后鳃类生物（Opisthobranchs；英语发音：/ɵˈpɪsθəbræŋks/）是软件动物门腹足纲异鳃类的一个大型及多样的生物群组，原来是一个亚纲级的分类元，但这个分类由于还包括在陆地生活的有肺类物种（如：蜗牛及蛞蝓），不是一个单系群，现时已被弃用。真后鳃类（Euopisthobranchia）是一个尝试对这个分类修订的单系群，但踢走了一些传统上一直归入后鳃类的分类元，如：囊舌类（Sacoglossa）及Acochlidiacea。原来后鳃类及有腩类的所有物种，现时都已包括在异鳃类（Heterobranchia）这个新的分类元里。这个分类元本来也是亚纲级的，现时已成为不分级分类支序。

Opisthobranchs (/əˈpɪsθəˌbræŋks, -θoʊ-/) are a large and diverse group of specialized complex gastropods that used to be united in the subclass Opisthobranchia, but are no longer considered to represent a monophyletic grouping because it contains land snails and slugs, the Pulmonata. Euopisthobranchia is a revised collection of opisthobranchs that is monophyletic, but this group leaves out some "traditional" opisthobranchs including the Sacoglossa and the Acochlidiacea. The subclass Heterobranchia now contains the species which used to be assigned to Opisthobranchia plus the Pulmonata.