The chitons have an elongate, elliptical body covered by a flexible shield of overlapping calcareous plates. Chitons are rare in the geological record, but fossils interpreted as chitons are known from the Cambrian to the Recent. We have not found any web sites covering fossil Amphineura. The gastropods are characterized by an asymmetrical spiral-coiled calcareous shell. The group contains the familiar snails and slugs.
Gastropods are marine, fresh water, and terrestrial.
The fossil record stretches from the early Cambrian to the Recent. To learn more about living gastropods go to the Gastropods page in the Natural History segment of Nearctica . We have not found any web sites specifically about gastropods. Try some of the links in the general paleontological page. The bivalves are characterized by bilateral symmetry and two calcareous valves connected by a hinge.