Mollusks are an amazingly diverse group of animals that live in a wide variety of environments.
Some mollusks are excellent swimmers, others crawl or burrow in mud and sand. The number of living species of mollusks has been estimated to range from 50,000 to 130,000. Everyone is probably familiar with some type of mollusk. The word Mollusca is translated from Latin as soft-bodied but few physical characteristics are unique to all mollusks. Most mollusks can be described as free-living, multicellular animals that possess a true heart, and that have a calcareous exterior skeleton that covers at least the back or upper surface of the body.