from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. Any of various marine gastropod mollusks of the subclass Opisthobranchia, characterized by gills, a shell that is reduced or absent, and two pairs of tentacles.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. Any of a large and diverse group of specialized complex marine gastropods previously united under Opisthobranchia within the Heterobranchia, characterized by two pairs of tentacles and a single gill behind and to the right of the heart.

from The Century Dictionary and Cyclopedia

  • n. A member of the Opisthobranchiata.
  • Having posterior gills; specifically, of or pertaining to the Opisthobranchiata.


From New Latin Opisthobranchia, order name : Greek opistho-, behind; see opisthognathous + Greek brankhia, gills.
(American Heritage® Dictionary of the English Language, Fourth Edition)


  • Aldabra supports little besides tortoises, beach flies, opisthobranch mollusks, and polychaete worms.

    The Song of The Dodo


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