from the GNU version of the Collaborative International Dictionary of English
- n.pl. A division of gastropod Mollusca, in which the breathing organs are usually situated behind the heart. It includes the tectibranchs and nudibranchs.
from The Century Dictionary and Cyclopedia
- Same as Opisthobranchiata.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea hares
Sorry, no etymologies found.
The mollusk taxon that is best represented on the Internet is probably the Opisthobranchia, the sea slugs.