Chitons (Class Polyplacophora) have a small, oval-shaped, flattened, bilaterally symmetrical body covered with eight overlapping calcareous shell plates. They can flex the body and fasten onto an uneven rock substratum using the strong muscular foot on the undersurface. Chitons feed on encrusting algae, sponges and bryozoans by scraping the surface with a long tongue-like radula. Females are generally triggered to deposit eggs externally after nearby males release sperm, although some species brood their young in the mantle cavity.