The Cartilaginous Fishes (Class Chondrichthyes) include sharks, skates, and rays.
1) They are cold-blooded vertebrates.
2) Their skeleton is made of cartilage instead of bone. Cartilage is softer than bone (it makes up your outer ear or the end of your nose).
3) They breathe through gills.
4) Their teeth, on the other hand, are very hard and when they lose them, biting into tough prey, they can replace them within days. Many chondrichthyes, including sharks, make new teeth as needed their whole lives.
5) They have 2 pairs of fins, one pair in the front (pectoral fins) and one pair in back. Sharks are famous for their large dorsal fin seen above the water as they swim along the surface.
Chondrichthyes have remained almost unchanged since the time of the dinosaurs.
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