Correct Option: C

There are over 20,000 species of fish, divided into three groups : bony fish, cartilaginous fish and jawless fish. Bony fish, which are the most numerous, have skeletons, of bone, and swimbladders (gas-filled organs) to keep them afloat. Cartilaginous fish, such as sharks, rays and ratfish, are mostly marine hunters; they have skeletons made of cartilage and sandpaper-like skin. The primitive jawless fish have sucker-like mouths, and include lampreys and hagfish.