which probably

20

306 LHE CRUSTACEA

serves to warn intruders from entering the burrows of these shore-
living crabs. In the case of purely aquatic species, the function of
these organs is less easy to understand.

The range of size in Decapoda is greater than in any other
group of Crustacea. Some Natantia do not exceed half an inch
in length, one Pagurid is adult when 8 mm. long, a species of
Porcellanid has a carapace measuring 3 mm. by 5 mm., and some
Brachyura are no larger. The largest forms are found among the

Fic. 183.

Parapagurus pilosimanus (Paguridae), lodged in a colony of zoantharian polypes.
(From Alcock, Natwralist in Indian Seas.)

Reptantia ; some Palinuridae and Astacura reach one or even two
feet in length and are bulky in proportion. The largest living
Arthropod is the Japanese crab Macrocheira (or Kaempferia) Kaempferi,
of which the carapace may measure 15 inches in length, and the
extended chelipeds of the male may span more than 10 feet.

PALAEONTOLOGY.

Fossil remains of Decapods are not known with certainty from
any Palaeozoic deposits. Many genera from the Devonian upwards

THE DECAPODA 307

have indeed been described as belonging to this group, but in no
case is enough known of their characters to enable more to be said
than that they agree with the “caridoid” groups of the Malacostraca
in the possession of a carapace and of a tail-fan.

In the Mesozoic rocks many undoubted Decapods occur, includ-
ing representatives of all the chief groups now living. Many
genera of Penaeidea are found from the Jurassic, perhaps from
the Triassic period onwards, some of the earliest even resembling
closely the existing genus Penaeus, to which they have been referred.
Acger, from Triassic and Jurassic rocks, presents characters which
suggest an aflinity with the Stenopidea. ‘l'rue Caridea appear later,
in the Upper Jurassic, some at least presenting primitive characters
in the retention of exopodites on the ambulatory limbs. Fresh-
water Caridea of doubtful affinities occur in the Miocene. The
Eryonidea are especially interesting since the few existing deep-

Fic. 184.

Larger cheliped of Ocypoda macrocera, from the inner side, showing the stridulating
mechanism. 4, file-like series of ridges on propodite ; b, ridge or scraper on ischiopodite
against which the ridges of the propodite can be rubbed when the limb is flexed. (From
Alcock, Naturalist in Indian Seas.)

sea forms appear to be only the surviving remnants of what was in
the Mesozoic period a dominant group. The genus ELryon (Fig. 185)
appears in the Trias and persists until the earlier Cretaceous. The
Glyphaeidae, a wholly extinct group having much the same range
in time as have the fossil Eryonidae, have been supposed to stand in
the direct line of descent of the Scyllaridea. True Seyllaridea occur
probably in the Jurassic, certainly in the Cretaceous period. The
existing genus Linuparus, or a very close ally, dates back to the
upper Chalk. Astacura are known from Jurassic and later deposits
in considerable numbers. Zryma, from the Lias, and Hoploparia
(Cretaceous and Tertiary) are well-known forms.

The Anomura are almost unknown as fossils, except for some
Thalassinidea referred to the existing genus Callianassa occurring
from the Upper Jurassic onwards. The Brachyura, on the other
hand, are well represented. The earliest forms present characters
of the Dromiacea, and are referred, for the most part, to the extinct
family Prosoponidae, which Bouvier has shown to have close rela-
tions with the most primitive of existing Brachyura, the Homolo-

308 LHE CRUSTACEA

dromiidae. One of the oldest, and at the same time one of the
most completely known, is Palaeinachus (Woodward) from the
Forest Marble (Lower Oolite), which has many generalised characters.
Later forms belonging to Prosopon (v. Meyer) and other genera give
evidence, according to Bouvier, of the divergence of a Homoline
and of a Dynomeno-Dromiine line of descent leading to such forms as

Eryon propinquus (from the Jurassic rocks of Solenhofen), under-side. (After Oppel.)

Homolopsis (Bell) and Dromiopsis (Reuss) from the Upper Cretaceous,
and to the existing Homolidae, Dynomenidae, and Dromiidae. The
remaining Brachyura have not yet yielded results of so much phylo-
genetic interest. The Oxystomata appear about the middle of the
Cretaceous system and the Brachygnatha about the same time. In
the Tertiary many Brachyura are found, representing the chief
existing types of the group.

rr

THE DECAPODA 309

AFFINITIES AND CLASSIFICATION.

The resemblances between the lower Decapoda, especially the
Penaeidea, and the Euphausiacea have been mentioned in dealing
with the latter Order, and justify the alliance of the two Orders in
the Division Eucarida. It may be mentioned that the exopodites
of the thoracic legs, the absence of which still survives in text-books
as distinguishing the Decapoda from the ‘“ Schizopoda,” are at least
as strongly developed in many Caridea (Hoplophoridae, ete.) (Fig.
160, p. 270) as in Euphausiacea or Mysidacea. Coutiére has recently
called attention to some curious resemblances between certain
primitive Caridea and the Lophogastrid Mysidacea. These
resemblances, however, by no means outweigh the important
differences between the two groups, and may be either primitive
characters derived from the common caridoid stock or convergences
due to similarity of habits.

The classification of the Decapoda is a very difficult problem,
and none of the schemes hitherto proposed can be regarded as
entirely satisfactory. The traditional classification of the group
into the long-tailed Macrura and short-tailed Brachyura was estab-
lished by Latreille in 1806; but the difficulty of defining these
groups is shown by the varying limits which have been assigned to
the intermediate group of Anomura established by Milne-Edwards
in 1834. Boas, in 1880, was the first to make a radical departure
from this system. He pointed out that the Brachyura and Anomura
were only single branches of the Decapod stock, and by no means
equal in systematic value to the Macrura, which included several
other branches not more closely connected with each other. In
other words, just as in the classification of the Malacostraca as a
whole, so within the Order Decapoda, the retention of the primitive
“caridoid facies” does not necessarily imply close affinity between
the groups exhibiting it. Boas proposed a division of the Order
into the two primary groups of Natantia and Reptantia as defined
below. This division is undoubtedly a more natural one than those
formerly employed, although it is hardly more easy to find constant
and exclusive structural characters by which to define the sub-orders
than it was in the case of the Macrura, Anomura, and Brachyura.
A further difficulty is presented by the small group of Stenopidea,
which combine, to some extent, the characters of Natantia and
teptantia, and may perhaps deserve separation as a third sub-order.
Important modifications of Boas’s scheme have been introduced by
Ortmann and by Borradaile, and the classification of the last-named
author has been adopted here, with some alterations, chiefly of a
formal kind, as, on the whole, the most satisfactory yet proposed.
Borradaile’s chief innovations are the inclusion of the Thalassinidea,

310 THE CRUSTACEA

formerly ranked with the Macrura, among the Anomura, the
establishment of a group Brachygnatha, opposed to the Dromiacea
and Oxystomata among the Brachyura, and the abandonment of the
old divisions Cyclometopa and Catometopa among the families
which he unites as Brachyrhyncha, These changes appear to be
quite justified on morphological grounds, and to conduce to clearness
in the delimitation of the groups. Much work remains to be done,
however, in readjusting the subdivisions of the smaller groups, and,
in particular, the classification of the Caridea is still in a very
unsatisfactory condition.

Although abandoned as a systematic category, the name Macrura
may still be used (as it has been above) as a convenient descriptive
term for those Decapoda which retain more or less the caridoid
facies, that is to say, the Natantia with the Palinura and Astacura
among the Reptantia.

With regard to many of the generic names mentioned below, it
is necessary to warn the student that recent “reforms” of nomen-
clature have resulted in lamentable confusion, more especially in
the naming of long-known and familiar Decapoda, and it is not safe
to assume that when an author mentions ‘“ Astacus” or “ Crangon”
he is referring to the genera including the common Crayfish and
the edible Shrimp.

ORDER Decapoda, Latreille (1802).
Sup-OrperR 1. Natantia, Boas (1880).

Body almost always laterally compressed ; rostrum usually compressed,
and serrated ; first abdominal somite not much smaller than the rest ;
antennules generally with stylocerite ; antennal scale generally large and
lamellar ; legs usually slender, except sometimes a stout chelate limb or
pair, which may be any one of the first three pairs, with basipodite and
ischiopodite very rarely coalesced and with only one fixed point in the
carpo-propodal articulation (with some doubtful exceptions), sometimes
with exopodites, podobranchiae hardly ever present on the first three
and never on the last two pairs; male genital apertures in articular
membrane ; pleopods always present in full number, well developed, used
for swimming.

TrIBE 1. PENAEIDEA.

Pleura of second abdominal somite not overlapping those in front ;
autennae generally with stylocerite ; mandibular palps straight; first
maxillipeds without expansion at base of exopodite, endopodite long ;
second maxillipeds with terminal segments normal ; third maxillipeds
with seven segments; third legs chelate (except when legs are much
reduced), not stouter than first pair ; first pleopods of male with petasma ;
gills dendrobranchiate.

Family Penarrpar. Sub-Family CeraraspINak. Cerataspis, Gray.

THE. DECAPODA 311

Sub- Family ARisternan. Aristeus, Duvernoy (Fig. 168, p. 289);
Benthesicymus, Spence Bate. Sub-Family Sicyonmnar. Sicyonia, H.
Milne-Edwards. Sub-Family Penaninar. Penaeus, Fabricius ; Solenocera,
Lucas. Family Sercestipar. Sub-Family Sercestrnan. Sergestes, H.
Milne-Edwards. Sub-Family Levcrrertnar. Leucifer, H. Milne-Edwards
(= Lucifer, J. V. Thompson). [Sub-Family AmpHiontnar. Amphion,
H. Milne-Edwards. (The validity and the systematic place of this genus
are still doubtful.) }

TRIBE 2. CARIDEA.

Pleura of second abdominal somite overlapping those in front ;
antennae generally with stylocerite; mandibular palp, if present, straight ;
first maxillipeds with expansion at base of exopodite, endopodite short ;
second maxillipeds usually with last segment articulating laterally with
preceding ; third maxillipeds with four to six segments ; third legs never
chelate ; first pleopods of male without petasma ; gills phyllobranchiate.

Family PasIPpHAEIDAE. Pasiphaea, Savigny ; Psathyrocaris, Wood-
Mason (Fig. 160, p. 270). Family Brestnmpar. Bresilia, Calman.
Family HopLopHortpak (ACANTHEPHYRIDAE). Hoplophorus, H. Milne-
Edwards ; Acanthephyra, A. Milne-Edwards. Family NEMATOCARCINIDAE,.
Nematocarcinus, A. Milne-Edwards. Family Atyrpar. Atya, Leach ;
Caridina, H. Milne-Edwards ; Limnoceridina, Calman. Family Sryto-
DACTYLIDAE. Stylodactylus, A. Milne-Edwards. Family PsaLIpopoDIDAE.
Psalidopus, Wood-Mason and Alcock (Fig. 168, p. 272). Family
PANDALIDAE. Sub-Family Panpatinag. Pandalus, Leach ; Heterocarpus,
A. Milne-Edwards (Fig. 148, p. 259) ; Pandalina, Calman. Sub-Family
THALASSOCARINAE. Thalassocaris, Stimpson. Family ALPHEIDAE,
Alpheus, Fabricius ; Athanas, Leach. Family Hippotyripar. Hippolyte,
Leach (=Virbius, Stimpson) ; Spirontocaris, Spence Bate; Latreutes,
Stimpson. Family RayncwocineTipar. Rhynchocinetes, H. Milne-
Edwards. Family PALAEMONIDAE. Sub-Family PALAEMONINAE.
Palaemon, Fabricius; Palaemonetes, Heller; Leander, Desmarest. Sub-
Family Pontontinar. Pontonia, Latreille ; Typton, Costa. Sub-Family
HYMENOCERINAE. Hymenocera, Latreille. Family GQNATHOPHYLLIDAE.
rmiathophyllum, Latreille. Family Procrsstpan. Processa, Leach (Nika,
Risso). Family GLyPHOCRANGONIDAR. Glyphocrangon, A. Milne-Edwards.
Family CRANGONIDAE. Crangon, Fabricius ; Paracrangon, Dana,

TRIBE 3. STENOPIDEA.

Pleura of second abdominal somite not overlapping those in front ;
antennae without stylocerite ; mandibular palp curved inwards ; first
maxillipeds without expansion at base of exopodite, endopodite short ;
second maxillipeds with terminal segments normal; third maxillipeds
with seven segments ; third legs chelate, one or both much longer and
stouter than first two pairs; first pleopods of male without petasma ;
gills trichobranchiate.

Family Stenopipag. Stenopus, Latreille ; Spongicola, de Haan.

312 THE GRUOSTACEA

Sus-OrpDER 2. Reptantia, Boas (1880).

Body not compressed, often depressed ; rostrum often absent, depressed
if present ; first abdominal somite distinctly smaller than the rest ;
antennules without stylocerite ; antennal scale generally small or absent ;
legs strong, the first pair usually, the others never, stouter than their
fellows, basipodite and ischiopodite almost always coalesced in the first
pair, generally also in the others, two fixed points in the carpo-propodal
articulation, exopodites never present, podobranchiae often on some of
the first four pairs ; male genital apertures on coxopodites or on sternum ;
pleopods often reduced or absent, not used for swimming.

SECTION 1. PALINURA.

Abdomen extended, well-armoured, with well-developed pleura and
broad tail-fan ; carapace fused at sides with epistome ; rostrum generally
small or absent; exopodites of maxillipeds with flagella directed forwards ;
third legs like the first, chelate or simple ; appendix interna present on
some pleopods, at least in female ; exopodites of uropods not distinctly
segmented ; branchiae numerous.

TrisE 1. ERYONIDEA.

Antennae with exopodite, first segment not fused with epistome ; first
four pairs or all the legs chelate ; first pleopods present.

Family Eryonrpar. Polycheles, Heller; Pentacheles, Spence Bate
(Fig. 162, p. 271); Hryon, Desmarest (Fossil) (Fig. 185, p. 308).

TRIBE 2. SCYLLARIDEA.

Antennae without exopodite, first segment fused with epistome ;
none of the legs chelate except sometimes the last pair in the female ;
first pleopods absent.

Family Patinurtpan, Palinurus, Fabricius ; Linuparus, White ;
Palinurellus, von Martens. Family Scynuartpar. Scyllarus, Fabricius ;
Tbacus, Leach ; Thenus, Leach.

SECTION 2. ASTACURA.

Abdomen as in Palinura ; carapace not fused at sides with epistome ;
rostrum well developed ; exopodites of maxillipeds as in Palinura; first
three pairs of legs chelate ; no appendix interna on pleopods ; exopodites
of uropods divided by a suture ; branchiae numerous.

TRIBE NEPHROPSIDEA.

Family NerHropsrpan, Nephrops, Leach ; Neplropsis, Wood-Mason
(Fig. 161, p. 270); Homarus, H. Milne-Edwards. Family PARASTACIDAE.
Parastacus, Huxley ; Paranephrops, White. Family Astactpar. Astacus,
Fabricius (Potamobius, Samouelle) ; Cambarus, Erichson.

ee

THE DECAPODA 313

SEcTION 3. ANOMURA.

Abdomen rarely as in Palinura, generally soft, or bent upon itself,
pleura generally small or absent, tail-fan often reduced ; carapace not
fused with epistome; exopodites of maxillipeds with flagella, when
present, bent inwards ; third legs unlike the first, never chelate ; ap-
pendix interna sometimes present; uropods rarely absent ; exopodites
sometimes segmented ; branchiae few.

TRIBE 1. GALATHEIDEA.

Abdomen bent upon itself, symmetrical; body depressed; rostrum
often well developed ; first legs chelate; tail-fan well developed.

Family AncLemar. Aeglea, Leach. Family Uroprycaipar. Urop-
tychus, Henderson ; Chirostylus, Ortmann. Family GaLaTHEIDAE. Sub-
Family GauatHEetInag. Galathea, Fabricius; Munida, Leach (Fig. 150,
p- 260). Sub-Family Munipopstnar. Munidopsis, Whiteaves. Family
PORCELLANIDAE. Porcellana, Leach ; Petrolisthes, Stimpson.

TRIBE 2. THALASSINIDEA.

Abdomen extended, symmetrical ; body compressed ; rostrum some-
times well developed ; first legs chelate, rarely sub-chelate ; tail-fan well
developed.

Family Aximaxr. Azius, Leach (including Hiconaxius, Spence Bate,
and Iconaxiopsis, Aleock (Fig. 149, p. 260), as subgenera) ; Calocaris, Bell.
Family Laomepimpar. Laomedia, de Haan; Jaxea, Nardo. Family
CaLLIaANassipak. Sub-Family CaniranasstnaE. Callianassa, Leach ;
Callianidea, H. Milne-Edwards. Sub-Family Upocresrnar. Upogebia,
Leach (= Gebia, Leach). Family THatassrmipar. Thalassina, Latreille.

TRIBE 3. PAGURIDEA.

Abdomen nearly always asymmetrical, either soft and twisted or bent
under thorax ; rostrum generally small or absent ; first legs chelate ; tail-
fan not typical, uropods (when present) adapted for holding the body
into hollow objects.

Family PytocHELipar. Pylocheles, A. Milne-Edwards (Fig. 151,
p- 261). Family Pacuripar. Sub-Family Pacurinar. Pagurus,
Fabricius ; Clibanarius, Dana. Sub-Family Eupacurinar. Eupagurus,
Brandt ; Sptropagurus, Stimpson ; Parapagurus, 8. I. Smith (Fig. 183,
p- 306). Family Cornosiripar. Coenobita, Latreille; Birgus, Leach
(Fig. 152, p. 262). Family Lrrnopmar. Sub-Family LirHopinar.
Lithodes, Latreille ; Neolithodes, Milne-Edwards and Bouvier (Fig. 153,
p- 262). Sub-Family HapaLoGastrRinaE. Hapalogaster, Brandt.

TrIBE 4, HIpPpPIDPA.

Abdomen bent under thorax, symmetrical ; rostrum small or absent ;
first legs styliform or sub-chelate ; tail-fan not adapted for swimming.

ain) THE CRUSTACEA

Family ALBUNEIDAE. Albunea, Fabricius. Family HIppiDAr.
Hippa, Fabricius ; Remipes, Latreille.

Section 4. BRACHYURA.

Abdomen small, symmetrical, bent under thorax, tail-fan not
developed ; carapace fused with epistome at sides and nearly always in
the middle ; exopodites of maxillipeds with flagella, when present, bent
inwards ; first legs always, third legs never, chelate ; no appendix interna
on pleopods ; uropods rarely present, never biramous ; branchiae gener-
ally few.

TriBeE 1. DROMIACEA.

Last pair of legs modified, dorsal in position ; female openings on
coxopodites ; first pleopods present in female; branchiae sometimes
numerous ; mouth-frame quadrate.

Susp-TRIBE 1, DROMIIDEA.

Sternum of female with longitudinal grooves; vestiges of uropods
usually present ; branchiae 14-20 on each side ; eyes completely sheltered
by orbits ; no linea homolica on carapace.

Family HoMmoLopRomtIIDAs. Homolodromia, A. Milne-Edwards.
Family Dromipak®. Dromia, Fabricius. Family DyNoMENIDAE.

Dynomene, Latreille.

Sus-TrRIBE 2. HoMOLIDEA.

Sternum of female without longitudinal grooves; no uropods
branchiae 8-14 on each side; eyes not completely sheltered by orbits
linea homolica usually present on carapace.

Family Homonipan, Homola, Leach. Family LatTRErLuDAr.
Latreillia, Roux.

we we

TRIBE 2. OXYSTOMATA.

Last pair of legs normal or modified ; female openings generally on
sternum ; first pleopods wanting in female ; branchiae few ; mouth-frame
triangular, produced forwards over epistome.

Family Dorteetpar. Dorippe, Fabricius ; Ethusa, Roux ; Cyclodorippe,
A. Milne-Edwards. Family Ranryipar. Ranina, Lamarck. Family
CanapeipAk, Sub-Family Canapprnar. . Calappa, Fabricius. Sub-
Family OrirHytnak. Orithya, Fabricius. Sub-Family Marurinar,
Matuta, Fabricius. Family Leucosipar, Sub-Family LEucosIIna®.
Leucosia, Fabricius ; Hbalia, Leach. Sub-Family Intnar. Ilia, Leach.

TRIBE 3. BRACHYGNATHA.

Last pair of legs normal, rarely reduced or dorsal in position ; female
openings on sternum ; first pleopods wanting in female ; branchiae few ;
mouth-frame quadrate.

THE DECAPODA 315

Susp-TRIBE 1. BRACHYRHYNCHA,

Body not narrowed in front ; rostrum reduced or wanting ; orbits well
formed.

Family _CorystIpax. Corystes, Latreille. Family Porrunipar.
Sub-Family Carcryinar. Careinus, Leach (Careinides, Rathbun). Sub-
Family Portrumninar, Portwmnus, Leach. Sub-Family Caroprrrnar.
Catoptrus, A. Milne-Edwards. Sub-Family Caruprnar. Carupa, Dana.
Sub-Family Portuninan. Portunus, Fabricius. Sub-Family CapHyrinar.
Caphyra, Guérin. Sub-Family THanamirinar. Thalamita, Latreille.
Sub-Family PopopHTHaLMINAE. Podophthalmus, Lamarck. Family
PoTAMONIDAE, Sub-Family Deckenttnak. Deckenia, Hilgendorf. Sub-
Family PSEUDOTHELPHUSINAR. Pseudothelphusa, Saussure. Sub-Family
PoTAMONINAE. Potamon, Savigny (= Thelphusa, Latreille). Sub-Family
TRICHODACTYLINAR. T'richodactylus, Latreille. Family Aretecycrmay
Sub-Family AcanrHocyciinag. Acanthocyclus, Milne-Edwards and Lucas.
Sub-Family Taunar. Thia, Leach. Sub-Family ArELEcyciinar. Atele-
cyclus, H. Milne-Edwards. Family Cancrtpar. Sub-Family Cancrinaer.
Cancer, Linnaeus. Sub-Family Prrmwetinar. Pirimela, Leach, Family
XANTHIDAE. Sub-Family Xanrurnar. Xantho, Leach. Sub-Family
CARPILIINAE. Carpilius, Leach. Sub-Family Eristnar. Etisus, H.
Milne-Edwards. Sub-Family Mrnrppryar. Menippe, de Haan. Sub-
Family Oztrnar. Ozius, H. Milne-Edwards. Sub-Family Eriparinar.
Eriphia, Latreille. Sub-Family Trapezimnar. Trapezia, Latreille.
Family Gonopiactpar. Sub-Family Ruartzorrvar. Rhizopa, Stimpson.
Sub-Family Prionopractnak. Prionoplax, H. Milne-Edwards. Sub-
Family Gonopiactnar. Gonoplaz, Leach. Sub-Family CarcinopLaciNae.
Careinoplax, H. Milne-Edwards. Sub-Family Hexapoprnar. Hevapus,
de Haan. Family PinnorHeripar. Sub-Family PrnnorHEerINnan. Pinno-
theres, Latreille. Sub-Family PrINNoTHERELIINAE. Pinnotherelia, Milne-
Edwards and Lucas. Sub-Family XenopHrHatminar. NXenophthalmus,
White. Sub-Family AsTHENOGNATHINAE. — Asthenognathus, Stimpson.
Family Prenopiacipar. Ptenoplar, Aleock and Anderson. Family
PaLicIDAE. Palicus, Phippi (= Cymopolia, Roux). Family GrapstDar.
Sub-Family Puacustnar. Plagusia, Latreille. Sub-Family SEsar-
MINAE. Sesarma, Say. Sub-Family Grapstnae. Grapsus, Lamarck ;
Planes, Bowdich (= Nautilograpsus, H. Milne-Edwards). Sub-Family
VARUNINAE. Varuna, H. Milne-Edwards. Family GrcarcrnrDar.
Gecarcinus, Leach ; Cardisoma, Latreille. Family Ocyropipar. Sub-
Family Macroputuatminan. Macrophthalmus, Latreille. Sub-Family
Ocypopinak. Ocypoda, Fabricius (Fig. 155, p. 264); Gelasimus, Latreille.
Sub-Family Myctirtyar. Myctiris, Latreille. Family Hapatocar-
CINIDAE., Hapalocarcinus, Stimpson.
ey

Sup-Trise 2, OxXYRHYNCHA.

Body narrowed in front ; rostrum usually distinct ; orbits generally
incomplete.

316 THE CROSTACHA

Family Hymenosomipags. Hymenosoma, Desmarest. Family Matrpa8.
Sub-Family Inacuinan. Jnachus, Fabricius ; Macrocheira, de Haan ;
Macropodia, Leach. Sub-Family ACANTHONYCHINAE. Acanthonya,
Latreille. Sub-Family Pistnar, Pisa, Leach ; Hyas, Leach. Sub-Family
Manag. Maia, Lamarck (= Mamaia, Stebbing); Pericera, Latreille ;
Mithrax, Leach. Family PARTHENOPIDAE, Sub-Family PARTHENOPINAE,
Parthenope, Fabricius; Lambrus, Leach. Sub-Family EvMEDONINAE.
Eumedonus, H, Milne-Edwards.

LITERATURE.

1. Alcock, A. Materials for a Carcinological Fauna of India. Nos. 1 to 6.
(Brachyura.) Journ. Asiatic Soc. Bengal, lxiv., Ixv., lxvii., Ixviii., lxix.,
1895-1900.
2. —— An Account of the Deep-Sea Brachyura collected by the
‘“ Investigator,” pp. ii+ 85, 4 pls. 4to. Calcutta, Indian Museum, 1899.
A Descriptive Catalogue of the Indian Deep-Sea . . . Macrura and
Anomala . . ., pp. 286+iv, 3 pls. 4to. Calcutta, Indian Museum, 1901.
A Catalogue of the Indian Decapod Crustacea in the . . . Indian
Museum. Part I. Brachyura: Fasciculus 1, Introduction and Dromides
or Dromiacea, pp. ix.+80, 8 pls. 1901; Part II]. Anomura: Fase. 1,
Pagurides, pp. xi+197, 16 pls., 1905; Part III. Macrura: Fasc. 1, The
Prawns of the Penews Group, pp. 55, 9 pls., 1906.

. Bate, C. Spence. Report on the Crustacea Macrura. Rep. Voy. ‘‘ Challenger,”
Zool. xxiv. pp. 90+942, 157 pls., 1888.

6. Bell, Thomas. A History of the British Stalk-eyed Crustacea. 8vo.
London, 1853. Issued in parts, 1844-53. ’

. Boas, J. FE. V. Studier over Decapodernes Slaegtskabsforhold. Kgl.
Danske Vidensk. Selsk. Skrifter (6), i. (2), pp. 25-210, 7 pls., 1880.
Kleinere carcinologische Mittheilungen. 2. Ueber den ungleichen
Entwicklungsgang der Salzwasser- und der Siisswasser-Form von Palae-
monetes varians. Zool. Jahrb. Abth. Syst. iv. pp. 7938-805, pl. xxiii.,

1889.

9. Borradaile, L. A. Wand Crustaceans; Marine Crustaceans, pts. i.-vil.,
ix.-xi., xiii. Gardiner’s Fauna . . . Maldive and Laccadive Archipelagoes.
Cambridge, 1901-1904.

10. —— On the Classification of the Decapod Crustaceans. Ann. Mag. Nat.

Hist. (7), xix. pp. 457-486, 1907.

11. Bouvier, E. L. Le systéme nerveux des Crustacés Décapodes et ses rapports
avee l'appareil circulatoire. Ann. Sci. Nat. Zool. (7), vil. pp. 73-106,
pl. vii, 1889.

or

STi

12. —— Recherches anatomiques sur le systéme artériel des Crustacés Déca-
podes. Ann Sci. Nat. Zool. (7), xi. pp. 197-282, pls. vill.-xi., 1891.
A .
13. Sur Vorigine homarienne des Crabes: Etude comparative des Dro-

miacés vivants et fossiles. Bull. Soc. Philomath. Paris (8), vill. pp. 34-
110, 1896.

14. Brooks, W. K. Luoifer: A Study in Morphology. Phil. Trans. elxxiii. pp.
57-137, 11 pls., 1882.

15. Bumpus, H. C. The Embryology of the American Lobster. Journ. Morph.
Vv. pp. 215-262, pls. xiv.-xix., 1891.

16.

fle

36.

THE DECAPODA 317

Coutiére, H. Les ‘‘ Alpheidae,” Morphologie externe et interne, formes
larvaires, Bionomie. Ann. Sci. Nat. Zool. (8), ix. pp. 1-559, pls. i.-vi.,
1899.

Doflein, F. Brachyura. Wiss. Ergeb. deutschen Tiefsee-Expedition .. .
“Valdivia,” vi. pp. xii+314, and Atlas, 58 pls., 1904.

. Faxon, W. A Revision of the Astacidae. Mem. Mus. Comp. Zool. Harvard,

x. No. 4, pp. vi+ 186, 10 pls., 1885.
Reports . . . ‘* Albatross.” XV. The Stalk-Eyed Crustacea. Mem.
Mus. Comp. Zool. Harvard, xviii. pp. 292, 67 pls. and map, 1895.

. Henderson, J. Rk. Report on the Anomura. Rep. Voy. ‘‘ Challenger,” Zool.

XXVil. pp. 7+215, 21 pls., 1888.

. Herrick, F. H. The American Lobster: A Study of its Habits and Develop-

ment. Bull. U.S. Fish Commission for 1895, pp. 1-252, 64 pls., 1895.

. Huxley, T. H. On the Classification and Distribution of the Crayfishes.

Proc. Zool. Soc. London, 1878, pp. 752-788, 7 figs.

. Marchal, P. Recherches anatomiques et physiologiques sur l'appareil

excréteur des Crustacés Décapodes. Arch. Zool. expér. (2), x. pp. 57-275,
9 pls., 1892.

. Miers, E. J. On the Classification of the Maioid Crustacea or Oxyrhyncha,

with a Synopsis of the Families, Sub-Families, and Genera. Journ. Linn.
Soc. London, Zool. xiv. pp. 634-673, pls. xii., xiii., 1879.

Report on the Brachyura. Rep. Voy. ‘‘ Challenger,” Zool. xvii. pp.
' 50+ 362, 29 pls., 1886.

. Milne-Edwards, H. Observations sur le squelette tégumentaire des Crus-

tacés Décapodes et sur la morphologie de ces animaux. Ann. Sci. Nat.
Zool. (3), xvi. pp. 221-291, pls. viii.-xi., 1851.

7. Milne-Edwards, A., and Bouvier, E. L. Reports... “Blake.” XXXIII.

Description des . . . Paguriens . . ., Mem. Mus. Comp. Zool. Harvard,
xiv. No. 3, pp. 172, 12 pls., 1893; XXV. Description des . . . Gala-
théidés . . ., op. cit. xix. Noy 2, pp..141, 12 pls., 1897; XXXIX. Les
Dromiacés et Oxystomes, op. cit. xxvii. No. 1, pp. 127, 25 pls., 1902.
Considérations générales sur la famille de Galathéidés. Ann. Sci.
Nat. Zool. (7), xvi. pp. 191-327, 1894.

. — Crustacés Décapodes . . . ‘‘Hirondelle”. . . 1'¢ Ptie, Brachyures et

Anomures. Résultats des Campagnes scientifiques . . . Monaco, Fasc.
vii. pp. 112, 11 pls., 1894 ; also Crust. Décap. . . . ‘‘ Hirondelle” (Supplé-
ment) et . . . ‘‘ Princesse Alice,” op. cit. Fasc. xiii. pp. 106, 4 pls., 1899.

. — Expéd. Scient. du ‘‘ Travailleur” et du “Talisman.” Crustacés

Décapodes, 1'e Ptie, pp. 396, 32 pls., 1900.

. Mocquard, M. F. Recherches anatomiques sur l’estomae des Crustacés

podophthalmaires. Ann. Sci. Nat. Zool. (6), xvi. pp. 1-311, 11 pls., 1883.

. Miller, F. Die Verwandlung der Garneelen. Arch. Naturgesch. xxix. pp.

8-23, pl. ii., 1863. Translated in Ann. Mag. Nat. Hist. (3), xiv. pp. 104-
115, pl. iv., 1864.

3. Ortmann, A. Die Decapoden-Krebse des Strassburger Museums. 8 pts.

Zool. Jahrb. Abth. Syst. v.-vii., 1890-1894.
Das System der Decapoden-Krebse. Op. cit. ix. pp. 409-453, 1896.

. Prentiss, C. WV. The Otocyst of Decapod Crustacea ; its Structure, Develop-

ment, and Functions. Bull. Mus. Comp. Zool. Harvard, xxxvi. No. 7, pp.
166-251, pls. i.-ix., 1901.

Przibram, H. Experimentelle Studien iiber Regeneration. 4 papers. Arch.
Entwicklungsmechanik, xi., xili., xix., xxv., 1901-1907.

318 THE CRUSTACEA

37. Rathbun, Mary J. Les Crabes d’eau douce (Potamonidae), 3 parts. Nouv.
Arch. Mus. d’Hist. Nat. Paris, vi., vii., viil., 1904-1906.

38. Reichenbach, H. Studien zur Entwicklungsgeschichte des Flusskrebses.
Abh. Senckenberg. naturforsch. Ges. xiv. (1), pp. 137, 19 pls., 1886.

39. Sars, G. O. Bidrag til Kundskaben om Decapodernes Forvandlinger. 3
papers. Arch. Math. Naturvid. ix., xili., xiv., 1884-1890.

40. Thompson, J. Vaughan. Zoological Researches, vol. i. 8vo. Cork, 1828.

CHAPTER XVI
THE STOMATOPODA

DIVISION HOPLOCARIDA.
Order Stomatopoda, Latreille (1817).

For a definition of the Division Hoplocarida, see p. 149.

Historical—The common and conspicuous Squilla mantis of the
Mediterranean can hardly have escaped notice in antiquity, and it
is surprising that it cannot be identified with certainty among the
Crustacea mentioned by Aristotle. It was described by Rondelet
(1555) under the generic name which it still bears. The group
Stomatopoda, as defined by Latreille in 1817, had practically the
limits now assigned to it, though some larvae were admitted to
generic rank along with the adults. By H. Milne-Edwards the group
was extended to include not only the ‘‘Schizopoda,” but also some
larval and adult Decapods (Phyllosoma, Leucifer, ete.). Restricted
by subsequent writers to the single family Squillidae, the Order has
generally been ranked along with “Schizopoda” and Decapoda in
the group Podophthalma, though Huxley and, later, Grobben have
pointed out the great differences separating the Stomatopoda from
the other stalk-eyed groups.

The first details as to the larval metamorphosis of the Order
were given by F, Miiller (1862-64). Claus, in a remarkable memoir
(1871), traced out several developmental series. Later workers,
especially Brooks (1886) and Hansen (1895), have succeeded in
referring many larvae to the various genera and species of adults.
It is to be noted, however, as Hansen has pointed out, that the
number of specific forms among the larvae exceeds that of the
known adult species.

MorpPHOLOGY.

The general appearance of the Stomatopoda is highly character-
istic and very constant throughout the group. Its most striking
features are due to the great development of the abdominal region
and its appendages, the small size of the carapace, and the large
and peculiarly formed raptorial limbs.

319

THE CRUSTACEA

Go
is)
°

The body (Fig. 186) is more or less flattened dorso-ventrally.
The carapace is fused dorsally with at least two of the thoracic
somites, two others are represented by indistinct vestiges over-
lapped by its hinder edge, while the last four are free and com-
pletely developed. The lateral wings of the carapace project more
or less horizontally, roofing over on each side a widely open channel

Fic. 186.

Squilla mantis, male, from the side. a’, antennule ; a’, antenna; p, penis; sc, scale or
exopodite of antenna ; th1, th?, th8, first, second, and last thoracic appendages.

within which lie the epipodites of the anterior thoracic appendages,
and which corresponds to the branchial cavity of other forms.
Anteriorly the carapace does not extend to the front of the head
(Fig. 187), leaving uncovered two movably articulated segments,

Fia. 187.

Anterior part of body of Squilla mantis, from above. a’, antennule; a’, antenna; @.s,
antennular segment of head ; ec, carapace; 0.s, ophthalmic segment of head ; 7, rostral plate ;
se, scale or exopodite of antenna.

which carry respectively the eyes and the antennules, and which
are commonly regarded as representing the ocular (0.s) and
antennular (a.s) somites. A small rostral plate (7), movably
articulated with the front edge of the carapace, overlies the
antennular segment.

That part of the head lying between the point of attachment of
the antennae and that of the mandibles is much elongated, forming

THE STOMATOPODA 321

a narrow “neck,” which, except for the lateral wings of the carapace
projecting on either side, recalls the similarly formed “neck” of
Lewifer and of the Tracheliferlarva of Jazea. The anterior thoracic
somites are much abbreviated and crowded together. The first and
second are apparently not distinct from the carapace in the adult.
The third and fourth are at most represented dorsally by small
sclerites overlapped by the hinder part of the carapace. The
fifth and succeeding thoracic somites are complete, and movably
articulated. The abdominal somites often increase in width
posteriorly, and their horizontally extended pleural plates may
become greatly expanded in certain species.

The telson (Fig. 188, ¢) is very broad and its posterior margin
is generally cut into sharp teeth ; it is firmly united to the preced-
ing somite in certain species of Gonodactylus (Protosquilla, Brooks).

Fic. 188.

Caudal fan of Sywilla mantis, wpper surface. en, endopodite ; ex, exopodite ;
p, process from peduncle of uropod ; ¢, telson.

The surface of the carapace and of the body-somites is often
ornamented with longitudinal keels, and the telson is always more
or less elaborately sculptured.

Appendages.—The antennules (Fig. 187, a) have an elongated
peduncle of three segments, which bears three comparatively short
flagella. Of these, the two on the outer side spring from a
common stalk which is unsegmented ; the inner flagellum is also
unsegmented for a short distance from its base.

The antennae (Fig. 187, a”) have a protopodite of two segments,
a large exopodite, and a comparatively feeble endopodite. The
exopodite consists of a small basal segment and an oval mem-
branous scale (sc) with setose margins; the endopodite has two
elongated proximal segments and a short flagellum.

The mandibles (Fig. 189, A) carry a slender palp of three
segments. The oral edge is crescentic and strongly serrate, its
two cornua corresponding respectively to the incisor and molar
processes of other Malacostraca. The proximal cornu projects
upwards into the cavity of the mouth.

The mazillulae (Fig. 189, B) have two endites, the distal

21

322 THE CRUSTACEA

one terminating in a strong curved spine. A vestigial palp is
present (p).

The mazillae (Fig. 189, C) have a peculiar and characteristic
form which cannot be closely compared with that of the corre-
sponding appendage in other Malacostraca. They appear to consist
of four segments, of which the first and second are indistinctly
separated.

The first five pairs of thoracic appendages are similar in structure
and are commonly called maxillipeds, though, as they possess no
endites or other adaptations for mastication, the name is hardly
appropriate. Each consists of only six segments (there is no
evidence to show how these are related to the seven segments
commonly recognised in other Malacostraca) and terminates in a

Fia. 189.
Mouth-parts of Squilla mantis. A, mandible, seen from the inner, or oral, side; B,
maxillula; C, maxilla. i, incisor process; m, molar process; o, papilla bearing opening (of

maxillary gland’); p, palp.

prehensile “hand” or sub-chela; there are no exopodites, but
epipodites (Fig. 190, A, ep) are present on all five pairs in the
form of discoid membranous plates or vesicles attached to the
basal segment by a narrow neck. The first pair of limbs (Fig. 190,
A) are long and slender and the terminal segment is minute; the
second pair are very massive, forming powerful weapons (Fig. 186,
th?) ; the third, fourth, and fifth pairs resemble each other and are
less powerful. In each case the terminal segment is flexed upon
the preceding one in such a way that its point is directed forwards,
an arrangement which recalls the peculiar inverted chela of the
Amphipod Tvischizostoma. The last three pairs of thoracic limbs
(Fig. 186, th’) are slender, biramous, and without epipodites. The
protopodite is very distinctly composed of three segments, of which
the second is elongated. The inner (and anterior) of the two
rami is the stouter and consists of two segments; the outer is
slender and unjointed. According to Claus, the development of

THE STOMATOPODA 323

the limb shows the outer branch to be the endopodite and the
inner the exopodite, the relative positions of the two being reversed
in the course of development.

The pleopods (Fig. 190, B, C) are remarkable in carrying the
branchial apparatus. The broad and flattened protopodite has
articulated with it at some distance from each other the endopodite
and exopodite, each of which is lamellar and membranous and is
obscurely divided into two segments. From the inner edge of the
endopodite springs a short appendix interna (7), bearing a group
of coupling-hooks. The branchiae (dr) consist of a main stem
springing from the anterior face of the exopodite near its base,
extending horizontally inwards, and carrying on its lower edge a

Fie, 190,

A, first thoracic appendage of Squilla mantis. B, second pleopod, showing the branchial
appendage. C, the same, after removal of the branchial filaments. br, branchial appendage ;
en, endopodite ; ep, epipodite ; ex, exopodite ; i, appendix interna.

’

series of tufts of ramified branchial filaments. In the female all
the pleopods are similar, but in the male the first pair have the
endopodite modified.

The uwropods form, with the telson, a broad tail-fan (Fig. 188).
The short protopodite runs out into a flattened plate (p) lying
between and below the rami, divided distally into two sharp teeth.
The exopodite is distinctly divided into two segments.

Alimentary System.—The stomach is large and thin-walled and
is divided into two chambers. Its armature is slightly developed
as compared with that of most Decapods. ‘The anterior or cardiac
chamber is large and extends in front of the mouth as far as the
base of the rostrum. In its posterior wall lie two pairs of rod-like
sclerites, the upper pair articulating with an unpaired plate which
forms the floor of the smaller pyloric chamber and projects as a
median keel into its cavity. The intestine is very narrow, but
expands somewhat at about the fifth abdominal somite to form the

324 THE CROSLACEA

rectum. <A pair of glandular sacs lying in the telson on either side
of the anus have been observed in the larva and perhaps open into
the rectum. It is not known whether they persist in the adult.

The digestive gland is very voluminous. It forms a compact
mass of glandular tissue closely investing the intestine throughout
the whole of its length and sending out on each side a series of
diverticula segmentally arranged corresponding to the last three
thoracic and the abdominal somites, and it finally terminates in a -
series of ramifying processes, which radiate throughout the telson
and even penetrate into the peduncles of the uropods. It was
formerly stated that this gland originated as a series of segmentally
arranged diverticula from the alimentary canal, and that it com-
municated with the intestine by a series of apertures on each side
throughout its whole length. It appears, however, that this is not
the casd, but that the gland-follicles open into a pair of longitudinal
ducts which unite to enter the dorsal part of the pyloric chamber
of the stomach.

Circulatory System.—The Stomatopoda are unique among the
Eumalacostraca in possessing an elongated tubular heart extending
through nearly the whole length of the thoracic and abdominal
regions, and provided with numerous segmentally arranged pairs of
ostia.

The details of the circulatory system have been most fully made
out in the later larval stages by Claus, but the older accounts of the
adult by Audouin and Milne-Edwards and by Duvernoy, though
incomplete, show that no very profound changes occur in the adult.
The anterior part of the tubular heart, lying in the maxillary region,
is dilated, and its dorsal wall is perforated by a pair of large ostia.
Anteriorly, it gives off a median aorta which sends branches to
brain, eyes, antennules, and antennae, and a pair of antero-lateral
arteries to the carapace and viscera. Behind the region of the first
thoracic appendages the heart is of uniform diameter, and bears
twelve pairs of ostia and fourteen pairs of lateral arteries arranged
for the most part in correspondence with the segmentation of the
body. Posteriorly the heart is continued into a short caudal aorta
running into the telson.

From one of the lateral arteries of the first pair there originates
an unpaired arteria descendens, which pierces the ventral ganglionic
mass between the first and second thoracic ganglia, to communicate
with a subneural artery which underlies the nerve-cord throughout
its whole length. This subneural artery further communicates
with the heart by means of its lateral branches, which anastomose
in the various somites, sometimes on one side, sometimes on both,
with branches of the lateral arteries. Capillary networks of great
complexity are formed in the brain and in the ventral ganglia. A
point of some interest is the unsymmetrical origin of the arteries

THE STOMATOPODA 325

which supply the rostrum and the dorsal “ Zoea ”-spine of the larval
carapace.

The blood from the respiratory appendages of the pleopods ~
passes to the pericardium by a series of afferent canals in the
abdomen.

Excretory System.—It is stated by Kowalevsky that the maxillary
gland is well developed in the Stomatopoda, but no details as to its
structure appear to have been published. A papilla on the posterior
surface of the maxilla in Squilla mantis (Fig. 189, C, 0) bears a
minute terminal pore which may be the aperture of the duct of
this gland.

Nervous System.—The oesophageal connectives are elongated,
and a postoral antennal commissure is present. The first eight
pairs of ganglia in the ventral chain are coalesced, but the remain-
ing nine are widely separated.

Sense-Organs.—The paired eyes are always set on movable
peduncles and vary greatly in size in the different species. The
nauplius-eye, often present in the larvae, does not appear to have
been found in the adult. Sensory filaments are developed on the
outer branch of the external flagellum of the antennules.

Reproductive System.—The testes lie in the abdomen and have
the form of fine convoluted tubes uniting posteriorly in an unpaired
piece which lies in the telson and passing anteriorly into the vasa
deferentia. Each vas deferens opens to the exterior at the end of
a long penis springing from the inner side of the proximal segment
of the last thoracic appendage, and differing from the corresponding
organs of other Malacostraca not only in its great length but also in
the fact that it is more or less strongly chitinised and is divided by
a movable articulation about the middle of its length. In the
posterior thoracic somites lie a pair of convoluted tubular glands
which in their form and disposition have a remarkable similarity to
the testes, being united anteriorly by a short unpaired piece and
continued posteriorly into ducts which traverse the penes along-
side of the vasa deferentia and open beside them at the tip. These
glands and their ducts never contain spermatozoa and their function
is unknown. The spermatozoa are spherical in form, without pro-
cesses of any kind, and appear to be simple nucleated cells.

The ovaries are, in the mature female, very voluminous and
closely approximated, so that they appear to form a single-lobed
mass which extends through the abdomen and as far forward as the
hinder limit of the carapace. In reality the two ovaries are only
united, as is the case with the testes, by an unpaired portion lying
in the telson. The oviducts open near the middle line on the
sternal surface of the sixth thoracic somite, together with a small
pocket-like invagination of the integument which functions as a
receptaculum seminis. On the ventral surface of each of the three

326 THE CRUSTACEA ;

last thoracic somites of the female les a glandular mass, sending
numerous fine ducts to the exterior. This is in all probability to
be regarded as a cement-gland.

The eggs are of very small size, and are agglutinated together
into a cake-like mass which either lies free in the burrow inhabited
by the female or is carried by means of the last three pairs of
chelate feet.

DEVELOPMENT.

Little is known of the embryonic development of the Stomato-
poda, but their later history is extremely remarkable, on account
of the prolonged larval life; the complicated metamorphosis, and
the fact that the larval forms of the various species differ from each
other more widely than do the adults. The later stages, which
may reach a great size, form a conspicuous element of the pelagic
fauna in the warmer seas, and many species were described by the
older observers as adult animals under several generic names. It
is very probable, as Hansen points out, that several forms of larvae
belong to species and even genera which in their adult state are
still to be discovered.

Two main types of larvae can be distinguished, corresponding
to the old genera Frichthus, Latreille, and Alima, Leach, and the
former can be further subdivided into a number of larval genera,
Gonerichthus, Lysioerichthus, ete.

Though the earlier stages of all these are still very imperfectly
known, it is certain that great differences exist between them as
to the degree of development at the time of hatching. The
longest series of larval stages appears to be passed through by
certain Hrichthus-torms, especially by those to which the names
Lysioerichthus and Coroniderichthus have been given (larvae of Lysio-
squilla and Coronida). In the youngest known stage of this series
(Fig. 191, A) three regions of the body can be distinguished: (1)
An unsegmented cephalic region bearing the median and paired
eyes, antennules, antennae, mandibles, maxillulae, and maxillae,
and giving rise to the great carapace which envelops the greater part
of the body; (2) a thoracic region of eight somites, all of which are
free from the carapace, the first five bearing biramous swimming-
feet, while the last three are without appendages ; (3) a broad tail-
plate representing the still unsegmented abdomen. In the following
stages the abdominal somites are successively segmented off in front
of the tail-plate, which remains as the telson, and their appendages
at the same time develop in regular order from before backwards,
the uropods at first not differing from the appendages in front of
them and not preceding them in order of development. The first
and second thoracic limbs early lose their exopodites, and the
second pair become greatly enlarged and assume their characteristic

THE STOMATOPODA 327

form. The third, fourth, and fifth pairs undergo retrograde changes,
losing their exopodites and remaining for some time as shapeless
stumps, only later to resume their course of development into
chelate limbs. It does not seem to be the case, however, as is
sometimes stated, that they actually disappear. The last three

Fic. 191.

Consecutive stages of a larva of the first Hrichthus-type. (According to Hansen, the larva
represented in C and D belongs to a different species from those shown in A and B.) «@,
antennule ; #”, antenna ; al, first pleopod ; «6, uropod ; I-V, first five thoracic appendages ; 6-8,
last three thoracic somites. (After Claus, from Korschelt and Heider’s Hmbryology.)

thoracic somites remain for a long time devoid of appendages, and
it is only at a late stage, when the appendages in front and behind
are well developed, that rudiments of appendages begin to appear
on them (Fig. 192). The adult form is only assumed after a
considerable size has been reached, the carapace diminishing in
size, becoming coalesced with the anterior thoracic somites, and

328 THE CRUSTACEA

losing its spines, and the appendages gradually assuming their

definitive characters. The development of the antennae appears

to be peculiar in that the endopodite develops as a lateral branch,

the distal portion of the larval append-

age becoming the large exopod.

In a second series of larval forms of

ee the Hrichthus-type (Fig. 193), belonging

to the genera Pseuderichthus, Gonerichthus,

ete. (Pseudosquilla and Gonodactylus), the

youngest stage known possesses already

four or five pairs of pleopods, and the

last six thoracic somites are without any
trace of appendages.

The larvae of the Alima-type (Fig.
194), belonging to the genus Squilla, are
known to leave the egg at a stage cor-
responding with that last described.
They are distinguished from all the pre-
ceding forms by the generally more
slender body and short and broad cara-
pace, and more constantly by differences
in the armature of the telson and raptorial
limbs.

Lister has described a very remark-
able larva, which appears to correspond
to a metanauplius-stage. The form of
the carapace makes it very probable that
it belongs to the Stomatopoda, and, if
so, it shows that some members of the
order leave the egg at a much earlier
stage than has hitherto been supposed.

The great size attained by some of
these larvae, especially by those of the
Alima-type, which may exceed two and

Fic. 192. a half inches in length, has given rise to
Fee ene test Erie the suggestion ‘that they, are abuormally
S-type. a, antennule; a’, an- rs s A
tenna; «1-03, pleopods; a6, uropods; hypertrophied forms which, by being
br, rudiments of gills; I-VIII, tho-
racic appendages. (After Claus, Swept out to sea, have been prevented
Pepto ne and Heider’s Em- from completing their metamorphosis.

“A As in the similar cases of the Phyllo-
soma-larvae among Decapods and the Leptocephalus-larvae of eels,
however, there appear to be no grounds for accepting this view,
and it is definitely rejected by Hansen as a result of his extensive
studies on the group.

The metamorphosis of the Stomatopoda is of great importance
in helping to interpret the larval forms of the Decapoda. While

THE STOMATOPODA 329

the regular order of differentiation of the somites from before back-
wards is preserved, the retarded appearance of the posterior thoracic
appendages shows the beginning of the process which has led to the
suppression of these somites and appendages in the typical Zoea.

Notes oN HApits, ETC.

The Stomatopoda are exclusively marine, the adults generally
inhabiting burrows in the sand or mud of the sea-bottom in shallow

Fic. 193.

Larva of the second Erichthus-type (the Pseuderichthus group). «’, antennule; @’, antenna ;
a, first pleopod ; «6, uropod ; ep, epipodite; I, II, first two pairs of thoracic appendages.
(After Claus, from Korschelt and Heider’s Embryology.)

water (up to 180 fathoms), chiefly in the tropics, but extending
north to Britain and Japan, and south as far as Auckland. Many
species seem never to wander far from their burrows, into which
they retreat with great rapidity when alarmed, and are thus seldom
obtained by the ordinary methods of collecting. The larval stages,
on the other hand, are exclusively pelagic, of glass-like transparency,
and occur in great numbers in the plankton of the warmer seas.
All the Stomatopoda appear to be of active, predatory habits. The
range in size within the group is about from 38 to 340 mm.

30 LHE CROSLACEHA

1S)

PALAEONTOLOGY.

The oldest undoubted Stomatopods are found in the Jurassic
rocks of Solenhofen, and are referred to the genus Sculda, Miinster,
differing in many details from the living forms. Species referred to
the genus Squilla occur in the Cretaceous deposits of Westphalia

Fic. 194,
Young larva of the Alima-type. a’, antennule; w’, antenna; @1-a5, pleopods; I, II, first
and second thoracic limbs ; 6-8, last three thoracic somites. (After Brooks, from Korschelt
and Heider’s Embryology.)

and the Lebanon, in which latter larvae of the Hrichthus-type have
also been recognised. Species of Sguilla also occur in the London
Clay and other Tertiary deposits.

AFFINITIES AND CLASSIFICATION.

Perhaps the most aberrant character of the Stomatopoda, and
one which separates them not only from the other Malacostraca
but from all other Crustacea, is the presence of distinct and

THE STOMATOPODA 331

movable ophthalmic and antennular “somites.” Whatever be the
morphological value of these segments of the head, there can be no
doubt that their separation in the Stomatopoda is a secondary and
not a primitive character.

The movable rostral plate is a character of some interest from
its resemblance to that of the Leptostraca; but it is to be noted
that the spiniform rostrum of the larval Stomatopod is not articu-
lated, while, on the other hand, the Decapod Rhynchocinetes shows
the possibility of the ordinary rostrum becoming divided off by a
movable joint from the carapace.

The lamellar epipodites of the first five pairs of thoracic limbs
recall those of the Syncarida ; the bifurcation of the outer flagellum
of the antennules is only paralleled among the Caridean Decapods ;
the modification of the first pair of pleopods in the male may be
compared with that found in the Euphausiacea and the Penaeid
Decapods ; the possession of an appendix interna on the pleopods
is shared by the Leptostraca and the lower Eucarida. Other
characters, such as the structure of the maxilla and the segmenta-
tion of the thoracic limbs, cannot be closely compared with those of
any other Malacostraca. It seems most probable that the Stomato-
poda are a lateral offshoot from the main stem of the Malacostraca,
of which, in the absence of connecting links, it is as yet impossible
to determine the exact relations.

The existing Stomatopoda form a very homogeneous group,
within which only one family can be recognised, while many of the
genera are separated by comparatively slight differences.

OrvdER Stomatopoda, Latreille (1817).

Family Squrtipar. Squilla, Fabricius (Fig. 186); Lysiosqualla,
Dana; Pseudosquilla, Dana ; Gonodactylus, Latreille ; Coronida, Brooks.

LITERATURE.

1. Bigelow, R. P. Report upon the . . . Stomatopoda collected by the Steamer
“Albatross”... Proc. U.S. Nat. Mus. xvii. pp. 489-550, 3 pls., 1895.

2. Brooks, W. K. Report on the Stomatopoda. Rep. Voy. ‘‘ Challenger,”
Zool. xvi. pp. 114, 16 pls., 1886.

8. Claus, C. Die Metamorphose der Squilliden. Abh. kgl. Ges. Wiss. Gottin-
gen, xvi. pp. 111-163, 8 pls., 1871.

Die Kreislaufsorgane und Blutbewegung der Stomatopoden. Arb.
zool. Inst. Wien, v. pp. 1-14, 3 pls., 1883.

5. Grobben, C. Die Geschlechtsorgane von Squilla mantis, Rond. S.B. Akad.
Wiss. Wien, Ixxiv. Abth. i. pp. 389-406, 1 pl., 1876.

6. Hansen, H. J. Isopoden, Cumaceen und Stomatopoden der Plankton-
Expedition. Ergeb. Plankton-Exp. ii. pp. 105, 8 pls., 1895.

7. Jurich, B. Die Stomatopoden der deutschen Tiefsee-Expedition. Wiss.
Ergeb. deutschen Tiefsee-Expedition . . . ‘‘ Valdivia,” vil. pp. 361-
408, pls. xxv.-xxx., 1904.

10.

Wile

THE CRUSTACEA

. Lister, J. J. Note on a (? Stomatopod) Metanauplius Larva. Quart. Journ.

Microsc. Sci. (n.s.) xli. pp. 433-437, 1898.

. Miers, HE. J, On the Squillidae. Ann. Mag. Nat. Hist. (5), v. pp. 1-30 and

108-127, pls. i.-iii., 1880.

Miller, F. Bruchstiick zur Entwickelungsgeschichte der Maulfiisser.
Arch. Naturgesch. xxviii. pp. 353-361, pl. xill., 1862; Ein zweites
Bruchstucka sy) Ops cin xix PPsll/ plies wlsGor

Orlandi, S. Sulla struttura dell’ intestino della Sqwilla mantis, Rond.
Atti Soe. Ligustica, xii, pp. 112-138, pls. iii.-iv., 1901.

INDEX

Note.—Page-numbers in thick type refer to the sections on classification.

Abdomen, 6; of Amphi-
poda, 225 ; of Branchio-
poda, 34; of Cirripedia,
113; of Copepoda, 74 ;
of Cumacea, 184; of
Decapoda, 259; of Iso-
poda, 198; of Lepto-
straca, 152; of Malaco-
straca, 144; of Mysidacea,
172; of Stomatopoda,
321

Abdominal appendages of

Amphipoda, 232; of
Leptostraca, 156; of
Malacostraca, 146

Abdominalia, 108, 139
Acanthephyra, 311
Acanthephyridae, 311
Acanthocope, 207, 219
Acanthocyclinae, 315
Acanthocyclus, 315
Acanthonotozoma, 241
Acanthonotozomatidae, 241
Acanthonychinae, 316
Acanthonyx, 316
Acanthosoma, 297
Acanthotelson, 168
Acartia, 102
Acetes, 273
Achtheres, 80, 83, 100, 103
Acontiophorus, 78, 79, 103
Acrothoracica, 1, 106, 108;
definition, 140; mor-
phology, 108
Adductor muscle of Bran-
chiopoda, 44; of Cirri-
pedia, 116 ; of Ostracoda,
57, 64; of Leptostraca,
157
Adhesive organ
chiopoda, 43
Aega, 208, 220
Aeger, 307
Aeginae, 220
Aegisthus, 103

of Bran-

Aeglea, 277, 313
Aegleidae, 304, 313
Aesthetases, 20; of Cope-
poda, 76, 85
Aetideus, 102
Affinities of Amphipoda,
239; of Branchiopoda,
51; of Cirripedia, 138 ;
of Copepoda, 101; of
Cumacea, 188 ; of Deca-
poda, 309 ; of Euphausi-
acea, 251; of Isopoda,
218; of Leptostraca, 160;
of Mysidacea, 181; of
Stomatopoda, 330; of
Syncarida, 168 ; of Tan-
aidacea, 194
Ala of Cirripedia, 111
Albunea, 265, 314
Albuneidae, 314
Alcippe, 115,
139, 140
Alcippidae, 140
Alcirona, 219
Alcock, 254, 288
Alepas, 110, 128, 140
Alicella, 239, 240
Alima, 326, 328, 330
Alimentary system, 14 ; of
Amphipoda, 233; of
Branchiopoda, 42 ; of
Branchiura, 98 ; of Cirri-
pedia, 115; of Copepoda,
82; of Cumacea, 187 ;
of Decapoda, 279; of
Euphausiacea, 247; of
Isopoda, 207 ; of Lepto-
straca, 156; of Mysi-
dacea, 176 ; of Ostracoda,
63; of Stomatopoda, 328;

Lee 2205

Amesopodidae, 220
Amesopous, 203, 220
Ampelisca, 241
Ampeliscidae,
241
Ampharthrandria, 71; de-
finition, 103
Amphaskandria,
definition, 102
Amphilochidae, 241
Amphilochus, 241
Amphion, 311
Amphioninae, 311
Amphipoda, 2, 143 ; affini-
ties and classification,
239 ; definition, 224; de-
velopment, 237 ; habits,
etc., 238; historical notes,
224; morphology, 225 ;
palaeontology, 239
Amphithoe, 241
Amphithoidae, 229, 235,
241
Anal respiration in Cope-
poda, 82
Anarcturus, 220
Anamixidae, 241
Anamixis, 241
Anaspidacea, 1, 143, 162,
169
Anaspides, 7, 8, 25, 147,
162-168, 169
Anaspididae, 169
Ancestral type of Crus-
tacea, 26; of Malaco-
straca, 144
Anceus, 219
| Anchialina, 182
Anchialus, 180, 182
Ancinus, 220

236,

235,

(fle vi

~I

>

of Syncarida, 166; of Anelusma, 110, 118, 114,

Tanaidacea, 193
Alpheidae, 258, 311
Alpheus, 282, 283, 311
Amblyops, 173, 181

303

115, 138, 140
Anisopoda, 190
Annulus ventralis, 291
| Anomalocera, 84, 102

334

THE CRUSTACEA

Anomopoda, 29, 40; deti- |
nition, 53

Anomostraca, 162

Anomura, 253, 309 ; defini-
tion, 313

Anostraca, 1, 29, 39, 48;
definition, 53

Antenna, 11; of Amphi-
poda, 228 ; of Branchio-
poda, 35; of Cirripedia,
114; of Copepoda, 77 ;
of Cumacea, 185; of
Decapoda, PAS 1B Ose
Euphausiacea, 245 ; of
Isopoda, 198 ; of Lepto-
straca, 152; of Malaco-
straca, 144; of Mysi-
dacea, 173; of Ostra-
coda, 59; of Stomato-
poda, 321 ; of Syncarida,

164; of Tanaidacea,
191

Antennal gland, 16; of
Amphipoda, 235; of

Decapoda, 285; of Eu-
phausiacea, 247; of
Leptostraca, 156; of
Mysidacea, 178
Antennular fossa of Bra-
chyura, 257
Antennule, 10; of Amphi-
poda, 226; of Apoda,
129; of Branchiopoda,
35; of Branchiura, 95;
of Cirripedia, 113; of
Copepoda, 75; of Cum-
acea, 185 ; of Decapoda,
264; of Huphausiacea,
244; of Isopoda, 198 ;
of Leptostraca, 152;
of Malacostraca, 144 ;
of Mysidacea, 173 ; of
Ostracoda, 58 ; of Stoma-
topoda, 321; of Syn-
earida, 164; of Tanai-
dacea, 191
Anthura, 211, 219
Anthuridae, 197,
205, 216, 219
Anuropodinae, 219
Anuropus, 207, 219
Aora, 231, 241
Aoridae, 235, 241
Apoda, 1, 106 ; definition,
140 ; morphology, 128

198,

Apodemes in Decapoda,
263

Apodidae, 53

Appendix interna, 147 ; of
Decapoda, 2733 of Eu-
phausiacea, PANG oie

Leptostraca, 156; of
Stomatopoda, 323

Appendix maseulina, 274

Apseudes, 187, 190, 191,
193, 194, 195

Apseudidae, 191, 192, 193,
194, 195

AUS AOsai Onell ean obs
29, 30, 36, 37-40, 42,
43, 45, 46, 48, 50, 53

Arachnomysinae, 181

Arachnomysis, 173, 181

Archaeomysinae, 181

Archaeomysis, 176, 181

Arcturidae, 197, 204, 212,
220

Arcturus, 220

Argathona, 220

Argathoninae, 220

Argulidae, 104

Argulus, 72,
100, 104

Arietellus, 102

Aristeinae, 278, 304, 311

Aristeus, 288, 289, 311

Aristotle, 71, 106, 254, 319

Armadillidinae, 220

Armadillidium, 220

Armadillo, 220

Do-Olsmnoo,

| Artemia, 438, 50, 53

Arthrobranchia, 14, 275
Arthrostraca, 147
Artotrogus, 82, 103
Ascidicolidae, 75, 78, 81,
89, 103
Ascidicola, 103
Asconiscidae, 221
Asconiscus, 221
Ascothoracica, 1, 106, 107 ;
definition, 140 ; develop-
meut, 127 ; morphology,
125

Asellidae, 205, 206, 216,
219
Asellota, 196; definition,

219
Asellus, 198, 199, 204, 208,
210, 211, 213, 219
Astacidae, 257, 277, 304,
312
Astacilla, 220
Astacillidae, 220
Astacura, 2533 definition,
312
Astacus, 264, 278,
283, 285, 291, 312
Asterocheres, 103
Asterocheridae, 76, 78, 82,
84, 103
Asterope, 59, 62,
67, 69

282,

64, 66,

Asteropidae, €9

Asthenognathinae, 315

Asthenognathus, 315

Asymmetrica, 106,
definition, 140

Atelecyclidae, 315

Atelecyclinae, 315

Atelecyclus, 315

Athanas, 265, 311

Atya, 311

Atyidae, 266, 268, 282,
304, 311

Atylidae, 241

Atylus, 241

Auditory setae, 19

Audouin, 3, 286, 324

Aurivillius, 107

Autotomy, in Amphipoda,
231; in Decapoda, 273

Axiidae, 313

Axius, 313

es

Baird, 30

Bairdia, 64, 69

Bairdiidae, 62, 63, 69

Balanidae, 115, 140

Balaninae, 111

Balanus, 107, 108, 111,
112, 122, 138, 140

Barnacle goose, 106

Barybrotes, 220

| Barybrotinae, 220

Basipodite, 7

Basis, 7

Bate, C. Spence, 183, 190,
225, 254

Batea, 241

Bateidae, 241

Bathynella, 162, 169

Bathynomus, 198, 199, 204,
211, 217, 218, 219

‘* Bauchwirbel” of Cope-
poda, $1

Belisarius, 83, 103

Belon, 254

Beneden, van, 72, 190

Benthesicymus, 311

Bentheuphausia, 245, 246,
248, 251, 252

Bentheuphausiinae, 252

Bernard, 5, 47

Beyrichia, 68

Birgus, 261, 262, 284, 303,
304, 313

Boas, 148, 171, 244, 254,
256, 259, 268, 274, 309

Bodotria, 188

Bodotriidae, 188

Boeck, 225

Bomolochidae, 103

Bomolochus, 103

Bonnier, J., 197, 214, 215,
i)

Bopyridae, 208, 221

Bopyrina, 212; definition,
221

Bopyroid stage of Isopoda,
215

Bopyrus, 221

Boreomysinae, 182

Boreomysis, 173, 175, 176,
178, 180, 182

Borradaile, 254, 277, 303,
309

Bosmina, 63

Bosminidae, 53

Bouvier, 254, 255, 256,
276, 283, 307, 308

Bovallius, 196, 225

Brachygnatha, 253 ; defini-
tion, 314

Brachyrhyncha, 253; de-
finition, 315

Brachyura, 253 ; definition,
314

Bract of Branchiopoda, 37,
39

Brady, 56, 68, 72

Brain, 16 S

Branchiae,“14 ; of Amphi-
poda, 231; of Cirripedia,
115; of Cumacea, 184,
186 ; of Decapoda, "O75 ;
of Euphausiacea, 246 ;. of
Isopoda, 204; of Mysi-
dacea, 175; of Ostra-
coda, 61, 64; of Sto-
matopoda, 323; of Syn-
carida, 165; of Tanai-
dacea, 191

Branchial formulae, 280

Branchial glands, 286

Branchinecta, 17, 30, 38,
53

Branchiopoda, 1 ; affinities
and classification, 51 ;|
definition, 29; develop-
ment, 48; habits, etc.,
50 ; historical notes, 29 ;
morphology, 31; palae- |
ontology, 50

Branchiostegite
poda, 255

Branchipodidae, 53

Branchipodites, 50

Branchipus, 10, 15, 18, 24,
29, 36, 40, 43, 45, 46, |
53

Branchiura, 1, 71, 100, |
101; definition, 104 ;|
development, 99; mor-

of Deca-

phology, 95

INDEX

335

Branchuropus, 207, 219

Bresilia, 311

Bresiliidae, 311

Brisson, 3

Brooks, 292, 295, 319

Bruntz, 116

Brush-like appendage of
Ostracoda, 62

Buccal frame of Brachyura,
257

Budde-Lund, 196

Bullar, J. F., 197

Burmeister, 91, 107, 147

Bythotrephes, 54

Cabirops, 221

Cabiropsidae, 221

Calanidae, 102

Calanus, 8, 12, 13, 73, 74,
88, 89, 102

Calappa, 314

Calappidae, 314

Calappinae, 314

Calceoli of Amphipoda, 237

Caligidae, 76, 91, 103

Caligus, 72, 83, 103

Callianassa, 256, 283, 301,
307, 313

Callianassidae, 313

Callianidea, 274, 313

Calliaxis, 301

Calliopiidae, 241

Calliopius, 241

Calocalanus, 75, 102

Calocaris, 301, 313

Calyptomera, 293; defini-
tion, 53

Calyptopis-stage
phausiacea, 249

Cambarus, 291, 312

Campecopea, 220

Campylaspis, 185, 186, 188

Cancer, 3, 254, 315

Cancerilla, 82, 103

Cancridae, 315

Cancrinae, 315

Cancrion, 215, 221

Candacia, 102

Candaciidae, 102

Canthocamptus, 103

Canu, 86, 101

Caphyra, 315

Caphyrinae, 315

of Eu-

Capitulum of Cirripedia,
109

Caprella, 224, 227, 233,
242

Caprellidae, 226, 231, 232,
233, 236, 242
Caprellidea, 224;

tion, 242

defini-

| Carapace, 6; of Branchio-
| poda, 31; of Branchiura,
95; of Cumacea, 184;

of Decapoda, 255; of
Euphausiacea, 242; of
Leptostraca, 151; of
Malacostraca, 144; of
Mysidacea, 171; of Os-
tracoda, 56; of Sto-

matopoda, 320 ; of Tanai-
dacea, 191
Carcinides, 315
Carcininae, 315
Carcinoplacinae, 315
Carcinoplax, 315
| Carcinus, 303, 305, 315
Cardisoma, 284, 315
Caridea, 253; definition,
311
Caridina, 266, 277, 311
Caridoid facies of Malaco-
straca, 144
Carina of Cirripedia, 110
Carino-lateral plates
Cirripedia, 111
Carpenter, 218
Carpiliinae, 315
Carpilius, 258, 315
Carpopodite, 146
Carpus, 146
Carupa, 315
Carupinae, 315
Cassidina, 204, 220
Castration, parasitic, 292
Catometopa, 290, 310
Catophragmus, 111, 140
Catoptrinae, 315
Catoptrus, 315
Caudal furea, 7,
Furea)
Caullery, M., 214
Cavolini, 254
Cement glands,
Cirripedia, 116
Centropages, 77, 102
Centropagidae, 83, 99, 102
Cephalic flexure of Deca-
poda, 257
Cephalogaster, 208
Cerataspinae, 278, 310
Cerataspis, 279, 280, 310
Ceratiocaris, 159, 160
Ceratocuma, 188
Ceratocumidae, 188
Ceratothoa, 220
Cercops, 232, 240, 242
Cervical groove of Deca-
poda, 256 ; of Syncarida,

of

35 (see

20)5 Vo

163 ; of Mysidacea, 171
Cervinia, 103
Cetochilus, 88

336

THE CRUSTACEA

Chaetilia, 220
Chaetiliidae, 220
Chalimus, 91
Chelipeds, 271
Chelura, 241
Cheluridae, 241
Chiridotea, 199, 202,
210, 220
Chirocephalus, 36, 39, 53
Chirostylus, 313
Chondracanthidae, 82, 92,
103
Chondracanthus, 86, 103
Choniostoma, 103
Choniostomatidae, 86, 93,
103
Chonopeltis, 104
Chthamalidae, 140
Chthamalinae, 111
Chthamalus, 112, 140
Chun, 19, 244
Chydorus, 53
Circulatory system, 15; of
Amphipoda, 234; of
Branchiopoda, 43; of
Branchiura, 98 ; of Cirri-
pedia, 115; of Copepoda,
82; of Cumacea, 187;
of Decapoda, 283; of
Euphausiacea, 247; of
Isopoda, 208 ; of Lepto-
straca, 156; of Mysi-
dacea, 177; of Ostracoda,
64; of Stomatopoda, 32;
of Synearida, 166; of
Tanaidacea, 193
Cirolana, 198, 199, 219
Cirolaninae, 198, 216, 219
Cirrhipédes, 107
Cirri of Cirripedia, 114
Cirripedia, 1; affinities and
classification, 138; defini-
tion, 106 ; development,
121) habitsysetess lava:
historical notes, 106;
palaeontology, 138
Cladocera, 1, 29, 40, 49;
definition, 53

208,

Cladocopa, 1, 56; defini-
tion, 69

Claspers, 11

Classification of Amphi-

poda, 239 ; of Branchio-
poda, 52; of Cirripedia,
138 ; of Copepoda, 101 ;
of Cumacea, 188; of De-
capoda, 309; of Euphau-
siacea, 251; of Isopoda,
218; of Leptostraca,
160; of Malacostraca,
147 ; of Mysidacea, 181;

of Ostracoda, 68; of
Stomatopoda, 330; of
Synearida, 168 ; of Tan-
aidacea, 194
Claus; 3; 75 10; 30536; 37;
ee Oe (25 Os Til.
79, 85, 88, 98, 101, 107,
146, 147, 151, 190, 191,
194, 2138, 225, 240, 244,
249, 254, 275, 292, 319,
322, 324
Clausia, 103
Clausidiidae, 103
Clausidium, 103
Clausiidae, 103
Clibanarius, 313
Clistosaccus, 130,
Clypeoniscus, 221
Clytemnestra, 103
Coelom, 16
Coenobita, 284, 288, 303,
304, 313
Coenobitidae, 259, 261, 313
Colomastigidae, 241
Colomastix, 241
Conmensalism of Decapoda,
304
Compartments
pedia, 111
Complemental males, 107,
118, 132
Oonchoderma,
117, 140
Conchoecia, 58, 60, 69
Conchoeciidae, 69
Conchostraca, 1, 29, 39,
49 ; definition, 53
Conilera, 210, 219
Copepoda, 1 ; affinities and
classification, 101; de-
finition, 71; habits, etc.,
99 ; historical, 71
Copepodid stages of Eu-
copepoda, 88

131, 141

of Cirri-

115, 116,

Copilia, 103

Copulatory appendages of
Branchiura, 97 ; of Cope-
poda, 81; of Decapoda,
274; of Euphausiacea,
247

Corallana, 219

Corallaninae, 219

Cornea, 18

Corneagen cells, 18

Coronida, 326, 331

Coroniderichthus, 326

Coronula, 112, 140

Corophiidae, 229, 235, 241

Corophiwm, 234, 241

Corycaeidae, 82, 83,
100, 103

84,

Corycaeus, 85, 103

Corystes, 315

Corystidae, 279, 315

Coutiére, 146, 267, 277,
283, 288, 291, 309

Coxa, 7

Coxal glands of Amphi-
poda, 235

Coxal plates of Isopoda,
198, 202; of Amphi-
poda, 226, 230

Coxopodite, 7

Crangon, 276, 287, 311

Crangonidae, 266, 268, 273,
311

Crangopsis, 181

Cressa, 241

Cressidae, 241

Crinoniscidae, 221

Crinoniscus, 221

Crista dentata, 269

Cruregens, 219

Crustacea, definition, 2

Cryptoniscan stage of Iso-
poda, 214

Cryptoniscina, 212 ; defini-
tion, 221

Cryptophialidae, 140

Cryptophialus, 107,
115, 139, 140

Crystalline body, 18

Ctenopoda, 29, 40; defini-
tion, 53

Cubaris, 220

Cuma, 183, 188

Cumacea, 2 ; affinities and
classification, 188 ; defi- -
nition, 183; develop-
ment, 187 ; habits, ete.,
187 ; historical notes,
183 ; morphology, 185,
187

Cuvier, 3, 107

Cyamidae, 226, 230, 231,
233, 242

Cyamus, 224,
232, 242

Cyathura, 211, 219

Cyclaspis, 188

Cyclestheria, 48, 50, 53

Cyclodorippe, 314

Cyclometopa, 310

Cyclopidae, 76,
100, 103

Oyclops, 11, 71, 72; 73, 76,
78, 79, 84, 86, 103

Cyclops-stages of Eucope-
poda, 88

Cyclosphaeroma, 218

Cylindroleberis, 69

Cyllopodidae, 241

114,

230, 231,

79,1830

Cyllopus, 241
Cymodoce, 220
Cymopolia, 315
Cymothoa, 220

Cymothoidae, 199, 203,
204, 208, 209, 216, 219

Cymothoinae, 212, - 213,
220

Cyprididae, 57, 60,
63, 64, 67, 69
Cypridina, 58, 59, 61, 62,
63, 65, 68, 69

Cypridinidae, 57, 59, 61,
64, 65, 66, 67, 69

Cypridopsidae, 69

Cypridopsis, 69

Cypris, 18, 57, 67, 69

Cypris-stage, of Ascotho-
racica, 127; of Cirri-
pedes, 24, 107, 121;
of Rhizocephala, 133

Cyproniscidae, 221

Cyproniscus, 221

Cyrtopia-stage of Euphau-
siacea, 249

Cystisoma, 241

Cystisomatidae, 241

Cythere, 68, 69

Cythereis, 57, 61, 69

Oytherella, 58, 59, 60, 62,
69

Cytherellidae, 67, 69

Cytheridae, 57, 58, 61 62,
66, 67, 69

Ozerniavsky, 181

62,

Dactylerythrops, 172, 181

Dactylopodite, 146

Dactylus, 146

Dajidae, 221

Dajus, 221

Dana, 72, 190, 224, 244,
249

Danalia, 221

Daphnia, 20, 29, 33, 40, |

53
Daphniidae, 53
Dart of Rhizocephala, 135
Darwin, 107, 108, 111,
TG, daly; 1185123;
128, 129, 139
Darwinula, 58, 67, 69
Darwinulidae, 62, 69
Decapoda, 2, 143 ; affinities
and classification, 309 ;
definition, 253 ; develop-
ment, 292; habits, etc.,
303; historical
254; morphology, 255 ;
palaeontology, 306
Deckenia, 315

notes, |

INDEX

337

Deckeniinae, 315

De Geer, 72

Delage, 107, 132, 133, 135,
197, 225

Della Valle, A., 225

Dendrobranchiate, 277

Dendrogaster, 125,
127, 128, 140

Dendrogastridae, 140

Dermal glands, 20 (see |
Glands)

Desinosoma, 219

Deuterocerebrum, 17

Development of Amphi- |
poda, 237; of Ascotho- |
racica, 127 ; of Branchio- |
poda, 48 ; of Branchiura,
99 ; of Cirripedia, 121 ; |

126, |

of Cumacea, 187; of
Decapoda, 292 ; of|
Eucopepoda, 87 ; of)
Kuphausiacea, 249 ; of

Isopoda, 213 ; of Lepto-
straca, 158 ; of Ostra-
coda, 67 ; of Mysidacea,
179; of Rhizocephala, |
133 ; of Stomatopoda, |
326; of Tanaidacea, |
194
Dexamine, 241

| Dexaminidae, 241
Diaizis, 102 |
| Diaptomus, 102

Diastylidae, 188

Diastylis, 184, 185, 186,
188

Diastyloides, 185, 188

Dichelaspis, 110, 140

Dichelestiidae, 83, 103

Dichelestium, 103

Digestive gland, 15

Dimorphism, sexual,
in Decapoda, 291 ;
Tanaidacea, 194

Diosaccus, 103

Diporodelphya, 86

Doflein, 19

Dohrn, 123, 183

Dolops, 95, 104

Dorippe, 314

Dorippidae, 290, 314

Doropygus, 75, 103

Dorsal organ of Amphipoda,
237; of Branchiopoda, |
43 ; of Isopoda, 213; of
Mysidacea, 180 ; of Syn-
carida, 164; of Tanai- |
dacea, 194

Dromia, 283, 314

Dromiacea, 253 ; definition,
314

el

21 ;
in

Dromiidae, 256, 289, 290,
308, 314

Dromiidea, 253 ; definition,
314

Dromiopsis, 308

| Duplorbis, 130, 131, 133,

141
Duvernoy, 324
Dwarf males of Cirripedia,
aa l/
Dynamene, 220
Dynomene, 314
Dynomenidae, 308, 314

Ebalia, 314

EKectinosoma, 103

Edriophthalma, 3, 147

Edwards (see Milne-
Edwards)

Kiconaxius, 277, 305, 313

Ekman, 36

Hlaphocaris, 297

Eiminius, 111, 140

Embryology, 22

Endites, 37

Endophragmal system, 263

Endopodite, 7

Endoskeleton of Branchio-
poda, 44

Endostome of Brachyura,
257

End-saec, 16

Enterognathus, 90, 95, 103

Entomostraca, 3, 27

Entoniscidae, 208, 217, 221

Entoniscus, 221

Entosternite of Branchio-

- poda, 44; of Decapoda,
263

Ephippium of Cladocera, 48

Epicarid stage of Isopoda,
214

Epicaridea,
tion, 220

Epimeral suture, 256

Epimeron, 4 (footnote)

Epipodite, 8 ; of Cumacea,
186 ; of Decapoda, 275 :
of Euphausiacea, 246 ; of
Isopoda, 199 ; of Lepto-
straca, 154; of Malaco-
straca,"146; of Mysi-
dacea, ‘175; of Sto-
matopoda, 322; of Syn-
carida, 165; of Tanai-
dacea, 192

Epistome of Decapoda, 257

Ergasilidae, 103

Ergasilus, 103

Erichthina, 296

Erichthus, 326, 330

196; detini-

22

iss)
LoS)
[oe)

Eviphia, 315
Eriphiinae, 315
Eryma, 307

Eryon, 307, 312
Eryonidae, 288, 312

Eryonidea, 253, 304; de-

finition, 312

Hrythrops, 181

Estheria, 16, 32, 38, 40,
49, 50, 53

Kthusa, 314

Etisinae, 315

Htisus, 315

EHucalanus, 79, 82, 83, 85, |

102

_ Eucarida, 2, 143; defini-
tion, 149

Huchaeta, 102

Euchaetomera, 176, 181

Eucopepoda, 1, 71 ; defini-

tion, 102 ; development, |

73 5 |

87; morphology,
parasitic, 89

Eucopia, 181

Eucopiidae, 1738, 174, 175,
176, 181

Kudorella, 188

Eukyphotes, 259

Eumalacostraca,
definition, 148

EKumedoninae, 316

Eumedonus, 316

Eupagurinae, 313

Hupagurus, 286, 302, 313

Huphausia, 244, 248, 251,
252

Kuphausiacea, 2, 143;
athnities and classitica-
tion, 251; definition,
244 ; development, 249;
habits, ete., 251; his-
torical notes, 244 ; mor-
phology, 244

Huphausiidae, 252

Euphausiinae, 252

Hurycercus, 53

Eurycope, 219

Hurydice, 219

Kurydicinae, 219

Husiridae, 241

Husirus, 241

Huthemisto, 241

EHwvadne, 54

Kxcorallana, 219

Excorallaninae, 219

Excretory system, 16; of
Amphipoda, 235; ° of
Branchiopoda, 435; of
Branchiura, 98 ; of Cirri-
pedia, 116 ; of Copepoda,
83; of Cumacea, 187 ;

1, 148;

THE CRUSTACEA

of Decapoda, 285 ;
Euphausiacea, 247 ;
Isopoda, 210 ; of Lepto-
straca, 156; of Mysi-
dacea, 178 ; of Ostracoda,
64; of Stomatopoda,
325 ; of Synearida, 166 ;
| of Tanaidacea, 193

| Exites, 37

Exopodite, 7

Exoskeleton, 4

| Eyes, 17; of Amphipoda,
| 236; of Branchiopoda,
46; of Branchiura, 98 ;
of Cirripedia, 117; of
Cumacea, 184 ; of Deca-
poda, 287; of Eucope-
poda, 84; of Euphausi-
acea, 248; of Isopoda,
211; of Mysidacea, 178;

Fabricius, J. C., 254

Fabricius, O., 151

Facial region of Brachyura,
258

Faxon, 254, 255, 291

Filamentary appendages of
Cirripedia, 115

Fischer, 30

Flabellifera, 196; defini-
tion, 219
Flabellum of Branchio-

poda, 59

Flagellum of Branchiura, 96

Fossil Crustacea, 25 (see
Palaeontology)

Fowler, 107

Fracture-plane in Caprel-
lidae, 231 ; in Decapoda,
273

Frena, ovigerous, of Cirri-
pedia, 115

Fritsch, A., 167

Frontal appendages
Branchiopoda, 36

Frontal band of Copepoda,
91

Frontal filaments of Cirri-
pedia, 123

Frontal organs of Branchio-
poda, 46; of Copepoda,
85 ; of Decapoda, 292 ;

Frontal plate of Brachyura,
257

Frontal tentacle of Ostra-
coda, 66

of

of
of

| of Ostracoda, 665 of
Stomatopoda, 325; of
Synearida, 166

Hye-stalks (see Ocular
peduncles)

Glands,

Furea, 7; of Branchio-
poda, 35; of Cirripedia,
113 ; of Copepoda, 75 ;
of Leptostraca, 152 ;
of Ostracoda, 58

| Furcilia-stage of Euphau-

siacea, 249

Galathea, 313

Galatheidae, 313

Galatheidea, 253; defini-
tion, 313

Galatheinae, 313

Gammaridae, 231, 235, 241

Gammaridea, 224; defini-
tion, 240

Gammarina, 224

Gammarus, 225, 235, 238,
239, 241

Gampsonyx, 167, 168

Gasocaris, 168

Gastric mill, 14

Gastrolith, 282

Gastrosaccinae, 182

Gastrosaccus, 172, 182

Gebia, 313

Gecarcinidae, 304, 315

Gecurcinus, 315

Gelasimus, 263, 315

Genital valves of
poda, 81

Gerstaecker, 190, 225

Giard; A., 197,, 21145205;
292

Giesbrecht, W., 72, 73, 76,
79, 85, 86, 90, 101, 102

Gigantocypris, 57, 67, 69

Gills (see Branchiae)

Gland, antennal, 16

Gland, maxillary, 16

20; of Amphi-

poda, 235 ; of Branchio-

poda, 43; of Branchi-

ura, 98; of Cirripedia,

116; of Copepoda, 83 ;

of Ostracoda, 64; of

Tanaidacea, 193

Cope-

Glyphaeidae, 307

Glyphocrangon, 311
Glyphocrangonidae, 311

| Glyptonotus, 220

Gnathia, 200, 208, 218,
219

Gnathiidae, 197, 204, 205,
219

Gnathobase, 8, 39

Gnathophausia, 172, 173,
174, 175, 176, 178, 180
181

Gnathophyllidae, 311

Gnathophyllum, 311

INDEX

339

Gnathopod, 146 ;
Amphipoda, 230;
Mysidacea, 174

Gnathostomata, 101

Gonads, 21

Gonerichthus, 326, 328

Gonodactylus, 321, 328,
331

Gonoplacidae, 315

Gonoplacinae, 315

Gonoplax, 315

Goodsir, H., 183

Grapsidae, 304, 315

Grapsinae, 315

Grapsus, 315

Green gland, 16

Grobben, 84,
319

Groom, 107

Gruvel, 107

Gurney, R., 211

Gyge, 203, 221

Gymnomera, 29, 40; de-
finition, 54

Gymnoplea, 71; definition,
102

of |
of

147, 162,

Haan, W. de, 254

Habits, etc., of Amphipoda,
238; of Branchiopoda,
50; of Cirripedia, 137 ;
of Copepoda, 99; of |
Cumacea, 187 ; of Deca-
poda, 303 ; of Euphan-
siacea, 251 ; of Isopoda,
216; of Leptostraca,
159; of Mysidacea, 180 ;

of Ostracoda, 67 ; of
Stomatopoda, 329 ; of |
Syncarida, 167 ; of

Tanaidacea, 194
Haemocera, 93, 103
Haemocoel, 15
Halocypridae, 57, 60, 61,

62, 66, 67, 69
Halocypris, 63, 69
Hansen, 7, 72, 78, 79,

107, 129, 130, 145, 146,

148, 152, 154, 156, 171,

173, 174, 183, 191, 197,

198, 218, 225, 229, 240,

266, 276, 288, 319, 326,

328
Hansenomysis, 178, 181
Hapalocarcinidae, 305, 315 |
Hapalocarcinus, 315
Hapalogaster, 313
Hapalogastrinae, 313
Haplophthalmus, 220
Haplopoda, 29; defini- |

tion, 54

Harpacticidae, 75, 76, 78,
79, 81, 83, 87, 99, 103
Harpacticus, 103
Hatschek, 27
Haustoriidae, 241
Haustovius, 241
Head-region of Crustacea, 4
Heart, 15 (see Circulatory
system)
Heider, 22
Helleria, 220
Hemioniscidae, 211, 221
Hemioniscus, 208, 212, 221
Henderson, 254
Hepatic caeca (see Ali-
mentary system)
Hepato-pancreas, 15
Herbst, J. F. W., 254
Hermaphroditism, 21; in
Cirripedia, 117 ; in Deca-
poda, 292; in Isopoda,
212
Herpyllobiidae, 82, 93, 104
Herpyllobius, 104
Heterarthrandria, 71, 76;
definition, 102
Heterocarpus, 259,
311
Heterocope, 86, 102
Heteromysinae, 181
Heteromysis, 175, 181
Heterorhabdus, 102
Heterotanais, 193, 195
Hexapodinae, 315
Hexapus, 315
Hippa, 314
Hippidae, 314
Hippidea, 2535 ; definition,
313
Hippolyte, 266, 287, 311
Hippolytidae, 311

288,

Historical notes, 2; on
Amphipoda, 224; on
Branchiopoda, 29; on
Cirripedia, 106; on
Copepoda, 71; on Cu-

macea, 183; on Deca-
poda, 254; on Euphau-
siacea, 244 ; on Isopoda,
196; on Leptostraca,
151; on Mysidacea,
171; on Ostracoda, 56 ;
on Stomatopoda, 319;
on Syncarida, 162; on
Tanaidacea, 190
Hoek, 107, 116
Holognathidae, 220
Holognathus, 220
Holopediidae, 53
Holopedium, 53

| Holt, 178, 181, 248

| Ingolfiella, 225,

Homarus, 282, 291, 299,
300, 312

Homola, 314

Homolidae, 256, 308, 314

Homolidea, 253; defini-
tion, 314

Homolodromia, 314

Homolodromiidae, 278,

304, 307, 314
Homolopsis, 308
Hoploearida, 2, 143; de-

finition, 149 (see Sto-

matopoda)
Hoploparia, 307
Hoplophoridae, 268, 288,

304, 311
Hoplophorus, 311
Huxley, 42, 148,

255, 256, 319
Hyalella, 239, 241
Hyas, 316
Hymenocaris, 159
Hymenocera, 265, 311
Hymenocerinae, 311
Hymenosoma, 316
Hymenosomidae, 316
Hyperia, 230, 241
Hyperiidae, 241
Hyperiidea, 224 ;

tion, 241
Hyperina, 224
Hyperiopsidae, 241
Hyperiopsis, 241
Hypodermic impregnation

in Isopoda, 213
Hypostoma, 7

180,

defini

Tbacus, 312

Ibla, 116, 119, 120, 140

Iconaxiopsis, 260, 313

Idotea, 202,, 205,
220

Idoteidae, 202, 208, 220

209,

| Idya, 103

Ilia, 314
Iliinae, 314

| Ilyocryptus, 53

Inachinae, 316

Inachus, 316

226, 231,
233, 240, 242

Ingolfiellidae, 242

Ingolfiellidea, 224 ;
nition, 242

Ingolfiellina, 225

Tsaea, 241

Isaeidae, 241

Ischiopodite, 146

Ischium, 146

Isokerandria, 71, 102% de-
finition, 103

defi-

222

THE CRUSTACEA

340
Isopoda, 2, 143 ; aber-
rantia, 190 ; aflinities

and classification, 218 ;
definition, 196 ; develop-
ment, 213: habits, etc.,
216 ; historical notes,
196 ; morphology, 198 ;
palaeontology, 218

Jaera, 193, 202,
Janira, 208, 219
Jassa, 241
Jassidae, 235, 241
Jaxea, 301, 313
Jordan, H., 167
Jurine, 30, 72

213, 219

Kaempferia, 306

Kentrogon-stage of Rhizo-
cephala, 135

Kishinonye, 292

Knipowitsch, 107

Kochlorine, 140

Kochlorinidae, 140

Koehler, 117

Koleolepas, 139, 140

Koonunga, 25, 147, 162-
167, 169

Koonungidae, 169

Korschelt, 22

Kowalevsky, 325

Kvrithe, 64, 69

Krohn, 107

Kroyer, H., 72, 183, 224

Labrum, 7; of Cirripedia,
114; of Copepoda, 78 ;
of Ostracoda, 59

Lacaze-Duthiers, 107

Laemodipoda, 224

Lafystiidae, 241

Lafystius, 241

Lagena of MRhizocephala,
131

Lamarck, 3, 72, 107

Lambrus, 316

Lampropidae, 188

Lamprops, 185, 188

Lanceola, 241

Lanceolidae, 241

Lankester, 4, 9, 30, 40,
42, 43, 45

Laomedia, 313

Laomediidae, 313

Laophonte, 103

Laphystiopsidae, 241

Laphystiopsis, 241

Lateral plates of Cirripedia,
110

Latona,

?

36, 53

Latreille, 3, 27, 29, 30, 52,
W475 7 Ly 1905 196s 2247
254, 309, 319

Latreillia, 314

Latreilliidae, 314

Latreutes, 311

Laura, Y07,
127, 140

Lauridae, 140

Leach, 3; 147, 151,
196

Leander, 311

Leeuwenhoek, 71, 72

Lepadidae, 140

Bepasnd, UOts) LOS allo;
Ha TG, tly, Wei. ae
125, 188, 140

Lepechin, 183

Leperditia, 68

Lepidurus, 9, 12, 31, 53

Leptochelia, 193, 194, 195

Leptodora, 33, 34, 36, 40,
2, 43, 45, 49, 50, 54

Leptomysinae, 181

Leptomysis, 181

Leptostraca, 1, 145; affini-
ties and classification,
160; definition, 148,
151 ; development, 158 ;
magus etce., 159; his-
torical motes; Lol:
morphology, 151; palae-
ontology, 159

Lernaea, 3, 72,
103

Lernaeidae, 91, 103

Lernaeocera, 81, 100, 103

Lernaeodiscus, 131, 141

Lernaeopoda, 103

Lernaeopodidae, 80, 90, 92,
103

Lernanthropus, 15, 83,103

Leucifer, 273, 275, 287-
291, 295, 296; 298, 311

Leuciferinae, 311

Leucon, 188

Leuconidae, 185, 188

Leucosia, 314

Leucosiidae, 279, 314

Leucosiinae, 314

Leucothoe, 231, 241

Leucothoidae, 241

Leydig, 30, 46

Lichomolgidae, 103

Lichomolgus, 103

Ligia, 208, 209, 213, 220

125;

91, 92,

Ligidium, 210, 220
Ligiidae, 205, 206, 212,
220

Lilljeborg, 31, 107, 188
Lilljeborgia, 241

Lilljeborgiidae, 241
Limbs, general morphology,
i
Limnadia, 44, 53
Limnadiidae, 53
Limnetis, 35, 40, 49, 53
Limnocaridina, 277, 311
Limnoria, 220
Limnoriinae, 220
Linea \ anomurica,
dromiidica, 256 ;
Boe 256 ;
256
Linnaeus, 2, 72
Linuparus, 307, 312
Lipomerism, 4
Liriopsidae, 211,
Liriopsis, 221
Lister, J. J., 328
Lithodes, 313
Lithodidae, 261, 273, 275,
313
Lithodinae, 313
Lithotrya, 138, 140
Liver, 15 (see Alimentary
systein )
Longipedia, 103
Lophogaster, 181
Lophogastridae,
175, 176, 181
Loricula, 109, 110, 188
Lower lip, 7; of Amphi-
poda, 229 ; of Branchio-
poda, 36; of Copepoda,
78; of Ostracoda, 59 ;
of Tanaidacea, 191
Lucicutia, 102
Lucifer, 311
Luminous organs, 21; of
Copepoda, 83; of Deca-
poda, 288; of Euphau-
siacea, 248; of Mysi-
dacea, 174; of Ostracoda,
64
Liitken, 72
Lynceidae, 42, 44, 53
Lynceus, 53
Lyncodaphniidae, 42, 53
Lysianassa, 240
Lysianassidae, 237, 240
Lysioerichthus, 326
Lystosquilla, 326, 331

250s
homo-
thalassinica,

217, 221

173; eae

Macrocheira, 257, 258, 306,
316

Macrocypris, 60, 61, 63

Macromysis, 181

Macrophthalminae, 315

Macrophthalmus, 263, 264,
315

Macropodia, 316

INDEX

Macrothrix, 53

Macrura, 309, 310

Maia, 316

Maiidae, 316

Maiinae, 316

Malacostraca, 1, 3; classi- |
fication, 147 ; definition,
143 ; morphology, 144 |

Malaquin, 93

Males of Cirripedia, 118

Mamaia, 316

Mandible, 12; of Amphi-
poda, 229 ; of Branchio-
poda, 36; of Branchiura,
95; of Cirripedia, 114 ;
of Copepoda, 78 ; of Cu-
macea, 185; of Decapoda,
266; of Euphausiacea,
245; of Isopoda, 198 ;
of Leptostraca, 152; of
Malacostraca, 145; of
Mysidacea, 173 ; of Ostra-
coda, 59; of Stomato-
poda, 321; of Syncarida,
164 ; of Tanaidacea, 191

Mantle, 6; of Cirripedia,
108; of Rhizocephala, |
130

Masticatory stomach, 14

Mastigobranchia, 276

Mastigopus, 297

Matuta, 314

Matutinae, 314

Maxilla, 12 ; of Amphipoda,
229; of Branchiopoda,
36; of Branchiura, 95 ;
of Cirripedia, 114; of
Copepoda, 79; of Cu-|
macea, 185; of Decapoda,
266; of Euphausiacea,
246; of Isopoda, 198 ;
of Leptostraca, 153 ; of

|
|
|

Malacostraca, 145; of
Mysidacea, 173; of
Ostracoda, 61; of Sto-

matopoda, 322; of Syn-
cavida, 164; of Tanai-
dacea, 191

Maxillary gland, 16; of
Branchiopoda, 43; of
Branchiura, 98; of Cirri-
pedia, 116 ; of Copepoda,
83; of Cumacea, 187 ;}
of Leptostraca, 157; of |
Isopoda, 210; of Sto-
matopoda, 325 ; of Syn-
carida, 166; of Tanai-
dacea, 193

Maxilliped, 13 ; of Amphi-

poda, 229 ; of Branchiura,

96; of Copepoda, 79; of |

Cumacea, 186 ; of Deca-
poda, 268; of Isopoda,
198; of Malacostraca,
146 ; of Ostracoda, 61 ;
of Tanaidacea, 192
Maxillula, 12; of Amphi-
poda, 229 ; of Branchio-
poda, 36; of Branchiura,
95; of Cirripedia, 114 ;
of Copepoda, 78; of
Cumacea, 185 ; of Deca-
poda, 266; of Euphau-
siacea, 245 ; of Isopoda,
198; of Leptostraca,
153; of Malacostraca,
145 ; of Mysidacea, 173 ;

of Ostracoda, 61; of
Stomatopoda, 321; of
Synearida, 164; of

Tanaidacea, 191
Mayer, P., 225
Median eye, 17
Megalopa, 303
Meganyctiphanes, 245, 246,
247, 252
Meinert, F., 196
Meinertia, 220

| Melia, 305
| Melita, 233, 241

Melphidippa, 241
Melphidippidae, 241
Menippe, 315

Menippinae, 315
Meropodite, 146

Merus, 146

Mesenteron, 14

Mesentery of Rhizocephala,
sien

Metamorphosis, 23

Metanauplius, 24; of
Branchiopoda, 48; of
Decapoda, 292, 295; of
Eucopepoda, 88; _ of
Euphausiacea, 249; of

Stomatopoda, 328
Metastoma, 7 (see Lower
lip)
Metazoea, 301, 302
Metopa, 241
Metopidae, 241
Metridia, 102

Metschnikoff, 151, 244, 249 |

Meyer, H. von, 167

Microniscus, 214

Miers, 254

Milne-Edwards,
255

Milne-Edwards, H., 3, 9,
BONDH 12, la, Lol, Lied
183, 190, 224, 244, 254,
255, 286, 309, 319

A.,

- |
254,

341

| Mimonectes, 226, 241

Mimonectidae, 241

Miracia, 84, 103

Misophria, 82, 103

Misophriidae, 103

Mithrax, 316

| Moina, 53

Monoculus, 3, 72

Monolistra, 220

Monoporodelphya, 86

Monospilus, 33, 53

Monstrilla, 103

Monstrillidae, 93, 103

Montagu, 183, 190

Miiller, F., 107, 132, 190,
193, 194, 254, 292, 319

Miiller, G. W., 56, 59, 61,
62, 67, 68

Miiller, O. F., 29, 56, 72

Munida, 260, 313

Munidopsinae, 313

Munidopsis, 313

Munna, 211, 219

Munnopsis, 203, 219

Muscular system of Bran-
chiopoda, 44; of Cirri-
pedia, 116; of Lepto-
straca, 157

Myctirinae, 315

Myctiris, 315

Myodocopa, 1, 56; defini-
tion, 68

Mysidacea,
ties and
181; definition,
development, 179;
habits, ete., 180; his-
torical notes, 171 ; mor-
phology, 171; palaeon-
tology, 180

Mysidae, 173, 174,
Wife liosiion de

2, 143; affini-
classification,

iyjab 2

176,

| Mysidella, 181

Mysidellinae, 181

Mysidetes, 181

Mysidetinae, 181

| Mysiens, 244

| Mysinae, 181

| Mysis, 20, 172-178, 180,
181

| Mysis-stage of Decapoda,

294

“ Nackenorgan” of Clado-
cera, 46

Nannastacidae, 187, 188

Nannastacus, 185, 188

Nannoniscus, 219

Natantia, 253; definition,
310

| Nauplius, 11, 23, 25, 26,

Go
ae
i)

72; of Apoda, 129; of
Ascothoracica, 127; of
Branchiopoda, 48; of
Cirripedia, 107, 121;
of Decapoda, 292; of
Eucopepoda, 87 ; of Eu-
phausiacea, 249; of Os-
tracoda, 67; of Rhizo-
cephala, 133
Nauplius-eye, 17 ; of Bran-
chiopoda, 46; of Cope-
poda, 84; of Decapoda,
287; of Euphausiacea,
248 ; of Ostracoda, 66
Nautilograpsus, 315
Nebalia, 30, 147, 151, 152,
154, 156, 159, 160, 161
Nebaliacea, 1, 143, 151,
161
Webaliella, 153, 154, 155,
161
Nebaliidae, 161
Nebaliopsis, 158, 154, 155,
156, 159, 160, 161
Neck gland of Branchio-
poda, 43
Nematobrachion, 247, 252
Nematocarcinidae, 311
Nematocarcinus, 311
Nematoscelinae, 252
Nematoscelis, 246,
248, 251, 252
WNeolithodes, 262, 313
Nephrops, 256, 258, 300,
312
Nephropsidae, 312
Nephropsidea, 253 ; defini-
tion, 312
Nephropsis, 270, 312
Neptunus, 269
Nereicola, 103
Nereicolidae, 103
Nerocila, 206, 220

247,

Nervous system, 16; of
Amphipoda, 236; of
Branchiopoda, 44; of

Branchiura, 98 ; of Cirri-
pedia, 117 ; of Copepoda,
83; of Cumacea, 187 ;
of Decapoda, 286; of
Euphausiacea, 247; of
Isopoda, 210 ; of Lepto-
straca, 158; of Mysi-
dacea, 178 ; of Ostracoda,
65 ; of Tanaidacea, 193

Nettovich, 98

Nicothoé, 103

Nicothoidae, 103

Nika, 311

Niphargus, 239, 241

Nordmann, von, 72

THE CROSTACEA

Norman, 56, 68, 107, 181,
183

Notodelphys, 89, 103

Notophryxus, 221

Notopterophorus, 75, 103

Notostraca, 1, 29, 37, 48;
definition, 53

Nucleus of Sacculina, 136

Nussbaum, 116

Nyctiphanes, 251, 252

Octomeris, 111, 140

Ocular peduncles, 9; of
Branchiopoda, 46; of
Decapoda, 263; of Iso-
poda, 211; of Lepto-
straca, 158; of Mysi-
dacea, 172 ; of Stomato-
poda, 325 ; of Syncarida,
166 ; of Tanaidacea, 191

Ocypoda, 263, 264, 305,
307, 315

Ocypodidae, 315

Ocypodinae, 315

Oediceros, 241

Oedicerotidae,
241

Oithona, 103

Oken, 72, 107

Olfactory filaments, 20 ; of
Copepoda, 85

Ommatidia, 18

Oncaea, 103

Oncaeidae, 83, 103

Oniscidae, 210, 220

Oniscinae, 220

Oniscoidea, 196 ; definition,
220

Oniscus, 3, 213, 220

Onychopoda, 29;
tion, 54

Oostegites, 146; of Amphi-
poda, 232; of Cumacea,
186; of Isopoda, 203 ;
of Mysidacea, 176; of
Tanaidacea, 191

Oostegopod, 41

Operculata, 106, 110; de-

226, 236,

defini-

finition, 140
Operculum of Cirripedia,
110

Orbit of Decapoda, 257

Orchestia, 237, 241

Orchestiidae, 241

Orithya, 314

Orithyinae, 314

Ortmann, 181, 254, 309

Ostracoda, 1 ; affinities and
classification, 68; defini-
tion, 56; development,
673; habits, ete), 67;

56; mor-
56; palaeon-

historical,
phology,
tology, 68
Otocyst, 19 (see Statocyst)
Otolith, 19
Oviduet, 21
Oxycephalidae, 237, 241
Oxycephalus, 241
Oxyrhyncha, 253; defini-
tion, 315
Oxystomata, 253; defini-
tion, 314
Oxyuropoda, 218
Oziinae, 315
Ozius, 315

Packard, 151, 162, 167

Paguridae, 259, 277, 283,
285, 289, 304, 313

Paguridea, 253; definition,
313

Pagurinae, 313

Paguristes, 282,

Pagurus, 313

Palaega, 218

Palaeinachus, 308

Palaemon, 278, 311

Palaemonetes, 266,
311

Palaemonidae, 304, 311

Palaemoninae, 311

Palaeocaris, 168

Palaeocorystes, 218

Palaecogammarus, 239

Palaeontology of Amphi-
poda, 239; of Branchio-
poda, 50; of Cirripedia,
138 ; of Decapoda, 306 ;
of Isopoda, 218; of Lep-
tostraca, 159; of Mysi-
dacea, 180; of Ostra-
coda, 68; of Stomato-
poda, 330; of Synearida,
167

Palate of Brachyura, 257

Palicidae, 315

Palicus, 315

Palinura, 253 ; definition,
312

Palinurellus, 312

Palinuridae, 266, 305, 312

Palinurus, 285, 500, 301,
312

Palp, 9

Pancreatic glands of Cirri-
pedia, 115

Pandalidae, 288, 311

Pandalina, 277, 311

Pandalinae, 311

Pandalus, 267, 277, 287,
311

283

298,

Paracalanus, 102
Paracrangon, 273, 311
Paracyamus, 227, 242
Paradoxostoma, 60, 64, 69
Paradoxostomatidae, 69
Paragnatha, 7 (see Lower |
lip)
Paralamprops, 185, 188
Paramphithoe, 241
Paramphithoidae, 241
Paranaspides, 170
Paranebalia, 152, 153, 155,
161
Paranephrops, 312
Paranthura, 208, 219
Parapagurus, 306, 313
Paraphronima, 241
Paraphronimidae, 241
Parapontella, 102
Parasellidae, 205, 206, 219
Parasitic castration, 292
Parasitism of Amphipoda,
239 ; of Decapoda, 304 ;
of Cirripedia, 138; of
Copepoda, 100; of Iso-
poda, 216
Parastavidae, 25
276, 277, 278,
Parastacus, 312
Pardalisca, 241
Pardaliscidae, 241
Paries of Cirripedia, 111
Parthenope, 316
Parthenopidae, 316

ts. 20
304, 312

| Phaénna, 102

Parthenopinae, 316

Pasiphaea, 311

Pasiphaeidae, 268, 311

Peduncele, ocular, 9

Peduncle of Cirripedia, 108

Pedunculata, 106, 109;
definition, 140

Pelseneer, 45

Peltidiuim, 103

Peltogaster, 131, 133, 137,
141

Penaeidae, 266, 288, 290,
292, 305, 310

Penaeidea, 253 ; definition,
310

Penaeinae, 311

Penaeus, 266, 267, 275,

276, 278, 293, 294, 307,
311

Penilia, 53

Penis of Decapoda, 289 ;
of Cirripedia, 118; of
Tsopoda, 212

Pennant, 3

Pennatula, 72

Pennella, 100, 101, 103

Pentacheles, 271, 312

INDEX

| Peracarida, 2, 143 ; defini-

tion, 149

Peraeopods, 146; of Am-
phipoda, 230 ; of Deca-
poda, 269

Pereionotus, 226, 241

Pericera, 316

Perisomatie cavity of Sac-
eulina, 136

Petalophthalmidae, 176,
181

Petalophthalmus, 173, 174,
181

Petasma, 274

Petrarca, 125, 126,
140

Petrarcidae, 140

Petrolisthes, 313

127,

Philomedes, 57, 60, 66, 69

Phliantidae, 241

Phlias, 241

Phoreorrhaphidae, 241

Phorcorrhaphis, 241

Phosphorescence (see Lumi-
nous organs)

Photospheres of Euphausi-
acea, 248

Photidae, 235, 241

Photis, 241

Phoxocephalidae, 241

Phoxocephalus, 241

Phreatoicidae, 198, 204, |
219
Phreatoicidea, 196, 216; |

definition, 219
Phreatoicoides, 219 |
Phreatoicopsis, 219
Phreatoicus, 197, 219
Phronima, 228, 233, 234, |

236, 239, 241
Phronimidae, 236, 241
Phronimopsis, 241
Phrosina, 241
Phrosinidae, 241
Phryzus, 221
Phtisica, 227,

242
Phyllobranchiate, 277
Phyllocarida, 1, 145, 151
Phyllopoda, 52
Phyllosoma, 300, 301
Phylogeny, 25
Pinnotherelia, 315
Pinnothereliinae, 315
Pinnotheres, 315
Pinnotheridae, 2738, 305,

315
Pinnotherinae, 315
Pirimela, 315
Pirimelinae, 315

231, 240,

Pisa, 316
Pisinae, 316
Plagusia, 315
Plagusiinae, 315
Plakarthriinae, 220
Plakarthriuvm, 203, 220
Planes, 304, 315
Platophium, 241
Platyaspidae, 188
Platyaspis, 185, 188
Platyeopa, 1, 56; defini-
tion, 69
Platycuma, 187, 188
Platycyamus, 230, 242

| Platyscelidae, 238, 241

Platyscelus, 241

| Pleopods, 146 ; of Amphi-

poda, 232 ; of Cumacea,
187 ; of Decapoda, 273 ;
of Euphausiacea, 247 ;
of Isopoda, 204 ; of Lep-
tostraca, 156, 157; of
Mysidacea, 176 ; of Sto-
matopoda, 323 ; of Syn-
earida, 165; of Tanai-
dacea, 191

Pleural plates of Isopoda,
202

Pleurobranchia, 14, 275

Pleuromanuna, 85, 86, 102

Pleuron, 4

Pleuropodite, 146

Pleuroxus, 42, 53

Pleustes, 241

Pleustidae, 241

Podascon, 221

Podasconidae, 221

| Podobranchia, 14, 275
| Podoceridae, 241

Podocerus, 241

Podocopa, 1, 56 ; definition,
69

Podon, 54

| Podophthalma, 3, 147

Podophthalminae, 315
Podophthalmus, 263, 264,
315
Podoplea,
103
Poison spine of Argulus, 97
Pollicipes, 110, 115, 116,

117, 138, 140
Polyartemia,

39, 42, 47, 51, 52, 53
Polyartemiidae, 53
Polycheles, 288, 312
Polycheria, 231, 241
Polycope, 59, 60, 69
Polycopidae, 60, 69
Polycopsis, 60, 69
Polyphemidae, 45, 54

71; ‘definition,

aes

5

344

THE CROSPACEA

Polyphemus, 54
Pontella, 79, 102
Pontellidae, 84, 102
Pontocypris, 58, 67, 69
Pontogeneia, 241
Pontogeneiidae, 241
Pontonia, 311
Pontoniinae, 305, 311
Porcellana, 302, 303, 313
Porcellanidae, 313
Porcellidium, 103
Porcellio, 197, 206, 220
Portumninae, 315
Portumnus, 315
Portunidae, 315
Portuninae, 315
Portunion, 215, 216, 221
Portunus, 315
Post-abdomen, 33
Post-cephalic appendages,
12
Potamobius, 312
Potamon, 315
Potamonidae,
315
Potamoninae, 315
Praeanaspides, 168
Praniza, 219
Prawnus, 181
Pre-coxal segment, 7
Priapion, 212, 221
Primitia, 68
Prionoplacinae, 315
Prionoplaz, 315
Processa, 311
Processidae, 311
Proctodaeum, 14
Proepipodite, 146
Pronoe, 241
Pronoidae, 241
Propodite, 146
Propodus, 146
Prosoma of Cirripedia, 113
Prosopon, 308
Prosoponidae, 307
Proteolepadidae, 140
Proteolepas, 107, 128, 129,
139, 140
Proto, 251, 242
Protocaris, 50
Protocerebrum, 17
Protopodite, 7
Protosquilla, 321
Protozoea, 2938, 295, 297,
303
Psalilopodidae, 311
Psalidopus, 271, 272, 311
Psathyrocaris, 270, 311
Pseuderichthus, 328, 329
Pseudidothea, 220
Pseudidotheidae, 220

303, 304,

Pseudoculanus, 102
Pseudocuma, 188
Pseudocumidae, 188
Pseudocyclopia, 102
Pseudocyclopidae, 102
Pseudocyclops, 102
Pseudodiaptomus, 102
| Pseudomma, 173, 181
Pseudorostrum of Cuma-
cea, 184
Pseudosquilla, 328, 331
Pseudothelphusa, 315
Pseudothelphusinae, 315
Pseudo-tracheae of Isopoda,
205
Ptenoplacinae, 315
Ptenoplax, 315
Pterocuma, 185, 188

Pupa of Cirripedia, 125,
124

Pupal stage of Lernaea,
91

Pyenogonida, 3
Pygocephalus, 180, 181
Pylocheles. 261, 313
Pylochelidae, 259,
304, 313
Pyrgoma, 111, 140
Pyrocypris, 64, 69

jays;
PAT Te

Radius of Cirripedia, 111
Ranina, 264, 314
Raninidae, 256, 290, 314
Rathke, 254
Rathke’s organ, 208
Réaumur, 254
Receptacula seminis,
in Decapoda, 290 (
Spermatheca)
Regeneration, 10, 271
Remipes, 314
Reproductive system, :
of Amphipoda, 237 ; of
Branchiopoda, 47 ; of
Branchiura, 99 ; of Cir-
ripedia, 117 ; of Cuma-
cea, 187 ; of Decapoda,
289 ; of Hucopepoda, 86 ;
of Euphausiacea, 248 ;
of Isopoda, 211 ; of
Leptostraca, 158; of
Mysidacea, 179; of Os-
tracoda, 66; of Rhizo-
cephala, 131; of Sto-
matopoda, 325 ; of Syn-
carida, 167; of Tanai-
dacea, 193
Reptantia, 253 ; definition,
312
Respiratory system of ter-
restrial Decapoda, 284

21 ;

Resting eggs of Branchio-
poda, 47, 49

Retinula cells, 18 ”

Rhabdome, 18

Rhabdomeres, 19

Rhabdosoma, 226, 241

Rhincalanus, 79, 102

Rhizocephala, 1, 106, 107 ;
definition, 141; develop-
ment, 135 ; morphology,
130

Rhizopa, 315

Rhizopinae, 315

Rhizorhina, 93, 104

Rhynchocinetes, 255, 311

| Rhynchocinetidae, 311

Rocinela, 199, 220

Rondelet, 254, 319

Roots of Anelasma, 138 ;
of Liriopsidae, 217 ; of
Rhizocephala, 130, 132 ;
of Rhizorhina, 93

Rosenhof, 254

Rostral plate of Lepto-
straca, 152; of Stomato-
poda, 320

Rostro-lateral plates
Cirripedia, 111

Rostrum of Copepoda, 74 ;
of Cirripedia, 110; of
Decapoda, 255

of

| Rutiderma, 69
| Rutidermatidae, 69

Sacculina, 107, 130-134,
141; externa, 13875
interna, 135

Saint-Ange, Martin, 107

Sapphirina, 103

Sarcotaces, 137

Sars, G. O., 30, 40, 56, 68,
72, WOR, 108, sy, 7.
181, 183, 190; 191, 196,
214, 218, 225, 244, 249,
250, 251

Sarsiella, 59, 60, 62, 66,
69

Sarsiellidae, 69

Savigny, 3

Say, 183

Sayce, O. A., 162

Seale of antenna, 11; in
Euphausiacea, 245; in
Decapoda, 265 ; in Iso-
poda, 198; in Malaco-
straca, 145; in Mysi-
dacea, 173 ; in Stomato-
poda, 321; in Tanai-
dacea, 191

Scalpellum, 110, 116, 118,

119, 121, 138, 140

Scaphognathite, 266, 268

Scelidae, 241

Schaffer, 29

Schiddte, J. C., 196

Schizopoda, 148, 244

Schizopod-stage of Deca-
poda, 294, 297, 299

Scina, 241

Scinidae, 241

Scolecithrix, 102

Scottocheres, 86, 103

Sculda, 330

Scutum of Cirripedia, 110

Scyllaridae, 255, 266, 312

Scyllaridea, 253: defini-
tion, 312

Scyllarus, 290, 300, 312

Scyphacinae, 220

Scyphax, 220

Segmentation of egg, 22

Sella turcica, 263

Sense-organs, 91; of Am-
phipoda, 236; of Bran-
chiopoda, 46; of Bran-
chiura, 98 ; of Cirripedia,
117 ; of Decapoda, 287 ;
of Eucopepoda, 84; of
Tsopoda, 211 ; of Mysi-
dacea, 178; of Ostra-
coda, 66; of Stomato-
poda, 325; of Syncarida,
166

Sergestes, 287, 288,
299, 311

Sergestidae, 268, 273,
295, 304, 311

Sergestinae, 311

Serolidae, 197, 203, :
220

Serolis, 199, 208, 220

Sesarma, 315

Sesarminae, 315

Setae, 19

Setella, 103

Setobranchia, 277

Sexual dimorphism, 21

Shell-fold, 6

Shell-gland, 16

Sicyonia, 311

Sicyoninae, 311

Sida, 41, 53

Sididae, 44, 47, 53

Simocephalus, 44, 53

Simosa, 53

Siphonostomata, 78, 101

Siriella, 175, 177, 182

Siriellinae, 182

Size of Amphipoda, 239 ;
of Branchiopoda, 50 ; of
Cirripedia, 138 ; of Cope-
poda, 100 ; of Cumacea,

297,

288,

INDEX

| 188 ; of Decapoda, 306 ;
of Euphausiacea, 251; of
| Isopoda, 217; of Lepto-

straca, 159; of Mysi-
dacea, 180; of Ostra-
coda; 67; of Stomato-

poda, 329; of Synearida,
167 ; of Tanaidacea, 194

Slabber, 107, 254

| Sluiter, 137

| Smith, G., 132, 107, 136,
165, 170, 194, 292

Socarnes, 229, 241

Solenocera, 265, 311

Somite, 4

Spence Bate (see Bate)

Spermatheca of Eucope-
poda, 86 (see Recepta-
culum seminis)

Spermatophores, 21; of
Eucopepoda, 86; of De-
capoda, 290

Spermatozoa of Cirripedia,
118; of Decapoda, 299;
of Ostracoda, 67

Sphaeroma, 210, 213, 220

Sphaeromidae, 199, 203,
204, 205, 207, 209, 212,
216, 220

Sphaerominae, 220

Sphaerothylacus, 130, 137

Sphyrapus, 191, 195

Spinning-organ of Ostra-
coda, 59

Spirontocaris, 311

Spiropagurus, 289, 313

Spongicola, 305, 311

Squama (see Scale)

Squilla, 319-323, 328. 330,
331

Squillacea, 148

Squillidae, 331

Statocyst, 20; of Amphi-
poda, 237 ; of Decapoda,
287 ; of Eucopepoda, 85 ;
of Isopoda, 211 ; of Mysi-
dacea, 178 ; of Syncarida,
166 ; of Tanaidacea, 193

Stebbing, 139, 225, 240

Steenstrup, 72

Stegocephalidae, 241

Stegocephalus, 241

Stenasellus, 197, 219

Stenetriidae, 205,
219

Stenetrium, 219

Stenopidae, 311

Stenopidea, 253, 309; de-
finition, 311

Stenopus, 291, 311

Stenothoe, 241

206,

Stenothoidae, 241

Stephos, 102

Sternal canal of Decapoda,
263

Sternite, 4

Stilomysinae, 181

Stilomysis, 181

Stomach, 14

Stomatopoda, 2, 143, 319;
affinities and classifica-
tion, 330 ; development,
326; historical notes,
319; habits, ete., 329;
morphology, 319; palae-
ontology, 330

| Stomodaeum, 14
| Stridulating organs, 305

Stylocerite, 265 — >

Stylochetron, 247,248, 249,
252

Stylodactylidae, 268, 311

Stylodactylus, 271, 311

Stylopodite, 146

Sub-apical lobe of Branchio-
poda, 39

Subhyperini, 225

Suectoria, 107

Summer eggs of Branchio-
poda, 49

Swain, 218

Swammerdam, 29, 254

Sylon, 130, 131, 133, 141

| Symmetrica, 106; defini-

tion, 140

Sympodite, 7

Synagoga, 125, 126, 127,
140

Synagogidae, 140

Synearida, 1, 143 ; affini-
ties and classification,
168; definition, 148,
162; habits, etc., 167;

historical notes, 162;
morphology, 162

Synopia, 236, 241

Synopidea, 225

Synopiidae, 241

Synurella, 232, 233, 234,
241

Tachaea, 219

Talitridae, 231, 235, 239,
241

Talitrus, 241

Tanaidacea, 2, 143 ; aftini-
ties and classification,
194; definition, 190;
development, 194;

habits, etc., 194; his-
torical notes, 190; mor-
phology, 191

346

THE CRUSTACEA

Tanaidae, 191, 192, 193,
194, 195

Tanais, 190, 193, 195

Tapetum, 19

Tattersall, 178, 181, 248

Tegastes, 103

Telson, 4

Temora, 102

Tergite, 4

Tergum of Cirripedia, 110

Terrestrial Decapoda, 284 ;
Isopoda, 205

Thalamita, 315

Thalamitinae, 315

Thalassina, 304, 313

Thalassinidae, 291, 213

Thalassinidea, 253 ; defini-
tion, 313

Thalassocarinae, 311

Thalassocaris, 311

Thalestris, 103

Thamnocephalidae, 53

Thamnocephalus, 35, 53

Tharybis, 102

Thelphusa, 315

Thelphusidae, 304

Thelyeum, 290

Thenus, 312

Thia, 315

Thienemann, 211

Thiinae, 315

Thompson, J. Vaughan, 3,
107, 244, 254

Thompsonia, 137, 141

Thomson, G. M., 162

Thoracic appendages of
Amphipoda, 229; of
Branchiura, 96; of Cu-
macea, 186 ; of Cirripedia,
114 ; of Copepoda, 79,
81; of Decapoda, 268 ;

of Euphausiacea, 246 ;
of Isopoda, 198; of
Malacostraca, 145; of
Mysidacea, 174 ; of
Stomatopoda, 322; of
Syncarida, 164 ; of

Tanaidacea, 191

Thoracica, 1, 106 ; morpho-
logy, 108 ; definition,
140

Thoracostraca, 147

Thorax, 6

Thorell, 101

Thyropus, 241

Thysanopoda, 251, 252

Tiron, 236, 241

| Tironidae, 241

Tortanus, 102
Trachelifer, 301
Trapexa, 315
Trapeziinae, 315
Triangulus, 131, 141
Trichobranchiate, 277
Trichodactylinae, 315
Trichodactylus, 315
Trichoniscidae, 220
Trichoniscus, 220
Trilobita, 3
Trischizostoma,

241

236, 239,

| Tritocerebrum, 17

Trunk appendages, 12
Trypetesa, 140
Tryphana, 241
Tryphanidae, 241
Tubicinella, 138, 140
Turrilepas, 109, 138
Tylidae, 203, 212, 220
Tylos, 220

Typton, 305, 311

Upogebia, 274, 301, 313

Upogebiinae, 313

Urda, 218

Uronectes, 167, 168

Uropods, 147 ; of Amphi-
poda, 232; of Cumacea,
187 ; of Decapoda, 274 ;
of Euphausiacea, 247 ;
of Isopoda, 207 ; of My-
sidacea, 176; of Sto-
matopoda, 3235; of Syn-
carida, 166; of Tanai-
dacea, 193

Uroptychidae, 313

THE END

Uroptychus, 276, 313
Urothoe, 241

Valvifera, 196; definition,
220

Varuna, 315

Varuninae, 315

Vasa deferentia, 21

Vauntompsonia, 188

Vauntompsoniidae, 188

Vejdovsky, F., 162, 169

Verruca, 112, 138, 140

Verrucidae, 115, 140

Vibilia, 233, 241

Vibiliidae, 241

Virbius, 311

Vireia, 207, 220

Vitellophags, 22

Walking-legs of Decapoda,
Dae

Wall of Cirripedia, 110

Water-fleas, 29

Weismann, 30

Westwood, 225, 254

Williamson, 275

Winter eggs of Branchio-
poda, 47, 49

Wollebaek, 21, 292

Woodward, H., 168, 180

Xanthidae, 315
Xanthinae, 315
Xantho, 315
Xenobalanus, 113, 140
Xenophthalminae, 315
Xenophthalmus, 315
Xiphosura, 3

Zaddach, 30

Zenker, 56, 72, 81, 101

Zoea, 24, 25, 298, 296,
297, 301, 302%.

Zygosiphon, 184, 188

Printed by R. & R. Crark, Limirep, Edinburgh.

THE SENSE OF TOUCH IN MAMMALS
AND BIRDS

WITH SPECIAL REFERENCE TO THE PAPILLARY RIDGES
By WALTER KIDD, M.D., F.Z.S,,

Author of ‘ Use Inheritance,’ ‘ Direction of Hair in Animals and Man,’ ete.

Demy 8vo, Cloth, containing 174 Illustrations. Price 5s. net.
(Post free, price 5s. 4d.)

““This is, for the purposes of exact science, undoubtedly a valuable book. .. . 2 As regards the
highest mammal, man, it is well pointed out that the sense of touch has been from the very first of
extreme importance, and that ‘such use of this sense in man must have contributed greatly to
his better equipment for the struggle of his life, and thus in a broad way have been governed by
a slow, remorseless process of selection.’ The book is eminently one for specialists, but the
excellence of the numerous illustrations makes it also interesting to the general reader.’—London
Quarterly Review.

“Dr. Kidd’s book is the most important contribution to the matter since Miss Whipple’s paper
was published.” — The Spectator.

BY THE SAME AUTHOR

USE-INHERITANCE

ILLUSTRATED BY THE DIRECTION OF HAIR ON
THE BODIES OF ANIMALS

Demy 8vo, Paper Covers. Price 2s. 6d. net.
(Post free, price 2s. 8d.)

**Such a book as this is calculated, at least, to give pause to the Weismannians. Dr, Kidd has
broken ground in a commanding position, and we are anxious to see how his attack can be met.”
—The Irish Naturalist.

“This is an interesting contribution to the dynamic or I amarckian principles of evolution. .. .
The author seems to have made out a good case and to have been led by the legitimate use of the
inductive method to what seem to be valid and natural conclusions. ’’—Science.

“It is urged that . . . the doctrine that acquired characters are never inherited does not hold
good, and hence a Lamarckian explanation of the phenomena must be accepted. The case, as
argued by Dr. Kidd, appears to be a strong one, and it will be curious to note what the Weisman-
nists will have to say in reply.” —Knowledge.

THE DIRECTION OF HAIR IN ANIMALS
- AND MAN

Demy 8vo, Cloth, Illustrated. Price 5s. net.
(Post free, price 5s, 4d.)

**Dr. Kidd shows much ingenuity in explaining the various causes which, in his opinion, have
produced the different hair-slopes, and the illustrations with which the book is liberally furnished
ure of considerable assistance to the reader.” —Westminster Review.

“The description of the facts can be commended. There is evidence that considerable care has
been taken in the collection of observations, and the illustrations are excellent.”—Manchester
Guardian.

“That the direction of the hair-slope in mammals varies much is a fact well known to zoologists ;
but we are not acquainted with any general work, such as the present, in which the facts are put
together within one cover. The author has, therefore, in any case, accomplished a piece of work
which supplies a definite want in the literature of zoology. The usefulness of this general summary is
furthermore enhanced by numerous clear figures which show at a glance the essential facts. "— Lancet.

PUBLISHED BY
ADAM AND CHARLES BLACK, 4, 5, & 6 SOHO SQUARE, LONDON

THE
SCIENCE AND PHILOSOPHY
OF THE ORGANISM

THE GIFFORD LECTURES DELIVERED BEFORE THE
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BY

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IN TWO VOLUMES. DEMY 8vo. CLOTH

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Tus work rests chiefly upon the results of experimental embryology,
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concerned. The first volume deals with the science of the organism
and discusses the chief results of analytical biology in two parts, and,
in the author’s view, results in two main proofs of the autonomy of
life, or what may still be called, if in a modernised sense, “ vitalism,”
as distinguished from ‘‘ mechanism.” The second volume, continuing
the exposition of the science of the organism into a third part, contains
a detailed theory of animal movements, reflexes, instinct, and, in
particular, action, resulting in a third main proof of the autonomy of
life. The foundation of a complete system of scientific biology having
thus been laid, the remainder of the volume—forming its larger half—
is devoted to the philosophy, as distinguished from the science, of the
organism. The central part of this concluding discussion is devoted
to a thorough analy sis of the ek ola: teleology’ ” and its relation

to the inor ganic sclences. Ot
Dyw27—24 {950 ‘Go. __

PUBLISHED BY
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