Zoogeographic Regions in Canada Based on the
Occurrence of Freshwater Molluscs
1 Atlantic Coastal Region 6 Pacific Coastal Region
2 Lake Erie-Lake St. Clair Region 7 Beringian Refugium
3 Great Lakes- St. Lawrence Region 8 Subarctic Region
4 Red River-Assiniboine River Region 9 Arctic Region
5 Western Prairie Region
QL
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The Freshwater Molluscs of Canada
A female Pocket-Book mussel ( Lampsilis ventricosa ) with its
mantle flap extended and pulsating to simulate a wounded
minnow. This activity attracts fish, and increases the opportuni-
ties for juvenile mussels (glochidia) to attach themselves to a fish
after they are ejected from the parent. A period of attachment to
a fish of the proper species is necessary for maturation of most
juvenile freshwater mussels. (Photograph courtesy of John H.
Welsh, Boothbay, Maine.)
The Freshwater Molluscs
of Canada
Arthur H, Clarke
National Museum of Natural Sciences
National Museums of Canada
r-iATtG
,:; nD HAux
OF CANADA
D U CANADA
© National Museums of Canada 1981
Published by the
National Museum of Natural Sciences
National Museums of Canada
Ottawa, Canada K1A 0M8
Catalogue No, NM95-17/5
Printed in Canada
ISBN 0-660-00022-9
Edition franchise
Les Mollusques d’eau douce du Canada
ISBN 0-660-00023-7
Managing editor: Viviane Appleton
Text editor: Lorraine Smith
Production: Donald Matheson
James MacLeod
Design: Eiko Emori
Typesetting: The Runge Press Ltd.
Printing: D. W. Friesen & Sons Ltd
Contents
Acknowledgements 9
Introduction 1 1
Why Collect Shells? 11
How to Collect Freshwater Shells 12
Arrangement and Care of the Collection 16
Scientific Names 17
Mollusc Classification and Some Special Features 19
Distribution Patterns in Canada 21
Molluscs as Pollution Indicators 24
The Freshwater Molluscs 27
Key to the Families of Canadian Freshwater
Molluscs 29
Class Gastropoda (Snails) 31
Subclass Prosobranchia (Gill-breathing Snails) 33
Order Mesogastropoda 33
I Superfamily Viviparacea 33
Family Viviparidae (Mystery Snails) 33
II Superfamily Valvatacea 41
Family V alvatidae ( Valve Snails) 41
III Superfamily Rissoacea 55
Family Hy dr obiidae ( Spire Snails) 55
Family Truncatellidae (Looping Snails) 73
Family Bithyniidae (Faucet Snails) 11
IV Superfamily Cerithiacea 81
Family Pleuroceridae (Horn Snails) 81
Subclass Pulmonata (Lung-breathing Snails) 89
Order Basommatophora 89
V Superfamily Acroloxacea 89
F amily Acroloxidae (Primitive Freshwater
Limpets) 89
VI Superfamily Lymnaeacea 93
Family Lancidae (Limpet-like Lymnaeas) 93
Family Lymnaeidae (Pond Snails) 97
VII Superfamily Physacea 151
Family Physidae ( Tadpole Snails) 151
VIII Superfamily Planorbacea 175
Family Planorbidae (Ramshorn Snails) 175
Family Ancylidae (True Freshwater Limpets) 219
Colour Plates 229
Class Pelecypoda (Clams and Mussels) 245
Order Eulamellibranchia 247
IX Superfamily Unionacea (Freshwater Mussels) 247
Family Margaritiferidae (Pearly River-Mussels) 247
Family Unionidae (Pearly Mussels) 253
Subfamily Ambleminae (Button Shells and
Relatives) 254
Subfamily Anodontinae (Floater Mussels) 212
Subfamily Lampsilinae (Lamp Mussels) 312
X Superfamily Sphaeriacea 357
Family Corbiculidae (Little Basket Clams ) 357
Family Sphaeriidae (Fingernail Clams and Pea
Clams) 361
Subfamily Sphaeriinae (Fingernail Clams) 362
Subfamily Pisidiinae (Pea Clams or Pill
Clams) 386
Glossary 433
References 437
Index to Scientific and Common Names 441
Acknowledgements
I am grateful to Arthur R. Clarke, the late Louise R. Clarke,
the late Fran^oise Dehenne, F. Wayne Grimm, Brian T.
Kidd, Judith J. McDonald and the late Dr. D, G. S. Wright
for field assistance; to Walter MacKay Drycott, the late
Reverend H. B. Herrington and several other colleagues for
contributing some valuable specimens; and to Muriel F. I.
Smith and Jane M. Topping for laboratory assistance.
Dr. G. L. Mackie gave constructive criticism on the section
on Sphaeriidae.
I am also indebted to Dr. Aurele LaRocque, who, through
energetic application of his expert knowledge of molluscs
and of the French language, provided the fine translation for
the French edition of this book.
The watercolour paintings are by Valerie Fulford
(Figures 110, 128, 129, 131, 134-38, 140, 142, and 143),
Jacques Blais (Figure 139), and Aleta Karstad Schueler (all
others). Photographs are by the Canadian Conservation
Institute of the National Museums of Canada (most of the
Pisidium , using a scanning electron microscope), the
National Museum of Natural Sciences (Unionacea and
Corbicula ), and A. M. Frias-Martins (all others). My work
was supported by the National Museum of Natural Sciences
and by the Arctic Biological Station, Fisheries and Oceans
Canada.
9
Introduction
Why Collect Shells
Canadians are exceedingly fortunate in having an abun-
dance of beautiful unspoiled forests, lakes, and rivers.
Thousands have found that frequent escape to these open
spaces for fresh air, peace, and relaxation is essential for
their mental and physical well-being.
As with music and art, knowledge enhances the
appreciation of nature. Handbooks for the identification of
trees, flowers, mushrooms, mammals, birds, fishes, and
insects are justifiably popular. Interest in seashells, fresh-
water shells and land snails is also widespread. In fact, many
people who wish to make natural-history collections find
mollusc shells more practical and desirable than anything
else.
There are many reasons why people collect shells. Shells
are beautiful, intriguing, and free for the taking, and
collecting them is fun. Shells are easy to find, and unlike
plants and other animals require very litde special
preparation or preservation. In addition to healthful
exercise, shell collecting provides an interesting diversion
in unfamiliar regions. Shells make excellent souvenirs
because, as faunal samples, they represent the very essence
of any exotic region.
Shell collecting often brings about good companionship
with other collectors. It many also lead to membership in
local shell clubs or in national and international organiza-
tions. Enthusiastic shell collectors live in all parts of the
world, and a great many of them are eager to exchange their
exotic native shells for our ordinary ones, which to them
are just as exotic.
As familiarity with molluscs grows, most collectors
discover that living molluscs are fascinating creatures to
observe. Original and important contributions to science
can be made in this way. Many molluscs are beautiful and
colourful, some can ascend and descend through the water
apparently at will, others have soft parts that look like and
pulsate like an injured minnow (see frontispiece), and all
n
have interesting feeding and reproductive habits. A great
many basic facts about our most common species are still
unknown. For example, during which times of the year do
they reproduce in different regions? What do they eat? What
are their major predators? And what are their limits of
distribution? It is still possible, in fact, to discover new
species that are entirely unknown to science.
A shell collector's interest might originally be aroused by
seashells. Later, freshwater shells and land snails might
be added to the collection, especially by someone who lives
in an inland location. Many collectors then decide to
specialize in freshwater or land shells. Several popular
handbooks exist for the identification of seashells, but non-
technical books on freshwater or land molluscs are very
scarce, and comprehensive texts covering all of Canada do
not exist.
This book is about the freshwater shells of Canada. It
attempts to describe and illustrate all the species that live in
this country, to provide keys and descriptions for their
identification, and to present information about their
ecology and their relationship to man.
How to Collect Freshwater Shells
Freshwater molluscs are abundant animals and are usually
not difficult to collect. The successful collector, however,
must learn to recognize a likely habitat.
In general, well-vegetated portions of unpolluted lakes,
ponds, and slow-flowing rivers are the most productive
localities for freshwater snails (class Gastropoda), which
occur there on submersed vegetation, on rocks, and on the
bottom from the water’s edge out to a considerable depth.
Freshwater mussels (family Unionidae) are found princi-
pally in rivers and lakes, partly buried in the bottom, where
the water is about one-third of a metre to two metres deep.
The greatest diversity of species occurs in rather fast-
flowing portions of hard-water rivers, that is those
containing a moderate or high concentration of dissolved
limestone, such as the rivers of southern Ontario and
southern Manitoba. Fingernail clams and pill clams (family
Sphaeriidae) are most abundant in the muddy and fine
sandy bottoms of lakes. They burrow just below the bottom
in water a few centimetres to many metres deep.
12
Several important exceptions to these general rules exist.
Temporary springtime, that is vernal, pools often support
thriving colonies of snails, especially Aplexa hypnorum and
Gyraulus circumstriatus in the east and Planorbula campes-
tris and Stagnicola caperata in the west. Tiny spring-fed
pools in the west may contain^. montanensis. Wave-beaten
rocky shores of large lakes may harbour the rare limpet
Acroloxus coloradensis on the undersurfaces of boulders.
Arctic muskeg pools often teem with Physajennessi jennessi
and S’, arctica. Brackish-water estuaries may support rich
freshwater-mollusc populations in very shallow water above
the level of the lower saltwater layer. Deep water in large
lakes may harbour Fossaria decampi and species of Valvata
and Pisidium. Rocky creeks in the far east may contain the
pearly freshwater mussel Mar garitif era margaritifera , and
those in the far west the related species M. falcata.
Freshwater molluscs can be collected by hand and put in
a pocket. But in most cases hand-picking is slow, and
pocketed specimens are likely to be crushed. Therefore,
although not essential, a certain amount of equipment is
very useful.
The usual gear used in collecting freshwater molluscs
includes
1) a pair of hip-waders or, in warm weather, tennis shoes and
a bathing suit
2) a dip net for sweeping underwater plants and scraping the
bottom
3) a glass-bottomed box or bucket for observing the bottom
(used mainly when collecting freshwater mussels)
4) a supply of suitable jars and vials with leakproof caps
5) 80 per cent ethyl alcohol or 70 per cent isopropyl alcohol
(70 per cent ordinary rubbing alcohol and 30 per cent water)
for preserving the catch
6) cloth bags with string or cloth-strip closures for fresh-
water mussels
7) field labels made of plastic or durable paper (that is, with
high rag content)
8) a field notebook
9) pencils, or a pen and waterproof ink
10) forceps
1 1) a flat pan for sorting small specimens
12) detailed maps of the region to be explored.
13
Additional useful gear includes Nembutal or propylene
phenoxetol for relaxing and extending specimens, 10 per
cent formalin buffered with borax for initial preservation of
specimens (but not for long-term storage), rope and a small
dredge for collecting in deep water, a rowboat, outboard
motor, oars and life-jackets, an underwater face-mask, fins
and snorkel, and Scuba gear,
A widely used collecting technique is as follows: the
collector wades into a river and walks slowly upstream,
carefully scanning the bottom through the glass-bottomed
bucket. A sunny day is best for visibility, and the lower the
water level the better. By working upstream, the collector
will find that disturbed mud drifts behind, leaving the water
in front clear. Partly buried freshwater mussels will be
obvious, and fully buried ones will reveal themselves as
white slits in the river-bottom. These are the mantle edges
as seen between the slightly gaping valves. The glass-
bottomed bucket, which should be tied to the collector’s
waist, is a convenient receptacle for mussels.
Once the search for mussels has been completed and the
specimens have been placed in cloth bags, the glass-
bottomed bucket can be set aside. The dip net is now used
for collecting snails from vegetation and various small
molluscs from the river bottom. Rocks should also be picked
up, examined all over for snails, and then replaced in their
original position. Restoring the habitat as closely as possible
to its original state is an important aspect of responsible
and conservation-oriented collecting. Live specimens
should be put into jars with enough water to keep them
alive. It takes at least 30 minutes to search a productive
locality efficiently. Some collectors, in fact, will spend four
to six hours at a collecting site to ensure that the rare
species, as well as the common ones, have been found.
If snails and sphaeriids are to be kept alive, they should be
cool and uncrowded, that is in water that is about ten times
greater in volume than the specimens themselves and in
a jar large enough to provide half that much air volume.
Mussels will remain alive for at least a day if placed in cloth
bags kept out of the sun and moistened every few hours.
They should not be kept crowded in a bucket of water,
because they will soon deplete the dissolved oxygen and die.
14
If specimens are to be of any interest to serious collectors
or of any value to science, accurate records must be kept.
Minimal data should include
1) the name of the water body the specimens were found in
2) the distance and direction from the centre of the nearest
city, town, or village
3) the province, or state, and country
4) the date
5) the collector’s name.
Accessory valuable data are
1) the depth of the water where the specimens were
collected
2) the kind of bottom (mud, sand, boulders, for example)
3) the kind and density of vegetation
4) the size (approximate width or area) of the water body
5) the approximate current speed
6) the water temperature
7) any other relevant observations
Collection sites are referred to as stations, and these are
best numbered consecutively in a continuous series. The
station number and usually the minimal data are written on
a field label placed in the container with the specimens.
Jars of living snails should also have the station number
written on the cap, because the snails may eat the label.
The same number and the minimal and accessory data are
recorded in a field notebook. On an extended trip, carbon
copies of field notes should be mailed home periodically.
A lost field-book can ruin a collecting trip.
Many collectors will wish to remove and discard the soft
parts of their specimens soon after collection, before the
animals die and begin to decompose. Freshwater mussels
and fingernail clams are usually cleaned by boiling. This
causes the valves to gape, and the cooked, firm body of the
clam can then be easily removed. The soft parts of large
snails can also be loosened by boiling, and then “un-
screwed” from their shells. A bent pin is useful for this.
Small snails and pill clams can be spread out on a flat pan or
a newspaper and simply allowed to dry out. Soaking in
preserving fluid prior to drying is helpful, but is not
necessary if an open-air drying area is available and if only a
few small molluscs are involved.
15
Many collectors might be interested to know that
freshwater mussels from unpolluted habitats are edible.
They may be steamed, roasted, fried, or made into chowder.
The reader is urged to experiment. If the water is clean
enough to drink, the mussels are clean enough to eat.
A note on conservation is necessary here. Some of our
freshwater species are, or are becoming, very rare because of
habitat disruption, increased urbanization, pollution, or
over-collecting. Certain freshwater mussels, especially
Simpsoniconcha ambigua and species oiDysnomia , are
particularly threatened. Collectors are urged to be conserva-
tion minded — to collect only as many live specimens as they
need, and never to collect all available specimens of any
species in a particular locality. The responsible collector
also avoids disrupting habitats. Live collecting is not always
necessary because empty shells often make perfectly good
specimens for the collection. Beach-drift specimens or
empty shells left by muskrats are often in excellent
condition.
For more extensive information on collecting see How to
Collect and Study Shells , published by the American
Malacological Union and available for US $2.50 from the
Department of Malacology, Academy of Natural Sciences of
Philadelphia, 19th and the Parkway, Philadelphia, Pa.
19103, USA. Another useful publication, available from the
same source for US $1.50, is entitled Papers on Rare and
Endangered Mollusks of North America , and was originally
published in the scientific journal Malacologia (vol. 10,
no. 1, 1970).
Arrangement and Care of the Collection
After they are cleaned or preserved, all the specimens from a
particular collecting station should be sorted into vials or
boxes by species; that is, each species should have its own
container. A slip of paper bearing the station number and
the species or subspecies name should accompany each
such lot. Each lot is then catalogued as follows:
1) a catalogue number is assigned and written in india ink
directly on the shell or on a small label that is placed with
the shells inside each closed container
2) that same catalogue number is written on a larger label,
along with the name of the species or subspecies and author,
16
all minimal data and, if space permits, any accessory data,
and is placed in the shallow cardboard boxes described
below
3) the same information is entered in a ledger book (the
catalogue).
In this way, the data associated with each species lot will be
protected from loss, and the lasting value of the collection
will be assured.
Museums use dustproof cabinets with large, shallow
wooden drawers to house mollusc collections. Shallow
cardboard boxes of various multiple sizes (say 5 x 3.5 x
2 cm deep, 5x7x2 cm, 10x7x2 cm, etc.) are placed in
the drawers, and all lots of the same species are placed
together in horizontal or vertical rows. The species are
arranged together with other species of the same genus, all
genera in the same family being stored together, and so on.
These are all arranged in systematic, or phylogenetic, order,
that is in their presumed evolutionary sequence, from the
most primitive to the most advanced groups. The drawers
are also labelled to indicate the genera or species they
contain. The arrangement of species in this book follows
the phylogenetic order advocated by Taylor and Sohl (1962)
and Moore (1969).
In practice, many collectors are obliged to use miscel-
laneous vials and boxes. Cigarette boxes make good
containers for small shells, and may be stored in shoe boxes
on shelves. Many kinds of containers will do, but of course
uniformity enhances the appearance of the collection.
Scientific Names
Systematics has been defined as the science of deducing
evolution in action. Through classification and the use of
names, it seeks to show evolutionary relationships among
animals and plants.
Living creatures are usually divided into two major
groups, the Animal Kingdom and the Plant Kingdom. The
major divisions of the Animal Kingdom are called phyla
(Chordata, Arthropoda, Mollusca, for example). Phyla are
further subdivided into classes, classes into orders, orders
into families, families into genera, genera into species, and
sometimes species into subspecies. Occasionally, to show
17
relationships more precisely, it is necessary to use additional
categories, for example subclass between class and order,
and subgenus between genus and species.
A species includes all individuals potentially able to breed
together to produce similar individuals. Some species have
common names, but these may be local and not known to
people who live elsewhere or speak another language. The
scientific name of an animal is understood internationally
and is vastly preferable to a confusing variety of local
common names.
The scientific name of a species consists of the genus
name, with the first letter capitalized; the subgenus name, if
applicable, in round brackets, also with the first letter
capitalized; and the specific name, uncapitalized. It is usual
also to include the name of the author who first described
and named the animal and the date of publication.
Following approved practice, if the specific name used for
the animal in this book is now in a different genus from the
one originally proposed, the original author and date are
placed in round brackets. An example is Stagnicola
(Hinkleyia) montanensis (Baker, 1913). This species was
first described and named by F. C. Baker in 1913. However,
Baker named it Galba montanensis.
A subspecies is a population, or group of populations, that
is significantly different from other populations of that
species but is still potentially able to breed with those
populations. Subspecies of the same species also occupy
different areas. If these areas overlap, widespread interbreed-
ing can be expected in that zone. A subspecies name
consists of the complete species name followed by the
subspecific name. The same rules concerning authors,
dates and use of brackets apply. An example is Stagnicola
(Stagnicola) catascopium preblei (Dali, 1905). This subspe-
cies was described by W. H. Dali in 1905 as the species
Lymnaea preblei.
The interested reader is referred to Ross (1974) and Mayr
(1969), and to the scientific journal Systematic Z oology , for
fuller discussion of classification procedure and the
formation of scientific names.
is
Molluscan Classification and Some Special
Features
Snails, slugs, clams, mussels, scallops, oysters, chitons,
tooth shells, squids and octopuses are all molluscs. The
features these animals have in common constitute a good
definition of what molluscs are.
The phylum Mollusca may also be defined as comprising
all invertebrate animals that are soft-bodied, non-seg-
mented, have a muscular foot for burrowing or crawling,
and possess a mantle — an enveloping sheet of tissue that in
most species secretes a calcareous shell. With the major
exception of pelecypods (bivalves), most molluscs also have
a head with tentacles, eyes, mouth, and a radula — a rasping
organ in the floor of the mouth.
Seven classes of living molluscs are usually recognized:
Monoplacophora, Polyplacophora, Aplacophora, Scapho-
poda, Pelecypoda, Gastropoda, and Cephalopoda. Only the
two largest classes, Pelecypoda and Gastropoda, live in fresh
water, and only Gastropoda live on the land. All of the
classes, however, are found in the sea. General information
on molluscan classes is given in most textbooks on general
biology. For detailed information on marine groups,
however, consult Abbott (1974) or Bousfield (1960), and on
land snails Pilsbry (1939-48) or Burch (1962).
Canadian freshwater gastropods belong to two
subclasses — Prosobranchia (also called Streptoneura) and
Pulmonata (which, together with Opisthobranchia, are also
called Euthyneura). Most prosobranchs have an operculum
(used to seal the shell aperture), breathe by means of gills,
and individuals are either male or female. Pulmonates have
no operculum, breathe by means of a pulmonary sac, or
lung, and are hermaphroditic. Canada has four superfami-
lies of freshwater prosobranchs (divided into six families)
and four superfamilies of pulmonates (also containing six
families).
Most systems of classification do not subdivide the class
Pelecypoda into subclasses but only into about five orders.
All Canadian freshwater bivalves belong to the order
Eulamellibranchia. This group is characterized by
1) a hinge containing a few teeth of diverse shapes and sizes
2) two large adductor muscles of about the same size, one
anterior and one posterior
3) a partly closed mantle with well-developed siphons
4) leaf-like gills within the mantle cavity.
Two superfamilies are represented in Canada — Sphaeriacea
and Unionacea.
The major external and internal features of prosobranch
and pulmonate snails and of eulamellibranch bivalves are
illustrated on the front and back endpapers.
Snails have many unique features, but their feeding
organ — the radula—is one of the most interesting. This is a
tough, elongate, moveable membrane in the mouth that
bears many similar transverse rows of tiny sharp teeth. The
radula is pressed against the food and pulled back and forth.
This action rasps the food into tiny particles and carries it
back into the mouth.
Scientists have shown that the number and shape of the
radular teeth in each transverse row are very useful in
classification. All Canadian prosobranch snails, for exam-
ple, typically have 7 teeth in each transverse row. The
formula for this is usually 2-1-11-2, meaning that each
row has 2 marginal teeth, 1 lateral, 1 central, another lateral,
and 2 more marginals, in that order. The shape of the teeth
and the number of projections on each (the “cusps”) differs
from family to family, but is generally similar within
families and very similar within genera. Similarly, the
pulmonates are characterized by having radular teeth set in
rows, with one distinctive central tooth in each row flanked
by many teeth on either side. These teeth may or may not
be separable into laterals and marginals. Each family of
pulmonates has very distinctive radulae. For detailed
information on radulae see the fascinating book by Solem
(1974).
Another uniquely molluscan feature is the glochidium
larva of freshwater mussels. These animals retain their
young for various lengths of time in modified portions of the
gills. The young mussels, the glochidia, are released by the
parent when its light-sensitive mantle-spots are stimulated,
for example by the shadow of a passing fish. Mussels of the
genus Lampsilis and their relatives even possess special
mantle structures apparently designed to lure fish into their
vicinity. The glochidia of each species of mussel, with a
few exceptions, must attach to the gills or fins of a fish
belonging to one, or a few, species for further development
to take place. Most glochidia never accomplish this, but
those that do succeed remain attached for a few weeks and
metamorphose into tiny mussels. They then drop to the
bottom and take up the normal life of a mussel, that is they
crawl around siphoning water for respiration and to obtain
phytoplankton as a source of nourishment and growth.
Distribution Patterns in Canada
Every region of Canada has its own species of freshwater
molluscs. For example, that part of southern Ontario which
includes Lake Erie and Lake St. Clair and the rivers and
streams draining into them harbours twelve species of
freshwater mussels and one species of pill clam that occur
nowhere else in Canada. Such an area is called a zoo-
geographic region. Several such regions exist in Canada
(see front endpaper).
The most clearly defined regions, that is those in which
many species have similar distributional limits, are the Lake
Erie-Lake St. Clair Region, the Red River-Assiniboine
River Region, and to a lesser extent the Pacific Coastal
Region. The other regions have boundaries that are not
sharply defined. A general knowledge of the zoogeographi-
cal regions of Canada will nevertheless be very useful to
a collector.
There are many interesting reasons why Canadian
species are distributed as they are, and why Canadian
zoogeographic regions exist as they do. These reasons
involve the glacial and postglacial history of the country, its
climate, geology, and geography, and the biology of the
species themselves. For more details than those that follow,
see Clarke (1973),
During four different periods of the Pleistocene epoch,
which itself lasted from about one million to about five
thousand years ago, most of Canada was covered with
glacial ice. For freshwater molluscs the most important
non-glaciated regions were a part of the Yukon Territory
and Alaska known as the Beringian Refugium, and the large
area south of the glacial ice, most of which is in the United
States. Within the glaciated region all the freshwater
molluscs were wiped out, of course, but each time the ice
receded they reinvaded the previously ice-covered region.
21
Many species, especially most of the freshwater mussels
and all of the large prosobranch snails (Viviparidae and
Pleuroceridae), require continuous waterways for migra-
tion. Glochidia of freshwater mussels may be carried over
long distances while attached to their fish hosts. The
present distributions of freshwater mussels and large
operculate snails were therefore brought about largely by
postglacial stream confluences, for example the drainage
pathways taken by glacial meltwater. Such species are most
useful for delimiting zoogeographic regions. On the other
hand, most small snails and many small clams (sphaeriids)
are probably carried about imbedded in the feathers of water
birds or in mud attached to their feet. Sphaeriids may also
be transported while clamped to the feet of large aquatic
flying insects. Therefore, the present distributions of small
molluscs tend to transcend zoogeographic and drainage-
system boundaries.
The zoogeographic regions based on the occurrence of
freshwater molluscs in Canada are as follows:
1 ) The Atlantic Coastal Region
This area was populated by freshwater molluscs chiefly
from the Atlantic Coastal Plain to the south. Character-
istic species and subspecies are Lyogyrus granum ,
Margaritifera margaritifera,Anodonta cataracta cata -
racta, A. implicata , an dLampsilis ochracea.
2) The Lake Erie-Lake St. Clair Region
This rich drainage area in south-central Ontario was
populated from the Ohio -Mississippi system when
glacial meltwater in that region flowed south. It has
twelve unionid species not found elsewhere in Canada,
including Quadrula pustules a, Cyclonaias tuber culata,
Pleurobema coccineum,Ptychobranchus fasciolaris, and
Obliquaria reflexa. Some of its species also extend into
Region 3 .
3) The Great Lakes -St. Lawrence Region
The mollusc fauna of this area was derived from both
the Atlantic Coastal Plain and the American Interior
Basin. Characteristic species are Valvata perdepressa,
Pleurocera acuta , Goniobasis livescens,Acella halde-
mani , and Alasmidonta marginata.
22
4) The Red River -Assiniboine River Region
This rich area was populated from the upper Mississippi
River by migration through glacial meltwater channels
and possibly through recent confluence. Characteristic
species, many of which are found in Regions 2 and 3 but
originate from another source, include Cincinnatia
cincinnatiensiSyAmblema plicata,Fusconaia flava ,
Quadrula quadrula , and Propter a aiata . Some of the
species extend into Region 5.
5) The Western Prairie Region
This large region in southern Manitoba, Saskatchewan,
and Alberta was populated from the American Interior
Basin. Its characteristic species and subspecies are
Rakerilymnaea bulimoides,Stagnicola caperata,
Promenetus exacuous megas , Planorbula campestris,
and Helisoma trivolvis subcrenatum.
6) The Pacific Coastal Region
This region covers most of British Columbia and was
populated from the Pacific coastal area in the United
States. Characteristic species ar eFossaria truncatula ,
Physa columbiana, Margaritif era falcata,Gonidea angu-
lata, andAnodonta nuttalliana. As some species occur
only in the Columbia River system, that area might be
designated as a distinct subregion.
7) The Beringian Refugium
In Canada this region covers only the Yukon River
system in the Yukon Territory and northern British
Columbia and some small river systems in the
northwestern Northwest Territories. It was a refuge
area during the glacial period for many species, most of
which have now spread beyond its borders. Its most
distinctive species ar c Lymnaea atkaensis,Stagnicola
kennicotti , andAnodonta beringiana.
8) The Subarctic Region
The largest faunal zone in Canada, this region extends
south of the tree line from Labrador to the mouth of
the Mackenzie River. It largely coincides with the
Boreal Forest botanical region, and was populated
chiefly from adjacent regions to the south. Characteris-
tic species and subspecies are Stagnicola catascopium
preblei , Anodonta grandis simpsoniana , Sphaerium
nitidum , and Pisidium conventus.
23
9) The Arctic Region
This area extends north of the tree line to the southern
part of the Arctic Archipelago, and its fauna was
probably derived chiefly from the Beringian Refugium.
No freshwater molluscs occur farther north. Character-
istic species and subspecies are Valvata sincera helicoi-
dea^Stagnicola arctica , and Physa jennessi jennessi.
Thus, a collector travelling from one zoogeographic
region to another will encounter different species. The
whole molluscan fauna will not change, however, because
most species occur in more than one zoogeographic region.
For example, the common freshwater mussel Elliptio
complanata is found in Regions 1, 3, and 8, the abundant
pulmonate snail Stagnicola elodes occurs everywhere except
in the Arctic Region, and the ubiquitous pea clam Pisidium
casertanum occurs in all regions.
Molluscs as Pollution Indicators
Mollusc populations are affected by all three kinds of water
pollution— thermal, inorganic, and organic.
Thermal pollution sometimes occurs where river water is
used for industrial cooling. This may heat the water enough
to kill molluscs outright or adversely affect their reproduc-
tive cycles. If the warming is minor, however, mollusc
populations may actually increase.
Inorganic pollution is principally industrial. It may
poison water to the extent of killing all molluscs. Inorganic
pollution that kills some species but not others, however,
is difficult to detect biologically; no precise tolerance limits
are known for any species of freshwater mollusc exposed
to particular inorganic pollutants. Freshwater mussels live
for many years, and during each winter form a more or less
distinct growth ring on their shells. Chemical analysis of
the shells can reveal if water pollution from radioactive
materials or heavy metals has occurred, and when.
Organic pollution is usually caused by sewage and
insecticides. Chemical analysis of the soft parts of molluscs
can reveal recent pollution by insecticides. In natural water,
sewage is first attacked by bacteria that use oxygen. Because
bacteria increase rapidly in the presence of sewage, all the
oxygen dissolved in water may be used up. Nevertheless, as
the sewage is degraded and if no more sewage is added, a
sewage-polluted river will become reoxygenated down-
stream, and the water will become clean.
In water with little oxygen, pulmonate snails that come to
the surface to breathe air have an advantage over other
molluscs that must extract dissolved oxygen from water
with their gills. Gill-breathing molluscs are therefore the
first to be killed by low oxygen concentrations. A few gill-
breathers (for example Amblema plicata,Anodonta cata-
racta cataracta,A . grandis grandis , Sphaerium transversum ,
S, striatinum , andCampeloma decisum) appear to be
reasonably tolerant of low oxygen concentrations. Pulmo-
nates, however, are much more tolerant.
Low diversity, and especially the presence of only a single
species (usually of the genus Physa), is often indicative of
organic pollution. Physa , in fact, may be unusually
abundant in mildly polluted water because the species of
fish that would normally prey upon it cannot tolerate the
polluted environment. As a general rule, the presence of
highly diverse communities of freshwater molluscs gives
assurance of clean water.
No freshwater mussels are found in grossly polluted
water. Their absence from mildly polluted habitats may be
caused by the absence of their fish hosts, which may be
more susceptible to low oxygen than the mussels. The
presence of dense mussel beds indicates clean (but not
necessarily drinkable) water, partly because the substantial
amount of oxygen required over the long term is obviously
available and partly because the mussels themselves filter
and purify the water. High mussel diversity also indicates
high fish diversity, and implies good fishing.
The excellent recent volume edited by Hart and Fuller
(1974) gives a more detailed picture of the relationship
between molluscs and water pollution.
25
The Freshwater Molluscs
The following section contains illustrations, range maps,
descriptions, and comments about the distribution, ecology,
and biology of all the species and subspecies of freshwater
molluscs known to inhabit Canada. A few that have not
been recorded in Canada but are likely to migrate here are
also included.
Many species, especially freshwater mussels used in the
manufacture of pearl buttons, have long-standing common
names. Such names are given here. For species that do not
have them, I have proposed common names. In doing so,
I tried not simply to translate the scientific names but to
suggest names that give useful information about the
morphology, ecology or distribution of the species.
The structural terms used in the key and in the text are
defined on the endpapers and in the glossary.
The key that follows is meant to facilitate identification of
unknown molluscs by leading the collector directly to the
families they belong to. As familiarity with freshwater
molluscs grows, the family is identified more readily, but, to
begin with, use of the key will be helpful. The next step in
identification should be to compare the illustrations of the
species in that family and examine the range maps. Finally,
by reading the texts on description and habitat, the collector
should be able to pinpoint the species the specimen
belongs to.
The specimens illustrated in the black-and-white plates
that face each of the species descriptions are from the
collection of the National Museum of Natural Sciences,
Ottawa, and were collected over many years in Canada and
the northern United States. The caption under each plate
indicates either the specimens’ actual measurements or the
percentage enlargements. For plates 1 to 90, the captions
give the largest dimension of all the specimens illustrated,
but in plates 91 through 144 the measurements are those
of only the largest of the two pairs depicted. The pea clams
illustrated in plates 160 to 179 were photographed through a
scanning electron microscope, and only the magnifications
are given.
27
The colour plates are reproductions of watercolours
painted from actual specimens especially for this book. The
specimens appear in taxonomic order on the plates, and
are identified by their scientific name and by the number
allotted to that species or subspecies in the text. Information
on where the specimens were obtained can be found in the
corresponding species descriptions, under the captions for
the black-and-white plates. The specimens are reproduced
2/3 of actual size, except for No. 136, which is life size.
It is helpful to remember that in all likelihood the first
species collected will be those most abundant in the region.
For example, among the freshwater mussels or clams of
eastern Canada Elliptio complanata is dominant, in the
prairies Lampsilis radiata siliquoidea is the most common,
and in British Columbia Anodonta kennerlyi an dMargariti-
ferafalcata are the most abundant. Among the Lymnaeidae,
the first species found is usually Stagnicola elodes , and
among the pill clams (Pisidium) probably P. casertanum.
Also important to remember is that living land snails are
sometimes found in shallow water, and that empty shells
of terrestrial snails commonly occur in beach drift. If a
Canadian “freshwater” snail does not appear in this book, it
is probably a land snail. These can be identified by using
Pilsbry (1939-48) or Burch (1962). In some parts of Canada,
for example in the Ottawa region and in the vicinity of
Hudson Bay, Pleistocene fossil marine shells also occur in
beach drift. In a few areas, such as the St. Lawrence River
estuary, some freshwater-tolerant marine molluscs also live
in close association with true freshwater species. Marine
molluscs can be identified by using Abbott (1974) or
Bousfield (1960).
The host fishes for freshwater mussels, where known, are
recorded under their standardized common names following
the list published by the American Fisheries Society (Bailey
etal. 1970).
28
Key to the Families of
Canadian Freshwater Molluscs
1 Shell double, i.e. composed of two halves or valves
Shell single, i.e, spiral or cap-shaped
2 Shell small, 25 mm long or less (except up to 50 mm
in Corbicula ), with small to medium-sized pseudo-
cardinal hinge teeth and with lateral hinge teeth both
in front of the pseudocardinal teeth and behind them
Shell larger, more than 25 mm long in most specimens,
and with hinge teeth not as above
3 Shell less than 25 mm long; lateral hinge teeth not
serrated
Shell up to 50 mm long; lateral hinge teeth finely
serrated
4 Shell small, cap-shaped, without hinge teeth and with a
clearly defined apex that is not near the margin
Shell spiral and not as above
5 Shell more than S mm long; Columbia River system
only
Shell 8 mm long or less
6 Apex sharply pointed, acute and located posteriorly and
to the left; rare
Apex blunt and located posteriorly and in the midline
or to the right; common
7 Living snail with an operculum
Living snail without an operculum
8 Shell medium-sized to large, i.e. more than 12 mm
high, and with a horny operculum
Shell smaller than 12 mm or with a calcareous
operculum
Pelecypoda (clams or
mussels) 2
Gastropoda (snails) 4
3
Superfamily UNIONACEA*
(3 families) (p. 247)
Family SPHAERIIDAE
(p. 361)
Family CORBICULIDAE
(p. 357)
(freshwater limpets) 5
7
Family LANCIDAE (p. 93)
6
Family ACROLOX1DAE
(P- 89)
Family ANCYLIDAE
(P- 219)
8
13
9
10
*The families of freshwater mussels or clams (super-
family Unionacea) are not separable on shell characters
alone; therefore, Unionacea is keyed out here as a unit.
29
9 Width more than half the height
Width less than half the height
10 Shell more than 9 mm high and with a calcareous
operculum; eastern Canada
Shell less than 9 mm high or with a horny operculum
1 1 Shell wider than high, with or without strong spiral
ridges, and with a nearly circular aperture; operculum
multispiral
Shell higher than wide, without strong spiral ridges,
and with an ovate aperture; operculum paucispiral
12 Shell small, up to 5,5 mm long, slender (width divided
by height about 0,55-0.60), with up to 7 whorls, an
ovate aperture, and a distinct lip that surrounds the
aperture; amphibious; southeastern Canada only
Shell relatively wider or with fewer than 7 whorls or
without a distinct lip that surrounds the aperture;
wholly aquatic; widespread
13 Shell disc-shaped or spire projecting only a little above
body whorl; shell width greater than height
Spire projecting much above body whorl; shell width
less than height
14 Shell dextral or right-handed
Shell sinistral or left-handed
Family VIVIPARIDAE
(P- 33)
Family PLEUROCER I DAE
CP- 81)
Family BITHYNIIDAE
(P- 77)
11
Family VALVATIDAE
(P- 41)
12
Family TRUNCATELLIDAE
following Taylor (1966).
DISTRIBUTION
Columbia River system from the Kootenay
and Wigwam rivers in southern British
Columbia south through Idaho, western
Wyoming, northern Utah, Washington, and
Oregon. Found also in the Olympic Penin-
sula of Washington.
ECOLOGY
In the northwest United States this species
lives on and under rocks and among
vegetation in large and medium-sized lakes,
in rivers, and in creeks. Currents at its river
localities may be rapid to slow.
70
17
Lithoglyphus virens
a: Creek near Olympia, Wash.; 8.1 mm,
b: Siuslaw River, Oreg.; 8.3 mm.
71
FAMILY TRUNCATELLIDAE
(Looping Snails)
Shells small, dextral, with an elevated spire, more or less
cylindrical, umbilicate or non-umbilicate, and smooth or
sculptured. Operculum horny and paucispiral. Dioecious.
A few species are intermediate hosts for blood flukes, which
are parasites of warm-blooded animals, including man. The
family is worldwide. Some species live in fresh water, others
are amphibious, some live in the litter zone of salt-water
beaches, and others are wholly terrestrial.
73
18
Pomatiopsis lapidaria
(Say, 1817)
River-Bank Looping Snail
DESCRIPTION
Shell small, up to about 5.5 mm high,
slender (W/H ca. 0.55-0.60), rather strong,
and with about 7 flatly rounded whorls.
Nuclear whorl rounded and projecting
slightly above the following whorl. Spire
high, acute, subtending an angle of about
45°, and with slightly bulging sides. Whorls
flatly rounded and separated by incised
sutures. Aperture ovate, barely touching the
penultimate whorl. Lip thickened and sur-
rounding the aperture. Umbilicus mainly
exposed and deep. Periostraeum reddish
brown to brown. Sculpture consisting of
rather fine but prominent and crowded
collabral lines.
Similar to Hydrobia nickliniana (Lea,
1839) except that in H. nickliniana the lip is
not thickened, the aperture is larger, and
the whorls are more convex. Moreover,
H. nickliniana is aquatic, not amphibious;
it is a doubtful inhabitant of Canada but
it may occur in southern Ontario.
DISTRIBUTION
In Canada, this species has been found at
only a few places in southern Ontario,
namely the Sydenham River at Alvinston,
the Thames River near Chatham, and the
Ottawa River near Ottawa. In the United
States it occupies a broad area from the East
Coast to the midwest and south to Texas.
ECOLOGY
Amphibious. Lives on wet ground princi-
pally along the edges of streams. Eggs are
laid in the soil from spring to late summer.
It is capable of serving as the intermediate
host of the oriental blood fluke, Schistosoma
japonicum.
Another species of Pomatiopsis, P. cincin-
natiensis (Lea, 1840), is recorded from
southern Ontario by some authors, but I
have seen no specimens from Canada. It is
relatively wider than/ 5 , lapidaria and is also
amphibious.
74
a
IS
Pomatiopsis lapidana
a: Sydenham R. near Alvin ston, Ont.; 5.5 mm.
b: Thames R. near Chatham, Ont.; 5.2 mm.
75
FAMILY BITHYNIIDAE (Faucet Snails)
Shell small to small-medium, dextral, slender to broad, with
an elevated spire, umbilicate or non-umbilicate, and smooth
(in most species) or sculptured. Operculum calcareous and
paucispiral or with concentric growth lines. Tentacles long,
pointed, and tapering. The radula has 7 teeth in each row
(fomula 2- 1-1-1- 2) and each tooth has many cusps.
Dioecious. Eggs are laid in groups. The family is world-
wide. Previously known as Bulimidae. Bithyniidae and
Bithynia are now nomina conservanda.
77
19
Bithynia tentaculata
(Linnaeus, 1767)
Faucet Snail
DESCRIPTION
Shell large, up to 13 mm high, moderately
inflated (W/H 0.57-0.68), conical, with
5-3/4 whorls, and with a sharply rounded
apex. Nuclear whorl smooth, shining, and
decurrent. Spire acutely produced. Spire
whorls flatly convex and separated by
impressed sutures. Aperture less than half
the shell height, ovate, but acute above. Lip
continuous and somewhat thickened. No
umbilicus. Periostracum shining and pale
brown. Sculpture consists of growth rests
and crowded, fine collabral threads. Opercu-
lum white and calcareous.
This common species may be recognized
by its large size, calcareous operculum,
and lack of an umbilicus. It is often cited
as Bythinia tentaculata (L) or Bulimus
tentaculatus (L).
DISTRIBUTION
Introduced and now widespread in the
lower Great Lakes-St. Lawrence system,
also in the mid-Atlantic United States.
Native to Europe.
ECOLOGY
Lives in shallow water in large lakes, large
rivers and canals, where it feeds on filamen-
tous algae. Very abundant in favourable
situations. The breeding season is in July
and August, and egg capsules are deposited
principally on the shells of other
individuals.
78
19
Bithynia tentaculaia
a,b: Trent R. near Trenton, Ont.; a 9.6 mm, b 10.1 mm,
c: South Nation R. near Plantagenet, Ont.; 1 1.0 mm.
79
IV Superfamily Cerithiacea
FAMILY PLEUROCERIDAE (Horn Snails)
Shell small to medium-sized, dextral, of medium width,
high spired, rather heavy-shelled, non-umbilicate, and
smooth to highly sculptured. Operculum horny and
paucispiral. Tentacles long, tapering, and very narrow; foot
short and wide. The radula has 7 teeth in each row (formula
2- 1-1- 1-2) and each tooth is multicuspid. The animals
are dioecious but males lack a penis. Eggs are laid singly or
in small groups. Predominantly a North American family,
but with a few representatives in eastern Asia.
81
20
Pleurocera acuta
Rafinesque, 1831
Flat-sided Horn Snail
DESCRIPTION
Shell up to about 37 mm high, narrow
(W/H ca. 0.35-0.42), attenuated but vari-
able, and rather thick and heavy. About 14
flat- sided whorls (earliest whorls ordinarily
corroded away). Early whorls with 2 spiral
carinae but later whorls smooth and form-
ing an even, flat-sided cone. Body whorl
angular at the periphery and with or without
carinae. Aperture small, about 25% to 30%
the height of the shell, with a sigmoid outer
lip and a broad canal at the base. No
umbilicus. Periostracum blackish, brown-
ish, or yellowish brown. Sculpture, in
addition to that mentioned, consists of
sigmoid collabral lines. Operculum reddish
brown, corneous, and paucispiral with
3 whorls, an acentric, sunken nucleus, and
well-marked growth lines and fine striae.
Larger th&n Goniobasis livescens , with
flat-sided rather than flatly curved whorls,
no callus on the parietal wall (in G. livescens
a callus is present), a twisted instead of
smooth columella, and a body whorl that is
angular at the periphery rather than
rounded. Also the aperture is relatively
smaller, more angulate, and with a broad
canal below.
DISTRIBUTION
Great Lakes- St. Lawrence system, upper
Ohio-Mississippi drainage, and Erie Canal
and contiguous waters in New York State.
ECOLOGY
Found in quiet areas of large streams and in
lakes. A burrowing species that prefers
mixed sand and mud bottoms. Eggs are
deposited in sand-covered masses from
April to June.
82
20
Pleurocera acuta
a,b,c: Grand R., Grand Rapids, Mich.; a 26.7 mm,
b 24.6 mm, c 27.3 mm.
d: L. Erie near St. Williams, One.; 20.2 mm.
83
21
Goniobasis livescens
(Menke, 1830)
Great Lakes Horn Snail
DESCRIPTION
Shell up to about 25 mm high, rather
narrow (W/H ca. 0.38-0.50), more or less
attenuated but highly variable in shape, and
of medium thickness. Up to about 10 flat,
flatly rounded, or rounded whorls (but
earliest whorls ordinarily corroded away).
Early whorls with a low but prominent
spiral carina just above the suture. Later
whorls without a carina and, in many
specimens, bearing coarse, collabral wrin-
kles. Suture bordered below by a narrow,
pale-coloured band. Aperture sharply
rounded below, acute above, about 35% to
40% the height of the shell, and in some
specimens brownish within. No umbilicus.
Sculpture, in addition to carinae and wrin-
kles, of fine collabral lines and, in some
specimens, also a few low, spiral bands.
Colour yellowish, brown or black. Opercu-
lum brown, corneous, and paucispiral with
3 whorls, an acentric nucleus and radial
striae.
Sometimes confused withPleurocera
acuta. See that species.
DISTRIBUTION
Widespread in the Great Lakes-St. Law-
rence system. Also in the Erie Canal in New
York and in some contiguous water bodies.
ECOLOGY
Occurs in lakes, rivers, streams of all sizes,
and springs. Frequently found crawling
on stones in a few centimetres of water in
clear, rapid streams, but also lives at several
metres depth in lakes. Eggs are laid singly
or in small groups from April to August.
S4
ATT l
a
21
Goniobasis livescens
a,b: South Nation R. near Plantagenet, Ont.;
a 18.7 mm, b 17,6 mm.
c: Salmon R., Hastings Co., Ont.; 17.6 mm.
85
22
Juga plicifera (Lea, 1838)
Graceful Keeled Horn Snail
DESCRIPTION
Shell up to about 35 mm high, narrow
(W/H ca. 0.28-0,35), attenuate but variable.
About 15 whorls (the early whorls ordinarily
corroded away), with about 1 0 to 12 heavy
axial plicae on each whorl (in some
specimens obsolete on the latest whorls or
confined to the upper halves of those
whorls), and with numerous spiral cords.
Earliest 3 or 4 whorls very convex and more-
or-less smooth. Aperture rounded below,
acutely angled above, with a sigmoid outer
lip, and with a broad canal below the
columella. Periostracum blackish or brown.
Sculpture (in addition to above) of heavy
sigmoid growth rests and fine collabral
threads. Operculum ovate, with about
3 whorls, dark brown except paler above,
and with nucleus near centre of lower part.
This is the only species of Juga living
in the State of Washington and therefore the
only one from the northwestern United
States likely to be found in Canada.
3 . silicula (Gould, 1847) is a synonym.
DISTRIBUTION
Olympic Peninsula of Washington and
south in the Columbia and other drainage
systems to California. Doubtfully recorded
from Vancouver Island. Possibly in south-
ern British Columbia.
ECOLOGY
Occurs in muddy-sand bottoms of small and
medium-sized lakes and slow-flowing
streams. Like Pleurocera acuta , it burrows
in the substrate. The animal is pale dusky-
grey, with dark transverse stripes on the
head and tentacles. Distinguished from
Pleurocera and Goniobasis on the basis of
genitalia and egg-mass formation (see
Taylor 1966; Clarke 1976),
86
87
Subclass Pulmonata
(Lung-breathing Snails)
Order Basommatophora
V Superfamily Acroloxacea
FAMILY ACROLOXIDAE
(Primitive Freshwater Limpets)
Shell small, limpet- or cap-shaped, thin, with an ovate
aperture, distinct radial sculpturing, and an acute apex
located posteriorly and to the left of the midline. The
anatomy is dextral whereas in Lancidae and Ancylidae it is
sinistral. The radula has many (about 10 to 15) marginal
teeth and about 4 to 7 lateral teeth on each side of the central
tooth. The egg capsules are transparent, gelatinous, and
contain a small number of eggs. The family is predomi-
nantly Eurasian; there is but one North American species.
89
23
Acroloxus coloradensis
(Henderson, 1939)
Pointed Lake Limpet
DESCRIPTION
Shell up to about 4,6 mm long, 2.9 mm wide
and 1.2 mm high, limpet-shaped, thin
shelled, elliptical or ovate, and with a
prominent, characteristic apex. Apex
sharply pointed, pinched, thorn-like, located
behind the centre and directed to the left,
and radially striate with the striae continu-
ing over the surface of the shell to the
margin. Anterior, posterior, and lateral
surfaces all flattened, or anterior surface
slightly convex and/or posterior surface
somewhat concave. Anterior and posterior
margins rounded and lateral margins flatly
convex and, in some specimens, convergent
posteriorly, Periostracum of moderate thick-
ness, brown, and adherent. Surface sculp-
tured with fine radial striae and fine lines of
growth.
Can be easily distinguished by its sharp,
spine-like apex, which is directed poste-
riorly and toward the left margin. In other
freshwater limpets, the apex is rounded, not
pinched, and in the midline or on the right
of centre.
DISTRIBUTION
At the present time is known from only a
very few localities in the Rocky Mountains,
namely Purden Lake near Prince George,
British Columbia, Jasper National Park
in Alberta, and Montana and Colorado; in
eastern Canada only from Matheson and
Arkell, Ontario, and the Chibougamau area
of Quebec.
ECOLOGY
Rare. Characteristic of rocky, exposed por-
tions of oligotrophic and mesotrophic lakes,
where it occurs in shallow water on the
undersides of rocks. It has also been found
in a eutrophic pond (near Arkell, Ontario)
attached to logs. Egg capsules are pale
yellow and contain 2 or 3 eggs. The radula
formula is about 7-13-1-13-7.
90
23
Acroloxus color ademis
a,b: L. Gabrielle, Chibougamau region, Que. ; 4.7 mm.
c,d: Pond northeast of Arkell, Halton Co., Ont.;
4.7 mm.
91
VI Superfamily Lymnaeacea
FAMILY LANCIDAE
(Limpet-like Lymnaeas)
Shell small-medium, limpet- or cap-shaped, rather thin,
with an ovate aperture, concentric and radial striae, and a
distinct blunt apex located in the midline and subcentral to,
or in front of, centre. A ring-shaped muscle scar is visible
in the interior. The anatomy, jaw, and radula are similar to
Lymnaeidae, not to Acroloxidae or Ancylidae. The egg
capsules are sausage-shaped, transparent, gelatinous, and
contain only a few eggs. The family consists of only the
genus Lanx but there are three subgenera, Lanx y Fisher ola>
and Walkerola. It is restricted to Pacific coastal drainages
from the Columbia to the Sacramento River system.
93
24
Lanx (Fisher old) nuttalli
(Haldeman, 1841)
Greater Columbia-River
Limpet
DESCRIPTION
Shell limpet-like, up to about 13 mm long,
10 mm wide, 6 mm high, and with the apex
prominent in the midline and placed close
to the anterior end. Apex smooth. Anterior
and posterior margins more sharply rounded
than lateral margins. Anterior slope straight
or concave. Posterior slope convex. Interior
bluish or purplish in the central portion
but whitish around the edge. A subovate
muscle scar encircles the inner portion of
the shell; this scar is continuous except for a
gap on the right side. Periostracum brown
to brownish black. External sculpturing
consists of concentric growth rests, fine
concentric lines, and more or less discern-
ible radial striae.
The relatively large and heavy shell of
this species distinguishes it from all other
North American limpets. The anterior apex
and the discontinuous ring-like muscle
scar will distinguish L. nuttalli from other
species of Lanx .
ECOLOGY
Occurs in the Columbia River upstream
horn Richland, Washington, on diatom-
covered rocks in the main channel of the
river, which is free-flowing in that region.
Living specimens are accessible only dur-
ing periods of low water in the late summer
or early fall.
DISTRIBUTION
Columbia River and its tributaries in the
northwestern United States, Not yet found
living in Canada although recently
Dr, Leonard Kalas reported finding a bro-
ken shell in the Columbia River at Trail,
British Columbia.
94
24
Lanx nuttalli
a,b: Columbia R, near McNary Dam, Benton Co,,
Wash.; 12.2 mm
c,d: Another specimen, same locality; 9.4 mm.
95
FAMILY LYMNAEIDAE (Pond Snails)
Shell small to large, dextrally coiled, mainly thin-shelled,
with an elevated spire, with or without an umbilicus, and
without an operculum. Tentacles short, triangular, and
flattened. The jaw has 3 plates and the radula has a small
central tooth, a few bi- or tricuspid laterals and many bi-, tri-
or multicuspid marginals. Monoecious (male and female
organs in the same animal) and capable of self- or cross-
fertilization. Egg masses are gelatinous, transparent, colour-
less, sausage-shaped, and contain from a few to many eggs.
The family is worldwide.
97
25
Fossaria decampi (Streng, 1896)
Shouldered Northern Fossaria
DESCRIPTION
Shell up to about 1 1 mm high, 5 mm wide,
with 6 shouldered whorls (most specimens
are much smaller) and with aperture about
45% to 60% of the shell height, lymnae-
iform, dextral, and of medium thickness.
Nuclear whorls satiny, brown, and forming
a bluntly rounded apex. In many specimens
the brown colour extends to the penultimate
whorl and contrasts with the whitish body
whorl. Whorls abrupdy to roundly shoul-
dered, and separated by deep sutures.
Aperture narrow, abruptly arched and
rounded above, flattened laterally, and
broadly rounded below. Inner lip narrowly
reflected and, in its lower part, erect.
Umbilical chink prominent and bordered by
inner lip. Sculpture consisting of growth
rests and numerous fine, closely spaced
collabral lines and ridges.
This small species may be recognized by
its shouldered whorls, laterally flattened
body whorl, elevated and reflected inner lip,
and characteristic aperture that is narrowly
arched above and broadly rounded below.
DISTRIBUTION
Great Lakes-St. Lawrence drainage north
to the Hudson Bay lowlands and the
Mackenzie River, and west to British
Columbia. Its southern limits have not been
determined.
ECOLOGY
A cold-water species occurring only in large
lakes in the southern part of its range and
in both lakes and rivers in the northern part.
It lives among submersed vegetation and
on various kinds of bottom. Radula formu-
lae of 20-1-19 to 23-1-22 have been found.
The first lateral teeth are tricuspid.
98
25
Foss ana decampi
a: Halkett L., Prince Albert National Park, Sask.;
11 ,2 mm.
b: Edith L. near Jasper, Alta.; 9.4 mm.
99
26
Foss aria exigua (Lea, 1841)
Graceful Fossaria
DESCRIPTION
Shell up to about 9 mm high, 4 mm wide,
with 5-1/2 whorls (most specimens are
smaller) and with aperture about 45% to
50% of shell height, lymnaeiform, dextral,
narrow, attenuated, and thin-shelled. Nu-
clear whorls satiny and dome-shaped. Spire
extended and subtending an angle of about
40°. Spire whorls as high as wide, or higher
than wide, and roundly shouldered. Sutures
deeply impressed. Body whorl flattened,
subcylindrical and about 2/3 the length of
the shell. Aperture ovate, slightly flared
at base, outer lip thin, and inner lip slightly
reflected with the lower part nearly erect.
Umbilicus small and narrowly open, or
closed by the reflected lip. Periostracum
partly or wholly brown. Sculpture consist-
ing of fine collabral lines, irregular growth
rests and, in some specimens, poorly de-
fined spiral lines.
This small snail may be identified by its
narrow and attenuate form and its tall and
roundly shouldered whorls. Compare with
F. modicella andF. parva.
DISTRIBUTION
Great Lakes-St. Lawrence system north to
the Hudson Bay lowlands, west to Manitoba
and Minnesota, and south in the Ohio-
Mississippi system to Alabama.
ECOLOGY
Lives among vegetation in protected parts
of lakes and ponds, in backwater areas of
rivers, in swamps, and in subarctic muskeg
pools. Mud is the usual substrate. Radula
formulae of 20- 1-21 to 25-1-25 have been
recorded.
100
26
Foss aria exigua
a: Lower Red L., Minn.; 7.9 mm.
b: Attawapiskat R. near Attawapiskat, Ont.; 8.1 mm.
c : Winisk R. near Winisk, Ont.; 8.4 mm.
101
27
Fossaria ferruginea
(Haldeman, 1841)
Fragile Fossaria
DESCRIPTION
Shell up to about 8 mm high, 4 mm wide,
with 5 rounded whorls and with aperture
about 50% to 55% of shell height, lymnae-
iform, dextral and thin-shelled. Spire ex-
tended and subtending an angle of about
45°. Sutures impressed. Aperture ear-
shaped, outer lip convex and gently rounded
above, inner lip narrow and reflected.
Umbilicus closed by inner lip or left open
only as a small chink. Periostracum yellow-
ish brown or reddish and shining. Sculpture
of narrow, clearly defined collabral lines
and faint, irregular spiral lines.
Differs from F. truncatula in that the
whorls are sharply rounded above, the
sutures are not deep, the shell is very thin
0 truncatula is strong and solid), and the
umbilicus is nearly or completely closed.
DISTRIBUTION
Fraser River drainage (Hatzic Lake) and
Columbia River drainage (Duck Lake near
Creston) in British Columbia south to
central California.
ECOLOGY
The scant information available indicates
that it lives among dense vegetation in
eutrophic lakes. Other habitats, however,
may also be occupied. Nothing is known
about its reproduction, radula, or soft
anatomy.
102
27
Fossaria ferruginea
a: Duck L. near Creston, B.C.; 10.0 mm (spire broken).
b,c: Shuswap L. near Salmon Arm, B.C.; b 7.9 mm,
c 8.2 mm.
103
28
Fossaria modicella (Say, 1825)
Modest Fossaria
DESCRIPTION
Shell up to about 9,5 mm high, 5 mm wide,
with 5-1/2 whorls and with aperture about
45% to 55% of shell height, lymnaeiform,
dextral, elongated, and moderately thin-
shelled. Nuclear whorls satin-like and
bluntly dome-shaped. Spire moderately at-
tenuate and spire angle about 40° to 45°.
Whorls flatly rounded, without shoulders,
and not as high as wide. Sutures well
marked but not deep. Aperture subelliptical.
Outer lip thin and convex; inner lip slightly
thickened, narrow, somewhat reflected or
turned up, and straight or bent just above
the umbilicus. Umbilicus small and open.
Periostracum light brown or yellowish
brown. Sculpture consisting of fine colla-
bral lines and ridges, irregularly spaced
growth rests and, in some specimens,
numerous fine spiral lines.
Differentiated fromf. exigua by the
absence of whorl shouldering and by the
relative height of the whorls (height less
than width in modicella , equal or greater
than width in exigua ). Differs from
F. parva , in that the whorls are more flatly
rounded, the sutures are not deep, the
aperture is elliptical rather than rounded,
and the umbilicus is not partly obscured by
the inner lip.
DISTRIBUTION
North America south of the tree line, except
not recorded from the southeastern United
States or Mexico.
ECOLOGY
Occurs in perennial lakes, ponds, and
streams, and in vernal pools and ditches.
Also occurs on moist sandy or muddy
beaches. Vegetation is normally present,
and the most commonly observed substrate
is mud. The radula formula is reported as
25-1-25 but no doubt some variation exists.
For a discussion of the problematic
Fossaria modicella morph rustica see Clarke
(1973) and references cited there.
104
28
Fossaria modicella
a: Kakisa L. near Great Slave L., N.W.T.; 7,2 mm.
b: L. Manitoba, Man.; 7.1 mm.
105
29
Fossariaparva (Lea, 1841)
Amphibious Fossaria
DESCRIPTION
Shell up to about 8 mm high, 4 mm wide,
with 5-1/2 whorls and with aperture about
40% to 50% of shell height, lymnaeiform,
dextral, and of moderate thickness. Nuclear
whorls satiny, about 1-1/4 in number and
forming a rounded apex. Spire angle about
45°. Whorls very convex and rounded with
deep sutures. Aperture medium-sized, uni-
formly ovate or, in many specimens, with
inner lip centrally indented and continuous.
Outer lip thin and convex; inner lip wide
and reflected. Umbilicus clearly defined,
deep, and partly covered by the inner lip.
Periostracum yellowish brown to brown.
Sculpture is of crowded, fine collabral lines,
irregular growth rests, and obscure spiral
lines.
Distinguished by its roundly convex
whorls, incised sutures, rounded aperture,
reflected inner lip, and open umbilicus.
Its amphibious habits are also distinctive.
Compare with F. modicella, Bakerilymnaea
bulimoides morph perplexa, and B. dalli.
DISTRIBUTION
Occurs throughout most of North America
north of 36° latitude and south of the tree
line, except that it is absent from both
eastern and western coastal drainage sys-
tems, In the Rocky Mountains it extends
south to Arizona and New Mexico.
ECOLOGY
Amphibious. Lives on wet mud flats, lake
shores and river banks near the water’s edge,
and in marshes. Also occurs among vegeta-
tion submerged in shallow water but is more
prone than any other lymnaeid to leave the
water. Radula formulae of 16-1-16 to
24 1-24 have been recorded.
106
29
Fossaria parva
a: Wain wright Park, Wainwright, Alta.; 7.3 mm.
b,c: Pond near Whitemud Creek, west of Edmonton,
Alta. ; b 4.4 mm, c 5.0 mm.
107
30
Fossaria truncatula
(Muller, 1774)
Liver-Fluke Fossaria
DESCRIPTION
Shell up to about 1 1 mm high, 6 mm wide,
with 5-1/2 rounded whorls (most specimens
are smaller) and with aperture about 40%
to 50% of shell height, lymnaeiform, dex-
tral, and fairly solid. Nuclear whorls 1-1/4 in
number, with the first whorl very small
and the next much larger. Spire extended
and turreted; spire angle about 45°. Sutures
deeply impressed. Aperture ovate; outer
lip thin, convex, and abruptly rounded
above; inner lip folded back. Umbilicus
open and partly covered by the broad
reflexed inner lip. Periostracum pale yellow-
ish brown or greyish brown and shining.
Sculpture consisting of fine collabral lines
and fine, irregularly spaced spiral lines.
The strongly rounded whorls (shouldered
in many specimens), solid shell, deep and
partly obscured umbilicus, and general
appearance are such distinctive features that
identification of this species, once seen,
can confidently be made. Compare with
F. ferruginea.
DISTRIBUTION
Columbia River drainage in British Colum-
bia (Osoyoos Lake, stream near Bridesville,
Christina Lake, and Duck Lake near
Creston), and Yukon River drainage in the
Yukon Territory and Alaska. The species is
widespread in Europe and in central Asia.
It is also reported in Iceland and in scattered
localiues in Africa.
ECOLOGY
Occurs among vegetation in permanent
lakes, ponds, streams, and marshes. Usual
substrate is mud. The species is an interme-
diate host for the sheep-liver fluke. Fasciola
hepatica . The first lateral radula teeth are
tricuspid.
108
30
Fossaria truncatula
a: Osoyoos L., B.C.; 10.0 mm.
b: Stream near Bridesville, B.C.; 10.7 mm.
109
31
Bakerilymnaea bulimoides
(Lea, 1841)
Prairie Pond Snail
DESCRIPTION
Shell up to about 1 1 mm high, 7 mm wide,
with 5-1/2 whorls and with aperture length
about 40% to 63 % of the shell height,
lymnaeiform, dextral, and highly variable in
shape- The spire may be acutely pointed
and pinched (morph techella), acute but not
pinched (morphs alberta, perplexa , and
Vancouver ensis), subacute and somewhat
bulbous (morph bulimoides s. str.), or broad,
rounded, and obtuse (morph cockerelli).
Nuclear whorl smooth, satiny, and brown.
Sutures impressed. Body whorl inflated and
dominant, especially in morph cockerelli.
Aperture subovate. Outer lip with a thick-
ened internal varix (reddish-brown in many
specimens) behind the edge. Inner lip broad
and extending over the umbilicus but not
obscuring it. Periostracum brown to greyish
brown. Sculpture consisting of fine colla-
bral lines and, in some specimens, also of
finer spiral striae. Irregular dark-brown and
whitish collabral streaks may also be
present.
This highly variable species is best
distinguished by its characteristic shell
forms (in morphs techella, bulimoides s. str .
and cockerelli , see figures) and by its
expanded columella. Morphs alberta and
perplexa (which appear to be synonymous)
are similar to Fossaria parva but differ in
having slightly thicker shells and broader
reflected inner lips. Morph vancouverensis ,
a giant form (18 mm) from southern
Vancouver Island, is intermediate between
morphs techella and bulimoides s. str. in
shell form and may be a distinct subspecies.
Examination of the radula may be necessary
for positive identification. Species of Fos-
saria have tricuspid first lateral teeth, while
those of Bakerilymnaea are bicuspid.
DISTRIBUTION
Southern Manitoba to southeastern British
Columbia and southern Vancouver Island.
In the United States the region west of the
vicinity of the Mississippi River.
ECOLOGY
Lives in perennial-water habitats (lakes,
ponds, and slow-moving streams) and vernal
habitats (roadside ditches, temporary pools).
Ordinarily occurs among dense vegetation
that is growing on a mud bottom. Radula
formulae of 20-1-19 to 23-1-23 have been
recorded.
110
31
Bakerilymnaea bulimoides
a: Morph cockerelli : pool near Taber, Alta.; 5.5 mm.
b: Morph bulimoides s. str . : pool near Aldersyde, Alta.;
11.4 mm.
c: Morph techella: pool near Cayley, Alta.; 10.5 mm.
d: Morph perphxa : ditch near Eisenhower Junction,
Alta.; 4.7 mm.
Ill
32
Bakerilymnaea dalli
(Baker, 1907)
Small Pond-Snail
DESCRIPTION
Shell up to 6 mm high, 3.3 mm wide, with
5 whorls and with aperture about 45% to
55% of shell height, lymnaeiform, and
dextral. Whorls convex, roundly shouldered
and 5 in number. Nuclear whorl small,
flatly rounded, brownish and satiny. Sutures
very deep. Spire angle about 50°. Aperture
ovate and lip continuous in many speci-
mens. Outer lip evenly rounded. Inner lip
flatly reflected over the umbilicus, which is
small but clearly defined. Sculpture consist-
ing of fine collabral threads and finer but
somewhat obscure spiral striae.
Recognized by the large number of
whorls in relation to its very small size, by
its incised sutures, and by its roundly
shouldered whorls. Compare with Fossaria
parva.
DISTIBUTION
Southern Ontario and Ohio west and north
to the Prairie Provinces and eastern British
Columbia, and south to Arizona. Details
of its southern distribution have not been
worked out,
ECOLOGY
Lakes, ponds, small rivers, and marshes are
all suitable habitats for this small species.
Vegetation is present and bottom deposits
are of diverse types. Does not normally
occur out of the water and thereby differs
from Fossaria parva. Radula formulae of
22-1-21 and 21-1-21 have been recorded.
The first lateral teeth are bicuspid.
112
32
Bakerilymnaea dalli
a: Creek near Edson, Alta.; 5.4 mm.
b: Wigwam R., B.C.; 4.7 mm.
113
33
Radix auricularia
(Linnaeus, 1758)
European Ear Snail
DESCRIPTION
Shell up to about 30 mm high, 25 mm wide
(most specimens are half this size), with
5 whorls, swollen lymnaeiform, dextral,
thin, and fragile. Spire short, acute, and
pinched in many specimens. Body whorl
greatly swollen, enlarged, and constituting
more than 90% of the volume of the shell.
Aperture ear-shaped, patulous, dilated, and
even extending above the spire apex in some
specimens. Periostracum thin and pale
brown or golden. Sculpture consists of
crowded collabral lines, microscopic spiral
lines and often irregular malleations or
flattened spiral bands.
The bulbous body whorl and small,
sharply pointed spire of this large species
distinguish it from all others. Compare with
Lymnaea stagnalis sanctaemariae.
DISTRIBUTION
Native to Eurasia but has been widely
introduced in North America, especially,
but not exclusively, in the vicinity of major
cities. Known to occur in western Canada at
Banff, Alberta, and in British Columbia in
Kootenay Lake, the Okanagan River
system, and North Vancouver.
ECOLOGY
Occurs in lakes, ponds, and slow-moving
rivers. Mud is a frequent substrate. The
radula formula is approximately 50-1-50,
with the first lateral tooth tetracuspid.
114
33
Radix auricularia
a: Pond, Warm Spring, Park Co., Colo.; 25.0 mm.
b: Lava L,, Deschutes Co., Oreg,; 18.8 mm.
115
34
Radix peregra (Muller, 1774)
Wandering Snail
DESCRIPTION
Shell up to about 7 mm high, 5 mm wide,
with 3-1/2 whorls and with aperture height
about 75 % of shell height, obese lymnae-
iform, dextral, and thin-shelled. Whorls
flatly rounded. Nuclear whorl rounded,
shining and finely punctate. Spire short,
broad, and with spire angle exceeding 90°.
Body whorl ovate, dominant, and about 90%
as long as the shell. Aperture ovate, wide
and long, and with thin, broadly curved
outer lip and flattened inner lip that bears a
thin callus. Umbilicus closed by the re-
flected inner lip. Periostracum brownish.
Surface shining and sculptured by distinct,
fine, collabral lines and ridges and obscure
spiral lines.
Resembles Radix auricularia but North
American specimens are much smaller
and their apertures are less expanded. In
addition, the first lateral radular teeth are
tricuspid, not tetracuspid as ini?, auricu-
laria. Compare also with Pseudosuccinea
columella.
DISTRIBUTION
This is a common Eurasian and North
African species. It also occurs in Iceland. In
North America it is known only from a few
localities in southern Newfoundland.
ECOLOGY
Lives in ponds, other quiet waters, and
stagnant habitats. In this book it is placed in
Radix rather than Lymnaea because of its
close relationship toi?. auricularia.
116
117
35
Pseudosuccinea columella
(Say, 1817)
American Ear Snail
DESCRIPTION
Shell up to about 21 mm high, 12 mm wide,
with 4 whorls and with aperture height
about 65% to 75% of shell height, succine-
iform, dextral, thin, fragile and with a
capacious body whorl. Protoconch dark
brown, small, and about 1-1/4 whorls. Spire
sharply conic, rather short and narrow, and
with sutures consticted and well impressed;
spire angle about 50°. Whorls rounded and
enlarging rapidly. Aperture large, ovate, and
expanded ba sally. Outer lip thin and broadly
curved; inner lip arched and closely ap-
pressed to the parietal wall so only a narrow
slit is left open. In some specimens the
inside of the empty shell is visible through
the aperture almost to the apex. Columella
plait spirally twisted. Periostracum light
greenish brown to yellowish brown. Sculp-
ture consists of coliabral lines and streaks
and spiral lines.
This medium-sized species may be recog-
nized by its large ovate aperture and thin
shell. It resembles the terrestrial snail
Succinea ovalis but differs from that species
in the possession of a distinct protoconch
and a twisted columella. In living speci-
mens the tentacles are broad and triangular
and the eyes are on swellings near their
bases, whereas in S. ovalis the eyes are at
the ends of long peduncles and the tentacles
arc small protuberances near the bases of
the eye stalks. The head-foot region is also
smooth, while that of S. ovalis appears to
be covered with scales. Fundamental inter-
nal anatomical differences also exist.
DISTRIBUTION
Occurs from southern Manitoba and the
Great Lakes- St. Lawrence River system
south throughout North America east of the
vicinity of 100° longitude. Also occurs in
Central and South America. Has been
introduced into the western United States,
Europe, Australia, and South Africa.
ECOLOGY
Lives in lakes, ponds, and sluggish streams
among lily pads and reeds, and at the edges
of these water bodies on sticks and on mud.
The radula formula is approximately
35-1-35 and the lateral teeth are tricuspid.
U8
35
Pseudosuccinea columella
a: Meach L. near Hull, Que.; 8.8 mm.
b,c: Rideau R. near Ottawa, Ont,; b 11.1 mm,
c 12.7 mm.
119
36
Acella haldemani
(Binney, 1867)
Slender Pond Snail
DESCRIPTION
Shell up to about 25 mm high, 5 mm wide,
with 5-1/2 whorls and with aperture length
about 39% to 42% of shell length, slender
lymnaeiform, dextral, thin, and fragile.
Nuclear whorl long and ovate. Spire very
narrow and long; spire angle about 20°.
Whorls flat-sided, oblique, descending rap-
idly, and with impressed sutures that lie
at 45° relative to the shell axis. Aperture
long and narrow, not laterally expanded,
acute above, and flared below. Outer lip thin
and more or less broadly curved, and inner
lip erect, straight, long, and touching (in
most specimens) but not appressed to the
parietal wall. Umbilicus a slender chink
behind inner lip. Periostracum yellowish
white to brown. Sculpture consisting of fine
collabral lines and wrinkles.
The long and slender, almost needle-like
shell of this species cannot be mistaken.
It has a superficial resemblance to the
young of Lymnaea stagnalis but it is much
narrower and the spire sides are nearly
straight, rather than concave.
DISTRIBUTION
Great Lakes- St. Lawrence drainage and
vicinity in southern Ontario, southern Que-
bec, northern Vermont, New York, Ohio,
Illinois, Wisconsin, and Minnesota.
ECOLOGY
Rare. Occurs in widely separated localities
and is found only sporadically. Favourable
habitats are among reeds in eutrophic lakes
and ponds at a depth of about 0.3 to
1.0 metre. The radula formula is about
21-1-21 and the lateral teeth are bicuspid.
120
36
Acella haldemani
a,b: “New York”; 20.7 mm.
c: Georgian Bay, L. Huron, Ont.; 10.2 mm.
121
37
Bulimnea megasoma (Say, 1824)
Showy Pond Snail
DESCRIPTION
Shell up to about 47 mm high, 30 mm wide,
with 6 whorls and with aperture height
about 55% to 65% of shell height, swollen
lymnaeiform, dextral, and fairly thick and
solid. Nuclear whorls number 1-1/4, and are
satiny and yellowish to dark brown. Spire
rather short, with straight or convex sides,
conical with evenly rounded whorls and
impressed sutures. Body whorl dominant,
large, broadly rounded, inflated but not
bulbous, and comprising most of the shell
volume. Aperture large, acutely angled
above, flatly rounded laterally, rather
sharply rounded below, and chestnut-brown
to purplish within. Parietal wall flattened,
with a spirally twisted columella plait, and a
prominent callus that obscures the umbili-
cus. Periostracum glossy, brownish or
greenish and with or without collabral
streaks of muted green, orange, yellow-
brown, or purple. Sculpture principally of
coarse collabral lines and ridges.
This large, rotund, colourful species is
quite different from any other. Compare
with S ’ tagni cola catascopium.
DISTRIBUTION
Upper Albany, Winnipeg and Nelson River
drainages in the Canadian Interior Basin;
Great Lakes -St. Lawrence system east
to Lake Champlain; and upper tributaries of
the Ohio -Mississippi River system.
ECOLOGY
Occurs in large and small lakes, in slow-
moving rivers, and in pond areas of creeks.
Vegetation is of variable abundance and
the usual bottom is mud. Radula formulae
of 48-1-47 to 49-1-49 have been observed.
The lateral teeth are tricuspid.
122
37
Bulimnea megasoma
a: Marchington R. near Drayton, Ont.; 45.0 mm.
b: Wildgoose L. near Longlac, Ont.; 37.3 mm.
123
38
Lymnaea stagnalis jugularis
(Say, 1817)
Great Pond Snail
DESCRIPTION
Shell up to about 56 mm high, 27 mm wide,
with 7-1/2 whorls and with aperture height
about 48% to 58% of shell height, lymnae-
iform, dextral, and thin. Nuclear whorls
smooth, shiny, satiny, forming a pointed
apex and numbering about 1-1/2. Spire tall,
narrow, with concave sides (in many speci-
mens), with spire angle about 40° but
variable, and with flatly-rounded whorls and
impressed sutures. Body whorl capacious,
inflated, shouldered in some specimens,
roundly convex, and in volume constituting
most of the shell. Aperture ovate except
angled above; outer lip thin and fragile;
inner lip with a thin but prominent callus.
Columella twisted and forming a heavy,
oblique spiral plait. Periostracum light tan
to dark brown. Surface relatively smooth
except malleated in some specimens, with
prominent collabral lines, growth rests, and
fine spiral lines.
This large, thin-shelled species is recog-
nized by its long, narrow spire that has
concave sides and by its bulbous body
whorl. Compare it withL. stagnalis sanctae-
mariae.
L.s. appressa (Say, 1818) is a synonym.
Say’s first (1817) description of jugularis
is recognizable, but that publication
(Nicholson’s Encyclopedia) is very rare. In
later, more common editions the description
was altered and became equivocal.
DISTRIBUTION
Throughout Canada south of the tree line,
but absent from the region east of northern
James Bay and Hudson Bay and also from
the Atlantic Provinces. In the United States
it occurs throughout the Great Lakes- St.
Lawrence system, in the upper Mississippi
River system in Ohio and Illinois, and in
the Rocky Mountains south to Colorado.
ECOLOGY
Occurs in all perennial-water habitats.
Vegetation is always present and bottom
sediments are of diverse types; it is often
found among cattails ( Typha ). Radula for-
mulae of 37-1-36 to 46-1-46 have been
recorded, and the first lateral teeth are
bicuspid or tricuspid.
The nominal subspecies wasatchensis
Hemphill, recorded from western Canada
and United States, exhibits a relatively
longer spire, more rounded aperture, and
more inflated body whorl than typical
L. s . jugularis. These interrelated characters
are too irregularly expressed, however, to
merit separate taxonomic recognition for
those populations.
124
38
Lymnaea stagnates jugularis
a: Montreal R. near Montreal L., Sask.; 50.8 mm.
b: Rideau R., Ottawa, Ont.; 61.1 mm.
c: Lake near High River, Alta.; 51.5 mm.
125
39
Lymnaea stagnalis sanctae-
mariae Walker, 1892
Walker's Pond Snail
DESCRIPTION
Shell similar to that of Lymnaea stagnalis
jugularis but differing principally in relative
proportions. Aperture height is about 65%
to 70% of the height of the whole shell,
while inL. s. jugularis that ratio is less than
60% in nearly all specimens. Also the
aperture is very wide and patulous, and the
body whorl is capacious and almost globu-
lar. The spire is short, less acute, and has
only about 4 whorls, whereas in L. s. jugu-
laris it has 5 to 6 whorls. The last part of the
body whorl in many L. s. sanctaemariae is
also malleated or otherwise irregular.
DISTRIBUTION
Lake Superior watershed and adjacent parts
of the Lake Huron, Winnipeg River and
Wisconsin River watershed. Intergrades
withL. s. jugularis occur in adjacent pans of
the Nipigon, Attawapiskat, Severn, Hayes
and Nelson River systems in Canada.
ECOLOGY
Characteristic of large and medium-sized
lakes. Frequently found attached to large
rocks exposed to wave action, but is also
found in more protected habitats. Egg
masses are reported as thicker and more
solidly formed than inL. s. jugularis. The
radula, however, is similar in both sub-
species.
126
39
Lymnaea stagnalis sanctaemariae
a: Knee L., Man.; 51.7 mm.
b: Sandbar L. near Ignace, Ont.; 48.2 mm,
c: Ozhiski L,, Ont.; 39,8 mm.
127
40
Lymnaea atkaensis Dali, 1885
Alaskan Pond Snail
DESCRIPTION
Shell up to about 42 mm high, 30 mm wide,
with almost 6 whorls and with aperture
height about 50% to 65% of shell height,
lymnaeiform, dextral, rather thin, moder-
ately fragile, but variable in all characterise
tics. Nuclear whorls rough, shining, about
1-1/2 to 2 in number, and forming a pointed
apex. Spire short to long, moderately broad
to narrow with an angle of 30° to 60°,
scalariform, and with shouldered and
strongly convex whorls. Sutures constricted
and deeply impressed. Body whorl large,
irregular, malleated, and shouldered in
many specimens. Aperture large and ear-
shaped with thin and convex outer lip and
erect, continuous, reflected inner lip. Um-
bilicus moderately wide, deep, and revealing
earlier whorls except in specimens in which
it is partly obstructed by the reflected inner
lip. Periostracum straw-coloured or yellow-
ish brown. Sculpture consisting of fine
collabral striae, dark-brown growth rests,
spiral lines and bands, and irregular
malleations.
Differs conspicuously from all other
species within its geographical range except
Stagnicola catascopium> which extends
close to its range in British Columbia. That
species has flatly rounded whorls, sutures
that are well marked but not constricted and
deep, and (in most specimens) a lower spire.
The radulae and anatomy of the species
are also different.
DISTRIBUTION
Lakes in Alaska (including the Aleutian
Islands), the Yukon Territory, the North-
west Territories east to the vicinity of
Darnley Bay (about 69°50'N, 122°E), and
northern British Columbia in the Macken-
zie River system (Peace and Liard River
drainages) and presumably in the Yukon
River system. This is a Beringian relict
species.
ECOLOGY
Occurs in northern British Columbia in
clear, cold, oligotrophic lakes on rocks and
among sparse submersed aquatic vegetation
at depths of 0.3 to 5 metres. The radula has
both bicuspid and tricuspid lateral teeth,
and gross formulae of 4 1-1 -39 and 43-1-41
have been observed.
128
40
Lymnaea atkaemis
a,b: Lake near Paulatuk, N.W.T. (69°24'N, 124°33' W);
a 30.1 mm, b 35.4 mm.
129
41
Stagnicola ( Hinkleyia ) caperata
(Say, 1829)
Blade-ridged Stagnicola
DESCRIPTION
Shell up to about 16 mm high, 7 mm wide,
with 6-1/2 whorls and with aperture height
about 45% to 60% of shell length, lymnae-
iform, and dextral. Nuclear whorls brown
or reddish-brown, satiny, about 1-1/3 in
number, and forming a pointed apex. Spire
conoid, with flat or convex sides, with spire
angle about 60°, and with whorls flatly
rounded. Sutures impressed. Body whorl
inflated. Aperture ovate; outer lip thin and
reinforced by a varix which may be purple;
inner lip broad and expanded over the
umbilicus. Umbilical chink partly or wholly
open. Periostracum variable, yellowish
brown to blackish, and closely adherent.
Most unabraded specimens (when viewed at
25 X or 50 x magnification) exhibit fine,
low, compressed, blade-like spiral ridges
standing erect in spiral grooves that are
impressed in the underlying shell surface.
Recognized by its unique, microscopic,
spiral, blade-like periostracal ridges. Com-
pare with 5. montanensis and S. elodes.
DISTRIBUTION
Typically a prairie species. Positively re-
corded from southern Manitoba to southern
and central Alberta, and south in the United
States to Nevada and Utah. Also reported
from eastern Canada and the United States,
and even from the Yukon Territory, Alaska
and California, but these records are proba-
bly erroneous.
ECOLOGY
Found most frequently in temporary- water
habitats (ditches, shallow pools, vernal
ponds) or in spring-flooded margins of
permanent-water habitats. Also occurs
rarely in large permanent lakes, rivers, and
swamps. Radula formulae of 28-1-28 to
35-1-32 have been observed. The lateral
teeth are bicuspid.
130
41
Stagnicola caperata
a: Ditch near Cayley, Alta.; 10.0 mm.
b: Creek near Carstairs, Alta.; 1 1.0 mm.
131
42
Stagnicola ( Hinkleyia )
montanensis (Baker, 1913)
Mountain-Spring Stagnicola
DESCRIPTION
Shell up to about 1 5 mm high, 7 mm wide,
with 6-1/2 whorls and with aperture height
about 38% to 50% of shell height, lymnae-
iform, dextral, and of moderate thickness.
Nuclear whorls brown to reddish-brown,
about 1-1/3 in number, and forming a blunt
apex. Spire angle about 60°; spire sides
straight or bulging. Aperture relatively
small, and long ovate; outer lip curved;
inner lip rather straight, oblique, and
sometimes angled where it is appressed to
the previous whorl. Inner lip broadly re-
flected, sub-triangular, and exposing a small
distinct umbilicus. Periostracum brownish
and shiny. Under 25 X magnification the
sculpture is seen to consist of numerous
spiral rows of tiny crescents (on most
specimens) whose ends point away from the
aperture, and numerous irregularly-spaced
collabral lines.
Resembles S. caperata but differs con-
spicuously in its microsculpture. Compare
the two species.
DISTRIBUTION
Recorded in the Rocky Mountain region
from southwestern Alberta south to Nevada
and Utah. May also occur in British
Columbia.
ECOLOGY
Characteristic of clear, cold mountain
streams and small spring-fed pools. Has also
been found in a roadside ditch. A radula
formula of 28- 1 -32 has been reported.
132
133
43
Stagnicola (Stagnicola) arctica
(Lea, 1864)
Muskeg Stagnicola
DESCRIPTION
Shell up to about 22 mm high, 1 1 mm wide,
with 6-1/2 whorls and with aperture length
about 45% to 58% of shell length, lymnae-
iform, dextral, and unusually variable in
all features, but normally of moderate
thickness and with heavy columella devel-
opment. Nuclear whorls rounded, shiny,
yellowish-to-reddish brown, and about 1-1/2
in number. Spire angle about 50°; spire of
medium length and with impressed sutures
and convex whorls that are wider than high.
Body whorl convex but not inflated. Aper-
ture subovate and purplish brown within (in
many specimens). Outer lip convex, with
or without an internal varix; inner lip broad,
thick, and expanded over the umbilicus,
obscuring it in many specimens. Columella
plait heavy, moderate, or absent. Perios-
traeum variable, pale brown to blackish.
Sculpture variable and composed of colla-
bral lines and spiral ridges, bands, or
malleations.
Resembles the widespread Stagnicola
elodes but is smaller, with a proportionately
larger body whorl and much heavier colu-
mella development.
DISTRIBUTION
An arctic and subarctic species. Occurs
across northern Canada from Labrador to
the Yukon Territory and beyond into
Alaska.
ECOLOGY
Occurs in lakes, ponds, rivers, streams,
ditches, and muskeg pools. Vegetation
abundance and bottom sediments are vari-
able. Radula formulae from 29- 1 -27 to
31-1-30 have been reported, and the lateral
teeth are bicuspid. Stagnicola yukonensis
Baker is a synonym.
134
43
Stagnicola arctica
a: Moose R., Moose Factory, Ont,; 15.5 mm.
b: Hannah Bay, James Bay, Ont.; 15.7 mm.
135
44
Stagnicola ( Stagnicola )
catascopium catascopium
(Say, 1817)
Lake Stagnicola
DESCRIPTION
Individual populations of this species may
differ widely from each other. In some
populations shells may reach 33 mm in
height and 23 mm in width, but in other
populations these dimensions are halved.
Adult specimens have 5 to 6 whorls, and the
aperture length is between 50% and 70%
of shell length. Specimens may be with
or without a columella plait, an open
umbilicus, and strong surface sculpturing.
Whorls may be rounded to nearly globose,
shouldered or unshouldered, and with a
flattened to pyramidal spire. The aperture is
ovate to subquadrate, large to very large,
and variable in degree of flare. The varix
present behind the outer lip in many
specimens may be brown. The inner lip is
broad and partially or completely reflected
over the umbilicus. Sculpturing is strong to
weak, and may be composed of spiral lines,
ridges and flat bands, collabral lines of
growth, white varices, or any combination
of these characters.
Typically a rather large and heavy shell
with low spire, broad aperture, inflated
whorls, deep sutures, and thickened inner
lip. The only subspecies recognized as
distinct are those which occur as multiple,
contiguous populations and which can be
differentiated by more than a single charac-
ter, such as S. catascopium nasoni and
S’, catascopium preblei] these are discussed
in the following pages.
DISTRIBUTION
Generally extends across North America
below the tree line and south in the United
States to about 40°N. Within these limits
the only large area where the species is
absent is northern British Columbia, the
Yukon Territory and Alaska, that is the area
occupied by Lymnaea atkaensis.
ECOLOGY
Characteristic of large lakes and large rivers
although also found in smaller bodies of
water. Its most frequent habitat is on rocks
exposed to waves and currents. Radula
formulae of 31-1-30 to 35-1-35 have been
reported. The lateral teeth are bicuspid.
136
44
Stagnicola catascopium catascopium
a: Winisk R,, Ont.; 18.7 mm.
b: Mistassin L., Ont.*, 15.0 mm.
c: St. Lawrence R., Que.; 13.7 mm.
137
45
Stagnicola ( Stagnicola ) cata-
scopium nasoni (Baker, 1906)
Miniature Lake-Stagnicola
DESCRIPTION
Shell up to about 12 mm high, 8 mm wide,
with 4 whorls and with aperture height
about 60% to 75% the height of the shell,
broad lymnaeiform, rotund, solid, and with
expanded aperture and broad flaring lip*
Nuclear whorls dark brown, satiny, and
about 1-3/4 turns. Whorls rounded but not
inflated. Spire broad but acute and with
impressed sutures. Body whorl subglobose
and dominant. Aperture ovate, expanded,
and white or brownish within; outer lip
sharp but internally thickened; inner lip
broad, thickened, and reflected. Umbilicus
obscured by inner lip. Periostracum yellow-
ish or purplish brown. Sculpture consisting
of impressed spiral lines and fine, crowded
collabral ridges.
Distinguished from S', c, catascopium by
its unusually small size, solid appearance,
and wide, flaring aperture.
DISTRIBUTION
The Great Lakes from Lake Superior to
western Lake Ontario; Lake Geneva,
Wisconsin; Rainy River system and Lake of
the Woods.
ECOLOGY
In Lake of the Woods occurs on wave-
exposed black shale rocks at, and just below,
the water surface. Here the dark shells are
well camouflaged and resemble air bubbles.
Egg masses are about 5 to 6 mm long,
crescent-shaped, and contain from 8 to
20 pale-yellow eggs. The snails move rap-
idly, that is lik ePhysa gyrirta.
138
45
Stagnicola catascopium nasoni
a: L. Nipigon, Om,; 15.4 mm.
b: Batchawana Bay, L. Superior, Ont.; 13.6 mm.
139
46
Stagnicola ( Stagnicola ) cata-
scopium preblei (Dali, 1905)
Subarctic Lake-Stagnicola
DESCRIPTION
Shell up to 42 mm high, 28 mm wide, with
almost 7 whorls and with aperture height
about 55% to 65% of shell height, broad
lymnaeiform, dextral, variable in shape, and
with swollen whorls. Nuclear whorls
brown, about 1-1/2 in number, relatively
large, and forming an acute apex. Spire
short but acute with deeply impressed to
channelled sutures and inflated, shouldered
whorls. Aperture large, ovate to subquad-
rate; outer lip thin and irregularly curved,
with or without a reddish-brown internal
varix; inner lip broad, appressed to the body
whorl above and reflected over the umbili-
cus below but not obscuring it. Umbilicus
open and deep. Periostracum pale brown.
Sculpture coarse, of spiral ridges and bands,
collabral lines and ridges, and irregular
malleations.
Differs from S\ catascopium s. str. in that
the shell is larger, the umbilicus is entirely
open rather than closed or partly open, the
whorls are more uniformly shouldered,
and the aperture is relatively smaller.
DISTRIBUTION
Northern Saskatchewan and northern Man-
itoba in the Hayes, Nelson and Churchill
River systems.
ECOLOGY
Known only from large oligotrophic sub-
arctic lakes. One specimen had a radula
formula of 39-1-39 and bicuspid lateral
teeth. Details of its ecology are unknown.
140
46
Stagnicola catascopium preblei
a,b,c: Limestone L., northeastern Man,; a 37.6 mm,
b 33.5 mm, c 40.0 mm.
141
47
Stagnicola ( Stagnicola ) elodes
(Say, 1821)
Common Stagnicola
DESCRIPTION
Shell up to about 32 mm high, 14 mm wide,
with 7 whorls and with aperture height
about 45% to 55% of shell height, lymnae-
iform, dextral, variable in shape, and elon-
gate. Nuclear whorls rounded, shining, and
finely punctate. Spire rather long, average
spire angle about 45° but variable, whorls
rounded, and sutures impressed. Body
whorl convex, somewhat inflated, and con-
stituting about 2/3 the length of the shell.
Aperture subovate and more or less ex-
panded; outer lip thin, with or without an
internal varix, and with a brownish-purple
band within; inner lip broad and with a
prominent callus. Columella plait promi-
nent, heavy, and spiral. Umbilicus narrowly
open or closed. Periostracum yellowish
brown to blackish brown. Sculpturing is of
numerous coarse collabral and spiral lines, a
few growth rests, and (in many specimens)
with spiral bands or malleations or both.
The most abundant species of its genus.
In some populations specimens approach
S. proxima or S. reflexa in appearance.
Compare with those species.
DISTRIBUTION
Occurs throughout Canada below the tree
line, and south in the United States to about
38°N. In the Rocky Mountains it extends
farther south, that is to about 33°N.
ECOLOGY
Ubiquitous. Found in all kinds of aquatic
habitats. Especially numerous in thick
vegetation and on muddy substrates. Radula
formulae of 27-1-26 to 34-1-33 have been
observed.
Until recently, this species was known as
Stagnicola (or Lymnaea) palustris (Muller),
142
47
Stagnicola elodes
a; Pond, Quamichan, Vancouver Is., B.C.; 23.2 mm.
b: Pond, False R., Ungava Bay, Que.; 20.9 mm.
143
48
Stagnicola ( Stagnicola )
kennicotti Baker, 1933
Western Arctic Stagnicola
DESCRIPTION
Shell up to about 21 mm high, 10 mm wide,
with 7 whorls and with aperture height
about 35% to 45 % of shell height, lymnae-
iform, dextral, and solid. Nuclear whorls
satiny, 1-1/2 to 2 in number, and forming a
high, domed apex. Spire angle about 45°;
spire rather long, with straight sides and
rounded whorls. Sutures constricted, im-
pressed and, in many specimens, incised.
Aperture, roundly ovate; outer lip thin,
convex, and without an internal varix; inner
lip flattened, wide, reflected over the umbili-
cus and curved or angulate. Umbilicus
visible only as a small narrow chink.
Periostracum pale brown. Sculpturing is of
irregular collabral lines, low spiral ridges,
and spiral rows of tiny crescents between
the ridges.
Related to 5. arctica but differs in that the
aperture is smaller (height less than 45%
of shell height), the spire is longer, and no
columella plait is present.
DISTRIBUTION
Occurs in the Northwest Territories on the
mainland arctic coast of Canada from near
Bathurst Inlet to Liverpool Bay, as well
as on southern Victoria Island.
ECOLOGY
An arctic species. Found in large lakes,
small lakes, pools, and streams. Radula
formulae range from 29-1-29 to 33-1-32.
The lateral teeth are bicuspid.
144
48
Stagnicola kenmcotti
a; Creek, Bernard Harbour, N.W.T.; 15.1 mm (para-
type).
b,c: Lake near Bathurst Inlet, N.W.T.; b 12.9 mm,
c 13.6 mm.
145
49
Stagnicola ( Stagnicola ) proxima
(Lea, 1856)
Rocky Mountain Stagnicola
DESCRIPTION
Shell up to about 22 mm high, 1 1 mm wide,
with 6-1/2 whorls and with aperture height
about 45% to 55% of shell height, lymnae-
iform, and dextral. Nuclear whorls brown,
satiny, 1-1/2 to 2 in number, and rounded.
Spire sharply acute, pyramidal, pinched
in many specimens, and with spire angle
about 30° to 45°. Whorls flatly rounded and
sutures impressed or incised. Body whorl
large, well rounded to rotund. Aperture
medium-sized, ovate, and (in many speci-
mens) with a continuous lip; outer lip thin
and convex; inner lip broad, reflected over
the umbilicus, curved or straight, and
typically without a columella plait. Umbili-
cus narrow but distinct in most specimens.
Periostracum light brown to black. Sculp-
ture consisting of coarse collabral lines and
growth rests and less distinct spiral lines.
Resembles S', elodes but may be distin-
guished by its more rotund body whorl,
rounder aperture, more sharply acute and
pinched spire, and more rapidly enlarging
whorls. The two taxa are closely related,
however, and may be only subspecifically
distinct.
DISTRIBUTION
In the Rocky Mountains from British
Columbia and Alberta south to California.
ECOLOGY
A montane species. Occurs in lakes, ponds,
streams, and roadside ditches. Lives on
various substrates. The radula formula is
31-1-30 to 36-1-35 and the lateral teeth are
bicuspid. The nominate subspecies rowelli
appears not to be valid.
146
49
Stagnicola proximo.
a: Maligne L., Jasper National Park, Alta.; 9.7 mm.
b: Pond, Banff, Alta.; 15.2 mm.
c: Pond, Banff, Alta.; 11.2 mm.
50
Stagnicola ( Stagnicola ) reflexa
(Say, 1821)
Striped Stagnicola
DESCRIPTION
Shell up to about 35 mm high, 12 mm wide,
with 7 whorls and with aperture height of
most specimens about 44% to 50% of shell
height, lymnaeiform, dextral, slender, and
with flat-sided whorls. Nuclear whorls
about 1-1/2 in number, turreted and satiny.
Spire long, with slightly convex sides; spire
angle about 25° to 30°. Sutures impressed.
Last 2 or 3 whorls much elongated.
Aperture long; outer lip sharp and thin but
thickened internally by a brownish or
reddish varix; inner lip narrow and reflected
over the umbilicus and obscuring it com-
pletely or leaving only a small chink.
Columella oblique and in adult specimens
with a spiral plait. Surface light to dark
brown, with (typically) or without alternat-
ing zebra-like dark and light collabral bands,
and with numerous collabral ridges and
spiral grooves.
Resembles S. elodes but may be distin-
guished by its narrower form, more-elongate
later whorls, and in many populations by
its zebra-like dark and light bands.
DISTRIBUTION
Scattered areas in the southern and south-
western parts of the Canadian Interior
Basin, the Great Lakes- St. Lawrence
system throughout, and the upper Ohio-
Mississippi drainage area south to
about 37°N.
ECOLOGY
Occurs among vegetation in a variety of
perennial-water and vernal habitats, namely
lakes, ponds, sheltered areas of streams,
swamps, and ditches. The usual substrate is
mud. The radula has about 40 lateral plus
marginal teeth on each side of each central
tooth.
Stagnicola reflexa is considered by some
authors as a morphological variant of
5. elodes (Say).
148
50
Stagnicola reflexa
a: L, Superieur near Grand-Metis, Que.; 34.5 mm.
b: Pond near Starr L., Whiteshell Provincial Park,
Man,; 23.0 mm.
c: Chippawa, Welland Co., Ont.; 19.7 mm.
149
VII Superfamily Physacea
FAMILY PHYSIDAE (Tadpole Snails)
Shell small to medium-sized, sinistral (coiled to the left),
mainly thin-shelled, with an elevated spire, with or without
an umbilicus and without an operculum. Tentacles slender
and cylindrical, and foot narrow. The mantle in Physa has
numerous finger-like extensions that project from the
aperture over both sides of the shell. Jaw single, and radula
with teeth arranged in V-shaped rows. Many multicuspid
lateral and marginal teeth are on each side of the wide,
multicuspid central tooth. Monoecious and capable of cross-
or self-fertilization. Egg masses gelatinous, transparent,
whitish, and crescent-shaped. The family is worldwide.
151
51
Physa gyrina gyrina Say, 1821
Tadpole Snail
DESCRIPTION
Shell up to about 24 mm high, 16 mm wide,
with 5-1/2 whorls (most specimens are
much smaller) and with aperture 60% to
80% of shell height, sinistral, variable in
form, thin to slightly thickened, and more or
less transparent. Spire acute and of medium
length. Nuclear whorl small, rounded,
finely punctate, and generally red to reddish
brown. Whorls gendy rounded and loosely
coiled, that is overlapping the previous
whorl only to a line that is below, or at the
periphery of, that whorl. Sutures impressed
and bordered below by a narrow pale band.
Body whorl large and well rounded but
not strongly inflated. Aperture loop-shaped,
mainly basal, acute above, flady rounded
laterally, and rounded ba sally. Outer lip thin
to slighdy thickened, and bordered inside
by a prominent red or reddish collabral
band. Columella oblique, thin to slightly
thickened, and with an extensive wash of
callus on the parietal wall. Narrowly umbili-
cate or non-umbilicate. Periostracum pale
yellowish brown to greyish brown and with
a dull surface. Sculpture consists of numer-
ous coarse lines of growth; in some speci-
mens, one or more internal varices are
visible externally as whitish collabral bands;
and, in most populations, crowded, im-
pressed spiral lines cross the growth lines.
Well characterized by its small, acute, and
reddish apex; inflated whorls; and medium-
sized, rather thin shell. In Canada its closest
relatives are P. heterostropha and P. john-
soni ; compare with these. P. vinosa Gould,
1847, from Lake Superior appears to be a
thick-shelled ecologically induced variant of
P. gyrina .
DISTRIBUTION
Quebec west within the tree line to the
northwestern Northwest Territories, Alaska
and British Columbia. South in the central
and western United States to the Gulf of
Mexico and California.
ECOLOGY
Abundant. Occurs in almost all perennial-
water habitats and in temporarily flooded
pools and swamps. Often abundant in
mildly polluted water bodies; in fact, where
it occurs alone and in abundance, it is
indicative of organic pollution. Egg deposi-
tion occurs principally in the spring. The
animal moves quite rapidly.
152
51
Physa gyrina gyrina
a: Montreal R. near Montreal L., Sask.; 18,7 mm.
b: Pond near Nevis, Alta.; 19.7 mm.
c: L. de Montigny near Val-d f Or, Que,; 1 1.7 mm.
d: Macamic L. near La Sarre, Que.; 13.0 mm.
153
52
Physa gyrina latchfordi
(Baker, 1928)
Gatineau Tadpole Snail
DESCRIPTION
Shell up to about 26 mm high, 20 mm wide,
with 6-1/2 whorls and with aperture about
74% to 82% of shell height, sinistral,
variable in form, slightly thickened, trans-
lucent, and shouldered. Spire obtuse, short,
and with concave sides. Nuclear whorl
small, reddish, and forming a sharp apex.
Spire whorls flatly rounded and separated by
lightly impressed sutures. Body whorl
roundly but conspicuously shouldered, tab-
ulate above, and flatly rounded below.
Aperture ovate-quadrate and wider below
but also rather wide above. Outer lip thin
and fragile. Columella vertical, somewhat
thickened, and straight or somewhat curved.
No umbilicus. Periostracum yellowish
brown to brown and with a shiny surface.
Sculpture consists of fine collabral threads
and ridges and finer spiral rows of punctae.
Distinguished by its large, wide, and
strikingly shouldered shell. Intergrades oc-
cur with P. g . gyrina ; compare with that
subspecies.
DISTRIBUTION
Has been found in Meach Lake (the type
locality) and Pink Lake in the Gatineau
River system of western Quebec. Inter-
grades with P. g. gyrina occur in Lac
Lapeche and Lac Philippe, two other lakes
in the same river system.
ECOLOGY
Lives on gravel bottoms in wave -exposed
areas of large lakes. Its radula is similar
to that ofP. g. gyrina except that the central
tooth appears to have about 2 additional
cusps. Nothing else is known about its
biology or anatomy.
154
155
53
Physa heterostropha (Say, 1816)
Eastern Physa
DESCRIPTION
Shell up to about 21 mm high, 18 mm wide,
with 6 whorls (most specimens are much
smaller) and with aperture about 67% to
82% of shell height, sinistral, variable in
form, thin to slightly thickened, and translu-
cent to opaque. Spire obtuse and short.
Apex decollated in most specimens, but
when visible the nuclear whorl is small,
rounded, finely punctate, and generally red
to reddish brown. Whorls rounded or
shouldered and tightly coiled, that is over-
lapping the previous whorl to a line that
is above the periphery of that whorl. Sutures
impressed and bordered below by a narrow
pale band. Body whorl large and well
rounded and roundly shouldered in many
specimens. Aperture loop-shaped, mainly
basal, acute above, rounded laterally, and
sharply rounded ba sally. Outer lip thin to
slightly thickened, and bordered inside by a
prominent red or reddish collabral band.
Columella somewhat oblique, thin to
slightly thickened, and with an extensive
callus on the parietal wall. No umbilicus.
Periostracum pale yellowish brown to grey-
ish brown, and with a shiny surface.
Sculpture consists of numerous coarse lines
of growth and in a few populations also of
crowded, impressed spiral lines crossing the
growth lines.
Similar toP. gyrina and, in fact, both
names may turn out to apply to the same
species. Typical P. heterostropha differs
from P. gyrina in being more tightly coiled
and in having a lower spire, a somewhat
shouldered body whorl, weaker (or absent)
spiral sculpturing, and shiny periostracum.
DISTRIBUTION
Atlantic Provinces of Canada south at least
to New Jersey and Pennsylvania, and
perhaps farther south. Its taxonomic rela-
tionships need to be clarified.
ECOLOGY
Very common. LikeP. gyrina , occurs in all
kinds of perennial-water and temporarily
flooded habitats, usually among vegetation.
156
53
Physa heterostropha
a,b: Caribou Stream, Aroostook Co., Maine;
a 13.6 mm, b 12.1 mm.
157
54
Physa integra Haldeman, 1841
Solid Lake Physa
DESCRIPTION
Shell up to about 1 5 mm high, 9 mm wide,
with 5 whorls (most specimens are smaller)
and with aperture about 57% to 73% of shell
height, sinistral, variable in form, noticeably
thickened, and opaque. Spire acute and
rather short. Nuclear whorl small, rounded,
finely punctate, and brown. Whorls gently
rounded and loosely coiled, each overlap-
ping the preceding whorl up to a line that is
at, or below, the periphery. Sutures im-
pressed. Body whorl large, well rounded,
and somewhat shouldered in some speci-
mens. Aperture ear-shaped, acute above,
gently rounded laterally, and becoming
sharply rounded basally. Outer lip thickened
within by a heavy white callus (also clearly
visible externally) and bordered inside by
a brownish collabral band. Several whitish
bands representing previous growth stages
may be visible through the shell. Columella
thickened and reflected over the umbilical
region or forming a wide, flat expansion. No
umbilicus. Periostracum yellowish brown
to white, and with a dull to somewhat shiny
surface. Sculpture consists of coarse lines
of growth, whitish collabral bands, and
(in some specimens) fine spiral lines.
Shells ofP. integra are thicker and
heavier than shells of other species; they
have prominent white collabral bands and a
thick, flattened inner lip.
DISTRIBUTION
Throughout the Great Lakes- St. Lawrence
and Ohio -Mississippi systems.
ECOLOGY
Found in rather shallow water in lakes (but
deeper thanP. gyrina) in either exposed
or protected situations, and on clay, mud,
sand, or rocky bottoms. The male genitalia
are distinctive (see Te 1975). The radula
formula is approximately 130-1-130.
158
54
Physa Integra
a: St. Lawrence R., Cornwall, Ont.; 1 1.6 mm.
b: Mohawk, N.Y.; 14.3 mm.
159
55
Physa jennessi jennessi
Dali, 1919
Blunt Arctic Physa
DESCRIPTION
Shell up to about 9 min high, 5 mm wide,
with 5 whorls (most specimens are some-
what smaller) and with aperture 60% to 75%
of shell height, sinistral, thin, and transpar-
ent. Spire acute and short with a rounded
apex. Nuclear whorl large, rounded, and of
the same colour as later whorls. Whorls
gently rounded, the early whorls partly
enveloping the preceding whorl up to a line
located above the periphery, later whorls
enveloping to the periphery. Spire whorls
not misshapen or pulled up. Sutures shal-
lowly impressed and bordered below by
a narrow pale band. Body whorl dominant,
disproportionately enlarged, roundly shoul-
dered above, flattened laterally, sharply
rounded basally, and constituting about
5/6 to 7/8 of the shell length. Aperture ear-
shaped, mainly basal, acute above, flatly
rounded laterally, and rounded basally.
Outer lip thin and with or without a
brownish collabral band within the aper-
ture. In some specimens, broad white
collabral streaks mark previous growth
rests. Parietal wall covered by a rather
prominent and extensive but thin callus.
No umbilicus. Periostracum pale yellowish
brown to greyish brown and with a shiny
surface. Sculpture consists principally of
collabral striae and prominent growth rests.
Differs from P. j, skinneri principally in
that the penultimate and/or first pre-penulti-
mate whorl is not disproportionately pulled
up, while in P. j. skinneri that character is
pronounced. The parietal callus in
P. j, jennessi is also thicker and more
prominent.
DISTRIBUTION
Known from localities close to Hudson Bay
and James Bay and throughout the area
between Hudson Bay and the northern
Yukon Territory. Probably also occurs in
Alaska.
ECOLOGY
An arctic species. Found in small lakes,
ponds, woodland pools, muskeg pools,
small pools on top of flat boulders, and
slow-flowing streams. Vegetation present in
some habitats but absent in others; sub-
strates are rocks or mud. Its reproduction
has not been investigated. The radula is
similar to that of P.j. skinneri.
160
55
Physa jennessi jennessi
a,b: Creek, Bernard Harbour, N.W.T.; a 8.0 mm,
b 7.0 mm (paratypes).
c: Pool, Churchill, Man.; 8.4 mm.
161
56
Physa jennessi atheami
Clarke, 1973
Blunt Albino Physa
DESCRIPTION
Shell up to about 7 mm high, 5 mm wide,
with 4 whorls and with aperture 71% to 94%
of shell height, sinistral, variable in form,
subglobose, thin, and transparent. Nuclear
whorl large, rounded, about 0.7 mm wide,
elevated well above second whorl, and of the
same colour as later whorls. Spire short,
about 1/6 the length of the shell, acute to
slightly obtuse, with the first 3 whorls
enlarging evenly, flatly rounded, and sepa-
rated by impressed sutures. Sutures bor-
dered below by a narrow paler band. Body
whorl capacious, inflated, dominant,
roundly shouldered above, and flattened
centrally, giving the shell a characteristic
but misshapen appearance. Aperture large,
pendulous, acute above, flattened laterally,
and broadly rounded below. Columella
sigmoid (broadly S-shaped) and parietal
callus narrow above and broader below.
Umbilicus entirely absent or indicated by a
tiny slit. Periostracum pale yellowish white
and with a shiny surface. Sculpture consist-
ing of fine crowded collabral lines and
wrinkles and, on some specimens, a single
whitish narrow growth rest on the body
whorl. Impressed, microscopic spiral lines
that cross and interrupt the collabral wrin-
kles also occur on some specimens.
Differs from both/ 5 ,/, jennessi and
P. j. skinneri in its broader, more capacious
body whorl and the whitish colour of its
shell and soft parts. Also differs from
P. j. skinneri in its shorter, more regular
spire and the fewer and smaller finger-like
projections on the mantle.
DISTRIBUTION
Small lakes in the Banff- Jasper region of
the Rocky Mountains and in the upper
Athabasca River system downstream from
Jasper.
ECOLOGY
Has been recorded only from medium-sized
and small lakes, and in marshes with open
water. Bottom deposits are rock and gravel.
The soft parts of all specimens are predomi-
nantly or wholly whitish. The radulae of
specimens 6.5 mm long are about 1.5 mm in
length; they have 67 to 75 rows of teeth
with about 230 to 330 teeth in each row.
162
56
Physa jennessi a the arm
a,b: Horseshoe L, near Jasper, Alta.; a 7.8 mm,
b 5.8 mm (paratypes).
c: Marsh near Rochester, Alta.; 5.2 mm.
163
57
Physa jennessi skinneri
Taylor, 1953
Blunt Prairie Physa
DESCRIPTION
Shell up to about 12 mm high, 6.5 mm
wide, with 5-1/3 whorls (most specimens are
somewhat smaller) and with aperture about
61% to 78% of shell height, sinistral, thin,
and translucent. Nuclear whorl large,
rounded, finely punctate, and brown. Spire
rounded and unusual, appearing peculiarly
pinched and pulled-up, with the penulti-
mate whorl, or the next preceding whorl, or
both, markedly attenuate, that is much less
enveloped by the succeeding whorl than
are the earlier whorls and therefore more
exposed. Body whorl dominant, dispropor-
tionately enlarged, shouldered above, flat-
tened laterally, rather sharply rounded be-
low, and constituting about 5/6 of the shell
length. Aperture ear-shaped and mainly
basal. Outer lip broadly curved laterally and
characteristically arched centrally when
viewed from the outer side. Suture weakly
impressed. Parietal wall covered with a
thin callus. No umbilicus. Periostracum
pale yellowish brown to greyish brown and
with a moderately shiny surface. Sculpture
consists of collabral and spiral striae and
well-marked growth rests.
The large nuclear whorl, blunt apex, and
flattened body whorl distinguish P. jennessi
and its subspecies from theP, gyrina-
P . heterostropha complex. The elevated
penultimate or first pre-penultimate whorl
will differentiate P. j. skinneri from the
arctic P. j. jennessi, with which it should be
compared.
DISTRIBUTION
Southern Canada and northern United
States from Ontario northwest to the vicin-
ity of Great Slave Lake, west to British
Columbia, and south to Utah.
ECOLOGY
Occurs in lakes, ponds, marshes, and slow-
moving streams of all widths. Both vernal or
perennial habitats are utilized. Found prin-
cipally on muddy bottoms among thick
or moderately thick aquatic vegetation.
Recorded from depths of less than 1 m to
nearly 5 m. The radula of a specimen
1 1.3 mm tall is 2.2 mm long and bears
71 rows of teeth with up to about 230 teeth
in each row.
164
b
57
Physa jennessi skinneri
a: Lake near Banff, Alta.; 8.4 mm.
b: Dease L., northern B.C.; 9.7 mm.
c: Lake near Calgary, Alta.; 8,1 mm.
d: Lydia L. near Longlac, Ont.; 3.7 mm (juvenile).
165
58
Physa johnsoni Clench, 1926
Banff Springs Physa
DESCRIPTION
Shell up to about 9 mm high, 5 mm wide,
with 4.8 whorls (most specimens are
smaller) and with aperture 63% to 72% of
shell height, sinistral, variable in form, thin,
globose, and nearly opaque. Spire short
and acute. Nuclear whorl small, rounded,
and dark reddish brown. Whorls gently
rounded and loosely coiled, each partly
enveloping the preceding whorl to a line
located at, or below, the periphery. Sutures
well impressed and bordered below by a
narrow pale band. Body whorl dominant,
well rounded, and roundly shouldered.
Aperture ear-shaped, mainly basal, acute
above, flatly rounded laterally, and rounded
and flared basally. Outer lip thin and
without an internal dark band. Columella
oblique, slightly thickened, and not termi-
nating abruptly but continuing into the
outer lip. Parietal callus very thin and not
extensive. No umbilicus. Periostracum pale
yellowish brown to reddish brown and with
a shining surface. Sculpture consists of
numerous collabral lines and in abraded
specimens of irregular white collabral and
spiral bands.
Differs from P. gyrina by its small size,
lack of fine spiral striae on unabraded
specimens, prominent white spiral streaks
on abraded specimens, and general appear-
ance. Quite distinct from P. j. skinneri as
indicated by characters of the nuclear whorl,
spire, and body whorl.
DISTRIBUTION
Known only from several localities in Banff
National Park, Alberta.
ECOLOGY
Occurs in warm 33°C (92°F) and cold
springs. Substrates are rocks and gravel with
algae and moss. The radulae of two spec-
imens, 7.6 and 6.2 mm high, were both
1.7 mm long; respectively they bore 61 and
60 rows of teeth, with about 2 10 and
205 teeth in each full row.
166
167
59-64
Supplementary Western Physa
Species
Six additional species of Physa have recently
been identified from our British Columbia
material by Mr. George Te at the University
of Michigan; he is preparing a detailed
revision of the Physidae. These species are
differentiated and grouped principally on
anatomical features, but useful shell charac-
ters also exist.
59. Physa columbiana Hemphill, 1890
(Columbia River Physa), is medium-sized, up
to 15 mm high, 8 mm wide, thin to moder-
ately heavy, with a well-marked parietal callus,
flatly rounded whorls and a shiny surface.
Distribution restricted to the Columbia River
system. Its penial complex is similar to that
of two other nominate western species,
P. hordacea Lea andP. lordi Baird.
60. Physa concolor Haldeman, 1843 (Halde-
man’s Physa), is typically rather small, 7 mm
high, 4.5 mm wide, 4-1/2 whorls, thin-shelled,
with an extended spire, rounded whorls, and
shiny surface. Has been collected near Cres-
ton, British Columbia, and in Washington and
Oregon. Similar to P. Integra Haldeman in
shell characters and penial anatomy.
61. Physa hordacea Lea, 1864 (Vancouver
Island Physa), is small, about 8 mm high,
4.5 mm wide, 4-1/4 whorls, subcylindrical,
with a large nuclear whorl, blunt apex, flatly
rounded spire whorls, rather narrow aperture,
and shiny surface. Has been included in
Aplexa by previous authors, but exhibits a few
columellar mantle digitations, a character
that is in accordance with placement in Physa
rather than Aplexa. Apparendy endemic to
Vancouver Island.
62. Physa lordi Baird, 1863 (Giant Western
Physa), is large, 26 mm high, 19 mm wide,
thin-shelled, roundly inflated, with a pointed
low spire with concave sides, an unshouldered
body whorl, and a large aperture that is wider
below but still rather wide above. Resembles
P. gyrina latchfordi except that subspecies has
a rather heavy shell and strongly shouldered
whorls. Found from northern British Colum-
bia (Peace River system) south to the west-
central United States. P. virginea Gould is
tentatively considered a synonym.
168
59
Physa columbiana
Christina L. near Grand Forks, B.C.; 6.6 mm.
60
Physa concolor
Moses L., Grant Co., Wash.; 8,2 mm.
61
Physa hordacea
Long L., Nanaimo, B.C.; 5.8 mm.
62
Physa Iordi
a: Typical lordi : Vaseux L. near Okanagan Falls, B.C.;
1 1.9 mm.
b: Morph virginea : Anderson L., Jefferson Co,, Wash,;
18.4 mm.
169
63. Physa nuttalli Lea, 1864 (Nuttall’s
Physa), is medium-sized, 12 mm high, 7 mm
wide, 4-1/2 whorls, rather thin-shelled, with a
large nuclear whorl, a medium-length taper-
ing spire, flatly rounded whorls, an aperture
that is wide below and narrow above, a heavy
parietal callus, and with or without a brown-
ish band within the outer lip. Occurs in ponds
and ditches from southern British Columbia
(near the Columbia River) to California. The
penial complexes ofP. nuttalli andP. pro-
pinqua are similar.
64. Physa propinqua Tryon, 1865 (Western
Lake Physa), is rather large, 19 mm high,
1 3 mm wide, 5- 1 /2 whorls, thin-shelled, with a
medium-length tapering spire, flatly rounded
whorls, well-marked growth rests, a narrow
and thin parietal callus, an aperture of
medium width that is wider below, and with a
brown band within the outer lip. Principally
a lake species. Occurs on Vancouver Island
and throughout central and southern British
Columbia south to California.
170
63
Physa nuttalli
a,b: Pond near Randle, Lewis Co., Wash.; a 10.6 mm,
b 10.4 mm.
64
Physa propinqua
Upper Klamath L., Oreg.; 1 1.3 mm.
171
65
Aplexa hypnorum
(Linnaeus, 1758)
Polished Tadpole Snail
DESCRIPTION
Shell up to about 18 mm high, 7.5 mm
wide, with 7 whorls and with aperture 50%
to 60% of shell height, sinistral, elongate,
thin, and transparent Nuclear whorl
rounded, finely punctate, and amber-col-
oured. Whorls flatly rounded and relatively
tall, each partly enveloping the preceding
whorl up to a line located at the periphery of
that whorl. Spire elongate and constituting
about 1 /3 of the shell length. Sutures
impressed and bordered below by a narrow
white band. Body whorl flatly rounded and
sub-cylindrical. Aperture acute above,
rounded laterally, and flatly rounded below.
Outer lip thin, flatly rounded, and only
slightly thickened within. Columella
oblique, narrow, slightly twisted, and with a
very thin callus on the parietal wall. No
umbilicus. Periostracum polished, thin,
brownish (appearing blackish when con-
taining the soft parts), and often exhibiting a
greenish glint. Sculpture consists of fine
lines of growth and (in some specimens,
especially from arctic localities) fine spiral
lines.
The long, narrow, sinistral form, polished
and blackish surface (when alive), and lack
of mantle digitations are characters that
serve to identify this species positively.
DISTRIBUTION
New England to the District of Columbia;
north to the Gulf of St. Lawrence and James
Bay and across the subarctic to Victoria
Island, Banks Island and arctic Alaska; and
west to the Cascade Mountains. Also occurs
in Europe and northern Asia.
ECOLOGY
Lives principally in vernal habitats, i.e.
water bodies that dry up during parts of the
year. Often very abundant in temporary
shallow pools during the spring. Also
found, but rarely, in large permanent rivers
and lakes. Most occupied habitats have
thick vegetation and a mud bottom. Adult
specimens have about 350 teeth in each full
radula row. Unlike Physa, there are no
finger-like projections on the edge of the
mantle.
172
65
Aplexa hypnorum
a,b: Gatineau R., Pointe-Gatineau, Que,;a 16,0 mm,
b 15.0 mm.
c: Pond near Rocky Mountain House, Alta.; 1 1.0 mm.
173
VIII Superfamily Planorbacea
FAMILY PLANORBIDAE (Ramshorn Snails)
Shells small to moderately large, dextral or sinistral, flatly
coiled in most species and with a very low spire in a few,
umbilicus present, and operculum absent. Tentacles long,
slender, and cylindrical. An accessory breathing organ, the
pseudobranch, is present and functions as a gill when
atmospheric air is not available. Jaw in 3 or many segments,
and radula with teeth arranged in nearly horizontal rows.
About 10 to 40 tricuspid to multicuspid lateral plus
marginal teeth are on either side of the small bi-, tri-, or
tetracuspid central tooth. Monoecious and able to cross- or
self-fertilize. Egg masses gelatinous, transparent, colourless,
sausage-shaped, and with numerous yellow eggs. The
family is worldwide and some tropical species are intermedi-
ate hosts for blood parasites of mammals, including man.
175
66
Gyraulus circumstriatus
(Tryon, 1866)
Flatly Coiled Gyraulus
DESCRIPTION
Shell up to about 5 mm wide, 1.5 mm high,
with 4 whorls, planospiral, dextral, semi-
transparent, and showing the soft parts
within. All whorls are visible in both apical
and umbilical views, and, except for the
tipped-down (prosocline) aperture and colla-
bral sculpturing, the apical and umbilical
views are very similar. Whorls laterally
rounded, increasing in size slowly and with
outermost edge near centre. Aperture ovate,
with a thin outer lip and lacking a parietal
callus. Periostracum pale brown or whitish,
smooth, and shiny. Sculpture consisting
of fine spiral striae (in most specimens,
especially on the base), collabral striae, and
lines of growth.
Distinguished by being planospiral and
semi-transparent and in having slowly in-
creasing whorls and (typically) spiral striae.
Compare with G. parvus.
DISTRIBUTION
Prince Edward Island to New England,
west in the Great Lakes- St. Lawrence
system, northwest to northern Alberta and
British Columbia, and south in the Rocky
Mountains to New Mexico.
ECOLOGY
Characteristic of small vernal habitats such
as woodland pools, marshes, roadside
ditches, prairie ponds, and intermittent
streams. Vegetation is ordinarily thick, and
substrates are commonly mud. Radula
formulae of 14-1-13 to 16-1-16 have been
recorded.
176
66
Gyraulus circumstriatus
a,b,c: Pond near North Portal, Sask.; 3.7 mm.
d,e,f: Another specimen, same locality; 3. 1 mm.
177
67
Gyraulus deflectus (Say, 1824)
Irregular Gyraulus
DESCRIPTION
Shell up to about 8 mm wide, 3 mm high,
with 4-1/2 slowly enlarging whorls, planor-
boid, dextral, highly variable in form and
sculpturing, and with any combination
of hairy periostracum, a peripheral keel, or
surface malleations. In specimens without
such surface sculpturing the outer edge
of the body whorl is below' the midline.
Apical whorls submersed. Aperture suboval,
angled above, expanded at the outer edge
in keeled specimens, and inclined down-
ward. Inner lip with a thin callus. In many
specimens the body whorl is also deflected
downward near the aperture. Umbilicus
wide, deep, and showing all whorls. Perios-
tracum pale to dark brown and usually
hirsute, that is covered with hair-like projec-
tions arranged in spiral rows parallel to the
sutures. Non-hirsute specimens are spirally
striate.
This small species may be distinguished
from other species of Gyraulus by its size
(it is the largest species of the genus,
especially east of the Rocky Mountains), its
keeled, malleated, or hirsute surface (or, if
these features are absent, by the relatively
low placement of the outermost edge), and
by the contrasting appearance of its upper
and lower surfaces. Compare with other
species of Gyraulus.
DISTRIBUTION
Occurs throughout mainland Canada north
to the central arctic, throughout Alaska,
and south in the United States to Virginia
and Nebraska.
ECOLOGY
Occurs in all kinds of permanent-water,
eutrophic habitats. The usual substrate is
mud. Commonly lives on vegetation but is
occasionally found on the bottom. Egg
capsules are small, gelatinous, and often
contain 2 to 5 eggs. Observed radula
formulae are between 15-1-15 and 19-1-18.
Locomotion is rather rapid.
178
67
Gyraulus deflectus
a,b,c: Neddy Harbour Pond, Bonne Bay, Nfld,; 4.0 mm.
d,e,f: Ennadai L., N.W.T.; 6.3 mm.
g,h,i: Long L., Longlac, Ont.; 5.5 mm.
179
68
Gyraulus parvus (Say, 1817)
Modest Gyraulus
DESCRIPTION
Shell up to about 5 mm wide, 2 mm high,
with 4 whorls, dextral, depressed but not
entirely flat, and with rounded, rapidly
increasing whorls. Body whorl rounded and
periphery near centre. Spire flattened and
first 2 whorls immersed. Aperture proso-
cline, ovate, in the same plane as the body
whorl or somewhat below it, and with a thin
rounded outer lip and a thin parietal callus.
Umbilicus wide, shallow, and exhibiting
all whorls. Periostracum smooth and glossy,
pale brown to dark brown, and not hairy.
Sculpture not prominent but limited to fine
collabral striae and growth rests.
This small species may be recognized
chiefly by the absence of characters that
would assign it to other species, that is to
G. circumstriatus or G, deflectus. It is not
flatly coiled and semi-transparent, and the
upper and lower aspects are clearly different.
It also lacks a keel, malleations, or hirsute
periostracum, and the outermost edge is
near the centre of the body whorl.
DISTRIBUTION
Occurs throughout Canada and the United
States south of the tree line. Also reported
from Cuba and (questionably) from
northern Eurasia.
ECOLOGY
An abundant species. Lives on submersed
aquatic vegetation in all kinds of permanent
or temporary water-filled habitats that sup-
port vegetation. Bottom most frequently
muddy. Radula formulae vary from 13-1-13
to 17-1-17.
ISO
68
Gyraulus parvus
a,b,c: Peace R. near Point Providence, Alta.; 4. 1 mm.
d,e,f: Herben L. near Lake Louise, Alta.; 4.7 mm.
181
69
Gyraulus vermicularis
(Gould, 1847)
Pacific Coast Gyraulus
DESCRIPTION
Shell up to about 7 mm wide, 2.5 mm high,
with about 4 slowly enlarging whorls,
planorboid, dextral, and with nearly cylin-
drical whorls. The outermost edge of the
body whorl is at the midline. Apical whorls
submersed. Near the aperture the body
whorl is deflected downward. Aperture
elliptical and strongly slanted downward;
inner lip with a thin callus. Umbilicus wide,
shallow, and showing all whorls. Perios-
tracum smooth and pale brown. Sculpture
consists of low spiral threads and cords, fine
crowded collabral lines, and a few irregu-
larly spaced growth rests.
Resembles G. deflectus , but differs in
having more cylindrical whorls and in
lacking heavy malleations, a peripheral keel,
or hairy periostracum. The upper and lower
views are also more similar to each other
than in G. deflectus.
DISTRIBUTION
Occurs in the Pacific coastal drainage from
Alaska to California.
ECOLOGY
Lives in various kinds of perennial and
vernal eutrophic habitats (lakes, ponds,
sloughs, ditches, rivers, and creeks). Occurs
most frequently among vegetation. Nothing
has been published regarding its anatomy
or life history.
182
69
Gyraulus vermicularis
a,b,c: Upper Columbia L., B.C.; 6.9 mm.
d,e,f: Another specimen, same locality; 7.0 mm.
183
70
Armiger crista (Linnaeus, 1758)
Tiny Nautilus Snail
DESCRIPTION
Shell minute, up to about 3 mm wide, 1 mm
high, with 2-1/2 whorls, dextral, thin,
depressed, with a complete lip, and (in most
specimens) with many prominent triangular
blade-like ridges. Ridges especially elevated
at the shoulder of each whorl, inclined
forward, oriented parallel to lines of growth,
and numbering about 12 to 18 on the body
whorl. Spire flattened and sutures im-
pressed. Whorls increasing rapidly in diam-
eter, flattened above, rounded below, and
sharply rounded at the outermost edge,
which is located at the shoulder. Umbilicus
wide, deep, and exhibiting all the whorls.
Periostracum pale brown. In fossil speci-
mens the periostracum is absent, and only
nodular projections of the shell material are
visible. Sculpture, in addition to the ridges,
consisting of very fine spiral lines. Loose
and partly detached coiling occurs in some
specimens.
This tiny species is easily recognized by
its prominent ridges, characteristic shape,
and lip that surrounds the aperture.
DISTRIBUTION
Holarctic. Recorded from scattered locali-
ties in Canada from southern Ontario to
Alberta and the Northwest Territories, and
in the United States from Maine to Minne-
sota and Alaska. Also occurs in Europe,
northern Asia, and North Africa.
ECOLOGY
Lives among dense vegetation in eutrophic
ponds and slow-moving streams. The egg
capsules are about 1.5 mm in diameter and
contain 3 to 6 eggs. Radula formulae of
11-1-11 to 16-1-16 have been reported.
184
70
Armiger crista
a,b,c; Rideau R., Ottawa, Ont.; 1.5 mm.
d,e,f: L, Manitoba, Man.; 1.8 mm.
g,h,i: Marean L., northeast of Little Quill L., Sask.;
1.9 mm.
185
71
Promenetus exacuous exacuous
(Say, 1821)
Keeled Promenetus
DESCRIPTION
Shell up to 7 mm wide (most specimens are
6 mm wide or less), 2 mm high, with almost
4 whorls, planorbiform, biconvex, dextral,
and with the outermost edge of the body
whorl centrally located and prominently
keeled. In most specimens the keel is sharp
but in some it is rounded. Whorls expanding
rapidly, broadly convex above and below,
angled on the outer edge, and wider than
high. Spire low, convex, or flattened. Base
of aperture s trongly slanted inward, almost
triangular or ovate, and expanded at the
outer edge. Outer lip thin to slightly
thickened and inner lip with a thin callus.
Umbilicus rather narrow, extending to the
apex, and exhibiting all the whorls, Perios-
tracum pale to dark brown. Collabral
sculpture consisting of crowded threads and
widely spaced growth rests.
Easily distinguishable from other species
by its biconvex, flattened form, its promi-
nent peripheral keel, its wide and strongly
prosocline aperture, and its rapidly expand-
ing whorls. Compare with/ 3 , e. megas.
DISTRIBUTION
Occurs throughout Canada south of the tree
line except in Newfoundland, Labrador
and subarctic Quebec. Also found in Alaska
and in other parts of the United States east
of the Rocky Mountains but its precise
limits there are unknown. In the western
prairies of Canada, it is replaced in most
(but not in all) localities by P. e, megas.
ECOLOGY
A common species. Lives in various kinds
of temporary-water and permanent-water
habitats, that is large and small lakes, ponds,
streams of various widths, roadside ditches,
and swamps. Submersed vegetation is al-
ways present and the usual substrate is mud.
Radula formulae of 16-1-16 to 18-1-18
have been recorded.
186
187
72
Promenetus exacuous megas
(Dali, 1905)
Broad Promenetus
DESCRIPTION
Similar to P. exacuous exacuous but its shell
is larger (6-9 mm wide), heavier, and has
a more prominent, pinched peripheral keel.
In fresh or alcohol-preserved specimens
the periostracum extends beyond the keel in
a blade-like lamina. Spiral sculpture is also
more apparent inP. e. megas, and (in many
specimens) the periphery is low, causing the
upper surface to be domelike and the lower
to be nearly flat. The most reliable distin-
guishing character, however, is gigantism.
DISTRIBUTION
Typically a western prairie subspecies.
Occurs from eastern Manitoba to British
Columbia and in adjacent parts of the
United States, Its southern limits have not
been determined.
ECOLOGY
Found in lakes, ponds, streams of various
widths, roadside ditches, and swamps. Most
abundant where vegetation is thick and
the substrate is mud. The radula formula of
an Alberta specimen, 5.6 mm wide, is
17-1-17.
1S8
72
Promenetus exacuous megas
a,b,c: Leith R. near Whitelaw, Alta,; 8,2 mm.
d,e,f; Another specimen, same locality; 7.0 mm.
189
73
Promenetus umbilicatellus
(Cockerell, 1887)
Umbilicate Promenetus
DESCRIPTION
Shell up to about 5 mm wide, 2 mm high,
with 4 whorls, planorbiform, depressed, and
dextral. Spire flattened or with the first
2 whorls slightly immersed. Whorls increas-
ing with moderate rapidity and with regular-
ity but somewhat expanded near the aper-
ture. Sutures impressed. Base of body whorl
flatly rounded. Aperture prosocline and
roundly convex except at the inner wall,
where it is abruptly concave and has a thin
callus. Umbilicus prominent, wide, deep,
and exhibiting all whorls. Sculpture con-
sisting of fine collabral lines and fine
revolving striae.
Distinguished by its small size, rounded
whorls, and prominent, deep umbilicus.
Compare with Planorbula campestris.
DISTRIBUTION
A western species, collected in prairie
localities from southern Manitoba to central
Alberta and southern British Columbia, In
the United States it ranges south in the
American Interior Basin to New Mexico.
ECOLOGY
Rather uncommon. Occurs in vernal ponds,
marshes, and springtime flooded margins
of intermittent streams. Associated with
dense vegetation and mud bottoms. Radula
formulae of 17-1-17 and 18-1-18 have
been seen.
190
73
Promenetus umbilicatellus
a,b>c: Lake near Galahad, Alta.; 4.0 mm.
d,e,f: Another specimen, same locality; 5,6 mm.
191
74
Menetus cooperi Baker, 1945
British Columbia Menetus
DESCRIPTION
Shell small, up to about 8 mm wide, 3 mm
high, with 4 whorls, dextral, flattened
apically, convex basally, and with a carina or
keel at the shoulder of the body whorl.
Apical whorls somewhat immersed. Whorls
expanding rapidly and separated by shallow
sutures. Body whorl with a rounded angula-
tion at the shoulder or with a carina at the
shoulder that, in different populations, may
be either poorly developed or prominent.
Aperture prosocline, wider than high, with a
thin lip and a callus deposit on the inner
wall. Umbilicus broad, with a rounded
angulation bounding it and exhibiting all of
the whorls. Periostracum pale to dark
brown, and dull to somewhat glossy. Fine
sculpturing consists of crowded delicate
collabral lines.
Resembles Promenetus exacuous , but in
that species the carina is located medially on
the side of the whorl, or lower, not at the
shoulder. Several subspecies of M. cooperi
and other closely related “species” have
been described but require evaluation. Al-
berta specimens are strongly carinate, while
those from coastal British Columbia locali-
ties are roundly carinate.
DISTRIBUTION
Occurs from northern California to south-
ern Alaska and east to central Alberta. In
the northern part of its range it is restricted
to localities near the coast.
ECOLOGY
Found among submersed vegetation in
perennial-water lakes, ponds, and slow-
moving portions of rivers and streams. The
radula formula is about 20-1-20.
192
193
75
Planorbula armigera
(Say, 1821)
Say’s Toothed Planorbid
DESCRIPTION
Shell up to about 8 mm wide, 3 mm high,
with 5 whorls, planorbiform, dextral, and
ordinarily with 1 set of 6 tooth-like pro-
cesses deep within the aperture. Spire con-
cave. Whorls rounded except obscurely
carinate above and below and slowly ex-
panding. Last part of body whorl expanded
and abruptly deflected downward. Aperture
ovate and inclined backward toward the
base. Denticles located within the aperture
about 1/4 whorl back and visible through
the aperture and, in cleaned shells, through
the shell wall. Rarely, a second set of 6 den-
ticles is located behind the first. Umbilicus
wide, deep, funnel-shaped, and showing
all whorls. Periostracum pale brown to
blackish. Sculpture consisting of fine lines
of growth and microscopic spiral striae.
This medium-sized species (larger than
most Gyraulus andPromenetus but smaller
than Helisoma) may be easily identified
by the presence of at least 1 set of 6 well-
developed denticles deep within the aper-
ture. In the western species Planorbula
campestris, only juvenile specimens bear
denticles and each set has 5 processes; the
adult is also much larger.
DISTRIBUTION
In Canada this species occurs from New
Brunswick to southeastern Ontario and
thence northwest to the vicinity of western
James Bay and beyond, within the tree line,
to the north-central part of the Mackenzie
River system. Also occurs in the Prairies
and south in the eastern and central United
States to Georgia and Louisiana. P,jenksii
(Carpenter, 1871) is a synonym.
ECOLOGY
Lives among vegetation in most kinds of
perennial-water habitats, especially stag-
nant, heavily-vegetated water bodies. The
usual substrate is mud. It is particularly
abundant in subarctic muskeg but is ordi-
narily rather uncommon elsewhere. Radula
formulae are 18-1-18 to 24-1-24. The
animal is blackish and quite active.
194
75
Planorbula armigera
a,bjC: Severn L., northern Ont.; 6.3 mm.
d,e,f: Kenogamisis L. near Geraldton, Ont.; 4.7 mm
(denticles visible through shell walls).
195
76
Planorbula campestris
(Dawson, 1875)
Prairie Toothed Planorbid
DESCRIPTION
Shell up to about 12 mm wide, 4 mm high,
with 6 whorls, planorboid, dextral, and in
most juveniles with 1 to 4 sets of 5 denticles
arranged one behind the other within the
aperture. Spire flat or centrally concave.
Whorls rounded, without carinae, and in-
creasing in size slowly. Last part of body
whorl very slightly expanded and in the
same plane as, or slightly lower than, the
penultimate whorl. Aperture ovate except
concave at inner lip. Denticles visible
through the shell wall and present in most
juveniles less than 4.5 mm in diameter and
in some specimens up to 9 mm. In full-
grown specimens denticles are absent.
Umbilicus wide, deep, funnel-shaped, and
exhibiting all whorls. Periostracum pale
to dark brown. Sculpture consisting of fine,
close collabral lines and sharp spiral lines
that together produce a satin-like texture.
Juvenile specimens resemble Promenetus
umbilicatellus except that their early whorls
are much darker than the body whorl (not
the case in P. umbilicatellus ), the whorls
enlarge more slowly, and in many speci-
mens denticles are visible through the shell
wall. Adults differ from Planorbula armi-
gera in attaining a much larger maximum
size, in having a body whorl that is not
sharply deflected downward and, if denticles
are present, in having 5 rather than 6 den-
ticles in each set.
DISTRIBUTION
Principally in the western prairies but also
on Vancouver Island and in southwestern
Yukon Territory. Extends south in the
United States to Utah and New Mexico.
ECOLOGY
Characteristic of vernal ponds, swamps, and
spring-time flooded portions of permanent
water bodies. Aquatic vegetation is ordi-
narily dense and substrates are mud. The
radula of a Saskatchewan specimen 7.6 mm
wide had 23 teeth on each side of the central
tooth.
196
76
Planorbula campestris
a,b ? c: Pond, Lintlaw, Sask.; 11,3 mm.
d,ed: Pond near Elk Point, Alta.; 1 1.3 mm.
197
77
Helisoma (Helisoma) anceps
anceps (Menke., 1830)
Two-ridged Ramshorn
DESCRIPTION
Shell up to about 20 mm wide, 12 mm high,
with 4-1/2 whorls (most specimens are
much smaller), planorbiform, dextral, mod-
erately strong, and (in most populations)
with a prominent carina on the upper
surface of the body whorl and another
around the umbilicus. Spire immersed to a
variable extent but ordinarily deeply re-
cessed. Aperture ear-shaped, expanded mar-
ginally, somewhat thickened, with a reddish
band internally, and with a callus deposit
on the inner wall. Carinae (where present)
rounded, sharp, or corded; the upper carina
located near the centre of the whorl or
toward (but not on) the shoulder. Umbilicus
deep and rather narrow. Periostracum pale
to blackish brown. Spiral striae present
on many specimens, Collabral threads fine
and closely spaced.
Distinguished by its dextral coiling,
medium size, and (on most specimens)
prominent carinae on the upper and lower
surfaces. For subspecies discrimination
compare with H. anceps royalense .
DISTRIBUTION
Occurs throughout most of southern Can-
ada south of the tree line. Also extends
south to Georgia and northwestern Mexico,
but the distributions of its subspecies in
the United States have not been worked out.
It has been introduced into Italy.
ECOLOGY
Lives in lakes, ponds, rivers and streams
among vegetation and on various substrates.
Absent from temporary-water habitats.
Radulae from 2 specimens of about 10 mm
diameter have 22 to 24 teeth on each side
of the central tooth; in larger specimens
more teeth occur. The soft parts are
sinistrally oriented and the shell is therefore
referred to as ultra-dextral.
198
77
Helisoma anceps anceps
a,b,c: Meach L. near Hull, Que.; 20.4 mm.
d,e,f: Montreal R. near Montreal L., Sask.; 13.8 mm.
199
78
Helisoma {Helisoma) anceps
royalense (Walker, 1909)
Lake Superior Ramshorn
DESCRIPTION
Shell up to about 17 mm wide, 10 mm high,
with 4-1/2 whorls, planorbiform, dextral,
moderately strong, and with a prominent
carina on the shoulder of the body whorl
and another around the umbilicus. Spire flat
to slightly immersed. Aperture ear-shaped,
marginally inflated, edged on the outside
with a dark-brown band, and with an
internal callus deposit on the inner wall.
Upper carina sharp or rounded and forming
a prominent shoulder. Body whorl laterally
flattened toward the base and all whorls
flattened on the upper surface. Umbilicus
deep and wide. Periostracum pale brown.
Collabral sculpturing typically coarse, and
in many specimens one or more dark
incremental growth rests are visible.
Differs from/f. anceps anceps by having a
prominent upper carina at the shoulder of
the body whorl, flatter upper and basal
lateral surfaces, a wider umbilicus, and (in
most populations) by coarser collabral
sculpturing.
DISTRIBUTION
Occurs in Lake Superior, Georgian Bay and
their drainage systems, and in adjacent
portions of the Albany, Attawapiskat and
Winnipeg River systems in northwestern
Ontario. Beyond this region a few other
populations (for example, those in the
Gatineau River system in Quebec) resemble
this subspecies, but its principal area of
occurrence is as defined above.
ECOLOGY
A distinctive subspecies. Has been collected
only from lakes and large rivers. Substrates
were chiefly sand or rocks; submersed
vegetation was moderately dense to dense.
The radula is similar to that of H. a. anceps.
200
78
Helisoma anceps royalense
a,b,c: Bamaji L. } Ont.; 13.8 ram.
d,e,f: Kenogamisis L. near Geraldton, Ont.; 15.0 mm.
201
79
Helisoma (Planorbella)
campanulatum campanulatum
(Say, 1821)
Bell-mouthed Ramshorn
DESCRIPTION
Shell up to about 15 mm wide, 6 mm high,
with up to 7 whorls, planorbiform, sinistral,
and variable in shape. Spire flattened.
Whorls more or less flattened. Early whorls
on upper side all visible and slightly
immersed. Penultimate whorl on upper side
below, or level with, body whorl, or project-
ing a little above it. Lower side commonly
exhibiting only the ultimate and penulti-
mate whorls. Aperture bell-shaped in pro-
file, abruptly expanded, inverted ear-shaped
in cross-section, directed slightly upward,
and with a callus on the inner wall.
Umbilicus narrow and deep, extending to
the apex of the shell, Periostracum brown-
ish. Spiral sculpture obscure or very fine.
Collabral sculpture consisting of coarse
closely spaced threads. In many specimens
coiling is irregular.
The medium size, sinistral coiling, com-
pressed whorls, flattened apex, and bell-
shaped aperture of H. campanulatum will
distinguish it from all other Canadian
species. For comparison with//, c. collinsi
see that subspecies.
DISTRIBUTION
In Canada distributed from Newfoundland
to southern Quebec and west to central
Saskatchewan. Two old records from the
lower Fraser River in British Columbia are
probably incorrect. In the United States it
is found from Maine and Massachusetts
to Illinois and Minnesota.
ECOLOGY
Common. Occurs in lakes and ponds of all
sizes and in slow-moving or backwater
portions of rivers. Vegetation is usually
present and bottoms are of all types. Radula
formulae are about 20-1-20 to 23-1-23.
The living animal is reddish brown or
blackish and is slow moving.
202
79
Helisoma campanulatum campanulatum
a,b,c: Constance Bay, Ottawa, R. near Ottawa, Ont.;
13.2 mm.
d,e,f: L. Gauvreau near Masham, Que.; 16.8 mm.
203
80
Helisoma ( Planorbella ) campan-
ulatum collinsi Baker, 1939
Low-spired Ramshorn
DESCRIPTION
Similar to H. c. campanulatum except that a
clearly developed spire is present. Popula-
tions of individuals in which earlier whorls
project above the body whorl an average
of 10% or more of the height of the body
whorl are considered to beH. c. collinsi.
DISTRIBUTION
Lake Superior, its drainage system, and in
headwaters of the Albany, Winnipeg and
Severn River systems. A related form, called
H. multivolvis (Case), occurs near Lake
Superior in northern Michigan and is
probably only an extreme morph of
H. c. collinsi.
ECOLOGY
Has been collected in lakes and in medium-
sized rivers. Substrates are sand or sand
and gravel; vegetation is present but varies
in abundance. The radula formula of a
specimen 12 mm wide was 22-1-21.
204
205
81
Helisoma (Pieros oma) corpu-
lentum corpulentum (Say, 1824)
Capacious Manitoba Ramshorn
DESCRIPTION
Shell up to 32 mm wide, 16 mm high, with
4-1/2 whorls, planorboid, sinistral, and with
a carina located near the outer edge of each
whorl both above and below. Upper side
flat centrally or slightly concave except for
the body whorl, which protrudes above
earlier whorls. Carinae on upper surfaces of
whorls sharp and forming a 90° angle at
the shoulder of early whorls but becoming
rounded and more centrally located on the
body whorl of mature specimens. Umbilical
carina forming an acute angle on the outer
edge of early whorls but also becoming
rounded and central on the body whorl.
Body whorl flattened and in some speci-
mens bent upward near the aperture. Aper-
ture large, dilated, higher than wide, and
extending above, or above and below, the
body whorl. Umbilicus wide, deep, and
extending to the apex. Periostracum light to
dark brown. Fine sculpture consisting of
prominent, crowded, strongly elevated colla-
bral riblets and microscopic collabral and
spiral striae.
Distinguished by its large and high form,
sharp carinae on the shoulders, laterally
flattened whorls, and coarse sculpturing.
Compare with//, c. whiteavesi,H. pilsbryi
infracarinatum, and H. trivolvis trivolvis.
DISTRIBUTION
Northwest and west of Lake Superior in the
Winnipeg, upper Albany and upper Severn
River systems, and in the upper Mississippi
River system in northern Minnesota.
ECOLOGY
Lives in large and small lakes and in rivers,
and often in exposed habitats. Vegetation
may be sparse to thick, and substrates are of
all kinds. Diverse radula formulae between
27-1-26 and 45-1-45 have been recorded.
206
81
Helisoma corpulentum corpulentum
a>b,c: L. Seul, northwestern Ont.; 25.8 mm.
d,e,f: L. la Croix, Rainy River Dist., Ont.; 23.6 mm.
207
82
Helisoma ( Pierosoma ) corpu-
lentum whiteavesi Baker, 1932
Whiteaves’s Capacious
Ramshorn
DESCRIPTION
Similar to if. c. corpulentum except that it is
relatively higher (the holotype is 24 mm
in diameter and 19 mm high), the upper side
is flatter, and the whorls are more tightly
coiled. The large ear-shaped aperture gives
the shell a Physa -like appearance.
DISTRIBUTION
Known only from Lac des Mille Lacs (the
type locality) and Greenwater Lake, both
northwest of Lake Superior in the Winnipeg
River system in northwestern Ontario.
ECOLOGY
This problematic and rare subspecies appar-
ently occurs in open-water habitats in lakes.
The radula formula is reported as 36- 1-36
to 42-1-42.
Another subspecies, H. c. vermilionense
Baker, 1929, is recorded from the Rainy
River system in northern Minnesota and
may occur in Canada, See Clarke (1973) for
additional details regarding both of these
subspecies.
208
82
Helisoma corpulenium whiteavesi
a,b,c: Greenwater L. west of L. Superior, Thunder Bay
Dist., Ont.; 23.5 mm.
Helisoma corpulentum vermilionense
d,e/: Vermilion L,, St. Louis Co., Minn.; 12.2 mm
(juvenile, paratype).
209
83
Helisoma (Pierosoma) pilsbryi
infracarinatum Baker, 1932
Greater Carinate Ramshorn
DESCRIPTION
Shell up to 32 mm wide, 18 mm high, with
4-3/4 whorls, planorbiform, sinistral, and
with sharp or rounded carinae above and
below. These carinae are more or less
centrally located but each may be rounded
and obsolete on the body whorl. Body whorl
overlapping the penultimate whorl, and in
many specimens the upper side of the shell
is smoothly concave and bowl-like. Body
whorl rounded on its outer side but with the
outermost edge below the centre. Aperture
ovate ear-shaped, higher than wide, and
flaring. Umbilicus wide and exhibiting 2 to
3 whorls. Periostracum yellowish to brown-
ish. ColJabral sculpture consisting of fine
riblets (2 to 4 per mm) and, in some
specimens, of one or more growth rests.
Differs from//, trivolvis in the possession
of a basal carina and in greater axial height.
May be distinguished from the//, corpulen-
tum group by its bowl-like (not flattened)
spire, by the carinae that are more or less
centrally located (not near the outer edges of
the whorls), and by the more sharply convex
lateral area of the body whorl.
DISTRIBUTION
In the boreal forest from southwestern
Quebec to east-central Alberta (Lac la
Biche) and farther south in the Rideau and
St. Lawrence rivers; in Georgian Bay; and
in the Qu’Appelle River system in
Saskatchewan.
ECOLOGY
Ordinarily occurs in lakes, ponds, or quiet
backwaters of streams, among vegetation,
and on various substrates. The radula
formula is approximately 30-1-30 to
37-1-37.
210
83
Helisoma pilsbryi infra canna mm
a,b,c: Rapids on Basswood R. west of L. Superior, Ont.;
23.0 mm (paratype).
d,e,f; Knee L. at outlet, northern Man.; 28.0 mm.
84
Helisoma (Pierosoma) trivolvis
trivolvis (Say, 1816)
Larger Eastern Ramshorn
DESCRIPTION
Shell up to about 32 mm wide, 16 mm high,
with 5 whorls, planorbiform, and sinistral.
Spire submersed and dished. Whorls more
or less carinate centrally or rounded above,
rounded below, and rounded on the outer
side. Apical depression wide, of moderate
depth, and exhibiting all whorls. Umbilical
region sunken and revealing 3 to 3-1/2
whorls. Aperture expanded, dilated at the
margin, ovate ear-shaped, with width equal
to or greater than height, with a callus
deposit on the inner wall, and typically with
a reddish-brown or purplish band within
the aperture. Umbilicus broad and deep.
Periostracum yellowish brown to brown.
Sculpture moderate and consisting of colla-
bral riblets (about 2 to 4 per mm), irregularly
spaced growth rests, and in many specimens
a more or less apparent spiral carina above.
This is the most abundant of the large
eastern helisomas. The close-to-centre posi-
tion of the upper carina will distinguish it
from the H. corpulentum group, in which
the carina is at the shoulder. The lack of a
lower carina will differentiate it from
H. pilsbryi infracarinatum , which has a
well-developed lower carina. Its substantial
axial height (more than 1 2 mm) will
separate it from the western H. trivolvis
subcrenatum and from the other species of
the genus. Compare//, t. binneyi.
DISTRIBUTION
In Canada occurs throughout the boreal and
deciduous forest regions from eastern Que-
bec and Nova Scotia to southeastern Mani-
toba and within a small area in central
Saskatchewan. Also extends throughout the
northeastern United States and farther
south, where it intersects other subspecies,
whose precise distributional limits have
not been established.
ECOLOGY
Characteristic of well-vegetated perennial-
water lakes, ponds, and slow-moving
streams. Mud is the usual substrate. Radu-
lae from Ontario specimens 25 mm in
diameter have about 3 1 to 34 teeth on each
side of the central tooth.
212
84
Helisoma trivolvis trivolvis
a,b,c: Montreal R. near Montreal L., Sask.; 26.8 mm.
d,e,f: Lake on Green R., N.B.; 23.7 mm.
213
85
Helisoma {Piero soma) trivolvis
binneyi (Tryon, 1867)
Binney’s Stout Ramshorn
DESCRIPTION
Resembles//, t. trivolvis except for the
following: (1) it is relatively higher, that is
within population samples the average ratio
of height to diameter, excluding the lip,
exceeds 0.57, whereas in H. t. trivolvis it
seldom exceeds 0.52; (2) a more or less well-
defined carina occurs on the undersides of
the whorls but not in H. r. trivolvis ; (3) the
body whorl is more expansive, causing the
apex and the umbilicus to be more deeply
immersed; and (4) the aperture is more
broadly expanded above and below.
DISTRIBUTION
Principally in the Pacific drainage from
southern British Columbia to California but
also in a few lakes in western Alberta. In
Lake Wabamun, Alberta, inter grades com-
pletely with//, t. subcrenatum. Populations
intermediate between H. t. binneyi and
H. t. subcrenatum — corresponding to
“//. binneyi randolphi” Baker, 1945, and
“//. columbiense ” Baker, 1945 — also occur
in British Columbia. Herein, H. t. binneyi is
used only for the extreme morph described
above. Intermediate populations are best
referred to as H. trivolvis Say, without
any subspecies name.
ECOLOGY
Occurs in eutrophic, well-vegetated lakes.
No detailed information is available regard-
ing its specific ecology or anatomy.
214
85
Helisoma trivolvis binneyi
a,b,c: Dragon L. near Quesnel, B.C.; 20,5 mm.
d,e,f: East end of Sylvan L., Alta.; 22.7 mm.
215
86
Helisoma (Pieros oma) trivolvis
subcrenatum (Carpenter, 1856)
Larger Prairie Ramshorn
DESCRIPTION
Similar to H . t. trivolvis except that its
height does not exceed 10 mm whereas the
height of adult//, t. trivolvis almost always
exceeds 10 mm and in most specimens
exceeds 12 mm; also its coiling is looser and
sutures deeper. Some populations exhibit
spiral, pale-coloured streaks or irregular
coiling. The two subspecies occupy distinct
zoogeo graphical regions.
DISTRIBUTION
Western North America from California
and Utah to Yukon Territory and Manitoba.
ECOLOGY
Occurs in nearly all perennial-water habi-
tats that support significant rooted vegeta-
tion. Mud is the most frequent substrate.
Specimens from Alberta about 20 mm wide
have radulae with 28 to 30 teeth on each
side of the central tooth.
216
86
Helisoma trivolvis subcrenatum
a,b,c: Loch Haven, Cypress Hills Provincial Park,
Sask.; 20.8 ram.
d,e,f: Third Vermilion L., west of Banff, Alta.; 26.8 mm.
217
FAMILY ANCYLIDAE
(True Freshwater Limpets)
Shell small to small-medium, not spiral but shaped like a
broad, low cone, mainly thin-shelled, with rounded or ovate
aperture, radial and concentric sculpturing, and a blunt apex
located either centrally or behind the centre and either in
the midline or to the right. The soft parts are sinistrally
organized, with a pseudobranch (false gill) on the left side.
The radula has about 8 to 37 bicuspid to multicuspid lateral
plus marginal teeth on each side of the bi- to tetracuspid
central tooth. The egg masses are small, ovate, gelatinous,
transparent and have a few whitish eggs. The family is
worldwide.
87
Laevapex fuscus
(CJB. Adams, 1841)
Dusky Lily-Pad Limpet
DESCRIPTION
Shell up to about 8 mm long, 5 mm wide,
3 mm high (most specimens are much
smaller), broad cone-shaped, thin-shelled,
more-or-less elliptical at the base and rather
low. Apex elevated, sharply rounded,
located to the right of the midline and
posterior of centre, and without microscopic
radial lines. Anterior slope slightly convex,
posterior slope concave, and lateral slopes
more or less straight. Aperture elliptical
or with sides a little flattened and conver-
gent posteriorly. Concentric lines of growth
very fine. Radial lines also seen on the sides
of some specimens below the apex. Perios-
tracum very thin, closely adherent, and pale
brown.
Distinguished from Ferrissia species by
having a smooth rather than radially striate
apex and by characters of the soft parts,
which are visible through the shell, that is
the presence of a dark pigment band across
the middle of the mantle and the presence of
epithelial attachment areas between the
anterior muscle scars and between the
posterior and the right anterior muscle
scars. These characters are best seen on
specimens that are well cleaned and have
had the periostracum removed by soaking in
a weak solution of laundry bleach in water.
DISTRIBUTION
Southern Ontario and Quebec to Massachu-
setts, south to Florida and Louisiana, and
west to Oklahoma, Kansas, and Iowa. Also
in the upper Albany River system in
northwestern Ontario.
ECOLOGY
Occurs in heavily vegetated permanent-
water habitats on the undersides of lily pads
and on other emergent vegetation. The
radula is similar to that of Ferrissia species
but the genitalia are distinctive, that is the
penis is large and without a flagellum; in
Ferrissia the penis, when present, is small
and has a club-shaped flagellum.
220
221
88
F errissia fragilis (Try on, 1863)
Oval Lake-Limpet
DESCRIPTION
Shell up to about 5.5 mm long, 3.2 mm
wide, 1.6 mm high (most specimens are
much smaller), broad cone-shaped, thin,
subovate, wider anteriorly than posteriorly,
low, and highly variable in form. Apex
elevated, rounded, located in the midline (or
a little to the right) behind the centre, and
sculptured with numerous very fine radial
striae that are visible at about 50 x magnifi-
cation. Anterior slope convex, posterior
slope concave, and lateral slopes straight.
Aperture suboval in one plane, abruptly
rounded anteriorly and posteriorly, and
flatly convex laterally. Lateral margins
converging posteriorly in many specimens,
causing the posterior margin to be more
sharply curved than the anterior. Perios-
tracum very thin, closely adherent, and pale
brown. Concentric lines of growth very
fine, and radial sculpture poorly marked.
Distinguished by its small size (less than
4 mm long in most specimens), thin shell,
rather straight sides that typically converge
posteriorly (in western Canadian speci-
mens), and its predominantly still-water
habitat. See Basch (1963) for a discussion of
the variation in this limpet.
DISTRIBUTION
Common in southwestern British Columbia
and in southern Ontario and Quebec.
Widely distributed in the United States.
ECOLOGY
Occurs principally in lakes, ponds, and
ditches. Often found on the stems of cattails
(Typha)^ near their bases. Also lives in slow-
flowing streams. The radula is similar to
that of other species of F errissia. A septate
morph resembling the marine genus Crepi-
dula (slipper limpets) exists in some locali-
ties in the United States,
Basch (1963) considers the morph occur-
ring from British Columbia to Oregon to
be distinctive, and has called it “form”
isabellae. It is larger than typical F, fragilis,
and approaches F. parallela in shell ap-
pearance.
222
223
89
Ferrissia parallela
(Haldeman, 1841)
Flat-sided Lake Limpet
DESCRIPTION
Shell up to about 7.6 mm long, 3.2 mm
wide, 2.7 mm high, limpet-shaped, thin-
shelled, long, narrow, and with aperture
sides straight and parallel or somewhat
convergent anteriorly. Apex elevated, ob-
tuse, located in the midline slightly behind
the centre and covered with very fine radial
striae, visible at 50 x and preserved princi-
pally on young specimens. Left and right
lateral surfaces flattened, posterior slightly
concave, and anterior a little convex. Aper-
ture long, ovate, and with lip all in the same
plane or slightly saddle-shaped, i.e. concave
at the ends and convex at the sides.
Periostracum very thin, closely adherent,
and yellowish brown. Lines of growth
mostly fine and well marked. Radial striae
on body of shell obscure but generally
distributed.
Easily distinguished by its long, narrow
shell, its straight, more or less parallel sides,
and its habitat.
DISTRIBUTION
Occurs in southern Canada from New-
foundland and Prince Edward Island to
southern Manitoba. According to the litera-
ture (Basch 1963), it is also found across
the northern United States.
ECOLOGY
Lives in lakes, swamps, and slow-flowing
rivers among thick or moderately thick
vegetation. Often found on stems of cattails
( Typha) and sedges (Scirpus) or on the
undersides of lily pads. Egg capsules are
white and most contain 1 to 3 eggs. The
central tooth of the radula has 2 large
central cusps and 2 small marginal ones; the
lateral and marginal teeth are multicuspid.
224
225
90
Ferrissia rivularis (Say, 1817)
Sturdy River Limpet
DESCRIPTION
Shell up to about 7 mm long, 4 mm wide,
3 mm high, limpet-shaped, thin to notice-
ably thickened, ovate, high or low spired,
and variable in form. Apex elevated,
rounded, located in the midline (or a little to
the right) behind the centre, and covered
with very fine radial striae. Striae preserved
best on young specimens and visible at 50 x *
Anterior slope convex, posterior concave,
and lateral slopes more or less straight.
Aperture oval with all margins convex and
in the same flat plane. Periostracum thin,
closely adherent, and pale brown. Lines
of growth mostly fine and irregular, radial
sculpturing obscure and principally
anterior.
Distinguished by its oval and often
thickened shell, by its relatively large size,
and by its habitat.
DISTRIBUTION
Eastern Canada from New Brunswick to
Saskatchewan. In the United States at least
from Maine to North Dakota, and North
Carolina to Wyoming.
ECOLOGY
Lives attached to rocks and mussel shells in
rivers and creeks, or attached to rocks in
exposed habitats in lakes. The radula
formula is 19-1-19 to 21-1-21, and the
cusps are the same as inF. parallela.
226
90
Ferrissia rivularis
a,b: Carp R. near Carp, Ont.; 4.8 mm.
c,d: Whitesand R. near Sheho, Sask.; 2.8 mm.
227
91 Margaritifera margaritifera
92 Margaritifera f ale ata
229
94 Amblema plicata
230
231
99 Elliptio complanata
101 Pleurobema coccineum
100 Elliptio dilatata
102 Alasmidonta viridis
232
104 Alasmidonta marginata
106 Alasmidonta varicosa
233
234
109 Lasmigona costata
111 Anodontoides ferussacianus
235
236
115 Anodonta grandis grandis
1 16 Anodonta grandis simpsoniana
237
119 Anodonta kennerlyi
120a Anodonta nuttalliana
238
120b Anodonta nuttalliana
121 Strophitus undulatus
122 Piychobranchus fasciolaris
124 Truncilla donaciformis
123 Obliquaria reflexa
239
125 T runcilla truncata
127 Carunculina parva
128 Obovaria olivaria
240
241
242
137 Lampsilis radiaia radiaia
138 Lampsilis radiata siliquoidea
135 Lampsilis fasciola
136 Lampsilis ochracea
243
141 Villosa iris
142 Dysnomia lorulosa rangiana 9 143 Dysnomia triquetra 9
244
Class Pelecypoda
(Clams and Mussels)
Order Eulamellibranchia
IX Superfamily Unionacea
Freshwater Mussels
FAMILY MARGARITIFERIDAE
(Pearly River-Mussels)
Shell large, bivalved, of medium thickness, with pearly
nacre, pseudocardinal hinge teeth well developed, and
lateral hinge teeth- only partly developed or absent. All
4 demibranchs (gills) are marsupial (have brood chambers
for glochidia), but the marsupial microstructure is less
complex and presumably more primitive than in Unionidae.
The glochidia are hookless but have irregular small teeth
at the ventral margin of the valves. The mantle is not united
posteriorly and does not form separate siphonal openings.
The family occurs only in North America and Eurasia.
247
91
Margaritifera margaritifera
(Linnaeus, 1758)
Eastern-River Pearl Mussel
DESCRIPTION
Shell up to 150 mm long, 65 mm high,
40 mm wide, and with shell wall 10 mm
thick at mid-anterior; long-oval, and with
straight or concave lower margin. Except for
closely spaced concentric lines the surface
is mainly smooth. Periostracum brown in
juveniles, black in adults, and eroded at
umbones. Nacre white or whitish, with or
without pink or purple suffusions. Beak
sculpture consists of a few coarse ridges
parallel to the lines of growth. Hinge teeth
incomplete: pseudocardinals erect and ser-
rated, 1 in the right valve and 2 in the left;
lateral teeth poorly developed or absent.
Muscle scars in beak cavity only partly
visible from below. The sexes are separate.
The long and slightly bent shape, black-
ish periostracum, strong pseudocardinal
teeth, and obscure lateral teeth serve to
readily distinguish this species.
DISTRIBUTION
Atlantic drainage of North America from
Goose Bay, Labrador, to the Little Schuyl-
kill River, Pennsylvania. Also occurs in
Eurasia from northern Spain and Scandina-
via east through northern USSR to Japan.
Especially abundant in Newfoundland and
Nova Scotia, but does not virtually pave
the bottoms of streams as the western
species M. falcata sometimes does.
ECOLOGY
Occurs in small and medium-sized running
streams. Often found on sandy shoals and
in pools under overhanging branches. The
breeding season occurs between June and
August. The glochidia are oval to almost
circular, with a narrow inward-directed
flange at the ventral edge of each valve, and
very small (0.06 mm long and 0.07 mm
high). Host fishes in Europe are the brown
trout and the minnow Phoxinus phoxinus. In
North America the native brook trout, as
well as the introduced brown trout, may be a
host. In Europe the species reaches at least
1 16 years of age. In North America it
appears to be restricted to soft water.
248
91
Margaritifera margaritifera
a,b,c,d: Burnt Berry Brook near Springdale, Nfid.; a and
d 1 14.3 mm.
The specimen illustrated in colour on page 229 is from
the Parrsboro R. near Parrsboro, N.S. (x 2/3).
249
92
Margaritifera falcata
(Gould, 1850)
Western-River Pearl Mussel
DESCRIPTION
Similar to Margaritifera margaritifera ex-
cept smaller (maximum length 125 mm,
with purple rather than white or whitish
nacre, relatively smaller anterior pseudocar-
dinal tooth in left valve, and muscle scars
in beak cavity entirely visible from below.
Hermaphroditic, whereas inAf. margariti-
fera the sexes are separate.
DISTRIBUTION
Distributed in Pacific drainages from Cali-
fornia and New Mexico north to the
southern interior of British Columbia, and
farther north near the coast to Revillagigedo
Island in southern Alaska. Also in the upper
Missouri drainage in Montana. In favour-
able localities in British Columbia the
mussels may be so abundant and closely
packed that they completely obscure the
stream bed.
ECOLOGY
Occurs in running streams wider than 4 m.
Found in sand or gravel substrates. Unlike
M. margaritifera , it occurs in hard as well as
in soft water. The gravid period is from
mid May to late June. Hermaphroditic. The
glochidia have not been described. Host
fishes are the chinook salmon, rainbow
trout, brown trout, brook trout, speckled
dace, Lahontan redside, and Tahoe sucker.
The greatest longevity so far determined
forM. falcata is about 67 years, but older
specimens probably occur.
250
92
Margaritifera falcata
a,b,c,d: Koksilah R. near Duncan, Vancouver Is., B.C.;
a and d 101.6 mm.
The specimen illustrated in colour on page 229 is from
the same locality (x 2/3).
251
FAMILY UNIONIDAE (Pearly Mussels)
Shells small to large, bivalved, thin and fragile to thick and
heavy, with pearly nacre, and with or without pseudocardi-
nal hinge teeth and/or lateral hinge teeth. All four
demibranchs (gills), or only one pair of demibranchs, are
marsupial, and the microstructure is more complex than in
Margaritiferidae. The glochidia are hookless or with hooks.
The mantle is drawn together posteriorly by the diaphragm,
and separate siphonal openings are present. The family is
worldwide but occurs principally in Europe, Asia and North
America,
For many years North American Unionidae have been
grouped into three subfamilies: Ambleminae (or Elliptioni-
nae), characterized principally by heavy hinge teeth, all four
demibranchs being marsupial, hookless glochidia, and a
short breeding season; Anodontinae, with hinge teeth
incomplete or absent, whole outer demibranchs only used as
marsupia, hooked glochidia, and short breeding seasons;
and Lampsilinae, with well-developed hinge teeth, posterior
part of outer demibranchs only used as marsupia, hookless
glochidia, and long breeding seasons. That classification
is now being revised by several workers (see e.g. Heard and
Guckert 1970), but the matter is still unsettled. In this book
the traditional subdivisions of Unionidae are therefore
retained.
SUBFAMILY AMBLEMINAE
(Button Shells and Relatives)
93
Gonidea angulata (Lea, 1839)
Rocky Mountain Ridged
Mussel
DESCRIPTION
Shell up to 125 mm long, 65 mm high,
40 mm wide, and with shell wall up to about
5 mm thick at mid-anterior; variable in form
but typically rather thin, trapezoidal in
shape, with posterior margin obliquely
flattened and relatively broad, and with a
sharp and prominent posterior ridge run-
ning from the umbo to the angular basal
posterior margin of each valve. Shell with
obscure radial sculpturing on the posterior
slope and readily apparent growth rests.
Periostracum yellowish brown to blackish
brown, without rays, smooth on the disc,
and roughened on the posterior slope. Nacre
centrally white or salmon, but pale blue
posteriorly and near the margin. Beak
sculpture composed of about 8 rather
coarse, concentric ridges that are straight in
the centre and curved at both ends. Hinge
teeth irregular and poorly developed; pseu-
docardinal teeth compressed, low, laterally
expanded, 1 in the right valve and none
or 1 in the left; lateral teeth absent.
DISTRIBUTION
Columbia River system in southern British
Columbia (Okanagan and Kootenay rivers)
and south in the Pacific drainage to
southern California.
ECOLOGY
In Vaseux Lake near Oliver, British Colum-
bia, large specimens occur in muddy sand
at a depth of 0.6 to 0.9 m along the shore-
ward edge of a bed of Potamogeton (pond
weed). Elsewhere occurs in rivers and lakes
and on various substrates. Four specimens
were collected on 6 August 1972 from
Vaseux Lake, and none were gravid.
Nothing has been published about its
reproduction, glochidia, or fish host.
254
93
Gonidea angulata
a,b,c,d: Vaseux L. near Oliver, B.C.; a and d 123.8 mm.
The specimen illustrated in colour on page 230 is
from the same locality (X 2/3).
255
94
Amblema plicata (Say, 1817)
Three-Ridge
DESCRIPTION
Shell to about 150 mm long, 105 mm high,
65 mm wide, and with mid-anterior shell
wall 15 mm thick; ovate, more or less
truncated posteriorly, and with heavy sculp-
turing. Shells of most specimens bear 3 or
4 heavy, rounded, diagonal, more or less
parallel centrally located ridges that are
directed toward the lower posterior edge. In
some old specimens the ridges are lacking.
Surface also bears a few short ridges on
the posterior slope perpendicular to the
lines of growth and irregular concentric
wrinkles over the whole shell. Periostracum
brown to blackish and without rays. Nacre
white and iridescent posteriorly. Beaks
elevated above hinge line, located close to
the anterior end, moderately inflated, and
deeply excavated. Beak sculpture consisting
of about 5 concentric single-looped ridges;
early ridges expanded anteriorly. Hinge
teeth massive and very strong; pseudocardi-
nals thick and heavy, subtriangular, erect,
deeply serrated, 2 or 3 in the right valve and
2 in the left; laterals of moderate length,
straight or slightly curved, 1 in the right
valve and 2 in the left.
Has the heaviest and most ponderous
shell of any mollusc in Canada. Easily
recognized by its impressive size and thick-
ness, and by its wide diagonal ridges.
DISTRIBUTION
Occurs in the Red River -Lake Winnipeg
drainage area, in the Great Lakes- St,
Lawrence system from Lake Michigan and
Lake Huron to Lake Erie (in the lakes
themselves and in their tributaries), and in
the whole Ohio-Mississippi River system.
ECOLOGY
Common in southwestern Ontario and in
southern Manitoba, Typically a river spe-
cies. Lives on or in various substrates.
Stunted individuals occur in Lake Erie. A
short-term breeder, with gravid period ex-
tending from May to July. Glochidia are
oval, without hooks, and measure about
0,21 mm in length and 0.23 mm in height.
Numerous fish hosts are known.
256
94
Amblema plicata
a, d: Grand R. near Dunnville, Ont.; 123.8 mm.
b, c: South Bay, Pelee Is., L, Erie, Ont
The specimen illustrated in colour on page 230 is from
McGregor Creek, Chatham, Ont. (x 2/3).
257
95
Fusconaia flava
(Rafinesque, 1820)
Pig-Toe
DESCRIPTION
Shell up to 100 mm long, 70 mm high,
40 mm wide, and with shell wall 8 mm thick
at mid-anterior; roughly triangular, bluntly
pointed at posterior basal region, with
ventral margin straight or slightly concave
posteriorly, and posterior ridge well marked.
Periostracum with a dull lustre, brown in
immature specimens and brownish black in
adults, and without rays or with obscure
rays only on the posterior slope. Nacre
whitish or tinged with salmon. Umbones
anterior of centre but in most specimens not
close to anterior margin. Beak sculpture
moderately fine and consisting of 3 to 5
small more or less concentric bars visible
principally on the posterior ridge. Pseudo-
cardinal hinge teeth moderately heavy and
with radial furrow, 1 tooth in the right valve
and 2 in the left; lateral teeth strong, of
medium length, straight or slightly curved,
1 or 2 in the right valve and 2 in the left.
Sometimes confused with the less com-
mon species Pleurobema coccineum, with
which it should be compared.
DISTRIBUTION
In Canada occurs only in the Lake Huron,
Lake St. Clair and Lake Erie drainage
basins of Ontario and in the Red River -
Nelson River system of Manitoba. In the
United States it lives in the same drainage
systems but is also widespread in the
Mississippi-Missouri system.
ECOLOGY
Relatively common within its range and
always found in company with several other
species of mussels. Occurs principally in
medium or large rivers but also in large
lakes, for example Lake Erie, Found in mud
or sand and among sparse or moderate
vegetation. Glochidia are ovate, hookless,
and measure about 0.15 mm in height and
width. Females are gravid in spring and
summer, all four demibranchs are marsu-
pial, and the host fish are bluegill, white
crappie, and black crappie.
258
95
Fusconaia flava
a, d: Sydenham R. near Strathroy, Ont.; 92.1 mm.
b. c: Rondeau Harbour, L. Erie, Ont.
The specimen illustrated in colour on page 231 is from
Big Creek near Port Rowan, Ont. (x 2/3).
259
96
Quadrula quadrula
(Rafinesque, 1820)
Maple-Leaf
DESCRIPTION
Shell up to 125 mm long, 100 mm high,
50 mm wide, and with shell wall 8 mm thick
at the mid-anterior; more or less quadrate,
rounded anteriorly, somewhat truncated
posteriorly, and sculptured on each valve
with 2 bands of nodules radiating from the
umbones, 1 centrally located and the other
on the posterior ridge. Periostracum yellow-
ish brown or brown, and with poorly defined
green radial bands in some specimens.
Annual growth rests well defined. Nacre
white. Beak sculpture consisting of tiny
nodules. Hinge teeth strong: pseudocardi-
nal teeth erect, conical, and serrated; 1 major
tooth (with a small one in front and another
behind) in the right valve and 2 in the left;
lateral teeth erect, 1 or 2 in the right valve
and 2 in the left.
Similar to Q. pustulosa except that the
nodules are restricted to 2 radial bands,
while in Q. pustulosa they occur over most
of the shell surface. Also more quadrate and
less ovate than Q. pustulosa .
ECOLOGY
Occurs in medium-to-large rivers where
currents are slow to moderate. Usual sub-
strates are mud or sand, and vegetation is
ordinarily present and sometimes dense.
Normally a minor element of unionid
communities that contain several species.
Adult females are gravid in late spring and
summer, and the glochidia are ovate,
without hooks, and measure about 0.08 mm
in length and height. The host fish is the
flathead catfish.
DISTRIBUTION
Southern Ontario in the Lake Erie and
Lake St, Clair drainages and Manitoba in
the Red River system. In the United States
it occurs in those drainage systems as well
as throughout the Ohio-Mississippi drain-
age system.
260
96
Quadrula quadrula
a,b>c,d: Grand R. near Byng, Ont; a and d 84,1 mm.
The specimen illustrated in colour on page 231 is from
the Grand R, near Dunnville, Ont. (x 2/3).
261
97
Quadrula pustulosa (Lea, 1831)
Warty-Back
DESCRIPTION
Shell up to 100 mm long, 85 mm high,
65 mm wide, and with shell wall 8 mm thick
at the mid-anterior; ovate-quadrate, rounded
in front, truncated behind, and sculptured
with elongate tubercles that are parallel
to the lines of growth and distributed chiefly
over the central part of each valve. If tuber-
cles are numerous some are also present
on the posterior slope. Periostracum yellow-
ish brown to chestnut-brown in adults and
yellowish with greenish rays in young
individuals. Annual growth rests well
marked in Canadian specimens. Nacre
white. Umbones prominent and, when not
corroded, sculptured with 3 or 4 coarse
ridges. Hinge teeth heavy: pseudocardinal
teeth erect, triangular, and serrated, 1 large
tooth in the right valve (with a small tooth
before and behind) and 2 in the left; lateral
teeth short and slightly curved, 1 or 2 in
the right valve and 2 in the left.
Similar to Q. quadrula but is more ovate,
has scattered rather than confined nodules,
and is relatively heavier.
DISTRIBUTION
Lake Erie and Lake St. Clair drainages in
southwestern Ontario and the United
States. Also in the Lake Michigan and
Ohio-Mississippi River drainages.
ECOLOGY
Not common in southwestern Ontario.
Occurs in rivers of various widths. Found
on gravel, sand, or mud bottoms. Females
are gravid from mid May to late August.
The glochidia are purse-shaped, without
spines, and measure about 0.23 mm in
length and 0.30 mm in height. The host fish
are the channel catfish, shovelnose stur-
geon, black bullhead, brown bullhead,
flathead catfish, and white crappie.
262
97
Quadrula pustulosa
a, d: Grand R., Port Maitland, Out.; 66.7 mm.
b, c: South Bay, Pelee Is., L. Erie, Ont.
The specimen illustrated in colour on page 23 1 is from
L. Erie off Pelee Is., Ont. (x 2/3).
263
98
Cyclonaias tuberculata
(Rafinesque, 1820)
Purple Pimple-Back
DESCRIPTION
Shell about 100 mm long, 100 mm high,
50 mm wide, and with shell wall 8 mm thick
anterio-centrally; outline circular except
flattened dorsally and anteriorly, com-
pressed, and with small or medium-sized
nodules scattered over the posterior and
central surfaces or more restricted. Nodules
rounded or elongate, and oriented perpen-
dicular to the lines of growth. Periostracum
brown or blackish, with poorly defined
brownish or greenish rays, and with annual
growth rests well marked. Nacre purple.
Beak sculpture of fine zigzag bars. Hinge
teeth heavy and strong: pseudocardinal
teeth massive and serrate, 1 in the right
valve (with an additional small tooth in front
and another behind) and 2 in the left; lateral
teeth of medium length and nearly straight,
1 in the right valve and 2 in the left. Beak
cavity narrow and deeply excavated.
The circular and compressed shape,
nodulous exterior, massive pseudocardinal
teeth, and purple nacre readily distinguish it
from all other species.
DISTRIBUTION
Lake Erie and the Sydenham River in
southern Ontario. In the United States it
occurs in Lake St. Clair, Lake Erie, Lake
Michigan and their drainage areas, and
in the Ohio-Mississippi River drainage
system.
ECOLOGY
An uncommon species in Canada. Occurs
in rivers of various sizes. Found on gravel or
mud bottoms. Gravid females have been
collected in the United States from late May
to the middle of August. The glochidia are
reported as 0.27 mm long and 0.35 mm
high, with short hinge line and rounded
anterior, and without spines. The host fish
is unknown.
264
98
Cyclonaias tuberculata
a, d: Huron R., Ann Arbor, Mich.; 79.4 mm.
b, c: South Bay, Pelee Is., L. Erie, Ont.
The specimen illustrated in colour on page 231 is from
the Huron R., Mich. (X 2/3).
265
99
Elliptio complanata
(Lightfoot, 1786)
Eastern Elliptio
DESCRIPTION
Shell up to about 125 mm long, 65 mm
high, 40 mm wide, and with shell wall
6 mm thick at mid-anterior; unusually
variable in form but typically of medium
thickness, somewhat trapezoidal or ellipti-
cal, obliquely truncated posteriorly, with
rounded posterior ridge, and compressed.
Shell unsculptured except for beak sculp-
ture and lines of growth. Periostracum
brownish or blackish and unrayed except in
some young specimens and in adults from
sandy substrates. Annual growth rests well
marked. Nacre purple in most specimens,
but pinkish or whitish in some. Beak
sculpture of concentric U-shaped ridges.
Hinge teeth well developed: pseudocardinal
teeth compressed and conical, 1 in the right
valve (a small accessory tooth may be
present in front of the large one) and 2 in the
left; lateral teeth narrow, of medium length
and nearly straight, 1 in the right valve and
2 in the left. Muscle scars not deeply
impressed.
Usually distinguished from£, dilatata by
its compressed and trapezoidal shape,
obliquely flattened posterior margin, beaks
that are not close to the anterior end, and
often by its thinner shell. More inflated
specimens are broadest near the posterior
slope, whereas E . dilatata is broadest in the
anterior region, more regularly tapered
posteriorly, and has beaks close to the
anterior end. Ligumia nasuta , which also
has purple nacre, differs from E. complanata
in its narrower shape, more delicate hinge
teeth, and centrally pointed posterior
margin.
DISTRIBUTION
Southern James Bay drainages and the
St. Lawrence system (except Lake Huron
south of Georgian Bay, Lake Michigan, and
most of Lake Brie) south in the Atlantic
drainage to Georgia.
ECOLOGY
Uncommon in James Bay drainages but
abundant elsewhere. Lives in shallow water
of permanent lakes, rivers and medium-
sized streams. Found on gravel, sand, clay,
or mud bottoms. Females are gravid in late
spring and early summer, and mature
glochidia are about 0.20 mm long, subovate,
and without hooks. The yellow perch is its
only known host.
266
99
Elliptic complanata
a, d: Ottawa R. near Pembroke, Out.; 77.8 mm.
b, c: Poucette L. near Port Elgin, N.R.
The specimen illustrated in colour on page 232 is from
the Ottawa R. near Pembroke, Ont. (x 2/3),
267
100
Elliptio dilatata
(Rafmesque, 1820)
Spike, or Lady-Finger
DESCRIPTION
Shell up to 125 mm long, 65 mm high,
45 mm wide, and with shell wall up to
12 mm thick at mid-anterior; variable in
form but normally long-ovate, rather thick
and strong, and somewhat inflated. Shell
unsculptured except for beak sculpture and
lines of growth. In some specimens the
growth lines are not evenly concentric, but
are disproportionately wide apart posteriorly
and give the shell a deformed appearance.
Periostracum yellowish brown to brown,
with indistinct greenish rays in many
specimens, and in Canadian specimens with
dark growth rests. Nacre purple in most
specimens but white or pale pink in some.
Beak sculpture consisting of 4 or 5 rather
heavy curved bars. Hinge teeth thick and
strong: pseudocardinal teeth conical and
serrated, 1 in the right valve (with 1 small
tooth in front and another behind) and 2 in
the left; lateral teeth of medium length and
nearly straight, 1 (or 2) in the right valve and
2 in the left. Muscle scars rather deeply
impressed.
Sometimes confused with E. complanata.
Compare with that species.
DISTRIBUTION
Common in the Great Lakes and their
tributaries from Lake Michigan to Lake
Erie; uncommon in Lake Ontario and in the
St. Lawrence River. Widespread in the
Ohio-Mississippi and Gulf of Mexico
drainages.
ECOLOGY
Often abundant. Occurs in rivers and lakes
of various sizes. Found on diverse sub-
strates. Hermaphroditic. The breeding sea-
son lasts from May to August. Glochidia
are oval except for the straight hinge line,
and measure about 0.20 mm in length and
0.22 mm in height. The host fish are gizzard
shad, flathead catfish, white crappie, black
crappie, and yellow perch.
268
100
EUiptio dilatata
a, d: Grand R., Cayuga, Ont.; 85.7 mm.
b, c: South Bay, Pelee Is., L. Erie, Ont.
The specimen illustrated in colour on page 23 2 is from
the Grand R. near West Montrose, Waterloo Co., Ont.
(x 2/3).
269
101
Pleurobema coccineum
(Conrad, 1836)
False Pig-Toe
DESCRIPTION
Shell up to 90 mm long, 65 mm high,
40 mm wide, and with shell wall 8 mm
thick at mid-anterior; more or less ovate,
more sharply rounded posteriorly than
anteriorly but not pointed, and with ventral
margin convex throughout; posterior ridge
obscure and rounded on most specimens.
Periostracum shiny, yellowish brown to
brown, but blackish in very old specimens,
and without rays (or with obscure rays) only
on the posterior slope. Nacre white or
pinkish. Umbones in most specimens close
to anterior margin. Beak sculpture coarse,
irregular, and visible principally on poste-
rior ridge. Pseudocardinal hinge teeth heavy
and radially channelled and grooved, 1 large
tooth in the right valve (with 1 additional
small tooth in front and another behind) and
2 in the left; lateral teeth strong and straight
or slightly curved, 1 in the right valve and
2 in the left.
Similar to the more abundant species
Fusconaia flava, with which it should be
compared.
DISTRIBUTION
Within Canada found only in Lake Erie and
tributaries of Lake Erie and Lake St. Clair
in southwestern Ontario. Farther south
it occurs throughout most of the Missis-
sippi- Missouri system.
ECOLOGY
Rare in Canada. Occurs in medium-sized to
large rivers and in Lake Erie. Found on
mud or sand, and with associated vegetation
sparse or absent. Moderate current is appar-
ent in its river localities. Gravid in late
spring and early summer. The glochidia are
subovate, without hooks, and measure about
0.1 5 mm in height and width. The outer
demibranchs only are marsupial. The host
fish is unknown.
270
101
Pleurobema coccineum
a, d: South Bay, Pelee Is., L. Erie, Ont.; 63.5 mm.
b, c: Rondeau Harbour, L. Erie, Ont.
The specimen illustrated in colour on page 232 is from
Rondeau Harbour, L. Erie, near Shrewsbury, Ont.
(x 2/3).
271
SUBFAMILY ANODONTINAE
(Floater Mussels)
102
Alasmidonta viridis
(Rafinesque, 1820)
Brook Wedge Mussel
DESCRIPTION
Shell up to 50 mm long (usually less),
30 mm high, 18 mm wide, and with shell
wall up to 2 mm thick; more or less
rhomboid in shape, quite thin, and some-
what inflated, especially at the rounded
posterior ridge. Shell smooth except for
lines of growth and beak sculpturing.
Periostracum dull yellowish brown to
greenish, and in many specimens covered
with rather obscure greenish rays. Nacre
white or bluish white, and iridescent poste-
riorly. Beak sculpture consists of 6 to
8 concentric ridges that are gently and
unevenly curved centrally and angular on
the posterior slope. Hinge teeth moderately
small; pseudocardinal teeth elevated, trian-
gular, 1 in the right valve and 1 split tooth in
the left (a smaller tooth may also be present
anterior to the major tooth); lateral teeth
irregularly developed, 1 or 2 in the right
valve and 2 in the left, but these may be
reduced or nearly absent.
Alasmidonta viridis was formerly known
as A. calceola (Lea, 1830).
DISTRIBUTION
Canadian specimens have come only from
southern Ontario in the Lake Huron, Lake
St. Clair, and Lake Erie drainages. In the
United States, A. viridis occurs in the
middle Great Lakes drainages and in the
Mississippi system from the Ohio River
drainage to the Tennessee River drainage.
ECOLOGY
Characteristic of small headwater streams,
but also occurs in larger rivers and in lakes.
Substrates are usually sand or gravel but
sometimes mud. A long-term (bradytictic)
breeder but details are not known. Glochid-
ia are subtriangular, with a ventral spine
on each valve, and measure about 0.30 mm
long and 0,26 mm high. Host fish are the
johnny darter and mottled sculpin.
272
102
Alasmidonta viridis
a, d: Irvine Creek near Dracon, Ont.
b, c: West branch of Grand R., Ayr, Ont.; 35.5 mm.
The specimen illustrated in colour on page 232 is from
Smith Creek, Poole, Ont. (x 2/3).
273
103
Alasmidonta heterodon
(Lea, 1830)
Dwarf Wedge Mussel
DESCRIPTION
Shell up to about 45 mm long, 25 mm high,
16 mm wide, and with shell wall about
1 mm thick in mid-anterior region; more or
less ovate or trapezoidal, roundly pointed
posterio-basally, thin but not unduly fragile,
with rounded posterior ridge, and of me-
dium inflation. Females more inflated pos-
teriorly than males. Sculpturing absent
except for lines of growth and beak sculp-
ture. Periostracum brown or yellowish
brown, and with greenish rays in young or
pale-coloured specimens. Nacre bluish
or silvery white, and iridescent posteriorly.
Beak sculpture composed of about 4 curved
ridges, which are angular on the posterior
slope. Hinge teeth small but distinct;
pseudocardinal teeth compressed, 1 or 2 in
the right valve and 2 in the left; lateral teeth
gently curved and reversed , that is, in most
specimens, 2 in the right valve and 1 in
the left.
The small size, roundly pointed posterior-
basal margin, and reversed lateral hinge
teeth readily distinguish this species.
DISTRIBUTION
Discontinuously distributed in the Atlantic
drainage from the Petitcodiac River in New
Brunswick (its only Canadian population)
to the Neuse River in North Carolina.
Common in the Petitcodiac River and in
portions of the Connecticut River system,
but uncommon to rare elsewhere.
ECOLOGY
Characteristic of medium-sized rivers with
slow-to-moderate current. Found on mud,
sand, or (rarely) gravel bottoms. A long-term
breeder, with gravid specimens recorded
in February and April. Glochidia are
roughly triangular, with hooks, and mea-
sure about 0.30 mm in length and 0.25 mm
in height. The host fish has not been
determined.
274
103
Alasmidonta heterodon
a,b,c,d: Ashuelot R. near Keene, N.H,; b and c
39,9 mm.
The specimen illustrated in colour on page 233 is from
the North R. near Salisbury, N.B. (X 2/3),
275
104
Alasmidonta marginata
Say, 1819
Ridged Wedge-Mussel
DESCRIPTION
Shell up to about 90 mm long, 50 mm high,
35 mm wide, and with shell wall about
2.5 mm thick in mid-anterior region;
roughly trapezoidal in shape, rather thin;
and with a prominent, inflated, sharply
rounded posterior ridge, and concave poste-
rior slope. Shell sculptured on the posterior
slope, with well-marked grooves and ridges
perpendicular to the lines of growth. Perios-
tracum yellowish, greenish, brownish or
blackish, paler on the posterior slope, and
prominently rayed in most specimens.
Nacre bluish white, and exhibiting in some
specimens greyish or greenish discoloura-
tions or suffusions of pale salmon. Beak
sculpture coarse and consisting of 5 or
6 heavy double-looped bars. Hinge teeth
characteristic : pseudocardinal teeth dorso-
ventrally compressed, well developed, 1 in
each valve; lamellate interdental projection
in left valve; lateral teeth absent.
The inflated posterior ridge, unique
hinge teeth, sculptured posterior slope, and
more or less trapezoidal shape distinguish it
from all other species except A. varicosa
of the Atlantic coastal region. In A. varicosa
the posterior ridge is evenly (not sharply)
rounded, the periostracum of some speci-
mens is paler anteriorly than posteriorly
(not the reverse), the shell does not exceed
75 mm in length, and it is not sharply
truncated posteriorly.
DISTRIBUTION
Great Lakes St. Lawrence system from
Lake Huron to the Ottawa River and the
vicinity of Cornwall, Ontario; Ohio-
Mississippi River system and Susquehanna
River system in the United States.
ECOLOGY
Occurs in rivers. Most common in riffles or
rapids on gravel or rocky bottoms. Her-
maphroditic. Gravid specimens have been
noted in July; probably a long-term breeder.
The glochidia bear hooks, and are about
0.34 mm in length and 0.37 mm in height.
The host fish are white sucker, northern
hog sucker, shorthead redhorse, rock bass,
and warmouth.
276
104
Alasmidonta marginata
a, d: Nottawasaga R. near Alliston, Ont.; 78.6 mm.
b, c: Thames R., Chatham, Ont,
The specimen illustrated in colour on page 233 is from
the Sydenham R. near Shetland, Ont. (x 2/3),
277
105
Alasmidonta undulata
(Say, 1817)
Heavy-toothed Wedge Mussel
DESCRIPTION
Shell up to 75 mm long, 45 mm high,
35 mm wide, and with shell wall about
6 mm thick at mid-anterior; triangular-
ovate, centrally inflated, and with thickened
anterior and low posterior ridge. Shell
smooth except for lines of growth and heavy
beak sculpture. Periostracum yellowish,
greenish, reddish brown or black, and with
greenish or blackish rays that are obscured
in old blackened specimens. Nacre whitish
anteriorly and bluish posteriorly, or modi-
fied with salmon or pink. Beak sculpture
very heavy and composed of about 5 prom-
inent single-looped curved ridges that ex-
tend far out on the disc (about 10 mm from
the umbonal apex). Hinge teeth incomplete:
pseudocardinal teeth strong and deeply
grooved, 1 in the right valve and 2 in the left
(the posterior one larger); interdental projec-
tion in left valve clearly apparent in many
specimens; lateral teeth vestigial or absent.
The pseudocardinal teeth are buttressed
below by a heavy ridge located behind the
impressed anterior adductor muscle scar.
The triangular form, modest size, thick-
ened anterior, characteristic hinge teeth,
and heavy beak sculpture distinguish this
species from all others.
DISTRIBUTION
Atlantic drainage from Nova Scotia and the
St. Lawrence River and its tributary rivers
south to Florida.
ECOLOGY
Occurs in rivers and lakes. Found especially
on sand or gravel bottoms. Reaches maxi-
mum size in outlet streams just below lakes.
Breeds from the middle of July to the middle
of the following June. Glochidia have
strong hooks and measure about 0.34 mm in
length and 0.36 mm in height. The fish
host is unknown.
278
105
Alasmidoma undulata
a,b,c,d; St. Lawrence R. near Quebec, Que.;a andd
73.0 mm.
The specimen illustrated in colour on page 233 is from
the St, Lawrence R. near Montreal, Que. f x 2/3).
279
106
Alasmidonta varicosa
(Lamarck, 1819)
Swollen Wedge-Mussel
DESCRIPTION
Shell up to about 70 mm long, 40 mm high,
30 mm wide and with shell wall about
2 mm thick in mid-anterior region; elliptical
to trapezoidal but with flattened ventral
margin and truncated dorso-posterior mar-
gin, rather thin, and with an inflated and
rounded posterior ridge and slightly concave
posterior slope. Shell smooth, or lightly
sculptured on the upper posterior slope,
with short grooves and ridges perpendicular
to the lines of growth. Periostracum yellow-
ish, greenish, brownish or blackish, and
(in most specimens) extensively rayed.
Nacre bluish white with olive or pinkish
suffusions. Beak sculpture coarse and con-
sisting of a few heavy single- or double-
looped ridges, but these ridges are rarely
preserved. Hinge teeth not well developed:
pseudocardinal teeth weak, flattened, 1 in
the right valve and 1 (smaller) in the left;
interdental projection in left valve poorly
developed or absent; lateral teeth absent.
Characters that distinguish it from the
closely related A. marginata are discussed
under that species. The inflated posterior
ridge and complete absence of lateral teeth
easily differentiate it from the other species
that it partially resembles, that is Lasmigona
compressa andL. costata.
DISTRIBUTION
Atlantic coastal drainage from Nova Scotia
and New Brunswick to North Carolina.
ECOLOGY
Usually found in rapids or riffles on rocky or
gravel substrates and in sandy shoals, that
is habitats similar to those of A. marginata.
More abundant in small rivers and creeks,
whereas A. marginata is more abundant
in larger streams. The breeding period lasts
from August to the following May, and
glochidia are similar to those of A. margi-
nata. The host fish has not been
determined.
280
106
Alasmidonta varicosa
a,b,c,d: Wallace R. near Pugwash, N.S.; a and d
SI. 2 mm.
The specimen illustrated in colour on page 233 is from
Molunkus Stream, Macwahoc, Aroostook Co., Me.
(x 2/3).
281
107
Lasmigona complanata
(Barnes, 1823)
White Heel-Splitter
DESCRIPTION
Shell up to 190 mm long, 125 mm high,
65 mm wide, and with shell wall 10 mm
thick in mid-anterior; circular-trapezoid in
juveniles but becoming ovate with age,
diagonally truncate posteriorly, and thick-
ened and rather strong anteriorly but thin
and brittle posteriorly. A prominent and
high dorsal projection (wing) occurs in
juveniles and half-grown specimens. The
wing is sculptured with radial ridges in
some southern specimens but, except for
growth rests and beak sculpture, the whole
shell is unsculptured in Canadian material.
Periostracum brown and indistinctly rayed
in juveniles, blackish brown and unrayed
in adults. Nacre white and tinged with
bluish white posteriorly. Beak sculpture
strong and composed of about 8 irregular or
broken double-looped ridges that, in some
specimens, are nodulous. Hinge teeth char-
acteristic: pseudocardinal teeth large, thick,
variable and irregular, 1 in the right valve
(sometimes with 1 or 2 smaller teeth on
either side of the large tooth) and 2 in the
left; interdental projection present and low,
or absent; lateral teeth vestigial or absent.
Easily recognized by its compressed ovate
shell, prominent dorsal wing, heavy pseudo-
cardinal teeth, and white nacre.
DISTRIBUTION
Lake Winnipeg-Nelson River system from
Alberta to western Ontario; middle Great
Lakes -St. Lawrence River system in tribu-
taries of Lake Michigan, Lake St. Clair
and Lake Erie; Ohio-Mississippi River
system throughout; and Alabama River
system.
ECOLOGY
Occurs in rivers of various widths greater
than about 7.5 m. Always found on sandy or
muddy bottoms. The breeding season lasts
from at least August to May. Glochidia
are subtriangular, with hooks, and measure
from 0.28 to 0.34 mm in length and 0.30 to
0.34 mm in height. The host fish are carp,
green sunfish, largemouth bass, and white
crappie.
282
107
Lasmigona complanata
a, d: McGregor Creek, Chatham, Ont.; 127.0 mm.
b, c: Minnedosa R. near Minnedosa, Man.
The specimen illustrated in colour on page 234 is from
the Seine R. near Winnipeg, Man. (x 2/3).
283
108
Lasmigona compressa
(Lea , 1829)
Brook Lasmigona
DESCRIPTION
Shell up to about 115 mm long, 55 mm
high, 40 mm wide, and 4 mm in mid-
anterior shell-wall thickness; trapezoid or
rhomboid-ovate, with a low to moderate
dorsal wing in immature specimens, com-
pressed, and rather thin but not fragile.
Rarely, a few faint radial grooves occur on
the upper posterior slope, but ordinarily the
shell is smooth except for beak sculpture
and lines of growth. Periostracum yellowish
brown, greenish or blackish brown, and
extensively but not prominently rayed in
most specimens. Nacre silvery white or
bluish and, in some specimens, cream- or
salmon-coloured near the beak cavities.
Beak sculpture strong, and composed of
about 8 variably irregular broken concentric
ridges. Hinge teeth characteristic: pseudo-
cardinal teeth strong, narrow, directed for-
ward, typically 1 in the right valve and 2 in
the left: interdental projection prominent in
left valve; lateral teeth long and narrow,
with 1 in the right valve and 2 in the left in
most specimens, but undeveloped near the
beaks or almost absent in some specimens.
Well characterized by its shape, colour,
beak sculpture, hinge teeth, and especially
its prominent interdental projection.
DISTRIBUTION
Hudson Bay drainage from Saskatchewan
to Ontario; Great Lakes- St. Lawrence
drainage from Minnesota to Quebec and
Vermont; Hudson River system in New
York; and upper Ohio-Mississippi system
south to West Virginia and Nebraska.
ECOLOGY
Occurs principally in rivers and streams of
various sizes, even sometimes in very small
creeks, 2 m wide or less. Rare in lakes.
Found on substrates of gravel, sand, or mud.
The breeding season lasts from August to
the following June. Normally hermaphro-
ditic. The glochidia are circularly triangu-
lar, with hooks, and measure about 0.34 mm
in length and 0.28 mm in height. The host
fish is not known.
284
108
Lasmigona compressa
a, d: Creek near Leggatt, Ont.; 78.6 mm.
b, c: Turtlelake R., Edam, Sask,
The specimen illustrated in colour on page 234 is from
the Red Deer R. near Hudson Bay, Sask. (x 2/3).
285
109
Lasmigona costata
(Rafinesque, 1820)
Fluted Shell
DESCRIPTION
Shell up to about 150 mm long, 75 mm
high, 50 mm wide, and with shell wall
6 mm thick in mid-anterior region; trape-
zoid-ovate, without a posterior wing in all
growth stages, of medium inflation, quite
thick and strong, and heavily sculptured.
The shell is sculptured on the posterior
slope with up to 20 heavy radial ridges, with
growth irregularities on the disc, and with
beak sculpturing on the umbones. Perios-
tracum yellowish, greenish or brownish,
and with generally distributed narrow
greenish or brownish rays that become
mostly obscure in mature specimens. Nacre
white or bluish white, with yellow or pink
tints centrally. Beak sculpture composed of
about 4 heavy double-looped concentric
ridges. Hinge teeth well developed: pseudo-
cardinal teeth strong and knob-like or
lamellar, 1 in the right valve and 2 smaller
ones in the left; interdental projection heavy
and prominent in the left valve; lateral teeth
rudimentary or absent.
The large size, characteristic shape, and
heavy posterior sculpturing make identifica-
tion of most specimens very easy. Small
specimens from some populations with
reduced sculpture may resemble L. com-
pressa , but they can be distinguished by
characters of the hinge teeth, beak sculp-
ture, and internal structure (that is relative
proportion of males to females).
DISTRIBUTION
Hudson Bay drainage in the Red and
Winnipeg River systems; Great Lakes-
St, Lawrence system from southern Lake
Huron and its tributaries to the Ottawa
River and Lake Champlain ; and entire
Ohio- Mississippi River system.
ECOLOGY
Occurs in canals, rivers, and lakes. Found
on gravel, sand, or mud bottoms. Like other
unionids it responds positively to increased
water hardness by becoming unusually
large and thick. The breeding season lasts
from the beginning of August to the middle
of May. The sexes are separate. Glochidia
are triangular, and measure about 0.36 mm
in length and 0.38 mm in height. A host
fish is the carp.
286
109
Lasmigona costata
a, d: Grand R. near Doon, Ont.; 109.5 mm,
b, c: Baker Creek near Niagara R. near Fort Erie, Ont.
The specimen illustrated in colour on page 235 is from
the St. Lawrence R. near Cornwall, Ont. (x 2/3).
287
no
Simpsoniconcha ambigua
(Say, 1825)
Mudpuppy Mussel
DESCRIPTION
Shell up to about 42 mm long, 20 mm high,
16 mm wide, and with shell wall almost
3 mm thick at mid-anterior; elongate ellipti-
cal, and sharply rounded at the ends but
more or less straight dorsally and ventrally.
Periostracum brownish and without rays.
Nacre whitish or with muted yellow or
purple suffusions, especially near the beak
cavity. Beak sculpture of 4 or 5 parallel,
V-shaped bars with their apices directed
toward the umbonal apex. Beaks sharp,
narrow, inclined forward, and located about
1/4 the distance from anterior to posterior.
Hinge teeth incomplete and irregular:
1 pseudocardinal tooth in each valve; lateral
teeth either rudimentary or lacking entirely.
This small, rare species resembles Carun-
culina parva , but may be distinguished by
the incomplete hinge teeth and characteris-
tic beak sculpturing. Compare also with
Alasmidonta heterodon and Villosa fabalis.
DISTRIBUTION
Lake St. Clair drainage (Sydenham River,
one record) in southern Ontario; central
Great Lakes drainages in the United States;
and Ohio-Mississippi drainage from Michi-
gan to Iowa and south to Arkansas and
Tennessee.
ECOLOGY
Usually found under flat stones in rivers but
also in mud or on gravel. The glochidial
host is an amphibian, the mudpuppy {Nectu-
rus maculosus). This is the only freshwater
mussel known to utilize an animal other
than a fish for glochidial attachment.
288
110
Simpsoniconcha ambigua
a,b,c,d: Troublesome R. above Lost Creek, Ky.; a and d
33.3 mm.
The specimen illustrated in colour on page 235 is from
the same locality (x 2/3).
289
Ill
Anodontoides ferussacianus
(Lea, 1834)
Cylindrical Floater
DESCRIPTION
Shell up to 95 mm long, 40 mm high,
40 mm wide, and with shell wall 1.5 mm
thick in mid-anterior region; elliptical,
much inflated, rather fragile, and with
unusual oblique beak sculpturing. Shell
unsculptured except for concentric lines
and low ridges associated with growth rests
and beak sculpture. Periostracum greenish
or brownish, with prominent dark annuli;
numerous, generally distributed, prominent
or obscure, narrow green or brown rays
and 2 or 3 broader dark rays on the low
rounded posterior ridge and posterior slope.
Nacre bluish white, slightly iridescent,
and with tints of cream in the beak cavity of
some specimens. Beak sculpture unique,
fine, and composed of several curved ridges
that are not parallel to the lines of growth
but follow an anteriorly expanded arc.
Several fine radial ridges also exist posterior
to the curved ridges. Hinge teeth absent
except for a narrow swelling of the shell
margin in front of the beak.
Characterized by its moderate size; thin,
inflated and subcyclindrical shell; and espe-
cially by its fine, oblique, subconcentric
beak sculpture,
DISTRIBUTION
James Bay and Hudson Bay drainage from
central Ontario to southeastern Saskatche-
wan; Great Lakes- St. Lawrence system
downstream to near Montreal; and
Ohio Mississippi River system south to
Colorado and Tennessee.
ECOLOGY
Usually found in slow-moving streams on
mud bottoms but also occurs in lakes and
sometimes on sand. The breeding season
lasts from August until May. Glochidia are
subtriangular, with hooks, and measure
about 0.32 mm in length and height. The
mottled sculpin and the sea lamprey are
host fish.
290
Ill
Anodontoides ferussacianus
a, d: Baker Creek near Niagara R. near Fort Erie, Om.;
69.9 mm.
b, c: Grand R., Riverview, Ont.
The specimen illustrated in colour on page 235 is from
the Souris R. near Souris, Man. (x 2/3).
291
112
Anodonta beringiana
Middendorff, 1851
Yukon Floater
DESCRIPTION
Shell up to 150 mm long, 75 mm high,
55 mm wide, and with shell wall about
3 mm thick at mid-anterior; elliptical,
broadly rounded anteriorly and more nar-
rowly rounded posteriorly, without a dorsal
wing, and moderately thin but relatively
strong. Surface roughened by lines of
growth but centrally shining. Periostracum
olive-green in juveniles but dark brown to
nearly black in old specimens. Nacre lead-
colour to dull blue, Umbones inflated and
elevated above hinge line. Beak sculpture
consisting of a few rather straight, irregular
bars parallel to the hinge line. Hinge teeth
absent.
Quite similar to very large specimens of
A. kennerlyi but distinguished by its larger
shell, dark periostracum, inflated beaks
that clearly project above the hinge line, and
lead-coloured to bluish nacre. Occurs in
more northern drainages than A. kennerlyi.
DISTRIBUTION
Yukon River drainage in the Yukon Terri-
tory and Alaska, and other drainages in
Alaska and in Kamchatka, USSR.
ECOLOGY
Known from rivers and lakes within its
range. The glochidia have been reported as
0.296 mm in height and width. Fish hosts
are the sockeye salmon, chinook salmon,
and three-spined stickleback.
292
112
Anodonta beringiana
a,b: Old Crow R. near Old Crow, Y.T.; 133.4 mm.
The specimen illustrated in colour on page 236 is from
a lake in Porcupine Valley near Fort Yukon, Y.T.
(x 2/3).
293
113
Anodonta cataracta cataracta
Say, 1817
Eastern Floater
DESCRIPTION
Shell up to 150 mm long* 75 mm high,
65 mm wide, and with shell wall about
1.5 mm thick at mid-anterior; elliptical,
roundly pointed posteriorly, inflated, thin,
fragile, and with inflated beaks that project
above the hinge line. Surface smooth except
for low concentric wrinkles and growth
rests. Periostracum shiny and grass-green,
or modified with yellow or brown, or simply
brown all over; in many specimens with
numerous narrow green rays covering the
disc and the central area, and a few broad
green rays on the posterior ridge and slope.
Nacre silvery or white, tinged with blue
or yellow, and iridescent. Beak sculpture
consisting of about 6 to 8 primarily double-
looped, curved, concentric bars that are
not nodulous. Hinge teeth absent.
Similar to A. c.fragilis , but that subspe-
cies has beak sculpture with 8 to 12 single-
looped bars and lacks green periostracum
(which is present in many, but not all,
A . c. cataracta). Compare also A grandis
grandis and A. g. simpsoniana.
DISTRIBUTION
Lower St. Lawrence River drainage and
Maritime Provinces south in the Atlantic
drainage to the Gulf of Mexico drainage. At
the north end of its range it intergrades with
A . c.fragilis , and in the middle of the St.
Lawrence system with A. grandis grandis.
ECOLOGY
Occurs in ponds, lakes, and streams of
various widths down to small brooks. Most
abundant on mud (where it is commonly
bright green) but also occurs on sand and,
less frequently, on gravel. The breeding
season lasts from July to the following April
or May. Glochidia are roughly triangular,
with hooks, and measure about 0.36 mm in
length and 0.37 mm in height. The host
fish are reported to be the pumpkinseed and
the carp.
294
113
Anodotua cataracta cataracta
a, d: Emerald L., North Dorset, Vt.; 101.6 mm.
b, c: L, Edward, Denmark Parish, N.B.
The specimen illustrated in colour on page 236 is from
a ditch near Quebec, Que. (x 2/3).
295
114
Anodonta cataracta fragilis
Lamarck^ 1819
Newfoundland Floater
DESCRIPTION
Shell up to about 90 mm long, 45 mm high,
25 mm wide, and with mid-anterior shell
wall 1.5 mm thick; long-elliptical with
bluntly pointed posterior located at or below
the midline, rounded or nearly straight
ventral ly, diagonally flattened dorso-posteri-
orly, and typically thin and fragile. Surface
marked by fine concentric wrinkles and
prominent growth rests. Periostracum shiny
or dull, straw-yellow to brown, and (in a
few pale specimens) with obscure fine green
rays on the disc and central area and a few
poorly defined broad green rays on the
posterior ridge and slope. Nacre silvery,
white or bluish, and centrally discoloured
with yellowish blotches in most specimens.
Beak sculpture consisting of about 8 to
12 fine, irregular, concentric, single-looped
bars that extend about 8 mm from the um-
bonal apex. Hinge teeth absent.
Characterized principally by its beak
sculpture, lack of green periostracum, and
small size. Compare with A. c. cataracta and
A. kennerlyi.
DISTRIBUTION
Typical specimens occur principally in
Newfoundland, but specimens exhibiting
intermediate characteristics between
A. c. fragilis and A. c. cataracta are common
throughout northern Nova Scotia, New
Brunswick, and eastern Quebec. Such
specimens are considered to be intergrades
and are referred to simply as Anodonta
cataracta or, more precisely, as A. c. cata-
racta x A, c. fragilis , or the reverse, with the
dominant morph cited first.
ECOLOGY
Occurs in diverse, permanent-water habitats
(ponds, lakes, and streams of various sizes)
as does A. c. cataracta . Found principally in
mud but also in sand and, less commonly,
in gravel. Undoubtedly a long-term breeder,
but no details are known about its reproduc-
tive period, glochidia, or fish host.
296
114
Anodonta cataracta fragilis
a, d: Wells Gully, Whitbourne, Nfld.; 69.9 mm.
b, c: Poucette L. near Port Elgin, N.B.
The specimen illustrated in colour on page 236 is from
the same locality as a and d (x 2/3).
297
115
Anodonta grandis grandis
Say, 1829
Common Floater
DESCRIPTION
Shell up to about 160 mm long, 100 mm
high, 7 5 mm wide, and with shell wall
4 mm thick at mid-anterior and 8 mm thick
near anterior pallial line. Shell highly
variable in form but typically ovate, inflated,
thin, and fragile. Surface smooth and shiny
except roughened with low, concentric
wrinkles and growth rests. Periostracum
yellowish brown, greenish, greenish brown
or blackish, and (in many specimens) with
extensive but poorly defined green rays
and concentric lighter and darker bands.
Nacre white or bluish white, rarely pinkish.
Umbones inflated, projecting well above
hinge line, and located about 30% of the
distance from anterior to posterior. Beak
sculpture variable but ordinarily heavy,
double-looped, and with the loop apices
elevated and forming 2 radial rows of
tubercules. Hinge teeth absent.
The above description is of typical
A. g. grandis. Most specimens from the
lower St. Lawrence system are much
smaller (about 75 mm long), are relatively
more elongated, have a dark and roughened
periostracum, and exhibit beak sculpture
in which the nodules are poorly developed.
Typical A, g, grandis , however, is character-
ized by its ovate inflated form and its double-
looped and nodulous beak sculpture.
DISTRIBUTION
Canadian Interior Basin from central
Ontario to central Alberta; Great Lakes -
St. Lawrence system east to near Montreal;
Ohio-Mississippi system throughout; and
Gulf of Mexico drainages in Louisiana
and Texas.
ECOLOGY
Occurs in permanent ponds, lakes and rivers
of various sizes. Found on all types of
substrates but is most abundant on mud.
The breeding season is reported to last from
early August to the following April or May.
Both dioecious (separate sexes) and monoe-
cious (hermaphroditic) specimens occur.
The glochidia are triangular-ovate, with
spines, and measure from 0.31 to 0.36 mm
long and 0.28 to 0.33 mm high. Numerous
fish species have been shown to act as hosts
(see Fuller in Hart and Fuller 1974).
298
115
Anodonta grandis grandis
a, d: Gatineau R. near Kazabazua, Que.; 120.7 mm,
b, c: L. Erie, Point Pelee, Ont.
The specimen illustrated in colour on page 237 is from
the Grand R. near Onondaga, Ont. (X 2/3).
299
116
Anodonta grandis simps oniana
Lea, 1861
Northern Floater
DESCRIPTION
Shell up to about 125 mm long, 55 mm
high, 45 mm wide, with shell wall 2 mm
thick at mid-anterior; variable but com-
monly elliptical, roundly pointed poste-
riorly, of medium inflation, thin, and rather
fragile. Surface roughened by fine concen-
tric wrinkles and prominent growth rests.
Periostracum brown in most specimens,
greenish or yellowish in others, and with
faint greenish rays and/or concentric darker
and paler bands in some specimens. Nacre
silvery, white, or bluish, and with or without
salmon or yellow suffusions near the beak
cavity. Beaks low but clearly projecting
above hinge line and located about 25% of
the distance from anterior to posterior. Beak
sculpture composed of 4 to 6 single-looped
or faintly double-looped curved bars that
are not nodulous. Hinge teeth absent.
May be distinguished from A. g. grandis
principally by its beak sculpturing that is
predominantly single-looped and not nodu-
lous; in grandis s. str. it is double-looped
and nodulous. Beak also farther forward and
shell relatively more elongate and com-
pressed than in A. g. grandis. Inter grades
occur between the two subspecies in their
zone of contact.
DISTRIBUTION
Canadian Interior Basin in the boreal forest
region from northern Quebec west to
central Alberta, and northwest to the mouth
of the Mackenzie River.
ECOLOGY
Has been found in permanent ponds, in
lakes, and in rivers more than about 9 m
wide. All kinds of substrates are inhabited
by this mussel. Gravid specimens with
glochidia have been collected between July
22 and August 24, but the duration of its
gravid period is not known. Glochidia are
triangular-ovate, with hooks, and measure
about 0.36 mm long and 0.35 mm high. The
host fish is unknown.
300
116
Anodonta grandis simpsoniana
a, d: L. St. Joseph near Rat Rapids, Ont.; 101.6 mm.
b, c: L. Cache near Chibougamau, Que. (49°50'N,
74°24'W).
The specimen illustrated in colour on page 237 is from
Wilson L. south of Nellie Lake, Ont. (x 2/3).
301
117
Anodonta imbecilis Say, 1829
Paper Pond- Shell
DESCRIPTION
Shell up to about 90 mm long, 50 mm high,
40 mm wide, and with shell wall 1 mm thick
at mid-anterior; elliptical, moderately in-
flated, pointed at mid-posterior, slightly
alate, and fragile. Shell smooth except for
very fine concentric striae, growth rests, and
beak sculpture. Periostracum green to
greenish brown, shiny, with numerous fine
green rays visible on the disc, and with a
few broad green or brown rays clearly
apparent on the posterior ridge and slope.
Nacre bluish white, silvery, and iridescent
posteriorly. Umbones flat and without pro-
jections above the hinge line. Beak sculp-
ture composed of about 6 fine, irregular,
concentric ridges, with the earlier ones
ridged and broken centrally, and the later
ones somewhat double-looped. Hinge teeth
absent.
The flat unelevated beaks, greenish frag-
ile shell, and characteristic beak sculpturing
distinguish this species from all other
Anodonta in Canada and the northern
United States.
DISTRIBUTION
Lake Erie and Lake St. Clair drainages in
southern Ontario (Grand and Sydenham
rivers) and adjacent parts of the United
States; Ohio-Mississippi system generally;
Gulf of Mexico drainage from the Ochlock-
nee River system in western Florida to the
Rio Grande River system; and southern
Atlantic coastal drainage from the Altamaha
River system in Georgia to the Gunpowder
River system in Maryland,
ECOLOGY
Occurs in muddy to somewhat sandy
habitats in slow-moving rivers, canals, and
lakes; rare on gravel bottoms. Hermaphro-
ditic, A long-term breeder, with gravid
periods probably overlapping in the summer
in different individuals. Glochidia are
roughly triangular, with hooks, and mea-
sure about 0.23 mm in length and height.
The creek chub and the green sunfish have
been implicated as host fish.
302
117
Anodonta imbecilis
a,b,c,d: Ohio Canal, Columbus, Ohio; a andd
69.9 mm.
The specimen illustrated in colour on page 238 is from
the Erie Barge Canal near Macedon, N.Y. (x 2/3).
303
118
Anodonta implicata Say, 1829
Alewife Floater
DESCRIPTION
Canadian specimens are up to about
125 mm long, 65 mm high, 40 mm wide,
and with shell wall about 3.2 mm thick
at mid-anterior and near the anteroventral
margin below the pallial line. (More-south-
ern specimens may be 20% larger and have a
shell wall 5 mm thick.) Shell long-elliptical,
thickened anteriorly, thinner posteriorly,
inflated in females and more compressed in
males, and with the posterior ridge well
defined and double in most specimens.
Surface marked with prominent concentric
growth rests, and in most specimens with
severe corrosion on the anterior and around
the umbones. Periostracum heavy, yellow-
ish, brownish or blackish, and in some
young specimens obscurely rayed. Nacre
ordinarily salmon or pinkish or, more rarely,
white or bluish. Beaks inflated and some-
what elevated. Beak sculpture composed of
about 8 heavy double-looped concentric
bars. Hinge teeth absent.
Adult is well characterized by its promi-
nent anteroventral thickening below the
pallial line, large size, dark, rayless perios-
tracum, and salmon or pinkish nacre.
DISTRIBUTION
Atlantic coastal plain from Nova Scotia
(Cape Breton) and eastern Quebec south to
the Potomac River system in Maryland.
ECOLOGY
Restricted to coastal streams and lakes that
can be reached by its anadromous host fish,
the alewife. Occurs principally in sand and
gravel, rarely in mud; the largest individuals
have been found in relatively rapid streams.
The breeding season is not known in detail
but probably occurs from about August or
September to June. Glochidia are rather
large, approximately triangular, and with
hooks at the tip of each valve. The host fish
is the alewife, a predominantly saltwater
fish that in the spring migrates into fresh
water to spawn. Some true freshwater fish
(white sucker, white perch, and pumpkin-
seed) have also been named as hosts, but the
distribution of A. implicata makes this
doubtful. Landlocked freshwater popula-
tions of the alewife also occur in the Great
Lakes, but A. implicata is not found there.
304
118
Anodonta imp It cam
a, d: Darlings L., Lakeside, N.B.
b, c: Branch of Denny Stream near Moores Mills, N.B.;
92.1 mm.
The specimen illustrated in colour on page 238 is from
Great Herring Pond near Buzzard’s Bay, Mass, (x 2/3).
305
119
Anodonta kennerlyi Lea, 1860
Western Floater
DESCRIPTION
Shell up to about 120 mm long, 65 mm
high, 40 mm wide (but commonly much
smaller), and with shell wall about 1.5 mm
thick at mid-anterior and 3 mm at antero-
ventral pallial line; elliptical, bluntly
pointed posteriorly, without a dorsal wing,
and relatively thin and fragile. Surface
roughened by lines of growth but shiny in
many specimens. Periostracum yellowish,
yellowish brown or brown, tinged with
green in some specimens, and with promi-
nent dark-brown growth rests. Nacre whit-
ish or bluish white, and in some individuals
centrally suffused with salmon. Umbones
flattened and barely projecting above hinge
line. Beak sculpture consisting of about
1 5 irregular concentric ridges that extend up
to 10 mm beyond the umbonal apex. Hinge
teeth absent.
The elliptical shape and lack of a dorsal
wing separate this species from the only
other Anodonta in British Columbia,
namely A. nuttalliana. Similar to A. berin-
giana but smaller and with lighter perios-
tracum. Compare also with A. cataracta
fragilh .
DISTRIBUTION
In British Columbia occurs abundantly on
Vancouver Island and other coastal islands
(including the Queen Charlone Islands)
and on the mainland from the Columbia to
the Fraser and Skeena River systems. Also
crosses the Continental Divide and occurs
in a few mountain lakes in the uppermost
North Saskatchewan and Athabasca River
systems of Alberta. Southward the species
extends in the Pacific drainage to Oregon.
ECOLOGY
Often abundant. Occurs in muddy or sandy
substrates in rivers and lakes. Probably a
long-term breeder, with the breeding period
beginning in early August. The glochidia
are triangular, with a straight hinge and
a spine at the ventral apex of each valve, and
measure approximately 0.30 mm in length
and height. The fish host is unknown.
306
119
Anodonta kennerlyi
a, d: Aberdeen L., Aberdeen, Wash.; 93.7 mm.
b, c: Still Creek, Queen Charlotte Islands, B.C.
The specimen illustrated in colour on page 238 is from
Horse L. east of 100 Mile House, Lillouet Dist., B.C
(x 2/3).
307
120
Anodonta nuttalliana Lea, 1839
Winged Floater
DESCRIPTION
Shell up to about 1 10 mm long, 75 mm
high, 45 mm wide, and with mid-anterior
shell wall about 3 mm thick; highly variable
in shape but ordinarily trapezoid-ovate,
centrally inflated, with posterior margin
obliquely flattened, and with a more or less
prominent dorsal wing. Some specimens are
relatively compressed, and in others the
dorsal wing is not well developed. Surface
roughened by lines of growth. Periostracum
yellowish green, yellowish brown or brown,
and with prominent dark-brown growth
rests in some populations. Nacre white or
bluish. Umbones flattened and projecting
only very slightly, or not projecting, above
hinge line. Beak sculpture consisting of
up to 20 or more fairly strong concentric
ridges that may be irregularly single- or
double-looped and that extend about 1 0 mm
beyond the tip of the umbones. Hinge teeth
absent.
The ovate and winged shape of
A. nuttalliana easily distinguishes it from
the other two Pacific-drainage A nodonta
species in Canada, namely A. kennerlyi and
A. beringiana , which are elliptical and lack a
dorsal wing. The numerous umbonal ridges
are characteristic of both A. kennerlyi and
A, nuttalliana and differentiate them from
all other Canadian species except A. cata-
racta fragilis from the Maritime provinces.
Synonyms include A. wahlamatensis Lea,
1839, and A. oregonensis Lea, 1839. In many
localities A. nuttalliana occurs together
with A. kennerlyi Lea, but intergrades have
never been observed. The two species are
therefore fully distinct.
DISTRIBUTION
Fraser and Columbia River systems in
southern British Columbia, and south to
central California. Absent from Vancouver
Island.
ECOLOGY
Occurs in rivers and lakes on muddy and
sandy bottoms. The largest Canadian speci-
mens seen are from Vaseux Lake and
Osoyoos Lake, both river-lakes in the
Okanagan River, a tributary of the Colum-
bia River. Little is known about its breeding
season, although gravid specimens with
immature larvae have been observed in
October. The glochidia and host fish are
unknown.
308
120
Anodonia nunalliana
a, d: Osoyoos L., Osoyoos, B.C.; 114.3 mm.
b, c: Okanagan L. near Vernon, B.C.
The specimens illustrated in colour on pages 238 and
239 are from: a) Box L. south of Nakusp, B.C.;
b) Vaseux L. north of Oliver, B.C. (x 2/3).
J
309
121
Strophitus undulatus (Say,, 1817)
Squaw-Foot
DESCRIPTION
Shell up to about 100 mm long, 55 mm
high, 45 mm wide, and with mid-anterior
shell wall about 3 mm thick; elliptical to
trapezoid, somewhat compressed to moder-
ately inflated, and of medium thickness.
Surface roughened by concentric wrinkles
and growth rests. Periostracum blackish
brown in adults (paler near the umbones),
and yellowish or greenish brown and with
green rays in juveniles. Nacre white or
bluish white, with suffusions of yellow or
salmon near the beak cavity, and with a
narrow band of olive-green or greenish
brown at the border. Beak sculpture of 4 or
5 coarse concentric ridges that are approxi-
mately parallel to the growth lines. Hinge
teeth rudimentary: pseudocardinal hinge
teeth vestigial and indicated by a swelling of
the hinge line on each valve just anterior
to the beak or, rarely, by small clearly
discernable pseudocardinal teeth; lateral
teeth entirely absent.
The dark periostracum, vestigial pseudo-
cardinal hinge teeth, and characteristic
nacre readily distinguish this species. It is
closest in appearance to Anodontoides ferus-
sacianusj but that species is paler in colour,
has a thinner shell, and has fine, clearly
oblique beak sculpture.
DISTRIBUTION
Canadian Interior Basin in the Red River-
Nelson River system from western Ontario
to eastern Saskatchewan; Great Lakes -
St. Lawrence system throughout;
Ohio -Mississippi system from Minnesota to
Texas and from Pennsylvania to Tennes-
see; and Atlantic coastal drainage from
Nova Scotia to South Carolina.
ECOLOGY
Occurs principally in rivers and creeks but
occasionally in lakes. Inhabits all sub-
strates, but the finest specimens are from
sandy bottoms, especially in lake outlets.
The breeding season lasts from July to the
following April or May. The glochidia are
subtriangular , with hooks, and have been
reported as 0.36 mm long and 0.30 mm high
in one population, and as 0.46 mm long
and 0.36 mm high in another. The glochid-
ia are reputed to be able to complete their
development without a period of parasitism
on fish. Successful metamorphosis has
also been reported on fish, however, in
particular on the largemouth black bass and
the northern creek chub.
310
121
Strophitus undulatus
a, d: Creek near Leggatt, Ont.; 63,5 mm,
b, c: L. Winnipeg near Elk Is., Man.
The specimen illustrated in colour on page 239 is from
the Assiniboine R. near Amsterdam, Sask. posterior end
much curved and anterior end begins
back from inner edge of hinge-plate.
Well characterized in most specimens by
the prominent subconcentric ridge on each
beak. In this it resembles the more abundant
and widespread P. compressum , but in that
species the hinge plate is more than 3/4
the length of the shell, the shell is propor-
tionately much higher, and the anterior end
is not extended and pointed basally. Com-
pare also withP. lilljeborgi morph cristatum
andP. subtruncatum .
DISTRIBUTION
Introduced, probably from Europe, and now
widespread in the lower Great Lakes- St.
Lawrence River system. Also occurs in
Eurasia and Iceland.
ECOLOGY
Rare. In North America occurs chiefly in
large bodies of water. In Europe it is also
found in unpolluted rivers and canals. Litter
sizes of from 1 to 7 young have been re-
corded in Sweden.
404
166
Pisidium henslowanum
a; L. Ontario near Collins Bay, Ont. (x 16).
b,c,d: Prince Edward Bay, L, Ontario, Ont. (b x 22;
c and d x 19).
e,f,g,h: L, Ontario near Collins Bay, Ont. (x 1 1).
405
167
Pisidium (Cyclocalyx) lilljeborgi
Clessin, 1886
Lilljeborg’s Pea Clam
DESCRIPTION
Shell up to about 4 mm long, proportion-
ately high (H/L 0.82-0.94), moderately
inflated (W/L 0.59-0.73), triangular-ovate,
and rather thin shelled. Beaks prominent,
high, full, and located posterior of centre.
Dorsal margin short, posterior of centre,
openly curved and joining anterior and
posterior margins with angles; posterior
margin roundly truncate and vertical; ante-
rior margin elongate and distally rather
sharply rounded; ventral margin long and
curved. Hinge plate less than 3/4 of shell
length and rather heavy. Surface of shell
finely to rather coarsely striate, and slightly
dull to moderately glossy.
Details of hinge teeth, according to Her-
rington (1962), are as follows:
Laterals Al, A2 and P2 moderately
long (Al and A3 form a V); cusp of Al
proximal or on proximal side of center, or
central (somewhat blunt on top), of A2
proximal (high and sharp on top), of P2
distal (high, a rather steep incline and
sharp on top); cardinals close to anterior
cusps; C3 rather long, usually bent with
anterior end parallel with hinge-plate,
posterior end quite expanded; C2 short
and broad; C4 narrow, twice or more
as long as C2 [but only as long as C2 in
some specimens] . . . and extending . . .
diagonally along hinge-plate.
Occasionally specimens have ridges on
the beaks and may be shorter than the
typical form. These are called P . lilljeborgi
morph cristatum Sterki, 1928.
Differs from P, casertanum in that the
anterior margin joins the dorsal margin at
an angle, and the beaks are more elevated
and more prominent. Compare also with
P. subtruncatum.
DISTRIBUTION
Occurs throughout Canada as far north as
southern Baffin Island and southern Victo-
ria Island, throughout Alaska, in New
England and the northern tier of states, and
south in the Rocky Mountains to Colorado,
Utah, and California. Also found in Iceland
and in northern Europe.
ECOLOGY
Common. Lives in all permanent-water
habitats, especially lakes. Inhabits clay,
mud, sand, or gravel. Adult specimens
containing mature young have been found
only in summer, and litter sizes of up to
13 have been observed.
NOTE
Another species of Pisidium (P. waldeni
Kuiper, 1975), closely related toP. lillje-
borgi, has recently been recorded from arctic
Canada. It is reported to differ by having a
longer dorsal margin, a longer hinge plate,
and shorter cardinal teeth in the left valve,
as well as other characters. See Kuiper
(1975) for details.
406
167
Pisidium lilljeborgi
a: Oner L. near Shawville, Que. (x 14).
b,c: L. Saint-Simon, Rimouski Co., Que. (x 11).
407
168
Pisidium (< Cyclocalyx ) milium
Held, 1836
Quadrangular Pill Clam
DESCRIPTION
Shell small, up to 3 mm long, of moderate
height (H/L 0.62-0.88), greatly inflated
(W/L 0.60-0.95), and variable in shape but
more or less triangular and flattened ven-
trally (in end view). Beaks swollen, promi-
nent, and located rather far back. Dorsal and
ventral margins openly curved; posterior
margin truncated; and anterior margin long,
sloped above, and roundly pointed below.
Hinge plate narrow and less than 3/4 the
shell length. Surface with rather fine
concentric striae and a few prominent
growth rests. Periostracum thin, glossy, and
pale yellowish brown.
The dentition, according to Herrington
(1962), is as follows:
Laterals rather short; cusps inclined
to be sharp on top; cusps of left valve
toothpick-like, of A1 and A2 central or on
distal side of center, of P2 somewhat
distal; cardinals fairly near anterior cusps,
but varying, sometimes subcentral; C3
slightly curved and uniform in width; C2
and C4 nearly same thickness and about
parallel; C4 begins well over C2, slightly
curving or straight (C2 is the shorter of
the two).
The small size, roughly triangular shape,
prominent inflation, and flat but truncated
ventral margin formed by the two appressed
valves (when viewed from one end) are good
diagnostic characters for this species. It
resembles P. nitidum , but that species is
higher, has a more sharply curved ventral
margin, and the anterior cusps are more
distal and not as sharp.
DISTRIBUTION
Occurs from the Maritime Provinces to
British Columbia; in western Canada to
north of Great Slave Lake. Also found in
Alaska, the northern United States, south in
the Rocky Mountains to Colorado and
Utah, and in Europe.
ECOLOGY
Uncommon. Lives in lakes, ponds, and
slow-moving streams. Occurs on muddy
bottoms among vegetation. Swedish speci-
mens were observed to produce young from
June to September.
408
409
169
Pisidium (< Cyclocalyx ) nitidum
Jenyns, 1832
Shiny Pea Clam
DESCRIPTION
Shell small, up to about 3 mm long,
relatively high (H/L 0.80-0.92), of moderate
inflation (W/L 0.57-0.64), roughly rhom-
boidal in shape, and thin walled. Beaks
posterior of centre, broad, low, and curved.
Dorsal margin long and evenly curved;
anterior margin curved and steep above and
roundly pointed below; ventral margin long
and broadly curved; and posterior margin
roundly truncated and vertical or undercut.
Surface sculptured with fine striae (more
than 30 per mm). Periostracum pale yellow-
ish or greyish brown and very glossy.
The hinge teeth, according to Herrington
(1962), are as follows:
Laterals of moderate length, straight or
flaring outward at distal end; cusps rather
prominent, but inclined to be blunt on
top; cusp of A 1 distal or on distal side of
center, of PI, P2, and A2 rather distal;
cardinals subcentral; C3 gently curved, of
uniform width except at posterior end,
and almost parallel with hinge-plate; C2
slightly heavier than C4; C4 straight or
gently curved, about parallel with C2,
space between the two of uniform width,
straight or a little curved, and usually
directed across hinge-plate at a gentle
angle.
Distinguished by its small size, relatively
long hinge, shiny finely striate surface, and
details of dentition. Two well-marked
“ ‘forms” are known in addition to the typical
form. Form contortum is longer, has a nearly
straight ventral margin, and is more pointed
in the anterior basal region. Form paupercu-
lum is shorter, higher, heavier, and has a
more curved dorsal margin and more-
central cardinal teeth.
DISTRIBUTION
Broadly distributed throughout Canada, the
United States, Mexico, Eurasia, and North
Africa.
ECOLOGY
Common. Lives in all kinds of perennial-
water habitats, on various substrates, and
most commonly in shallow water. In each
litter, 2 to 7 young are ordinarily produced.
410
169
Pisidium nitidum
a,b,c,h,i: Typical nitidum: Pleasant Park, Cressy, Ont
(i a,b,c x ll;)jandi x 18),
d,e: Morph contortum: Klotz L. near Longlac, Ont.
(x 11).
f,g: Morph pauperculum: Rice L., Peterborough Co.,
Ont (x 11).
411
170
Pisidium (Cyclocalyx)
rotundatum Prime, 1852
Fat Pea Clam
DESCRIPTION
Shell small, up to about 3.3 mm long,
relatively high (H/L 0.80-0.92), greatly
inflated (W/L 0.70-0.76), ovate, and thin.
Beaks prominent, large, inflated, capped in
some specimens, and located about 1/3 of
the distance from posterior to anterior or
(usually) more centrally. All margins
rounded, the anterior and posterior margins
more sharply rounded than the dorsal and
ventral. Hinge plate short, narrow, curved,
and posterior of centre. Surface covered
with moderate-to-fine striae that are evenly
spaced. Periostracum yellowish brown and
glossy.
The hinge teeth, according to Herrington
(1962), are as follows:
Laterals short; cusps short and high
with near- vertical ends; cusps of A2
proximal, of P2 and A1 central or on
distal side of center; cardinals close to
anterior cusps; C3 curved, but not much
enlarged at posterior end. . C2 and C4
short; C2 almost parallel with hinge-
plate, straight, sometimes slightly curved,
or just a peg; C4 straight or slightly
curved, sometimes parallel with hinge-
plate, but more often directed slightly
downward, then not parallel with C2;
proximal end of posterior sulcus of right
valve closed by a pseudocallus on inner
side of proximal end of P3 and, therefore,
does not run out on top of hinge-plate.
Distinguished from its close relative
P. ventricosum by the more central position
of the beaks and the narrow hinge plate
(between the cardinals and A2). In P. ven-
tricosum the beaks are nearly posterior, and
the hinge plate is broad between the
cardinals and A2.
DISTRIBUTION
Widespread in Canada south of the tree line.
Also occurs in the northern tier of states in
the United States, and south in the Rocky
Mountains to Mexico.
ECOLOGY
Lives, as does P. ventricosum, in lakes,
permanent ponds, rivers, and streams.
Found among vegetation and in various
substrates but typically in mud. Nothing is
known about its life history.
412
170
Pisidium rotundatum
a: Pond in Byron Bog, London, Ont. (x 23).
b,c; Keefer L. near Kelowna, B.C. (x 19).
413
171
Pisidium {Cyclocalyx)
subtruncatum Malm, 1855
Short-ended Pea Clam
DESCRIPTION
Shell rather small, up to almost 4 mm long,
relatively high (H/L 0,74-0.94), inflated
(W/L 0.54-0.74), ovate, variable in shape,
and thin walled. Beaks narrow, prominent,
projecting above the hinge line, and located
far back. Dorsal margin short, curved,
posterior of centre and joining anterior
margin with an angle close to the anterior
cusps; anterior margin long or short and
rather sharply rounded centrally; ventral
margin long and openly curved; posterior
margin roundly truncate and joining dorsal
margin with an angle. Hinge short and
curved; hinge plate narrow. Striae evenly
spaced, fine, and numbering 30 or more per
mm. Periostracum glossy and yellowish
brown.
The hinge teeth, according to Herrington
(1962), are as follows:
Laterals rather long, cusps prominent;
cusps of A1 and A2 proximal to central, of
PI and P2 central; cardinals near anterior
cusps or subcentral; C2 and C4 roughly
parallel, posterior ends slightly nearer
inner edge of hinge-plate; C3 long and
not much curved; width of hinge-plate
and size of shell influences cardinals
considerably.
Resembles P. walkeri , but that species is
more compressed, the cusp of A1 is less
proximal, the left cardinals are not parallel,
and the periostracum is dull. Compare also
withP. lilljeborgi.
DISTRIBUTION
Occurs in Prince Edward Island and
throughout central Canada north to, and
slightly beyond, the tree line. Also found
from New York to Montana, south in the
Rocky Mountains to California and Colo-
rado, and in Europe.
ECOLOGY
Lives in lakes, ponds, muskeg pools, rivers,
and streams. Found among vegetation and
on various kinds of bottoms. Two litters
of young are born each year, and life spans
exceed 1 year.
414
415
172
Pisidium (Cyclocalyx) supinum
Schmidt, 1850
Hump-backed Pea Clam
DESCRIPTION
Shell medium-sized, up to about 4.5 mm
long, relatively high (H/L ca. 0.90), inflated
(W/L ca. 0.67), roughly trianglular, and
moderately thick to thick. Beaks high and
full; and each beak surmounted by an
oblique, more or less concentric raised
ridge. Dorsal margin short, strongly curved,
and joining the anterior and posterior
margins without angles; anterior margin
lengthened, flattened above, roundly
pointed below, and curving smoothly into
the long rounded anterior margin; posterior
margin truncated and only slightly rounded.
Hinge teeth typically thick and heavy.
Surface sculptured with moderately heavy,
concentric striae (about 16 to 18 per mm).
Periostracum yellowish brown and moder-
ately dull.
Hinge teeth similar to those ofP. hen-
slowanum , but much heavier and with the
cardinals farther from the anterior cusps.
Compare also with/ 3 , compressum and
P. subtruncatum.
DISTRIBUTION
This Eurasian and Icelandic species was
first discovered in North America near the
eastern end of Lake Ontario in about 1959.
It has not yet been observed elsewhere in
the Great Lakes-St. Lawrence system.
Living specimens were recently (1975)
found, however, in the Eastmain and La
Grande rivers in northern Quebec by
B. T. Kidd. Has also been recorded in late
Pliocene and Early Pleistocene deposits
in Idaho.
ECOLOGY
Uncommon in North America. In Europe it
is characteristic of rivers and is rare in lakes.
416
172
Pisidium supinum
a,b,c: Athol Bay, L. Ontario, near Athol, Ont. (x 14),
417
173
Pisidium (i Cyclocalyx ) variabile
Prime, 1852
Triangular Pea Clam
DESCRIPTION
Shell up to about 5 mm long, proportion-
ately high (H/L 0.72-0.97), of medium
inflation (W/L 0.54-0.68), triangular-ovate,
thick walled, and variable in shape. Beaks
prominent, full, and located posterior of
centre. Dorsal and posterior margins round
and continuous; ventral margin long and
more openly curved; anterior margin
roundly angled distally and joining the short
dorsal margin without an angle. Hinge plate
about 3/4 the length of the shell (or a little
more), heavy, and rather steeply curved.
Surface of shell glossy, and covered with
rather fine to quite coarse striae (but less
than 30 per mm).
The hinge teeth are described by Herring-
ton (1962) as follows:
Laterals rather short, incorporated into
hinge-plate; A3 and P3 tend to curve
around pit of sulcus; cusps blunt on top;
cusps of A1 distal, of PI, A2, and P2
central or on distal side of center;
cardinals central; C3 short, much curved,
posterior end much the larger; C2 short
and stout like an inverted D; C4 fairly
short, only slightly curved and directed
toward cusp of P2; considerable space
between posterior ends of C2 and C4.
Distinguished by its rather heavy and
roughly triangular shell, glossy surface, and
characteristic hinge teeth. The hinge teeth
are similar only to those ofP. compressum ,
but that species is smaller, with dull
periostracum, and in most specimens bears
a prominent concentric ridge on each beak.
DISTRIBUTION
Occurs throughout southern Canada and
northward into the subarctic. Also recorded
from most of the United States.
ECOLOGY
Common. Lives in virtually all natural
perennial-water habitats. Found in various
substrates (most frequently mud) and usu-
ally amid vegetation. Litter size varies from
at least 12 to 34. No anatomical studies
have been done on this species.
418
419
174
Pisidium (Cyclocalyx)
ventricosum Prime, 1851
Globular Pea Clam
DESCRIPTION
Shell small, up to about 3 mm long,
relatively high (H/L 0.82-1.00), greatly
inflated (W/L 0.80-0,95), ovate, and rather
heavy. Beaks large, swollen, and placed
far back on the shell. Dorsal margin
smoothly curved and passing imperceptibly
into anterior margin; anterior margin
sloped, broadly curved above, and roundly
curved centrally or in an area just below the
centre; ventral margin long, evenly rounded,
and continuing in an uninterrupted curve
into the posterior margin; posterior margin
flatly curved and undercut. Hinge plate
heavy and relatively short, that is less than
3/4 the length of the shell. Surface finely
striate (more than 30 per mm) and with
prominent growth rests in many specimens.
Periostracum yellowish brown to greyish,
and glossy.
Hinge teeth similar to those in P. rotun -
datum but heavier, and the hinge plate
between the cardinal teeth and A2 is
relatively wide, not thin.
This small species is well characterized
by its greatly inflated heavy shell and
prominent, swollen, posteriorly -placed
beaks. Compare with P. rotundatum and
P. milium.
DISTRIBUTION
Occurs throughout central Canada south of
the tree line and in isolated localities in
eastern Canada. Also recorded from across
the northern United States from Maine
to Washington, and south in the Rocky
Mountains to Mexico.
ECOLOGY
Lives in perennial-water lakes, ponds, rivers
and streams of all sizes. Aquatic vegetation
and muddy bottoms characterize typical
habitats. Nothing is known about its anat-
omy or reproduction.
420
174
Pisidium ventricosum
a: Mechanic Lake Brook near Alma, N.B. (x 27).
b,c: Reindeer L., Brocher, Man. (x 19).
421
175
Pisidium 0 Cyclocalyx ) walkeri
Sterki, 1895
Walker’s Pea Clam
DESCRIPTION
Shell up to about 6 mm long, relatively high
(H/L 0.80-0.90), moderately inflated
(W/L 0.54-0.68), somewhat ovate but ante-
riorly elongate, and rather thin walled.
Umbones moderately large and located
posterodorsally. Dorsal margin strongly
curved and tilted posteriorly; anterior mar-
gin long, slightly curved above and roundly
pointed below the centre; ventral margin
long and gently curved; posterior margin
flattened and vertical. Hinge plate less than
3/4 the shell length and not entirely parallel
with the dorsal margin. Surface of shell
dull to somewhat shining and with less than
30 striae per mm.
The hinge teeth, according to Herrington
(1962), are as follows:
Laterals rather long, cusps moderately
sharp; cusps of A1 central or on distal side
of center; of PI distal, of A2 proximal or
on proximal side of center, of P2 central;
cardinals subcentral; C2 short, much
curved (sometimes an inverted D); C4
much lighter, short, curved, directed
toward interior of shell; C3 parallel with
hinge-plate, varying in degree of curva-
ture, its posterior end enlarged.
The “form” ofP. walkeri called mainense
Sterki, 1903, is smaller and relatively short-
er, and with finer striae, a more rounded
anterior slope, left cardinal teeth that are
more nearly parallel, and a longer C2.
Differentiated from/ 5 , subtruncatum by
its coarser striae. Compare also with
P. casertanum .
DISTRIBUTION
Typical P. walkeri have been found from
New Brunswick to James Bay, and in
western Canada north into the Northwest
Territories. Also widely distributed in the
United States south to Virginia and Ari-
zona. P . walkeri form mainense is more
eastern, and is recorded from scattered sites
in subarctic eastern Canada, from New
Brunswick to Massachusetts, and in Illi-
nois. Both forms are considered together on
Map 175.
ECOLOGY
Rather uncommon. Occurs in permanent
lakes, ponds, rivers, and streams. Found
most frequently among vegetation and on a
variety of substrates. A single litter of young
are born during the 1-year lifetime of each
individual. The anatomy of this species has
not been studied.
422
423
176
Pisidium ( Neopisidium )
conventus Clessin, 1877
Arctic-Alpine Pea Clam
DESCRIPTION
Shell up to almost 3 mm long, of moderate
height (H/L 0.68-0.88), rather compressed
(W/L 0.44-0.65), more or less ovate or
trapezoid, variable in shape, thin, and
fragile. Beaks low, rounded, and located a
little posterior of centre. All margins curved
and with variable shape: for example, in
some specimens the anterior and posterior
margins are obliquely truncated and
roughly parallel, in others the anterior
margin is roundly pointed centrally and the
posterior margin is vertically truncated.
Hinge plate very long and narrow. Surface
of shell covered with fine concentric striae
and irregularly spaced growth rests. Perios-
tracum thin and pale yellow or whitish.
Details of the hinge teeth, according to
Herrington (1962), are as follows:
Laterals long and slender; cusps of Al,
PI, and A2 distal or on distal side of
center, of P2 distal; cardinals central or
subcentral; C2 at or on proximal end
of A2, short, close to inner edge of hinge-
plate or overhanging and either about
parallel with hinge-plate or with posterior
end slightly more interior; C4 slightly
longer than C2, slimmer, straight or
slightly curved, beginning above center of
C2 and parallel with it, or its posterior
end directed a little more toward the
interior; C3 moderately long, slightly
curved, almost parallel with hinge-plate,
posterior end enlarged somewhat, there-
fore, nearer inner edge of hinge-plate.
Well characterized by its small, thin,
fragile, and pale-coloured shell, its over-
hanging cardinal hinge teeth, its subtrape-
zoidal shape (when present), and its unusual
habitat.
DISTRIBUTION
Occurs in most of the nothern states of the
United States and northward throughout
most of Canada (to Victoria Island) and
Alaska. Also found in alpine lakes across
Eurasia and north to the Eurasian arctic
coast.
ECOLOGY
A cold water species. Lives principally at
considerable depths in large lakes within
the temperate parts of its range, and at all
depths within subarctic and arctic regions.
Two broods of young are produced each
year, 1 in summer and 1 in winter.
424
425
177
Pisidium ( Neopisidium )
cruciatum Sterki, 1895
Ornamented Pea Clam
DESCRIPTION
Shell up to about 2 mm long, proportion-
ately high (H/L ca. 0.94 -0.95), quite inflated
(W/L ca. 0.70-0.74), triangular, thick, and
heavy. Beaks prominent, elevated, and pos-
terior of centre. Each beak bears a heavy
U-shaped ridge whose ends are directed
ventrally and perpendicular to the lines of
growth. Dorsal margin short and rounded,
ventral margin long and flatly curved,
anterior margin steep and roundly pointed
basally, and posterior margin truncated
and joining the dorsal margin in a smooth
curve. Hinge plate very heavy and more than
3/4 the length of the shell. Surface dull
and with coarse concentric striae (about
16 per mm).
Details of the hinge teeth, according to
Herrington (1962), are as follows:
Laterals heavy and short, little more
than cusps; cusps of A1 and PI distal, of
A2 central or on either proximal or distal
side of center, of P2 on distal side of
center; cardinals central; C2 heavy, usu-
ally an inverted D; C4 slim, slightly
curved and directed toward cusp of P2 or
slightly inside; C3 parallel with hinge-
plate, curved somewhat on the outside,
the [greatly enlarged] posterior end mak-
ing the inside considerably curved; liga-
ment pit very short and wide, width
almost equalling length, and deepening
as it approaches inside of hinge-plate
where it breaks through, resembling in
this respect the European species
P. vincentianum.
Characterized by its very small size,
triangular shape, heavy shell, and strangely
shaped ridges on the beaks. Unlike any
other species.
DISTRIBUTION
Known only from a few mostly disjunct
localities in Ontario (Thames River) and
the central United States south to Arkansas
and Alabama.
ECOLOGY
Very rare. Reported to live in mud among
dead leaves and aquatic plants and to be
so covered with a black or brown coat that it
resembles a globule of soil. Its distribution
implies that it occurs only in hard-water
habitats. Nothing is known about its repro-
duction or anatomy.
426
177
Pisidium cruciatum
a,b: Honeoye Creek, Rush, N.Y. {a x 27; b x 41).
c,d: Raisin R, near Norwell, Mich, (c x 27; d x 1 1).
e-j: Grand R., Pottawattomie Bayou, Ottawa Co., Mich,
(x 16).
427
178
Pisidium (Neopisidium) insigne
Gabb, 1868
Tiny Pea Clam
DESCRIPTION
Shell very small, up to about 2 mm long,
relatively high (H/L 0.82-0,84), compressed
(W/L 0.47-0.59), elliptical, and thin shelled.
Beaks low, rounded, and close to centre.
Dorsal margin long and gently curved,
anterior end broad and roundly pointed,
ventral margin long and very gently curved,
and posterior margin roundly truncate.
Hinge plate narrow, long, and openly
curved. Surface finely striate (about 25 to
30 per mm). Periostracum brownish and (in
many specimens) with foreign material
adhering to it.
The hinge teeth, according to Herrington
(1962), are as follows:
Laterals long and slim, cusps rather
sharp on top; cusp of A2 distal or on distal
side of center, of P2 very distal (the
distance from this cusp to the cardinals
seems very great), of A1 distal or on distal
side of center, of PI distal; cardinals of
right valve subcentral or nearer anterior
cusps; C2 small, almost straight, parallel
with inside of hinge-plate; C4 small,
rather indistinct, slightly curved, almost
parallel with C2, posterior end a little
nearer inside of hinge-plate and a little
more posterior than C2; C3 slim, straight,
or slightly curved, frequently slightly
enlarged at posterior end, which is a little
nearer the inside of hinge-plate.
Characterized by its very small size, low
and elongate form, and broad rounded
anterior end. Compare with/ 5 , conventus
and with juvenile P. casertanum.
DISTRIBUTION
Known in Canada only from Prince Edward
Island, southern Ontario, and southern
British Columbia. Also occurs across the
northern United States and south in the
Rocky Mountains to Arizona and New
Mexico.
ECOLOGY
Found principally in slow-moving creeks
and spring creeks. Almost nothing is known
about its biology.
428
178
Pisidium insigne
a: Lidstone Creek, Prince Co., P.E.I. (x 22).
b,c: Long L., Wellington, B.C. (x 22).
429
179
Pisidium ( Neopisidium )
punctatum Sterki 5 1895
Perforated Pea Clam
DESCRIPTION
Shell minute, up to about 1.7 mm long,
relatively high (H/L 0.82-0.94), inflated
(W/L 0.56-0.71), ovate, quite thin, and full
of tiny holes that are clearly visible at
magnification of 50 x . In many specimens a
transverse more or less concentric ridge is
present near the umbones. Dorsal and
ventral margins openly curved; anterior
margin roundly pointed centrally and flat-
tened above; posterior margin somewhat
truncated, curved, and joining the dorsal
margin with an angle. Hinge plate more
than 3/4 shell length. In addition to the tiny
holes, the surface is covered with rather
coarse, concentric, evenly spaced striae.
Periostracum very thin and pale yellowish
brown.
The hinge teeth, according to Sterki
(1895), are as follows:
Hinge moderately strong; cardinal
teeth fine, in the left valve two, lamellar,
longitudinal, about equally long, a little
curved, almost parallel, the upper little
anterior; in the right valve one, longitudi-
nal, little curved, lamellar, the posterior
end slightly thickened; lateral teeth rather
small and thin, in the left valve one,
pointed, in the right valve two, the outer
quite small.
Best distinguished by its very small size,
regular but rather coarse striae, and tiny
holes (or punctae) that cover the shell. The
umbonal ridge, when present, is also dis-
tinctive. Closely related to P. punctiferum
Guppy, but that species is much larger,
more finely striate, and occurs only in the
southern United States.
DISTRIBUTION
Found in scattered localities in southern
Canada from Ontario to British Columbia,
and in the northern United States.
ECOLOGY
Uncommon. Occurs in lakes and in slow-
moving portions of rivers and streams.
Found among vegetation and usually on
muddy bottoms. Adults bear 2 litters of
young each year, 1 in the spring and 1 in
the fall.
430
179
Pisidium punctatum
a,b,c: Athol Bay, L. Ontario, Prince Edward Co., Ont.
(x 27).
431
Glossary
abaxial
outward, away from shell axis.
adaxial
inward, toward shell axis.
adductor muscle
a large muscle which closes the valves of a bivalved
mollusc shell.
alate
expanded like a wing.
ann uli (sing, annulus)
ringlike thickenings, generally related to previous
growth pauses.
apex
top of the spire, the first formed part of a gastropod
(snail) shell, pointed in most species.
arcuate
bent or arc-like.
beak
the earliest formed part of a bivalved shell. See umbo.
bifid
partly but not wholly split into two similar parts.
biconvex
convex on both sides.
calcareous
containing and/or resembling calcium carbonate.
callus
thickened shelly structure that covers inner lip or
columellar region of a gastropod shell.
cardinal
central or major, as in cardinal hinge teeth.
Carina
prominent spiral keel or ridge.
carinate
bearing one or more spiral keels or ridges.
collabral
conforming to shape of outer lip at an earlier growth
stage as shown by growth lines.
columella
centrally located pillar surrounding the axis of coiling
of a spiral gastropod shell.
conoid
shaped like a cone.
cusp
a projecting peak on a radular tooth,
decurrent
flowing downward.
dextral
right-handed or coiled in a clockwise direction when
viewed from above; when viewed from the front (apex
above) the aperture is on the right.
dimorphism
the condition of having two distinct forms, especially as
in sexual dimorphism, in which males and females
are visibly different.
dioecious
having the male reproductive system in one individual
and the female in another.
disc
the rounded anterior portion of a freshwater mussel
shell.
distal
far from the point of origin or attachment, opposite from
proximal.
dorsal
the back, or, in bivalved molluscs, the area that includes
the umbones and the ligament.
eutrophic lake
a shallow lake ordinarily characterized by an abundance
of plant and animal life and a muddy bottom with
high organic content. Oxygen concentrations are low in
deeper water during the summer. This is a late stage
in normal lake succession from the oligotrophic
condition through mesotrophic to eutrophic, leading
eventually to a marsh and finally to dry land,
globose
inflated and approaching the shape of a sphere.
glochidia (sing, glochidium)
the larvae of freshwater mussels (superfamily
Unionacea).
gravid
pregnant, that is with fertilized eggs or unborn young
within the body.
433
growth rest
a ridge formed during an intermediate stage of growth
when this area was the edge of the shell.
helicone
a cone twisted into a spiral form; the distally expanded
coiled tube that forms most gastropod shells.
hermaphrodite
an individual that has both male and female sexual
organs,
hinge
the structure that joins the two halves of a bivalve shell
at the dorsal margin. It is generally composed of an
elastic ligament and articulating hinge teeth.
hinge plate
the thickened edge of a bivalved mollusc shell to which
hinge teeth (if present) are attached.
immersed
depressed below the adjacent whorls, as an immersed
nuclear whorl.
impressed
lying below the general adjacent surface as if stamped
into it.
inflated
expanded and distended.
mterdentum
in freshwater mussels the area of the hinge plate
between the pseudocardinal and the lateral hinge teeth,
lamellae
thin plates or blade-like ridges.
lentic
characteristic of standing water, opposite to lotic.
lip
the structure surrounding, either entirely or in part, the
mouth or aperture of a snail shell.
lotic
characteristic of running water, opposite to lentic.
lymnaeiforxn
shaped more or less like a rypical Lymnaea, that is like
L. stagnalis.
malleate
bearing flattened areas as if hammered.
man tle
the fleshy sheet of tissue that secretes the shell of a
mollusc and is appressed to its inner surface. It encloses
the mantle cavity and most, or all, of the internal organs.
marsupial
in molluscs refers to the possession of a structure for
containing or enclosing the young.
mesotrophic lake
a lake of moderate depth with intermediate abundance
of plants and animals. See oligo trophic lake and
eu trophic lake.
monoecious
having both the male and female reproductive systems
in the same individual.
morph
a distinct form or colour phase of a variable species.
nacre
the pearly inner layer characteristic of some mollusc
shells.
nuclear whorl
the first turn of a spiral shell, beginning at the apex and
corresponding to part or all of the larval shell.
obtuse
an angle exceeding 90°.
oligotrophic lake
a deep lake with sparse plant and animal life, and with
low organic content in bottom deposits. Oxygen
concentrations in such a lake remain high in deep water
throughout the year. This is the first stage in normal
lake succession. See eutrophic lake and mesotrophic
lake.
operculum
a horny or shelly plate- like structure attached to the foot
of most prosobranch gastropods. It seals the shell
aperture when the animal is contracted within the shell.
ovate
oval; used also in combinations such as ovate-quadrate,
meaning intermediate between ovate and quadrate.
palatal lip
the outer lip of a snail shell, that is the portion of the lip
on the outer side of the aperture.
pallial line
an impressed line on the inner surface of a bivalved
mollusc shell that marks the zone of attachment of the
mantle to the shell.
parietal
in gastropods, pertaining to that pan of the aperture
adjacent to, or pressed against, the preceding whorl.
parthenogenic
capable of reproduction by direct development, without
fertilization of the eggs.
434
patulous
broadly expanded or limpet-like.
pauci spiral
consisting of few spirals or of less than one complete
spiral.
pelagic
capable of swimming, or floating, in open water for
extended periods.
penultimate
next to the last. The penultimate whorl is the one just
above the body whorl.
peristome
lip.
periostracum
the outer parchment-like layer of a mollusc shell.
plait
a spiral, flattened ridge on the columella.
planorboid
coiled approximately in a single plane or resembling
typical species of the family Planorbidae.
planospiral
coiled in a single plane.
plicae
broad ridges.
post-basaJly
located in the basal (ventral) region near the posterior
end.
prosocline
with plane of aperture inclined away from the axis in its
upper part, and toward the axis in its lower part. This
is characteristic of most prosobranch gastropods.
protoconch
the larval shell of a mollusc. It is still visible in some
partly mature and adult specimens.
pseudocardinal
the centrally located, short (or stump-like) hinge teeth of
most bivalve molluscs.
punctate
the surface pitted with tiny holes.
quadrate
more-or-less four-sided, resembling a square or rec-
tangle.
scalariform
loosely coiled with whorls not touching at the sides or
tending toward this condition. See illustration of
Valvata sincera ontariensis.
sculpture
impressed or raised markings.
sensu lato
in the broad sense (abbreviated s. lau)
sensu stricto
in the strict sense (abbreviated s. sir.)
septate
with one or more internal shelly partitions,
serrate
with a series of notches or grooves at the edge, like a
saw or a file.
shouldered
shaped like a shoulder, with a flattened upper surface
bounded by a definite angle.
sigmoid
shaped like an S.
sinistra!
left-handed or coiled in a counterclockwise direction
when viewed apically, that is from above. Viewed from
the front (apex above) the aperture is on the left.
sinuate
wavy or sinuous.
spire
the upper surface of a spiral snail shell. In most species
it is cone-shaped and tapers to a point (the apex). The
last whorl (the body whorl) is not considered to be
pan of the spire. In flatly coiled snails, especially
ramshorn snails (Planorbidae), the spire may be flat or
concave but is recognizable because it is less concave
than the base of the shell that contains the umbilicus.
spire angle
the angle at the apex formed by the cone of the spire,
sp.
abbreviation for species (singular).
spp.
abbreviation for species (plural).
ssp.
abbreviation for subspecies (singular),
sspp,
abbreviation for subspecies (plural).
435
striae
impressed lines or narrow grooves.
sub globose
inflated but not so much as to be round or globose.
substrate
the substance on which an organism lives or grows,
such as soil, gravel, or rocks.
suffusion
an overspreading, as with a tint of colour.
suture
a spiral line or groove marking the junction of adjacent
whorls,
tabulate
shaped like a table.
trapezoidal
shaped like a trapezoid, that is a four-sided geometric
figure similar to a rectangle but with only two parallel
sides.
truncate
shaped as if cut off.
umbilicus
the hollow centre (if present) of the axis of rotation of a
snail shell, visible from the base of the shell.
umbo
the apex, or juvenile shell, of one half (a valve) of a
bivalve mollusc.
umbones
plural of umbo.
varix
a prominent ridge or protrusion formed by expansion of
the shell aperture during a previous stage of growth.
ventral
the underside or lower pan of the shell. In bivalves it is
on the opposite side from the beaks and hinge.
verge
in some gastropods an organ of the male genital tract
that bears the penis.
vernal
occurring in the spring, for example a vernal pool.
whorl
a single complete turn of a spiral shell.
436
References
Serious students are referred to the following literature
for additional information. The list includes not only
the references cited elsewhere in this book by author
and date only, but also the important works published in
this field since 1968. For more extensive bibliographies
of Canadian freshwater molluscs, consult especially
Clarke (1973), LaRocque (1953), Taylor (1975), and the
section on Mollusca in th e Zoological Record, published
annually (since 1864) by the Zoological Society of
London.
Abbott, R.T.
(1974). American Seashells: The Marine Mollusca of
the Atlantic and Pacific Coasts of North America.
2nd ed. New York: Van Nostrand Reinhold. 663 pp.
Bailey, R.M.; Fitch, J.E.; Herald, E.S.; Lachner, E.A.;
Lindsey, C.C.; Robins, C.R.; and Scott, W.B.
(1970). A List of Common and Scientific Names of
Fishes from the United States and Canada. 3rd ed.
American Fisheries Society, Special Publication 6.
150 pp.
Baker, F.C.
(1928a). The Fresh- Water Mollusca of Wisconsin,
Part I: Gastropoda. Wisconsin Geological and Natural
History Survey, Bulletin 70. 507 pp.
(19286). The Fresh- Water Mollusca of Wisconsin,
Pan II: Pelecypoda. Wisconsin Geological and Natural
History Survey, Bulletin 70. 495 pp.
Baker, H.B.
(1925). Anatomy of Lanx, a Limpet-like Lymnaeid
Mollusk. Proceedings of the California Academy of
Sciences, Series 4, 14(8): 143-69.
Basch, P.F.
(1963). A Review of the Recent Freshwater Limpet
Snails of North America (Mollusca: Pulmonata).
Harvard University, Museum of Comparative Zoology
Bulletin 129(8): 401-61.
Berry, E.G.
(1943). The Amnicolidae of Michigan: Distribution,
Ecology, and Taxonomy. Miscellaneous Publications,
Museum of Zoology, University of Michigan, No. 57.
68 pp.
Bousfield, E.L.
(1960). Canadian Atlantic Sea Shells. Ottawa: Depart-
ment of Northern Affairs and National Resources,
National Museum of Canada. 72 pp.
Burch, J.B.
(1962). How to Know the Eastern Land Snails.
Dubuque, Iowa: Brown. 214 pp.
(1975a) Freshwater Sphaeriacean Clams (Mollusca:
Pelecypoda) of North America. Rev. ed. Hamburg,
Mich.: Malacologieal Publications. 96 pp. (Previously
published in 1972 by the U.S. Environmental Protec-
tion Agency in Biota of Freshwater Ecosystems,
Identification Manual No. 3. Washington, D.C.: U.S.
Government Printing Office. 31 pp.)
(19756) Freshwater Unionacean Clams (Mollusca:
Pelecypoda) of North America, Rev. ed. Hamburg,
Mich.: Malacologieal Publications. 204 pp. (Previously
published in 1973 by the U.S. Environmental Protec-
tion Agency in Biota of Freshwater Ecosystems,
Identification Manual No. 11. Washington, D.C.: U.S.
Government Priming Office. 176 pp.)
Clampitt, P.T.
(1970). Comparative Ecology of the Snails Physa gyrina
and Physa Integra (Basommatophora: Physidae). Mala-
cologia 10(1): 113-51.
Clarke, A.H.
(1973). The Freshwater Molluscs of the Canadian
Interior Basin. Malacologia 13(1-2). 509 pp.
(1976). Endangered Freshwater Mollusks of Northwest-
ern North America. Bulletin of the American Malaco-
logical Union Inc. for 1976: 18-19.
Clarke, A.H., and Berg, C.O.
(1959). The Freshwater Mussels of Central New York,
with an Illustrated Key to the Species of Northeastern
North America. Cornell University, Agricultural Exper-
iment Station, Memoir 367. 79 pp.
Dazo, B„C.
(1965). The Morphology and Natural History of
Pleurocera acuta and G onto basis livescens (Gastropoda:
Cerithiacea: Pleuroceridae). Malacologia 3(1). 80 pp.
Dundee, D.S.
(1957). Aspects of the Biology of Pomatiopsis lapidaria
(Say) (Mollusca: Gastropoda: Prosobranchia). Miscella-
neous Publications, Museum of Zoology, University
of Michigan, No. 100. 37 pp.
Goodrich, Calvin
(1942). The Pleuroceridae of the Pacific Coastal
Drainage, including the Western Interior Basin. Occa-
sional Papers of the Museum of Zoology, University
of Michigan, No. 469. 4 pp.
(1945). Goniobasis livescens of Michigan. Miscellaneous
Publications, Museum of Zoology, University of Mich-
igan, No. 64. 36 pp.
437
Haas, Fritz
(1969). Superfamilia Unionacea. Das Tierreich 88.
663 pp.
Hanna, G.D.
(1966). Introduced Molluscs of Western North Amer-
ica. Occasional Papers, California Academy of Sci-
ences, No. 48, 108 pp.
Hart, C.W., Jr., and Fuller, S.L.H. (eds.)
(1974). Pollution Ecology of Freshwater Invertebrates.
New York and London: Academic Press. 389 pp.
Heard, W.H.
(1965). Comparative Life Histories of North American
Pill Clams (Sphaeriidae: Pisidmm). Malacologia 2(3):
381-411.
(1975). Sexuality and other aspects of reproduction in
Anodonta (Pelecypoda: Unionidae). Malacologia 15(1):
81-103.
Heard, W.H., and Guckert, R.H.
(1970). A Re-evaluation of the Recent Unionacea
(Pelecypoda) of North America. Malacologia 10(2):
333-55.
Herrington, H.B.
(1962). A revision of the Sphaeriidae of North America
(Mollusca: Pelecypoda). Miscellaneous Publications,
Museum of Zoology, University of Michigan, No. 118.
74 pp.
Hubendick, Bengt
(1951). Recent Lymnaeidae, Their Variation, Morphol-
ogy, Taxonomy, Nomenclature, and Distribution.
Kunglica Svenska Vetenskapsakademiens Handlingar,
Fjarde Serien, 3(1). 223 pp.
(1964). Studies on Ancylidae, the subgroups. Goteborgs
Kungliga Vetenskaps och Vitterhets-Samhalles Hand-
lingar, Sjatte Foljden, Series B, 9(6): 1-72.
Johnson, R.I.
(1970). The Systematies and Zoogeography of the
Unionidae (Mollusca: Bivalvia) of the Southern Atlan-
tic Slope Region. Harvard University, Museum of
Comparative Zoology Bulletin 140(6): 263-449.
Kuiper, J.G.J.
(1975). Zwei neue boreal e Ptsidium-Arten: P. hinzi und
P. waldeni. Archivfiir Molluskenkunde 106(1/3):
27-37.
LaRocque, Aurele
(1953). Catalogue of the Recent Mollusca of Canada,
National Museum of Canada Bulletin 129 (Biological
Series 44). 406 pp.
Mackie, G.L.
(1973). Biology ofMusculium securis (Pelecypoda:
Sphaeriidae). . . . Ph.D. dissertation, University of
Ottawa. 175 pp.
Mayr, Ernst
(1969). Principles of Systematic Zoology. New York:
McGraw-Hill. 428 pp.
Moore, R.C. (ed.)
(1969). Treatise on Invertebrate Paleontology, Part N.
Mollusca 6, Bivalvia. Vol. 2 of 3. New York and
Lawrence, Kans.: Geological Society of America and
University of Kansas. N491-N951.
Morrison, J.P.E.
(1955). Notes on the Genera Lanx and Fisherola
(Pulmonata). Nautilus 68(3): 79-83.
Odhner, N.H.
(1929). Die Molluskenfauna des Takern. Sjon Takerns
Fauna och Flora, utgiven av K. Svenska Vetenskaps-
akademien. Stockholm: Almqvist and Wiksells. 129 pp.
Pilsbry, H.A.
(1925). The Family Lancidae Distinguished from the
Ancylidae. Nautilus 38(3): 73-75.
(1939-48). Land Mollusca of North America (North of
Mexico). Monographs of the Academy of Natural
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1(2): 575-994 (1940); 2(1): 1-520(1946); 2(2): 521-1113
(1948).
Ross, H.H.
(1974), Biological Systematies. Reading, Mass.: Addi-
son- Wesley Publishing Co. 345 pp.
Sinclair, R.M., and Isom, B.G.
(1963). Further Studies on the Introduced Asiatic Clam
(Corbicula) in Tennessee. Tennessee Department of
Public Health, Tennessee Stream Pollution Control
Board. 76 pp.
Solem, G.A.
(1974). The Shell Makers: Introducing Mollusks.
Toronto: John Wiley and Sons. 289 pp.
Sterki, V.
(1895). Two New Pisidia. Nautilus 8(9): 97-100.
Taylor, D.W.
(1966). Summary of North American Blancan Non-
Marine Mollusks. Malacologia 4(1): 1-172.
(1975). Index and Bibliography of Late Cenozoic
Freshwater Mollusca of Western North America.
Claude W. Hibbard Memorial Vol. 1. Museum of
Paleontology Papers on Paleontology, No. 10. 384 pp.
Taylor, D.W., and Sohl, N.F.
(1962). An Outline of Gastropod Classification. Mala-
cologia 1(1): 7-32.
Taylor, D.W.; WUter, H.J.; and Burch, J.B.
(1963). Freshwater Snails of the Sub-genus Hinkkyia
(Lymnaeidae: Stagnicola) from the Western United
States. Malacologia 1(2): 237-81.
438
Te, G.A,
(1975). Michigan Physidae, with Systematic Notes on
Physella and Physodon (Basommatophora: Pulmonata).
Malacological Review 8 (1/2) 7-30.
Vkn der Schalie, H., and Dundee, D.S.
(1955). The Distribution, Ecology and Life History of
Pomatiopsis cincinnatiensis (Lea), an Amphibious
Operculate Snail. Transactions of the American Micro-
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Index to Scientific and Common Names
References are to the consecutive numbers assigned to
the species in the text. Italic numbers indicate that
the taxon is briefly discussed under that species entry.
Family names are listed in the table of contents,
Acella haldemani 36
Acroloxus coloradensis 23
Actinonaias carinaia 131
acuta, Pleurocera 20
adamsi , Pisidium 160
Adam’s Pea Clam 160
Alaskan Pond Snail 40
Alasmidonta
calceola (= Alasmidonta viridis) 102
heterodon 103
marginata 104
undulata 105
varicosa 106
viridis 102
alata, Prop ter a 1 26
alberta, Bakerilymnaea bulimoides morph 31
Alewife Floater 118
ambigua, Simpsoniconcha 110
Amblema plicata 94
American Ear Snail 35
Amnicola
limosa 14
walkeri 15
amnicum, Pisidium 1 57
Amphibious Fossaria 29
anceps, Helisoma anceps 77
angulata , Gonidea 93
A nodonta
beringiana 1 12
cataracta cataracta 113
cataracta fragilis 1 14
grandis grandis 115
g randis simpsoniana 116
imbed lis 117
implicata 118
kennerlyi 119
nuttalliana 120
oregonensis {— Anodonta nuttalliana) 120
zoahlamatensis (— Anodonta nuttalliana) 120
A nodontoides feruss acianus 111
Aplexa hypnorum 65
appressa, Lymnaea stagnalis (= Lymnaea stagnalis
jugularis) 38
arctica, Stagnicola 43
Arctic-Alpine Fingernail Clam 147
Arctic-Alpine Pea Clam 176
armigera,Planorbula 75
A rmiger crista 70
Asiatic Clam 144
atheami, Physa jennesst 5 6
atkaensis, Lymnaea 40
auricularia, Radix 33
Bakerilymnaea
bulimoides 3 1
bulimoides morph alberta 31
morph bulimoides 3 1
morph cockerelli 3 1
morph perplexa 3 1
morph techella 31
morph vancouverensis 3 1
dalh 32
Banded Mystery Snail 2
Banff Springs Physa 5 8
BeanVillosa 140
Bell-mouthed Ramshorn 79
beringiana, Anodonta 112
binneyi, Helisoma trivolvis 85
Burney’s Stout Ramshorn 85
Bithynia tentaculata 19
Black Sand-Shell 133
Blade-ridged Stagnicola 41
Blunt Albino Physa 56
Blunt Arctic Physa 5 5
Blunt Prairie Physa 57
British Columbia Menetus 74
Broad Promenetus 72
Brook Lasmigona 108
Brook Wedge Mussel 102
Brown Mystery Snail 1
Bulimnea megasoma 37
bulimoides, Bakerilymnaea 3 1
bulimoides, Bakerilymnaea bulimoides morph 31
Bulimus tentaculatus (= Bithynia tentaculata) 19
Bythinia tentaculata (= Bithynia tentaculata) 19
calceola, Alasmidonta (= Alasmidonta viridis) 102
campanulatum , Helisoma campanulatum 79
Gampeloma
decisum 1
integrum 1
Gampeloma Spire Snail 10
campestris, Planorbula 76
Capacious Manitoba Ramshorn 8 1
caperata, Stagnicola 41
carinata, Actinonaias 131
cariosa, Lampsilis 134
Carunculina parva 127
casertanum, Pisidium 161
cataracta, A nodonta cataracta 113
catascopium, Stagnicola catascopium 44
chinensis, Cipangopaludina 3
Cincinnatia cincinnatiensis 10
dncinnatiensis, C incinnatia 1 0
cincinnatiensis, Pomatiopsis 1 8
Cipangopaludina chinensis 3
circumstriatus, Gyraulus 66
coccineum, Pleurobema 101
cockerelli, Bakerilymnaea bulimoides morph 31
441
collinsi, Helisoma campanulatum 80
coloradensis, Acroloxus 23
Columbiana, Physa 59
Columbia River Physa 59
columella, Pseudosuccinea 35
Common Floater 1 1 5
Common Stagnicola 47
complanata, Elliptio 99
complanata, Lasmigona 107
compressa, Lasmigona 1 08
comp res sum, Pisidiu m 162
concolor, Physa 60
contectoideSy Viviparus (= Viviparus georgianus) 2
contortum , Pisidium nitidum form 169
convenvus, Pisidium 176
cooperi, Menetus 74
Corbicula
fluminea 144
leana (= Corbicula fluminea ) 144
manilensis (= Corbicula fluminea) 144
comeum, Sphaerium 145
corpulentum, Helisoma corpulentum 8 1
costata, Lasmigona 109
crista, Armiger 70
cristatum, Pisidium lilljeborgi morph 1 67
cruciamm, Pisidium 1 77
Cyclonaias tuberculata 98
Cylindrical Floater 111
dalli, Bakerilymnaea 32
decampi,Fossaria 25
decepta, Marswnia 12
decisum, Campeloma 1
Deep-Water Spire Snail 16
Deer-Toe 125
deflectus , Gyraulus 67
Delicate Lamp-Mussel 136
dilataia, Elliptio 100
donaciformis, Truncilla 124
dubium, Pisidium 158
Dusky Lily-Pad Limpet 87
Dwarf Wedge Mussel 103
Dysnomia
torulosa rangiana 142
triquetra 143
Eastern Elliptio 99
Eastern Floater 113
Eastern Lamp-Mussel 137
Eastern Physa 53
Eastern-River Pearl Mussel 9 1
Elliptio
complanata 99
dilatata 100
e lodes, Stagnicola 47
equilaterale, Pisidium 163
European Ear Snail 33
European Fingernail Clam 145
European \hlve Snail 5
exacuous, Promeneius exacuous 7 1
exigua, Fossaria 26
fab ale, Sphae rium 146
fabalis, Villosa 140
falcata, Margaritifera 92
fallax, Pisidium 1 64
False Pig-Toe 101
fasciola, Lampsilis 135
fasciolaris, Ptychobranchus 122
FatMucket 138
Fat Pea Clam 170
Faucet Snail 19
Fawn’s-Foot 124
Ferrissia
fragilis 88
fragilis form isabellae 88
parallela 89
rivularis 90
ferruginea, Fossaria 27
ferrugineum, Pisidium 165
ferussacianus, Anodontoides 111
Flat-ended Spire Snail 1 1
Flatly Coiled Gyraulus 66
Flat-sided Horn Snail 20
Flat-sided Lake Limpet 89
Flat \hlve- Snail 4
flava , Fusconaia 95
Flumincola virens ( = Lithoglyphus virens ) 1 7
fluminea, Corbicula 144
Fluted Shell 109
Fossaria
decampi 25
exigua 26
ferruginea 27
modicella 28
modicella morph rustica 28
parva 29
truncatula 30
Fragile Fossaria 27
Fragile Paper-Shell 130
fragilis, A nodonta cataracta 114
fragilis, Ferrissia 88
fragilis, Leptode a 130
Fusconaia flava 95
fuscus, Laevapex 87
Gatineau Tadpole Snail 52
georgianus, Viviparus 2
Giant Columbia- River Limpet 24
Giant Columbia- River Spire Snail 1 7
Giant Fingernail Clam 150
Giant Manitoba Ram shorn 8 1
Giant Northern Pea Clam 1 59
Giant Promenetus 72
Giant Western Physa 62
Giant Western Spire Snail 17
Globular Pea Clam 174
Gonidea angulata 93
Goniobasis livescens 21
Graceful Fossaria 26
Graceful Keeled Horn Snail 22
grandis, Anodonta grandis 115
granum, Lyogyrus 13
442
Greater Carinate Ramshorn 83
Greater Columbia-River Limpet 24
Greater Eastern Pea Clam 1 58
Greater European Pea Clam 1 57
Great Lakes Horn Snail 21
Great Pond Snail 38
Grooved Fingernail Clam 150
Gyraulus
circumstriatus 66
deflecms 61
parvus 68
vermicularis 69
gyrina, Physa gyri na 51
haldemani, Acella 36
Haldeman’s Physa 60
Heavy-toothed Wedge Mussel 105
helicoidea, Valvata sincera 7
Hdisoma
anceps anceps 77
anceps royalense 78
campanulatum campanulatum 79
campanulatum collinsi 80
corpulentum corpulentum 81
corpulenium vermilionense 82
corpulentum white avesi 82
multivolvis 80
pilsbryi infracarinatum 83
trivolvis binneyi 85
trivolvis subcrenatum 86
trivolvis trivolvis 84
henslowanum, Pisidium 166
Henslow’s Pea Clam 166
Herrington’s Fingernail Clam 152
heterodon, A lasmidonta 1 03
keterostropha, Physa 53
hindsii, Lithoglyphus 1 7
hordacea, Physa 61
Hump-backed Pea Clam 172
Hy dr obi a nickliniana 18
hypnorum, Aplexa 65
idahoense, Pisidium 159
imbecilis, Anodonta 1 17
implicata, Anondonta 118
infracarinatum, Hdisoma pilsbryi 83
insigne, Pisidium 178
integra , Physa 54
integrum, Campeloma 1
iris, Villosa 141
Irregular Gyraulus 67
isabellae, Ferris si a fragilis form 88
japonicus, Viviparus (= Cipangopaludina chinensis) 3
jenksii, Planorbula (= Planorbula armigera) 75
jennessi, Physa jennessi 55
johnsoni, Physa 58
Juga
plicifera 22
silicula (= Juga plicifera) 22
jugularis, Lymnaea stagnalis 38
Keeled Promene tu s 71
kennerlyi, A nodonta 119
kennicotti, Stagnicola 48
Kidney Shell 122
lacustre, Sphaenum 153
lacustris, Probythinella 1 1
Lady-Finger 100
Laevapex fuscus 87
Lake Fingernail Clam 153
Lake Stagnicola 44
Lake Superior Ramshorn 78
Lampsilis
cariosa 134
fasciola 135
ochracea 136
ovata 139
ovata ventricosa (= Lampsilis ventricosa ) 139
radiata radiata 137
radiata siliquoidea 138
ventricosa 139
Lanx nuttalli 24
lapidaria, Pomatiopsis 18
Larger Eastern Ramshorn 84
Larger Prairie Ramshorn 86
Lasmigona
compla nata 107
compressa 108
costata 109
latchfordi , Physa gyrina 52
leana, Corbicula (= Corbicula fluminea) 144
Leptodea fragilis 130
letsoni, Pyrgulopsis 12
Ltgumia
nasuta 132
recta 133
Lilliput Mussel 1 27
lilljeborgi, Pisidium 167
Lilljeborg’s Pea Clam 167
limosa, A mnicola 1 4
Lithoglyphus
hindsii 1 7
virens 17
Liver-Fluke Fossaria 30
livescens, Goniobasis 21
Long Fingernail-Clam 156
Loosely Coiled \hlve Snail 8
lordi, Physa 62
Low-spired Ramshorn 80
Lymnaea
atkaensis 40
palustris (= Stagnicola elodes) 47
peregra ( = Radix peregra ) 34
stagnalis appressa (= Lymnaea stagnalis
jugularis) 38
stagnalis jugularis 38
stagnalis sanctaemariae 39
stagnalis wasatchensis (= Lymnaea stagnalis
jugularis) 38
Lyogyrus granum 1 3
443
macrodon, Truncilla 124
mainense, Pisidium walkeri form 175
malleatus, Viviparus (= Cipangopaludina chinensis) 3
manilensis, Corbictda (= Corbicula flwninea) 144
Maple-Leaf 96
Margatitifera
falcata 92
margaritifera 91
margaritifera, Margaritifera 91
ma rgmaia, A las mido nta 1 04
Mar stoma decepta 12
me gas, Promenetus exacuous 72
megasoma, Bulimnea 37
Menetus cooperi 74
mergella, Valvata 6
milium, Pisidium 1 68
Miniature Lake-Stagnicola 45
Modest Fossaria 28
Modest Gyraulus 68
modicella , Fossaria 28
montanensis, Stagnicola 42
Mountain-Spring Stagnicola 42
Mucket 131
Mudpuppy Mussel 110
multivolvis, Helisoma 80
Muskeg Stagnicola 43
nasoni, Stagnicola catascopium 45
nasuta, Ligumia 132
Newfoundland Floater 1 14
mcklintana, Hydrobta 18
nitidum, Pisidium 169
nitidum, Sphaerium 147
Northern Floater 116
Northern Riffle Shell 142
Northern V&lve Snail 7
nuttalli, Lanx 24
nuttalli, Physa 63
nuttalliana, Anodonta 120
Nuttall’s Physa 63
Obliquaria reflexa 123
Obovaria
olivaria 128
subrotunda 129
Occident ale, Sphaerium 152
ochracea, Lampsilis 136
olivaria, Obovaria 128
Olive Hickory-Nut 128
ontariensis, Valvata sincera 8
Ordinary Spire Snail 14
oregonensis, Anodonta ( = A nodonta nuttalliana ) 1 20
Oriental Mystery Snail 3
Ornamented Pea Clam 1 77
Oval Lake-Limpet 88
ovata, Lampsilis 139
Pacific Coast Gyraulus 69
palustris, Lymnaea (= Stagnicola elodes ) 47
palustris, Stagnicola (= Stagnicola elodes) 47
Paper Pond-Shell 117
parallela, Ferrissia 89
partumeium, Sphaerium 1 54
parva, Carunculina 127
parva, Fossaria 29
parvus, Gyraulus 68
patella, Sphaerium 148
pauperculum, Pisidium nitidum form 169
perdepressa, Valvata 4
peregra , Radix 34
Perforated Pea Clam 1 79
perplexa , Bakerilymnaea bulimoides morph 31
Physa
columbiana 59
concolor 60
gyrina gynna 51
gyrina latchfordi 52
heterostropha 53
hordacea 61
integra 54
jennessi atheami 56
jennessi jennessi 55
jennessi skinneri 57
Johns om 58
lordi 62
nuttalli 63
propinqua 64
vinosa 51
virginea 62
Pig-Toe 95
Pilsbry’s Spire Snail 12
Pink Heel-Splitter 126
piscinalis, Valvata 5
Pisidium
adamsi 160
amnicum 157
casenanum 161
compressum 1 62
conventus \16
crudatum 177
dubium 1 58
equilaterale 163
fallax 164
ferrugineum 165
henslowanum 166
idahoense 159
insigne 178
lilljeborgi 167
lilljeborgi morph cristatum 167
milium 168
nitidum 169
nitidum form contortum 1 69
nitidum form pauperculum 169
punctatum 179
punctiferum 179
rotundatum 170
subtruncatum 171
supinum 172
444
variabile 173
ventricosum 174
vincentianum 177
waldeni 167
walkeri 175
walkeri form mainense 175
Planorbula
armigera 75
campestris 76
jenksii (= Planorbula armigera) 75
Pleurobema coccineum 101
Pleurocera acuta 20
plicata, Amblema 94
plicifera,Juga 22
Pocket-Book 139
Pointed Lake Limpet 23
Pointed Sand-Shell 132
Polished Tadpole Snail 65
Pomatiopsis
cincinnatiensis 18
lapidaria 18
Pond Fin gemai l Clam 155
Prairie Pond Snail 31
Prairi e T oothed Planorbid 7 6
preblei, Stagnicola catascopium 46
Probyth ine lla la custris 1 1
Promenetus
exacuous exacuous 71
e: vacuous megas 72
umbilicatellus 73
propinqua, Physa 64
Proptera alata 1 26
proximo, Stagnicola 49
Pseudo succinea columella 35
Ptychobranchus fasciolaris 122
punctatum, Pisidium 179
punctiferum, Pisidium 179
Purple Pimple-Back 98
pustule sa, Quadrula 97
Pyrgulopsis letsoni 12
Quadrangular Pill Clam 168
Quadrula
pustulosa 97
quadrula 96
quadrula, Quadrula 96
radiata, Lampsilis radiata 137
Radix
auricularia 33
peregra 34
Rainbow Shell 141
rangiana, Dysnomia torulosa 142
recta, L igumia 133
reflexa, Obliquaria 123
reflexa, Stagnicola 50
rhomboideum , Sphaerium 149
Rhomboid Fingernail Clam 149
Ribbed Valve-Snail 6
Ridged-Beak Pea Clam 162
Ridged Wedge-Mussel 104
River- Bank Looping Snail 18
River Fingernail Clam 146
River Pea Clam 164
rivularis, Ferrissia 90
Rocky Mountain Fingernail Clam 148
Rocky Mountain Ridged Mussel 93
Rocky Mountain Stagnicola 49
rotundatum, Pisidium 1 70
Round Hickory-Nut 129
Round Pea Clam 163
rowelli, Stagnicola proximo (= Stagnicola proximo)
rqyalense, Helisoma anceps 78
rustica, Fossaria modicella morph 28
Rusty Pea Clam 165
Rusty Spire Snail 13
sanctaemariae, Lymnaea stagnalis 39
Say’s Toothed Planorbid 75
securis, Sphaerium 155
Shiny Pea Clam 169
Short-ended Pea C lam 171
Shouldered Northern Fossaria 25
Showy Pond Snail 37
silicula,Juga (= Juga plicifera) 22
siliquoidea, Lampsilis radiata 138
simile, Sphaerium 150
simpsoniana, Anodonta grandis 1 1 6
Simpsoniconcha ambigua 110
sincera , Valvata sine era 6
skinneri, Physa jennessi 57
Slender Pond Snail 36
Small Pond-Snail 32
Small Spire-Snail 15
Solid Lake-Physa 54
Somatogyrus subglobosus 16
Sphaerium
comeum 145
f abate 146
lacustre 153
nitidum 147
ocddentale 152
partumeium 154
patella 148
rhomboideum 149
rerun's 155
simile 1 50
striatinum 151
transversum 1 56
Spike 100
Squaw-Foot 121
Stagnicola
arctica 43
caperata 41
catascopium catascopium 44
catascopium nasoni 45
catascopium preblei 46
elodes 47
kennicotti 48
montanensis 42
palustris (= Stagnicola elodes ) 47
proximo 49
proxima rotvelli (= Stagnicola proximo) 49
reflexa 50
yukonensis (= Stagnicola arctica) 43
Striated Fingernail Clam 151
striatinwn , Sphaerium 151
Striped Stagnicola 50
Strophitus undulatus 121
Sturdy River Limpet 90
Subarctic Lake-Stagnicola 46
subcrenatum, Hdisoma trivolvis 86
subglobosus, Somatogyrus 16
subrotunda, Obovaria 129
subtruncatum, Pisidium 171
supinum, Pisidium 172
Swamp Fingernail Clam 1 54
Swollen Wedge-Mussel 106
Tadpole Snail 51
techella, Bakenlymnaea bulimoides morph 3 1
tentaculata, Bithynia 19
tentaculata, Bythinia {= Bithynia tentaculata) 19
tentaculatus, Bulimus (= Bithynia tentaculata) 19
Three-homed Warty-Back 1 23
Three-keeled Valve Snail 9
Three-Ridge 94
Tiny Nautilus Snail 70
Tiny Pea Clam 178
transversum, Sphaerium 156
Triangular Pea Clam 1 73
tricarinata, Valvata 9
Tricorn Pearly Mussel 143
triquetra, Dysnomia 143
trivolvis, Helisoma trivolvis 84
truncata, T runcilla 125
truncatula , Fassaria 30
T runcilla
donaciformis 124
macrodon 124
truncata 125
luberculata, Cyclonaias 98
Two-ridged Ramshorn 77
Ubiquitous Pea Clam 161
umbilicatellus, Promenetus 73
Umbilicate Promenetus 73
undulata, A lasmidonta 1 05
undulatus, Strophitus 121
Valvata
mergella 6
perdepressa 4
piscinalis 5
sincera heltcoidea 1
sincera ontariensis 8
sincera sincera 6
tricarinata 9
virens 6
vancouverensis, Bakerilymnaea bulimoides morph 3 1
Vancouver Island Physa 61
variabile, Pisidium 173
varicosa, A lasmidonta 1 06
ventricosa, Lampsilis 139
ventricosa, Lampsilis ovata (= Lampsilis
ventricosa) 139
ventricosum, Pisid ium 1 74
vermicularis, Gyraulus 69
vermiiionense, Helisoma corpulentum 82
Villosa
fab alls 140
iris 141
vincentianum, Pisidium 177
vinosa, Physa 51
virens, Lithoglyphus 17
virens, Valvata 6
virginea, Physa 62
viridis, Alasmidonta 102
Viviparus
contectoides (= Viviparus georgianus) 2
georgianus 2
japonicus (= Cipangopaludina chinensis) 3
malleatus (= Cipangopaludina chinensis) 3
viviparus 2
viviparus, Viviparus 2
wahlamatensis, Anodonta (= Anodonta
nuttalliana) 120
waldeni, Pisidium 167
walkert, Amnicola 1 5
walkeri, Pisidium 1 7 5
Walker’s Pea Clam 175
Walker’s Pond Snail 39
Wandering Snail 34
Warty-Back 97
zuasatchensis, Lymnaea stagnalis (= Lymnaea stagnalis
jugularis) 38
Wavy-rayed Lamp-Mussel 135
Western Arctic Stagnicola 48
Western Floater 1 19
Western Lake Physa 64
Western-River Pearl Mussel 92
whiteavesi, Helisoma corpulentum 82
Whiteaves’s Capacious Ramshorn 82
White Heel-Splitter 107
Winged Floater 120
Yellow Lamp-Mussel 134
yukonensis , Stagnicola (= Stagnicola arctica) 43
Yukon Floater 112
446
n:ay
MAI
3 1982
V
The Shell of a Freshwater Mussel or Clam
0 Quadrula quadrula)
Outside View
Disc
Posterior
ridge
Lines
of growth
Ligament
Posterior slope
j Umbo, or beak
Anterior margin
Inside View
Interdentum
Lateral hinge teeth
Posterior pedal retractor
(muscle scar)
Posterior adductor
(muscle scar)
Anterior pedal retractor
(muscle scar)
Anterior adductor
(muscle scar)
Pedal protractor
(muscle scar)
Beak cavity
Umbo
Pseudocardinal teeth
Pallial line
The Shell of a Pea Clam or Pill Clam ( Pisidium )
Inside View of Left Valve
Anterior lateral (A2)
Cusp
(C4)
Ligament
Posterior lateral (P2)
Cusp
Cardinal teeth
Beak
Anterior
inner lateral (Al)
Inside View of Right Valve
Cardinal tooth (C3)
Ligament
Posterior outer lateral (P3)
Anterior
outer lateral (A3)
Posterior inner
lateral (PI)
Drawings by Charles Douglas (reprinted from Clarke 1973)