any member of the superclass Osteichthyes, a group made up of the classes Sarcopterygii (lobe-finned fishes) and Actinopterygii (ray-finned fishes) in the subphylum Vertebrata, including the great majority of living fishes and virtually all the world's sport and commercial fishes. The scientific term Pisces has also been used to identify this group of fishes. Osteichthyes excludes the jawless fishes of the class Agnatha (hagfishes and lampreys) and the cartilaginous fishes constituting the class Chondrichthyes (sharks, skates, and rays) but includes the 20,000 species and more than 400 families of modern bony fishes (infraclass Teleostei) of the world, as well as a few primitive forms. The primary characteristic of bony fishes is a skeleton at least partly composed of true bone (as opposed to cartilage). Other features include, in most forms, the presence of a swim bladder (an air-filled sac to give buoyancy), gill covers over the gill chamber, bony platelike scales, a skull with sutures, and external fertilization of eggs.