Osteichthyes (class)

Class of acquatic animals characterized by possessing a skeleton at least partly composed of true bone (as opposed to cartilage) and typically a swim bladder (an air-filled sac to give buoyancy), a single pair of gills, gill covers over the gill chamber, bony platelike scales, a skull with sutures, and external fertilization of eggs. Modern bony fishes represent over 20,000 species in more than 400 families. In some classifications it is listed as a superclass instead of a class.