A class of fishes characterized by well-developed jaws and bony teeth; pectoral and pelvic girdles, each supporting paired fins; a cartilaginous skeleton that lacks true bone; toothlike scales of ectodermal and mesodermal origin; paired nostrils with blind olfactory sacs (not opening into the mouth); a vertebral column having either a straight or heterocercal posterior end; absence of a swim bladder; cranium without sutures; and internal fertilization.