O*pis`tho*bran"chi*a (?), O*pis`tho*bran`chi*a"ta (?), n. pl. [NL., from Gr. 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.
© Webster 1913.