Mollusca
Mollusca Diagram
Mollusca are a large phylum of Invertebrate animals. There are over 85,000 different species of mollusca. Invertebrate means these creatures don’t have a back bone or any other bones in its body, most just have a large shell around their body. The shell is mostly hardened calcium and over the course of evolution the shell has been lost in a few ways such as in slugs and octopus. Also the shell has moved to inside the body in animals like squids. There are 3 major classes of mollusca witch are bivalvia, gastropoda, and cephalopoda.
Bivalvia
Clams
The bivalvia class contains about 7,500 species of animals such as many common animals like clams, oysters, scallops, and muscles. These animals have 2 shells that cover the entire body and are held tightly shut. Cretan bivalvia have muscles strong enough to open and close the shell fast enough to propel the animal forward in order to eat other creatures and avoid predators. For others the shell acts as a layer of protection.
Gastropoda
Snail
Gastropoda is the largest group of mollusca and contains over 38,000 different types of species; they have either a single shell or no shell at all. Gastropods are often found in both salt and fresh water and on land. Gastropods include snails, whelks, periwinkles and slugs.
Cephalopoda
Giant Squid
Cephalopoda are very different from the rest of the mollusca and other Invertebrates. In many ways they are considered to be more evolved. There are over 600 types of this species in this strictly aquatic class. Some of these creatures are octopuses, squids, and cuddle fish. Squid have evolved its shell into an interior skeletal system with its shell used for support and protection. In cuddle fish it gives the fish its entire shape and support. Finally in octopus a skeletal system or a shell is completely inexistent.