Sharks are classified as vertebrates in the phylum Chordata. Although their skeletons are made of cartilage rather than hard bone, they are still considered vertebrates.
Sharks belong to the class Elasmobranchii, which is made up of around 1,000 species of sharks, rays and skates. The fins of cartilaginous fish, such as sharks, do not bend or fold into their bodies like those of bony fish. This makes their dorsal fins stand rigidly so that they poke ominously out of the water when the sharks are near the surface. However, most sharks do not swim near the surface of the water, preferring to stay near the bottom or mid-waters.