Dibranchiata :: Dibranchiata (n. pl.) An order of cephalopods which includes those with two gills, an apparatus for emitting an inky fluid, and either eight or ten cephalic arms bearing suckers or hooks, as the octopi and squids. See Cephalopoda..
Nudibranchiata :: Nudibranchiata (n. pl.) A division of opisthobranchiate mollusks, having no shell except while very young. The gills are naked and situated upon the back or sides. See Ceratobranchia..