In many echinoderms, this groove carries small captured food particles to the mouth of the organism, although in some types the feature has been altered to serve other functions. The mouth is located where the radiating ambulacra intersect. The side with the mouth in echinoderms is defined as the oral side . The side opposite is called the aboral side . Like most echinoderms, the skeleton of asterozoans is composed of numerous small calcite plates called ossicles which readily disarticulate upon the animal's death.
Asteroids are asterozoans whose internal body parts extend into the arms.
Unlike the ophiuroids, there is no sharp distinction between the arm structure and the central body structure. Most asteroids are predatory, preying on clams, corals, other echinoderms, or anything else unlucky enough to cross their path. Some asteroids can extrude their stomach through their mouth, killing and partially digesting their prey outside their body. Asteroids are among the most active echinoderms. The arms of ophiuroids are muscular extensions and contain only the ambulacra.