How do clams establish themselves on the sea bottom?

Certain kinds of clams, in early stages of life possess a gland that produces a thread-like material (byssus) that serves to anchor them to grains of sand or rocks. Other types of clams lack a byssal gland and use the foot to burrow into the seabed. As the clam grows, its wedge-shaped foot, which expands and contracts as it moves, becomes more important as a burrowing tool.