Cryptodonta

The valves of the shell are relatively thin and somewhat elongated. Unlike most other bivalves, species in this group have no hinge teeth on their shells. They have relatively primitive, `protobranchiate`, gills. ==Taxonomy== ...
Found on http://en.wikipedia.org/wiki/Cryptodonta

Cryptodonta

(from the article `bivalve`) ...protobranch ctenidia; large labial palps usually with palp proboscides, which effect feeding; foot with flat sole; marine; unattached; ...
Found on http://www.britannica.com/eb/a-z/c/165
No exact match found