What Helps Direct Water Over a Clam's Gills?

Two siphons, located in the clam's shell lining, move water in and out of the clam to filter oxygen and food out of the water. These siphons are located next to one another and rise vertically towards the sea bed to gather water. Cilia, which are small hair-like protuberances, create currents in the siphons. The shell is buried in sand or mud, while the fleshy body reaches up for water.

Cilia move back and forth, in a coordinated fashion, to move water along each siphon. Cilia in the very large gills retrieve oxygen, which is then exchanged with carbon dioxide, through the tiny hairs. Light and chemical sensors on each siphon are connected to the clam's nervous system through three ganglia. These sensors tell the clam when to siphon water. When high tide comes in, the siphons go to work and capture oxygen and food. When low tide occurs, clams and other shelled mollusks retreat to their shells until water returns.

The clam's cilia capture tiny bits of food that get passed to the mouth. Although breathing occurs in every cilia in the clam's body, the food makes its way to the mouth thanks to sticky mucus on each hair. Clams eat plankton and are not very mobile.