Download Common Shells of the Intertidal Zone

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• This visual guide is intended to aid
you in identifying fish commonly
captured while seining on the beaches
of Long Island.
• This guide does not list all possible
species.
• Always take photographs of all
captures, and use a comprehensive
field guide when any species
identification is debatable.
• When you discover living organisms,
return them to the water after study.
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Common Shells
of the
Intertidal Zone
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Northern Rock Barnacle
Barnacles look like tiny limestone volcanoes. Found almost everywhere
in the intertidal zone attached to rocks, shells, and artificial structures.
When underwater, the mouth of the shell opens, and the shrimp-like
barnacle rakes filters through the water to feed on plankton.
Figure 1a. Rock Barnacle Balanus balanoides
Figure 1b. Rock Barnacle feeding
Balanus balanoides
Common Slipper Shell
A common gastropod on Long Island. Lives secured to any hard objects,
including one another. Shell has a platform underneath, giving this animal
several common names, "boat shell" or "quarterdeck".
Figure 2b. Slipper Shell Crepidula fornicata
Figure 2a. Slipper Shell Crepidula fornicata
Periwinkle
A common gastropod on rocks and docks. These are herbivorous snails,
grazing on algal film growing on rocks. Can live for extended periods out
of water by closing up their operculum and waiting.
Figure 3b. Periwinkle Littorina littorea
Figure 3a. Periwinkle Littorina littorea
Mud Snail
A super-abundant
gastropod in protected
bays and estuaries. Shell
often looks eroded or worn
down. Found on both
sandy and muddy bottoms.
A scavenger and detritus
feeder.
Figure 4. Mud Snail Nassarius obsoletus
Oyster Drill
This univalve has a flared opening to the shell. Gets its name from its
feeding strategy. Grinds its way through the base of an oyster or other
bivalve and sucks out the flesh inside. Won't tolerate salinity lower than
15%.
Figure 5a. Oyster Drill Urosalpinx cinerea
Whelks
Figure 5b. Oyster Drill Urosalpinx cinerea
Long Island's largest gastropods, shells can exceed 17 cm. Two species
found here; the knobbed whelk has pronounced bumps on the body whorl
and spire, the channeled whelk has a groove around the body whorl and
small closely spaced bumps to the spire.
Figure 6c. Knobbed Whelk spire
Busycon carica
Figure 6a. Knobbed Whelk Busycon carica
Figure 6d. Channeled Whelk spire
Busycon canaliculatum
Figure 6b. Channeled Whelk Busycon canaliculatum
Moon Snail
A large gastropod,
predator of other snails.
The moon snail will
drill a neat round hole
in the shell of the prey.
Can be found in shallow beach flats to deep
water.
Figure 7a. Moon Snail Lunatia heros
Figure 7b. Moon Snail Lunatia heros
Blue Mussel
The blue mussel shell is
glossy bluish to black, and
grows to 10 cm long. Blue
mussels live in estuaries
and bays. They attach
themselves to any structure
with tough byssal threads.
They can form dense shoals,
which in turn provide structure
for a host of seaweed, small
fish and invertebrates.
Ribbed Mussel
Figure 9. Ribbed Mussel Modiolus demissus
Figure 8. Blue Mussel Mytilus edulis
This salt-marsh
organism is found halfburied in the banks of
intertidal streams and
mud flats. Shell has ribs
down the length (blue
mussel does not). Shell
grows to 10 cm long.
Bay Scallop
Figure 10a. Bay Scallop Argopecten irradians
A ribbed bivalve that is
about as wide as it is long.
Has two wings at the base
roughly the same size as
the other. One of the very
few bivalve species that can
swim to avoid predators.
Live less than 2 years. An
annular ring can be seen
on larger specimens. Live
scallops have dozens of
tiny blue eyes.
Figure 10b. Bay Scallop Argopecten irradians
Oyster
This bivalve is extremely
variable in shape. Shells
are thick and unequal.
The lower valve is
cemented to the hard
object the larval oyster
attached to. When
areas are healthy, can
grow in massive beds
providing habitat for many
organisms.
Figure 11a. Oyster Crassostrea virginica
Figure 11b. Oyster Crassostrea virginica
Jingle Shell
A small bivalve with
dissimilar shells. Upper
shell is variably shaped,
shiny and colored white
to gold. Lower shell is
flat, fragile and has a
large hole. Most less
than 5 cm.
Figure 12. Jingle Shell Anomia simplex
Razor Clam
This large bivalve is about
six times longer than it is
wide. Lives burrowed in
sand and mud, sometimes
in colonies.
Figure 13. Razor Clam Ensis directus
Soft-shelled Clam
Figure 14. Soft-shelled Clam Mya arenaria
Quahog
Also called 'hard
clam'. Shell thick
and strong, broadly
oval. Inside white
with a purple stain.
Nicknames of this
bivalve are based
on size; 'littlenecks'
up to about 4 cm,
'cherrystones' to
about 5 cm, and
'chowders' when
larger than that.
Figure 15. Quahog Mercenaria mercenaria
The shell of this bivalve is
elongated and thin. They
live burrowed into mud
flats at low tide. They
can detect a human approaching, and will spurt
out a fountain of water to
dig deeper. Also called
'steamer'.
Surf Clam
Shell moderately strong, sort
of triangular. Outside smooth,
white. Sometimes covered
with an olive to brown coating.
Found in sandy areas below
the intertidal zone on ocean
beaches. Can get quite large,
to 20 cm.
Astarte
A small, triangular bivalve found in
sandy ocean habitat. Shell is heavy
and thick, almost smooth with a
yellowish-brown to black coating.
Several very similar species found
on Long Island beaches. Grow to
about 2 cm.
Figure 17. Chestnut Astarte Astarte castanea
Eastern Sea Star
Figure 18a. Eastern Sea Star Asterias forbesi
Figure 18b. Eastern Sea Star, showing tube feet Asterias forbesi
This five-armed echinoderm
is most often called a
'starfish'. Has hundreds of
tube feet on the bottom of
each arm, which it uses to
move about as well as pry
open bivalves, its favorite
prey. Found low or below
the intertidal zone, in rocky
areas or mussel and oyster
beds.
Dwarf Brittle Star
Brittle stars are widely varied,
sometimes burrowing in sediments
and eelgrass beds. The dwarf brittle
star can occasionally be found in
Long Island tidepools. Central disc
about 5mm wide, arms around 2 to 3
cm long.
Figure 19. Dwarf Brittle Star Amphioplus squamata
Purple Sea Urchin
An echinoderm covered in short,
stout spines. Stiff exoskeleton
beneath. A grazer of seaweed,
occasional scavenger of dead
animals. Found below the
intertidal zone in rocky areas.
Figure 20a. Purple Sea Urchin Arbacia punctulata
Figure 20b. Purple Sea Urchin, exoskeletons Arbacia punctulata
Other Snail Eggs
Figure 24. Mud Snail and eggs Nassarius obsoletus
Small marine snails lay individual egg
cases attached to vegetation, shells,
or rocks. Several species of snails
lay eggs that may look quite similar,
so identification beyond 'snail eggs'
is suspect. Mud snail shown in figure
24.
Whelk Egg Case
This confusing object is a
long chain of egg cases
produced by channeled
and knobbed whelks. Each
pad has multiple embryos
inside.
Figure 21a. Whelk egg case Busycon spp.
Figure 21b. Channeled Whelk producing eggs Busycon canaliculatum
Moon Snail Collar
This is an egg mass made by
the moon snail. It is produced by
cementing eggs and sand into a
curved ribbon. Very fragile.
Figure 22. Moon Snail collar Lunatia heros
Skate Egg Case
This hooked pouch contains
a single embryo of one of the
species of skates in local waters.
When washed ashore, it has
often already hatched, leaving
an empty husk. Several species
of skate have very similar
egg cases. Sometimes called
'mermaid's purse'.
Figure 23. Skate Egg case Family: Rajadae