the ring attaches to a radial nerve which runs to the end of the limb. The nerves in each limb run through a canal at the base of the vertebral ossicles. Most ophiuroids have no eyes, or other specialised sense organs. However, they have several types of sensitive nerve endings in their epidermis, and are able to sense chemicals in the water, touch, and even the presence or absence of light. Moreover, tube feet may sense light as well as odors. These are especially found at the ends of their arms, detecting light and retreating into crevices. Digestion The mouth is rimmed with five jaws, and serves as an anus (egestion) as well as a mouth (ingestion). Behind the jaws is a short esophagus and a stomach cavity which occupies much of the dorsal half of the disk. Digestion occurs within 10 pouches or infolds of the stomach, which are essentially ceca, but unlike in sea stars, almost never extend into the arms. The stomach wall contains glandular hepatic cells. Ophiuroids are generally scavengers or detritivores. Small organic particles are moved into the mouth by the tube feet. Ophiuroids may also prey on small crustaceans or worms. Basket stars in particular may be capable of suspension feeding, using the mucus coating on their arms to trap plankton and bacteria. They extend one arm out and use the other four as anchors. Brittle stars will eat small suspended organisms if available. In large, crowded areas, brittle stars eat suspended matter from prevailing seafloor currents. In basket stars, the arms are used to sweep food rhythmically to the mouth. Pectinura consumes beech pollen in the New Zealand fjords (since those trees hang over the water). Eurylina clings to coral branches to browse on the polyps. Respiration Gas exchange and excretion occur through cilia-lined sacs called bursae; each opens between the arm bases on the underside of the disk. Typically ten bursae are found, and each fits between two stomach digestive pouches. Water flows through the bursae by means of cilia or muscular contraction. Oxygen is transported through the body by the hemal system, a series of sinuses and vessels distinct from the water vascular system. The bursae are probably also the main organs of excretion, with phagocytic "coelomocytes" collecting waste products in the body cavity and then migrating to the bursae for expulsion from the body. Musculoskeletal system Like all echinoderms, the