What are the three main groups of mollusks? Give an example of each and explain the characteristics of each animal that can be used to classify it. Sample Gastropods: A snail is a kind of gastropod. It has a single shell. Snails move along on their foot and obtain food using their radula. Bivalves: an oyster is an example of a bivalve. Oysters have two shells, are filter feeders, and do not move very much. They will produce pearls to protect themselves from irritants in their shells. Cephalopods: A squid is an example of a cephalopod. Squid have tentacles, a beak to crush their prey, and radula to strip the flesh from their prey. They also have large eyes, a complex nervous system, and move by jet propulsion.