Example of a ship worm
Bivalve shells vary in shape; some are longer or shorter and others are flat or round. The shell is added to in two ways; the valves grow larger when more material is cut by the mantle at the margin and there is a gradual thickening of the valves throughout the animal's life. the Family of Teredinidae have longer bodies, but the shell valve are reduced and restricted to the end of the body.
A foot is used as a digging instrument. This allows the worm to more easily dig through wood. shells are made up of two valves held together by a ligament of muscles. The valves are made of either calcite, or aragonite, most of the time aragonite is in the inner layer. The outside is periostracum, which is an organic substance. This is usually brown and can be broken down some what easily because of the organic nature.
A foot is used as a digging instrument. This allows the worm to more easily dig through wood. shells are made up of two valves held together by a ligament of muscles. The valves are made of either calcite, or aragonite, most of the time aragonite is in the inner layer. The outside is periostracum, which is an organic substance. This is usually brown and can be broken down some what easily because of the organic nature.