acephala
A*ceph"a*la, n. pl. Etym: [NL., fr. Gr. Acephal.] (Zoöl.) Defn: That division of the Mollusca which includes the bivalve shells, like the clams and oysters; -- so called because they have no evident head. Formerly the group included the Tunicata, Brachiopoda, and sometimes the Bryozoa. See Mollusca.