Bivalve (noun)
Any mollusc belonging to the taxonomic class Bivalvia, characterized by a shell consisting of two hinged sections, such as a scallop, clam, mussel or oyster.
Bivalve (noun)
A pericarp in which the seed case opens or splits into two parts or valves.
Univalve (adjective)
having one valve; typically used to refer to mollusks, notably slugs and snails.
Univalve (adjective)
consisting of a single valve or piece, used to refer to a shell.
Univalve (noun)
A univalve mollusk or its shell.
Wiktionary