24 Q 7

Explain how bony fishes differ from sharks and rays in the following systems or features: skeleton, scales, buoyancy, respiration, reproduction.

Sharks and rays have a cartelidge skeleton, while bony fish have a skeleton of bone. Sharks have placoid scales, while bony fish can have either ganoid scales (if they are non-teleosts), or cycloid or ctenoid scales (if they are teleosts). Bony fish use a swim bladder for bouyancy, while sharks use the placement of their fins, and their large, fatty liver for bouyancy. In bony fishes, respiration is primarily by gills supported by arches and covered by an operculum; but in sharks and rays, respiration is by means of five to seven pairs of gills leading to exposed gill slits. In sharks and rays, the sexes are separate, the gonads are paired,and the reproductive ducts open into cloaca. They can be either oviparous, oviviviparous, or viviparous, and have internal fertilization and direct development. In bony fish, most are dioecious with external fertilization and external development of their eggs. -SE

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