Molluscs

Phylum Mollusca

The phylum Mollusca has five classes including chitons, scaphopods, bivalves, gastropods, and cephalopods.  Animals in this phylum are characterized by having a soft body with a “head” and a “foot” region, and a mantle that secretes a shell.  While these are shared characteristics, different classes of molluscs can look very different from each other.  Only three of these classes, bivalvia, gastropoda, and cephalopoda, are commonly found in the salt marsh-tidal creek ecosystem.

Cephalopoda (“head” – “foot”) – Squid, octopus, cuttlefish, and nautilus are cephalopods.  Except for the nautilus, the shell is greatly reduced and found internally.  Eyes are well developed, and arms and tentacles surround the mouth to capture food and bring it towards a sharp beak.  Cephalopods will use their siphon to discharge waste and to quickly expel water brought in through the mantle to move.

Bivalvia (“two” – ”valves”) – This class includes clams, scallops, mussels, and oysters.  Bivalves have two shells that are joined at a dorsal hinge by a ligament and teeth. The shells protect the interior soft body of the animal.  Bivalves have filtering capabilities, meaning they suck in water and circulate it over the gills for respiration and capturing food.   They also filter out pollutants and nutrients, making bivalves important in supporting healthy water quality.

Gastropoda  (“stomach” – ”foot”)  –  Snails and sea slugs make up the gastropoda class. Snails have only one shell that is continuously secreted from their mantle, coiling around the body.  The apex, or top, of the shell is the oldest, with new whorls added as the snails grow.  Snails are able to seal their shell closed with their operculum, effectively protecting them from predators or water loss if exposed to the atmosphere.  Sea slugs, on the other hand, are gastropods that have reduced shells internally.

Atlantic brief squid C

Lolliguncula brevis

Characteristics:
Cephalopod; body covered in chromatophores; large eyes; arms and tentacles surround mouth and sharp beak

Characteristics:
Cephalopod; body covered in chromatophores; large eyes; arms and tentacles surround mouth and sharp beak
Range:
NJ to FL, and northern Gulf of Mexico
Size:
Up to 5in (13cm) in length
Habitat:
Estuaries, tidal creeks
Fun Fact:
Internal shell is referred to as the “pen shell” because it is said that sailors used to dip it in ink to write with
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Eastern mud snail D

Ilyanassa obsoleta

Characteristics:
Gastropod; black or dark brown conical shell

Characteristics:
Gastropod; black or dark brown conical shell
Range:
Native to Atlantic coast of the U.S., now invasive along the Pacific coast
Size:
Up to 1in (3cm) in length
Habitat:
Intertidal mud flats
Fun Fact:
Highly active scavengers, swarms of mud snails will break down organic matter on the surface of the mud
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Eastern oyster H

Crassostrea virginica

Characteristics:
Bivalve; shell narrow at the hinge and widening to a rough oval shape; gray exterior with glossy white interior

Characteristics:
Bivalve; shell narrow at the hinge and widening to a rough oval shape; gray exterior with glossy white interior
Range:
Atlantic coast of the U.S.
Size:
Shells average 2-6in (5-15cm) in length
Habitat:
Tidal creeks, intertidal in Southeast, also subtidal in NC
Fun Fact:
Oyster beds provide important living habitat for many species of fish and invertebrates
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Hard clam H

Mercenaria mercenaria

Characteristics:
Bivalve; thick oval shell with noticeable growth rings and tan exterior color

Characteristics:
Bivalve; thick oval shell with noticeable growth rings and tan exterior color
Range:
Atlantic coast of the U.S., the Gulf of Mexico
Size:
Shells average 2-5in (5-13cm) wide
Habitat:
Intertidal to subtidal; coarse, shelly sand
Fun Fact:
Most valuable clam harvested in the US; may live more than 40 years
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Marsh periwinkle D

Littoraria irrorata

Characteristics:

Gastropod; shell color dark brown to white

Characteristics:

Gastropod; shell color dark brown to white

Range:

New England to the Gulf Coast of Texas

Size:

Up to 1in (3cm) in length

Habitat:

Stalks of living and dead Spartina, low marsh to the upland border

Fun Fact:

Feeds on microalgae and detritus, plays a key role in decomposition and the recycling of marsh nutrients

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Ribbed mussel H

Geukensia demissa

Characteristics:

Bivalve; thin, long shells with brown, green, or purple exterior and iridescent interior

Characteristics:

Bivalve; thin, long shells with brown, green, or purple exterior and iridescent interior

Range:

Atlantic coast of the U.S. until northern FL

Size:

Shells average 2-5in (5-13cm) in length

Habitat:

Marsh platform

Fun Fact:

Grows in clusters near the base of Spartina plants and holds fast to the plant’s roots with byssal threads

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Channeled whelk C

Busycotypus canaliculatus

Characteristics:
Gastropod; 5-6 whorls; fine beading toward tip of spire

Characteristics:
Gastropod; 5-6 whorls; fine beading toward tip of spire
Range:
Atlantic coast of the U.S.
Size:
4-8in (10-20cm) in length
Habitat:
Sand and mud flats, oyster reefs, offshore to 60ft deep
Fun Fact:
Uses a muscular foot to hold bivalve prey while chipping at its hinge until it can pry the shells apart
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Knobbed whelk C

Busycon carica

Characteristics:
Gastropod; shell has an average of 6 whorls with protruding knobs evenly spaced; shell opening on the right

Characteristics:
Gastropod; shell has an average of 6 whorls with protruding knobs evenly spaced; shell opening on the right
Range:
Atlantic coast of the U.S.
Size:
4-10in (4-25cm) in length
Habitat:
Tidal creeks, often found on oyster reefs, up to 30ft deep
Fun Fact:
Lays a string of egg capsules that can often be found washed ashore
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