tectibranchia

‖n. pl. [ NL., fr. L. tectus (p. p. of tegere to cover) + Gr. &unr_; a gill. ] (Zool.) An order, or suborder, of gastropod Mollusca in which the gills are usually situated on one side of the back, and protected by a fold of the mantle. When there is a shell, it is usually thin and delicate and often rudimentary. The aplysias and the bubble shells are examples. [ 1913 Webster ]