Ragworm head. Close-up of the head of a ragworm (Nereis virens), showing its mouthparts. Ragworms are marine annelid worms that burrow in wet sand and mud using parapodia (un jointed limb-like outgrowths) and setae (bristles) for locomotion. These structures are also used as gills for respiration. Photographed in the White Sea, northwest coast of Russia.