Bivalvia, class Bivalvia, Lamellibranchia, class Lamellibranchia, class Pelecypoda
(noun) oysters; clams; scallops; mussels
Source: WordNet® 3.1
La*mel`li*bran"chi*a, La*mel`li*bran`chi*a"ta, n. pl. Etym: [NL. See
lamella, and Branchia, Branchiate.] (Zoöl.)
Definition: A class of Mollusca including all those that have bivalve
shells, as the clams, oysters, mussels, etc.
Note: They usually have two (rarely but one) flat, lamelliform gills
on each side of the body. They have an imperfectly developed head,
concealed within the shell, whence they are called Acephala. Called
also Conchifera, and Pelecypoda. See Bivalve.
Source: Webster’s Unabridged Dictionary 1913 Edition