sb. pl. Zool. [late L. acephala, a. Gr. ἀκέφαλα adj. neut. pl. = headless (sc. animalia).] Name given (by Lamarck) to one of the two great divisions of Mollusks. The sing. is supplied by ACEPHAL or more commonly ACEPHALAN.
1847. Carpenter, Zool., § 876. The Conchiferous Acephala, with scarcely an exception, have bivalve shells.
1863. Lyell, Antiq. Man, xxii. 442. A greater number of acephala or lamellibranchiate bivalves could be identified with living species than of gasteropods.
