ZOOLOGY with Basics of Ecology - H.V. Kovalchuk - 2003

Part II. SUBCORPORATION MULTICELLULAR ANIMALS – METAZOA

PHYLUM CHORDATA - CHORDATA

SUBPHYLUM VERTEBRATES, OR CRANIATES, - VERTEBRATA

CLASS BONY FISHES - OSTEICHTYES

The world fauna comprises about 20,000 species of bony Fishes, with 180 species found in Ukraine.

Their most essential difference from cartilaginous fishes is The Development of a bony Skeleton. The Biological Significance of this phenomenon is profound: Bone tissue is significantly stronger than Cartilage while providing the skeleton with lightness and mobility. In some fishes, the skeleton is cartilaginous-bony.

In bony fishes, the interbranchial septa have regressed, and the gill filaments and rakers are located on the gill arches; the gills are covered by a bony operculum, which plays a crucial role in enhancing Respiration. The development of a hydrostatic organ—the swim bladder—has improved the hydrodynamic characteristics of bony fishes and their ability to maneuver in the aquatic environment with minimal Energy Expenditure. The absence of a spiral valve in most of them, a feature characteristic of cartilaginous fishes, is compensated in bony fishes by an increase in the relative length of the intestines and the development of pyloric caeca, which increase their absorptive surface area. This enhances the intensity and efficiency of Digestion. An arterial conus is predominantly absent in The Heart. Fertilization is external. Eggs lack horny capsules. It encompasses 2 subclasses: Actinopterygii and Sarcopterygii.