Three main purposes: breathing, obtaining food, and eliminating waste products. Since clams are relatively immobile and
movement is usually limited to burrowing in the sand, their double-tubed siphon--which operates much like a snorkel--is their
lifeline. Inflowing water is pumped through the siphon, passed over the gills, and strained to remove food particles. After
receiving carbon dioxide from the gills and other waste products from the digestive tract, the water is expelled through the
outgoing siphon. Constant circulation of the water is maintained by the beating of a multitude of microscopic hairs (called
cilia) located inside the tube and in the gill chamber.