1. gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea hares; [syn: Opisthobranchia, subclass Opisthobranchia]
WordNet (r) 3.0 (2006):
subclass Opisthobranchia
n 1: gastropods having the gills when present posterior to the
heart and having no operculum: includes sea slugs; sea
butterflies; sea hares [syn: Opisthobranchia, subclass
Opisthobranchia]