BIVALVES include modern clams, scallops and oysters, and they live in both fresh water and seawater. Bivalves have a shell made of two halves, which are also called valves. In most bivalves, each half of the shell is a mirror image of the other (figure 1a). Bivalves feed on tiny bits of food found in the water or sediment. Some bivalves burrow into the sediment. Others live on the sediment surface or are attached to hard objects such as rock or coral.
At least 15 species of bivalves lived as dwellers in the Silurian reefs of Wisconsin. They were not common in the reefs, and only one species, shown above, is present in the diorama.