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Rays are most closely related to sharks and belong to the superoder Batoidea. The term "ray" is also used specifically for batoids in the order Rajiformes, the "true rays". Commonly the Rays include stingrays, skates, electric rays, guitarfishes and sawfishes. Rays are flat-bodied, and, like sharks, are a species of cartilaginous marine fish. Most rays have a flat, disk-like body, with the exception of the guitarfishes and sawfishes, while most sharks have a streamlined body.

Sharks are fish but unlike bony fish, they have a cartilaginous skeleton. Their bodies are streamlined and covered by the small tooth-like, dermal denticles protecting their skin from damage and parasites. They have several sets of replaceable teeth and five to seven gill slits. Sharks range in size from the small dwarf lanternshark, a deep sea species of only 7 in (17 cm) in length, to the whale shark, the largest fish of 39 ft (12 m) which filter feeds only on plankton, squid, and small fish.