Opisthobranchia

[əʊpɪs'θəʊbrænkɪə]

(noun.) gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea hares.

整理:梅尔巴--From WordNet

(n. pl.) Alt. of Opisthobranchiata

校對:马尔科姆