prosobranch
noun
pros·o·branch ˈprä-sə-ˌbraŋk 
plural prosobranchs
: any of a subclass (Prosobranchia) of gastropod mollusks that have the loop of visceral nerves twisted into a figure eight, the sexes usually separate, and usually an operculum
prosobranch adjective
Word History
Etymology
New Latin Prosobranchia, from proso- in front (from Greek prosō forward) + branchia gills (from Greek)
First Known Use
1851, in the meaning defined above