Zoology 10th Edition by Stephen Miller,John Harley

Exercise 9

Hagfishes comprise the class Myxini. They possess 5 to 15 pairs of pharyngeal slits and slime glands. They are marine scavengers of dead and dying fish. Lampreys comprise the class Petromyzontida. Adult lampreys possess a sucking mouth and rasping tongue and are predators of other fishes. Gnathostomes have jaws and paired appendages. The gnathostome class Chondrichthyes includes the sharks, skates, and rays. They possess placoid scales and a cartilaginous endoskeleton. Bony fishes include members of the classes Sarcopterygii and Actinopterygii. Sarcopterygians possess fins with muscular lobes and usually use lungs in gas exchange. Their descendants include the tetrapods. Actinopterygians have fins that lack muscular lobes and possess swim bladders that are used in buoyancy regulation. Adaptive radiation of this group has resulted in an amazing diversity of species.
What major characteristics distinguish each of the classes of fishes?