This group of cartilaginous fish include Rays, Sharks, Skates, Chimaeras. The species in this class have a flexible skeleton made of cartilage instead of bone.
Cartilage is the flexible substance found that gives human noses and ears their shape! Only their teeth, and sometimes their vertebrae, have calcium in them! That why when you find fossils of sharks you find teeth and vertebrae but no other bones.
Chimaeras have large heads and long bodies that taper to a whiplike tail. The skin is smooth and rubbery and has no scales. Sharks and skates and rays have gills that open to the outside, have no swim bladder, and have a sandpaper-like skin covering rather than scales. Sharks range in size from tiny to huge. Skates and rays are flat from top to bottom and have massive pectoral fins and long, sometimes whiplike tails.
Species in this class have paired fins, hard scales, a two-chambered heart, and a pair of nostrils. Most species have 5-7 gill slits on each side of their body. Some species produce egg cases, others give birth to live young.
These top predators of the ocean have been overfished for their fins which are considered a delicacy in Chinese soup dishes. Ninety percent of their populations have been decimated to the extent that it has disrupted the food chains in some areas. Many species are under threat of extinction if efforts to create protected marine parks are not successful.