Chordate Zoology - textbook - Y. V. Tsaryk - 2013

Chapter 4. DIVISION GNATHOSTOMES, or ECTOBRANCHIATES, GNATHOSTOMATA, seu ECTOBRANCHIATA. SUPERCLASS FISHES, PISCES

4.2. CLASS BONY FISHES, OSTEICHTHYES

Bony Fishes are the most numerous Class of Chordates. It comprises over 20,000 species, grouped into 451 families and 51 orders. Like cartilaginous fishes, they possess paired appendages—fins—and a Mouth with grasping jaws that may bear Teeth. The gill arches, with gill filaments attached, are concealed under a common operculum, resulting in only a single external gill slit on each side. The nostrils are paired. The Inner ear contains three semicircular canals. The hydrostatic organ—the swim bladder—develops as a dorsal outgrowth of the Esophagus (in lungfishes, a 'lung' develops as a ventral outgrowth). The Skeleton contains Bone tissue, and the scales are also bony. Evolutionarily ancient taxa may still retain a conus arteriosus in The Heart, but in most cases, a Swelling—the bulbus arteriosus—forms at the Base of the ventral aorta to prevent it from rupturing.

The eggs of bony fishes (roe) lack horny coverings. The size of mature individuals ranges from 1 cm to 7 m. Most bony fishes grow throughout their entire lives, which can last for over 100 years (beluga Huso huso).