Mollusks are soft-bodied invertebrates that usually have shells. They are found on land, in fresh water and in salt water. Many mollusks have bilateral symmetry and a fluid-filled cavity that provides space for the body organs.

There are three basic types of mollusks:

• Univalves, also known as gastropods, have a single shell (except for slugs). This is the largest group of mollusks that includes snails and slugs.
• Bivalves have two shells joined by a hinge. Scallops, clams and oysters are examples of bivalves.
• Cephalopods do not have any shells. They are the most specialized and complex mollusks which include squid, octopus and cuttlefish (which are NOT fish!).