Opisthobranchia opisthobranchia • opisthobranchiate · · · Info · Definitions · Characters · · Opisthobranchia · · Text Latin · · Script 15 · · Length 6 · · Syllables Definitions · · · (noun) gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea hares. Synonyms: subclass Opisthobranchia. · · Noun Definition 1 Characters · · O latin capital letter o U+004F a latin small letter a U+0061 b latin small letter b U+0062 c latin small letter c U+0063 h latin small letter h U+0068 i latin small letter i U+0069 n latin small letter n U+006E o latin small letter o U+006F p latin small letter p U+0070 r latin small letter r U+0072 s latin small letter s U+0073 t latin small letter t U+0074