/euh pis"theuh brangk'/, n.1. 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.adj.2. of or pertaining to the opisthobranches.Also, opisthobranchiate /euh pis'theuh brang"kee it, -ayt'/.[1850-55; < NL Opisthobranchia the subclass; see OPISTHO-, BRANCHIA]
* * *any marine gastropod of the approximately 2,000 species of the subclass Opisthobranchia. These gastropods, sometimes called sea slugs and sea hares, breathe either through gills, which are located behind the heart, or through the body surface. The shell and mantle cavity are reduced or lacking in most species. A pronounced twisting of the body, called torsion, characterizes gastropod development. Among opisthobranchs, however, torsion is usually limited, or individuals “detort” at metamorphosis. As a result, the mantle cavity, when present, generally lies at the side or rear of the animal rather than at the front. Each individual opisthobranch is a simultaneous hermaphrodite—i.e., both male and female reproductive organs occur in one individual.For more information on the major groups of opisthobranchs, see bubble shell; nudibranch; pteropod; sea hare.
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