Cartilaginous fish are a group of fish that have skeletons made of cartilage instead of bone. This group includes sharks and skates, which are two of the most well-known members. Sharks are predatory fish that have a streamlined body and multiple rows of sharp teeth. Skates are flat fish that have a diamond-shaped body and a long tail. Both sharks and skates have been around for millions of years and are found in many different habitats.