1. opisthobranch - Noun
2. opisthobranch - Adjective
opisthobranch (plural opisthobranchs)
(zoology) A gastropod with gills behind the heart, formerly thought to belong to a single group.
(of gills) Placed behind the heart.
Antonym: prosobranch
(of a gastropod) Having gills placed behind the heart.
Antonym: prosobranch