acephalæa

Century Dictionary and Cyclopedia

1. A modification by Lamarck of the name Acephala, given at first to that group as an ordinal name, and later to the bivalve shells as a class name. In Lamarck's system of classification of 1801 the Acephalæa were the second order of Mollusca, the Acephala of Cuvier, 1789, including cirripeds, tunicates, and brachiopods with ordinary bivalve mollusks. In 1809 Lamarck excluded the cirripeds, and in 1812 he excluded the tunicates, making Acephalæa a class of Evertebrata, with two orders, Monomyaria and Dimyaria. See Conchifera.