Sharks belong to the class Chondrichthyes, which also includes rays, skates, and chimaeras. Within this class, sharks are further classified into eight orders based on their physical characteristics, such as the shape of their teeth and the location of their gills. There are over 500 species of sharks, ranging in size from the pygmy shark, which is only six inches long, to the whale shark, which can grow up to 40 feet in length.