The mollusk has four body parts that consist of mantle, visceral mass, shell and foot. Each one has its own specific purpose. The types of mollusks are so varied that it is difficult to compare each one.
The visceral mass is where the heart and other major organs are located. The shell is what helps protect the mollusk from predators. The mantle is a layer of tissue that lays over the visceral mass, and it contains a gland that helps create the hard shell. The foot is located on the bottom of the body, and it secretes mucus so that the mollusk can move around. It moves around by contracting the foot muscle much like a snail. The mucus helps the mollusk glide across the surface. It also has a set of gills that helps it to breathe, so it does not have to come above water for air.