Source : Webster's Revised Unabridged Dictionary (1913)

Nudibranchiata \Nu`di*bran`chi*a"ta\, n. pl. [NL. See {Nude},
   and {Branchia}.] (Zo["o]l.)
   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}.