Giant Clam
- The umbo, the upper hump near the hinge of each shell, is the oldest part of the shell.
- The inner surface of the shell is lined by the mantle, so that the whole body lies in the mantle cavity, a large space between the two halves of the mantle.
- Strong muscles, the abductor muscles, are used to close the valves.
Clams use their shovel-shaped foot to burrow in sand or mud. When the clam is buried, water is drawn in and out of the mantle cavity through siphons formed by the fusion of the edge of the mantle. This allows clams to feed and obtain oxygen while buried in sediment.
Not all bivalves are burrowers. Mussels, for instance, secrete strong byssal threads that attach them to rocks and other surfaces.
Many bivalves bore in coral, rock or wood. The shipworm (Teredo) bores in mangrove roots, driftwood, and wooden structures such as boats and pilings. They use their small valves to excavate the wood, which is eaten. Symbiotic bacteria in the shipworm's gut digest the wood. Shipworms are an example of a fouling organism, one that settles on the bottom of boats, pilings, and other submerged structures.
Wood eaten by a shipworm