Aplacophora :: Aplacophora (n. pl.) A division of Amphineura in which the body is naked or covered with slender spines or setae, but is without shelly plates..
Placophora :: Placophora (n. pl.) A division of gastropod Mollusca, including the chitons. The back is covered by eight shelly plates. Called also Polyplacophora. See Illust. under Chiton, and Isopleura..