Cartilaginous fishes are a group of fish characterized by having a skeleton made of cartilage instead of bone. This group includes species such as sharks, rays, and skates. They are part of the class Chondrichthyes and are known for their streamlined bodies and powerful swimming abilities. These fishes typically have several unique features, including multiple gill slits and a lack of a swim bladder, which helps them maintain buoyancy. Cartilaginous fishes also have tough, sandpaper-like skin covered in tiny scales called placoid scales, which provide protection and reduce drag while swimming.