A group of mollusks that includes the sea slugs and sea hares. They have a small or absent shell and are typically brightly colored with conspicuous external gills.
- ‘In the traditional classification system, the class Gastropoda has been divided into three subclasses, Prosobranchia, Pulmonata, and Opisthobranchia.’
- ‘In fact, as with the Opisthobranchia, shell reduction has occurred independently a number of times in different lineages.’
- ‘However, as with Tritonia, many other members of the subclass Opisthobranchia also exhibit swimming behavior.’
- ‘The differences in protoconch shape may prove insufficient to differentiate Allogastropoda and shell-bearing Opisthobranchia.’
- ‘The latter group includes radically modified animals, the Opisthobranchia and Pulmonata, which undergo detorsion and essentially re-evolve bilateral symmetry.’
Modern Latin (plural), from opistho- to the rear + brankhia gills.