This slide shows a cross section through the body of a clamworm (Nereis virens). These predatory polychaete annelids are common in shallow waters along the Atlantic coast of North America.  Hiding by day in burrows in sand or mud bottoms, the worms come out at night to search for food, which is grabbed with powerful chitinous jaws on a muscular eversible pharynx.  Biramous lateral appendages called parapodia are easily seen on this cross section. These highly vascularized appendages serve both for locomotion (swimming or creeping along the bottom) and respiration, and they may also be supplied with various sensory structures.