The animal is bilaterally symmetrical. With a well-developed foot surrounded by a groove in which there are 6 to 88 pairs of gills. All chitons are marine inhabitants and most make a living by grazing algae from rocks and other hard substrates. They have no shell, but have calcareous spicules in the body surface. The foot is restricted to an anterior pedal shield or to a narrow groove running the length of the body.
Aplacophorans have a radula and a posterior mantle cavity.
Some are detritus feeders, others are predators. They range in length from 1 to 300 millimeters. These are two very small classes that many scientists combine to form the Class Aplacophora. The Caudofoveata are aberrant molluscs that lack shells. They are quite common in the deep sea buried in the soft sediments.