Silurian

Silurian

Silurian

Gastropoda and Bivalvia

Gastropoda and Bivalvia

Bivalve, (class Bivalvia), any of more than 15,000 species of clams, oysters, mussels, scallops, and other members of the phylum Mollusca characterized by a shell that is divided from front to back into left and right valves.

Gastropods are among the few groups of animals to have become successful in all three major habitats: the ocean, fresh waters, and land.

Trilobites

Trilobites

Trilobite, any member of a group of extinct fossil arthropods easily recognized by their distinctive three-lobed, three-segmented form.