Burrowing marine mollusk living on sand or mud; the shell closes with viselike firmness WordNet 3.0 & Open English WordNet

Clam is a common name for several kinds of bivalve molluscs. Wikipedia

Common name for several kinds of bivalve molluscs Wikidata

A marine or freshwater mollusks belonging to the class Bivalvia, whose body is protected by two symmetrical shells. OmegaWiki

A bivalve mollusk of many kinds, especially those that are edible; for example the soft-shell clam (Mya arenaria), the hard clam (Mercenaria mercenaria), the sea clam or hen clam (Spisula solidissima), and other species. The name is said to have been given originally to the Tridacna gigas, a huge East Indian bivalve. Wiktionary