- Opisthobranchia, subclass Opisthobranchia - gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea hares
--1 is a kind of class
--1 is a member of Gastropoda, class Gastropoda, Gasteropoda, class Gasteropoda
--1 has members: Nudibranchia, order Nudibranchia