inequivalve

In conchology, having unequal valves, as a bivalve mollusk; having one of the valves larger than the other: applied both to lamelli-branch bivalves, in which the valves are lateral, and to brachiopods, in which the valves are a dorsal and a ventral one.

Having unequal valves, as the shell of an oyster.

Having valves of different sizes

Any bivalve mollusc whose valves are of different sizes.