Class Aplacophora are mollusks without shells. They usually resemble worms, and are found in deep water, often more than 3,000 m. There are only about 300 species in this class, and besides lacking shells, they are all marine and generally very small.
Unlike Neomenioids, Chaetoderms lack a foot and pedal groove. They possess either a nearly or entirely cicumoral sensory cuticular shield. The midgut is separated into a stomach and glandular digestive diverticulum and they lack serial sets of lateroventral muscle bands. Chaetoderms are dioecious and chaetoderms that posses one pair of ctenidia in the mantle cavity.
