Their streamlined bodies allow easy movement through the dense medium. Tail muscles are organized for powerful force. The swim bladder provides buoyancy. All possess a streamlined body with a cartilaginous endoskeleton, gill slits, and fins. This group includes the sharks, skates, rays, and chimaeras.
Chimaeras are almost scaleless, with a body resembling a rat.
Bony fishes are the most numerous and diverse of the vertebrates. Descendants of ancestors that arose in the Silurian period have radiated into nearly every aquatic habitat. The ray-finned fishes are highly maneuverable thanks to their fins, which are supported by rays that originate from the dermis 3. The lobe-finned fishes bear fleshy extensions on the body. Amphibians A. Origin of Amphibians 1.