Swim bladder, also called air bladder, buoyancy organ possessed by most bony fish. The swim bladder is located in the body cavity and is derived from an outpocketing of the digestive tube.

The skeleton of bony fishes is made of bone and cartilage. The vertebral column, cranium, jaw, ribs, and intramuscular bones make up a bony fish’s skeleton.

Placoid scales are composed of a vascular (supplied with blood) inner core of pulp, a middle layer of dentine and a hard enamel-like outer layer of vitrodentine.

An operculum (gill cover) that is a flexible bony plate that protects the sensitive gills.

Examples are sharks, rays, dog-fish, skates, sturgion. Osteichthyes: These are fishes with bony skeleton. Examples are Tuna, Sardines, Codfish, Salmon, Trouts, Herring etc.

Bony fishes share several distinguishing features: a skeleton of bone, scales, paired fins, one pair of gill openings, jaws, and paired nostrils. Osteichthyes includes the largest number of living species of all scientific classes of vertebrates, more than 28,000 species.

The bony fish are divided into two classes: ray-finned fish and lobe-finned fish. The bony fish are characterized by a lung or swim bladder, a cover over the gills, and bones covering the head and pectoral girdles.

Bony fish also comprise virtually all freshwater species living in lakes, rivers, and streams. Sunfish, bass, catfish, trout, and pike are examples of bony fish, as are the freshwater tropical fish that you see in aquariums. Other species of bony fish include: Tuna.

flatworms

With an open circulatory system, blood and nutrients are not restricted to moving within blood vessels. Then, there is the closed circulatory system – this is the type vertebrates like fish, mammals, and amphibians have.

The closed circulatory system has more advantages over the open circulatory system. 1. The blood transfers faster in the closed system, thus oxygen, nutritients, and wastes transport fast also. 2.