The main body of a mollusk, which contains most of the organs, including a complete digestive and excretory tract as well as the reproductive organs. The visceral hump also includes the mantle, which consists of two external flaps of tissue that secretes the material that forms the shell on some species, and it protects the mantle cavity. The mantle cavity contains the gills, which excrete waste and circulate oxygen. Most mollusks have a shell, which sits on the visceral hump and a protects the main body from predators.