Mollusks are soft-bodied animals that usually have an internal or external shell. They are members of the phylum Mollusca and come from the Latin word molluscus, which means "soft." Mollusks include snails, slugs, clams, squids, and octopi. One reason these diverse organisms are grouped together is because of their similar developmental stages. Many aquatic mollusks have a free-swimming larval stage called a trochophore. The body plan of most mollusks has four parts: foot, mantle, shell, and visceral mass. As shown in figure 1, the parts of a mollusk are labeled. 
Miller, Kenneth, and Josheph Levine. Biology. Upper Saddle River, New Jersey: Prentice Hall, 2002. 701-703. Print.

This picture is labeled with parts of a mollusk.(figure 1)