Goby picture reproduced from http://www.zoo.ufl.edu/stmary (with permission)
Sunfish picture reproduced from http://www.seastudios.com/pages/gallery/molamola.html (with permission)
The Class Osteichthyes consists of the bony fishes and is the largest class of vertebrates, with over 24,000 species. These fishes have a skeleton much stiffer than that of the cartilaginous fish (sharks). Bony fish have an excellent sense of smell, like sharks and rays, but their sense of vision is also excellent.
Bony fishes range in size from the very small Philippine Goby Mugilogobius parvus (top left), which is only about 10 mm long, to the ocean sunfish Mola mola, which can grow up to 4 m in length and 1500kg in weight (top right).
As well as many vertebrae for structural support and calcium storage, the bony fishes have special adaptations to control their buoyancy. A special organ called the swim bladder acts as a gas-filled chamber to control their depth in the water.
Another prominent feature of the bony fishes is the operculum. This constitutes the lateral fleshy grooves on the fish that cover the chambers housing the gills. The operculum allows the fish to breathe (even if it is not swimming) by moving water currents over the gills. Other features include paired fins, dermal scales in the skin (in most species) and numerous vertebrae.