Bivalves are mollusks that show no cephalization, according to Clinton Community College. The biological makeup of mollusks does not include a head, central nervous system and sensory organs that are needed for cephalization in higher animals, notes Estrella Mountain Community College.
Bivalves include clams, scallops, oysters and mussels. These creatures have hinged shells that open and close due to powerful muscles. The internal physiology of bivalves includes a mouth, stomach, intestine, gills and anus. A foot anchors a bivalve to the ocean floor, and siphons move water in and out to get food and oxygen. Three pairs of ganglia form the nervous system, according to EMCC. The heart and kidneys excrete ammonia waste.
The shell of bivalves protects the internal organs and is made from calcium deposits secreted by the mantle. Blood flows through an open circulatory system, which means a bivalve's blood is not necessarily contained in arteries, veins and blood vessels, notes EMCC.
Bivalves filter feed, which delineates a system reliant on siphoning water currents over the mouth and gills. Mucous secretions trap food for consumption as water moves through the bivalve. The anus excretes waste through another siphon, according to McGraw-Hill. Bivalves are mollusks, a type of animal denoted by soft bodies and more than 110,000 distinct species. Mollusks include octopus, squid, snails and conchs.