Osteichthyes (o-sti-IK-thes) is made of two Greek roots that mean “bony fish” (bony -osteinos and fish –ichthys). Bony fish are a taxonomic group of fish that have bone. Class Osteichthyes includes all bony fishes. Like all fishes, Osteichthyes are cold-blooded vertebrates that breathe through gills and use fins for swimming. Bony fishes share several distinguishing features: a skeleton of bone, scales, paired fins, one pair of gill openings, jaws, and paired nostrils. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of 45 orders, and over 435 families and 28,000 species. It is the largest class of vertebrates in existence today.