Cartilaginous Fishes (Chondrichthyes)
The cartilaginous fishes:
sharks, skates, and rays
have developed high levels of urea in their blood. Shark's blood may contain 2.5% urea in contrast to the 0.01-0.03% in other vertebrates.
Cartilaginous fish (Class Chondrichthyes): The most primitive 'jawed' vertebrates evolved about 400 Mya. Their skeleton is composed of entirely cartilage.
cartilaginous fishes Fishes with a skeleton made of cartilage: sharks, rays, skates, and ratfishes (or chimaeras).
caryopsis Simple, dry, indehiscent fruit with a single seed that is fused to the ovary wall. Also called a grain. Example: wheat.
Cartilaginous fish first appeared during the Devonian period and expanded in diversity during the Carboniferous and Permian before nearly disappearing during the great extinction that occurred near the end of the Permian.
Class Chondrichthyes: Cartilaginous Fish
The class Chondrichthyes contains approximately 850 species of skates, rays, and sharks. They have jaws, lots of teeth, paired fins, and a cartilage endoskeleton.
Sharks (cartilaginous fishes) must continually swim to prevent depletion of the oxygen in waters surrounding them. Bony fish (teleosts) have an operculum over their gills and they swallow water and force it over their gills and out the operculum.
This includes the bony fish (Osteichthyes), the cartilaginous fish (Chondrichthyes) such as sharks and rays, and the jawless fish (Agnatha).
The vertebrate class of cartilaginous fishes, represented by sharks and their relatives.
chondrin
A protein-carbohydrate complex secreted by chondrocytes; chondrin and collagen fibers form cartilage.
This includes skeletal fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). An estimated 25,000 fish species exist, comprising a majority of vertebrates.
 See also: Organ, Animals, Vertebrates, Animal, Mammals
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