any gastropod mollusk of the order Opisthobranchia, as the sea slugs, sea butterflies, and sea hares, characterized by a vestigial or absent mantle and shell and two pairs of tentacles.
adjective
2.
of or relating to the opisthobranches.
Also, opisthobranchiate
[uh-pis-thuh-brang-kee-it, -eyt] /əˌpɪs θəˈbræŋ ki ɪt, -ˌeɪt/ (Show IPA).
Origin of opisthobranch
1850-1855
1850-55; < New LatinOpisthobranchia the subclass; see opistho-, branchia
any marine gastropod of the class Opisthobranchia (or Opisthobranchiata), in which the shell is reduced or absent: includes the pteropods, sea hares, and nudibranchs
Word Origin
via New Latin from Greek opisthen behind + -branch
