The Collaborative International Dictionary of English v.0.48:

Tectibranchiata \Tec`ti*bran`chi*a"ta\, n. pl. [NL., fr. L.
   tectus (p. p. of tegere to cover) + Gr. ? 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]