/ Thesaurus / O Synonyms of opisthobranchia Find synonyms for: Noun1. Opisthobranchia, subclass Opisthobranchia, classusage: gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea haresWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: devout Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language