Mollusks are the second largest species among animals.  The Phylum Mollusca refers to "soft body" animals.  All mollusks have a common body plan, and a hard shell protects most.  

Many mollusks feed by using a sharp razor tongue like organ called radula to scrape up food.

The three major  classes of mollusks are; Class Gastropoda (include snails and slugs).  Class Bivlavia (includes clams, mussels, and oysters), and Class Cephalopoda (include squids, octopi, and nautili).