bivalve

:  any of a class (Bivalvia synonym Pelecypoda) of typically marine mollusks (such as clams, oysters, or scallops) that have a 2-valved hinged shell, are usually filter feeders, and lack a distinct head

:  having or consisting of two corresponding movable pieces suggesting the shells of mollusks a bivalve speculum a bivalve cast

:  to split (a cast) along one or two sides (as to relieve pressure)