Opisthobranchia

2 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Opisthobranchia \O*pis`tho*bran"chi*a\, Opisthobranchiata
  \O*pis`tho*bran`chi*a"ta\, n. pl. [NL., from Gr. 'o`pisqen
     behind + ? gills.] (Zool.)
     A division of gastropod Mollusca, in which the breathing
     organs are usually situated behind the heart. It includes the
     tectibranchs and nudibranchs.


     [1913 Webster]

From WordNet (r) 2.0 [wn]:

  Opisthobranchia
       n : gastropods having the gills when present posterior to the
           heart and having no operculum: includes sea slugs; sea
           butterflies; sea hares [syn: {subclass Opisthobranchia}]