ACANTHOPTERYGII, the most specialized section of the bony fishes (Teleostii), characterized by the possession of spines on the first dorsal fin and by the absence usually of a duct connecting the air-bladder with the alimentary canal. (See FISH.) They include the perch, the mackerel, the bass (qq.v.) and other well known and important fishes besides numerous less noteworthy forms. In the perches and basses the anterior dorsal fin is armed with formidable spines.