A stingray is not a shark, but the two are closely related. They belong to the same group of fishes called elasmobranchs, members of the group Elasmobranchii, a subclass of Chondrichthyes, which also includes skates.
There are about 1,000 total species of the ocean- and freshwater-dwelling elasmobranchs in existence. All have skeletons made of cartilage rather than bone, several rows of teeth that are constantly replaced and five to seven gill slits. While rays are very similar to sharks on the inside, as a general rule, their gill slits are on the bottom, while a shark's are on the side.