Sharks and rays (elasmobranchs) differ from fish in an number of ways:-
- their skeletons are made of cartilage rather than bone,
-they don't have air-filled swim bladders to help with buoyancy control,
- they reproduce by internally fertilising a relatively small number of eggs whereas fish externally fertilise thousands of eggs.

Some sharks lay eggs, others give birth to live young, rays are generally oviparous.

The bodies of rays are generally rounder and flatter than those of sharks.
Their pectoral fins are enlarged and fused to form the body disc. Dorsal and caudal fins may be reduced or absent.
Rays are often dimensioned by their width rather than length as they may accidentally loose parts of their long tails.
Rays have their gills on the undersides of their bodies, whereas many sharks have their gills on the sides.

Sharks have large oily livers which helps to keep then afloat. Rays lack this device, they are negatively buoyant and must swim to stay off the bottom. Those with larger wings, such as eagle rays and mantas are more likely to be seen in mid-water.