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
- 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
Eastern mud snail D
Ilyanassa obsoleta
- 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
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
- 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
Hard clam H
Mercenaria mercenaria
- 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
Marsh periwinkle D
Littoraria irrorata
- 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
Ribbed mussel H
Geukensia demissa
- 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
Channeled whelk C
Busycotypus canaliculatus
- 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
Knobbed whelk C
Busycon carica
- 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
