The biggest bivalve mollusk is the clam Tridacna, native to the Indo-Pacific, which reaches a weight of 500 pounds. The giant squid , nearly sixty feet long, is the biggest cephalopod. The Alaskan king crab is the largest of the crustaceans, weighing up to 15 pounds, and measuring four to five feet across shell and claws. Called filter feeders, oysters and clams eat plankton. By pumping water through their bodies, the mollusks strain the microscopic organisms through their gills, which act as sieves.
Clams seem to squirt water through their siphons.
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. The red algae they sometimes consume, often composed of the microscopic one-celled dinoflagellates which appear in planktonic mass.