Bivalvia

noun

A class of bilaterally symmetrical molluscs which are laterally flattened and have a shell made of two hinged valves e.g. clams, mussels, scallops, cockles.

Body laterally compressed, has two valves hinged together dorsally. Head rudimentary but often have large foot and gills. Body does not have 8 dorsal shell plates, may or may not be flattened.

Bivalve shell is important both as cover for motile (free-living) organisms, and attachment substrate for sessile (attached) organisms. Over much of the SE Bering Sea shelf, dead shell probably provides a significant proportion of habitat for invertebrates requiring hard surface for attachment. Many snails lay their egg capsules on shell. Concentrations of bivalve and gastropod shell and shell fragments are called shell hash.