Answer: chondrichthyes
Since cartilage is less dense then regular bone, it allows cartilaginous fishes to move quick throughout water without using much energy. Cartilage is tough and flexible and allows fish with cartilaginous skeletons to grow to large sizes. Cartilaginous fishes are also known as chondrichthyes. Some examples of chondrichthyes are sharks, rays, skates, and chimaeras.
