Acephala
Acephala ({not transcribed}) , noun, plural
[New Latin, from Greek {not transcribed}, adj. neut. pl., headless. See Acephal.]
(Zoology) 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.