Project Description


Clams, Mussels, Scallops, Oysters

Bivalves are a diverse group of mollusks, second in number only to the gastropods. Scientists estimate there are about 10,000 species of bivalves.

Bivalves use their gills as filters

This scallop has hundreds of bright blue eyes

Shipworms are bivalves that bore through wood

Anatomy of a Bivalve

Bivalve Facts

The name bivalve refers to the two halves (valves) of the shell.

Commonly referred to as “clams,” “mussels,” or “oysters,” bivalves are found all over the world in both freshwater and marine environments.

Most bivalves spend their lives at least partly buried in the sand or mud.

They have a muscular foot that they use to burrow, although some, like the scallops, have the ability to “swim” by rapidly opening and closing the valves of their shell.

Razor clams live in shallow water along the coasts and are fast diggers

Bivalves have gills

Unlike gastropods most bivalves are filter feeders, and use their gills like strainers to filter the water for plankton to eat.

Bivalve anatomy

The shells of bivalves grow as the animal grows larger; you can usually see the ridges, called growth lines on most shells. Typically, both valves are mirror images of each other and are joined near the top of the shell by a flexible hinge. The two valves are closed by means of powerful muscles that are attached to the inside of each valve. Although they are usually hard to see, most bivalves have eyes, usually hundreds of them! Perhaps the best known are the many bright blue eyes of scallops.

Not all bivalves look the same

Not all bivalves look like clams. Shipworms look much more like worms than clams and you have to look closely at the watering pot clam to see the remains of its bivalve shells.

Bivalves need protection

Many bivalves represent important sources of food throughout the world, and as with many resources need to be monitored to ensure that they are not over-exploited. Many freshwater bivalves in the United States are threatened by pollution, dam construction, and poor agricultural practices.

Another threat to native bivalves is the introduction of non-native species. Zebra mussels, pictured here attached to a clam, were accidentally released into the rivers and lakes of the U.S. accidentally and have spread throughout the eastern half of the country. They can become so numerous that they out compete native mussels for plankton.