Sharks and rays are both cartilaginous fish, but a ray is identified by two things a shark never has: gill slits on the underside of the body, and pectoral fins fused to the head to form a flat disc.
The class they share is Chondrichthyes, which also holds the chimaeras, and a 2016 review of the group counted roughly 1,200 living species: a little over 500 sharks, a little over 600 rays and skates, and about 50 chimaeras. The split between sharks and rays is not a matter of shape — several sharks are flatter than several rays — but of where the gills open and how the fins attach.
- Living cartilaginous fishesAbout 1,200 species
- Rays and skates among themJust over 600
- The test that always worksGill slits: side for sharks, underside for rays
On this page
What "cartilaginous fish" actually covers
Chondrichthyes is the class of fishes whose skeletons are cartilage rather than bone, strengthened in places by a crust of mineral prisms instead of solid bone tissue. It holds three living groups: the sharks, the batoids — rays, skates, sawfishes, guitarfishes and torpedo rays — and the chimaeras, the deep-water ratfishes that most people never see. A review published in 2016 put the total at about 1,200 valid species, and new ones are described most years.
Two claims in the older version of this page need dropping. The first is that sharks and rays are the only animals with cartilaginous skeletons: the chimaeras have one too, and so do the lampreys and hagfishes, which sit outside the jawed vertebrates altogether. The second is the figure of 440 sharks. The described total passed 500 some years ago, and the eight living orders between them now hold more than that.
It is also worth being precise about the word species. Sharks and rays are not "two species" — they are two large groups, each holding hundreds. Within the subclass Elasmobranchii, sharks sit in the superorder Selachimorpha and rays in Batoidea, and the modern molecular evidence puts the batoids firmly inside the elasmobranch tree rather than beside it. If you want the ladder of ranks in full, the shark taxonomy guide lays it out.
How to tell a shark from a ray in one look
Start with the gills. A shark's gill slits open on the sides of the head, in a row behind the eye; a ray's open on the underside of the body, flanking the mouth. That single character sorts every elasmobranch alive and it does not care what shape the animal is.
The second test is the pectoral fins. In a ray they are fused to the side of the head and run forward past the eye, which is what makes the disc. In a shark they hang free under the body and you can see daylight between the fin and the head. Rays also lack an anal fin entirely, and their eyes usually sit on top of the head while the mouth sits underneath.
This matters because shape is unreliable in both directions. Angel sharks are flatter than many rays, with broad wing-like pectorals and a habit of lying buried in sand, and they are sharks: lateral gill slits, free fins. Wobbegongs are flattened carpet sharks that sit on the reef looking like something a ray would produce. In the other direction, the sawsharks and the sawfishes carry nearly the same toothed rostrum, and only the gills tell you that one is a shark and the other a ray.
Size is no guide either. Rays run from palm-sized skates to the giant manta, whose disc reaches about seven metres across — bigger than most sharks in the sea.
Breathing: why a ray can lie still and most sharks cannot
Both groups pull oxygen out of the water across gills held on cartilage arches, and neither has the hinged plate that covers a bony fish's gills. Each slit opens to the outside on its own. The difference is the route the water takes in.
A ray lying on the bottom has its mouth pressed into sand, so drawing water in through it would mean drawing in the sand as well. Instead it uses the spiracles, a pair of openings behind the eyes on the top of the head that are the reduced remains of a gill slit. Water goes in through the spiracles, over the gills, and out through the ventral slits. That is why a ray can stay motionless on the seabed for hours without suffocating.
Sharks are split on the same problem. Bottom-dwellers — nurse sharks, wobbegongs, angel sharks — keep large spiracles and pump water with the muscles of the throat, which is why you find them lying under ledges all day. Fast open-water species such as the shortfin mako have small spiracles or none, and rely on ram ventilation: they swim with the mouth open and let their own speed push water through. The two methods are not exclusive, and a number of species switch between them.
Swimming, and the speed figures that do not hold up
Rays swim with the disc. Eagle rays and mantas flap their pectoral fins like wings, an up-and-down oscillation that looks like slow flight; stingrays and skates pass a wave down the edge of the disc instead and skim along the bottom. The tail steers, and in most rays it carries no propulsive fin at all.
Sharks swim with the tail. The body flexes side to side, the caudal fin supplies the thrust, and the pectorals act as control surfaces that set the angle of attack. The shape of the fins follows the job: a tall, nearly symmetrical tail on fast open-water hunters, a long low one on reef sharks that need to turn rather than sprint.
The speeds in the old version of this page do not survive checking. Rays were credited with a cruise of 9 mph and a top speed of 22 mph, and no published measurement supports either. Sharks were said to reach 25 mph as a rule, with makos at 60 mph; the best evidence for the fastest sharks puts the shortfin mako's burst somewhere around 45 to 70 km/h, which is 30 to 45 mph, and ordinary cruising for almost every shark at a few kilometres an hour. Sixty miles an hour is a number that has been copied between websites, not recorded by an instrument.
Feeding, defence and who eats whom
Most rays feed on the bottom. Their teeth are flattened into crushing plates that break open crabs, clams and snails, and a stingray hunting in sand will blow jets of water to uncover buried prey. The mantas and devil rays went the other way and filter plankton, the same trade the whale shark and the basking shark took up independently. Sharks cover far more ground: crushing plates in the Port Jackson shark, needle teeth for gripping fish in the sand tiger, serrated blades in the tiger shark.
Defence is where the two groups diverge most sharply, because rays get eaten. A stingray's tail spine is venomous rather than poisonous — the distinction is whether the animal delivers the toxin or you have to eat it — and it is a serrated barb backed by a venom gland, used against something attacking from above. Electric rays generate a discharge strong enough to stun prey and see off a predator. Skates and stingrays also bury themselves, which works on everything except a shark reading electric fields through its ampullae of Lorenzini.
The predator they are hiding from is often a shark. The great hammerhead specialises in rays, pinning them against the bottom with the flat of its head. And the old claim that large sharks have no predators but people is not right either: killer whales kill white sharks, and the list of things that eat sharks is longer than it looks.
Frequently asked questions
What is a cartilaginous fish?
A fish whose skeleton is cartilage rather than bone. The group is the class Chondrichthyes, and it contains the sharks, the rays and skates, and the chimaeras or ratfishes. A 2016 review counted about 1,200 living species. The cartilage is stiffened in places by a surface crust of mineral prisms rather than replaced by bone.
What is the main difference between a shark and a ray?
Where the gills open and how the pectoral fins attach. A shark's gill slits are on the sides of the head and its pectoral fins hang free beneath the body. A ray's gill slits are on the underside and its pectoral fins are fused to the head to form a disc. Rays also have no anal fin.
Are sharks and rays related?
Closely. Both sit in the subclass Elasmobranchii, sharks in the superorder Selachimorpha and rays in Batoidea, and molecular work places the batoids inside the elasmobranch tree rather than as a separate branch beside it. They share the cartilage skeleton, the multiple gill slits, the placoid scales and the electroreceptive pores.
Do rays breathe differently from sharks?
They use the same gills but a different inlet. A ray on the seabed draws water in through the spiracles on top of its head and out through the gill slits underneath, so sand is not pulled in with it. Bottom-dwelling sharks do the same thing; fast open-water sharks ram water in through the open mouth instead.
Which is bigger, a shark or a ray?
Neither group wins outright. The whale shark is the largest fish alive at about 12.6 metres measured, but the giant manta reaches roughly seven metres across the disc, which is larger than the great majority of sharks. At the small end both groups have species that fit in a hand.
Why are some sharks mistaken for rays?
Because several have gone flat for the same reason rays did. Angel sharks and wobbegongs are ambush hunters that lie on the seabed with broad pectoral fins and a wide head, and sawsharks carry almost the same toothed snout as a sawfish. Checking whether the gill slits are on the side or underneath settles every one of these cases.
Do sharks eat rays?
Regularly. The great hammerhead is the best-known specialist, using the flat of its head to pin a stingray against the bottom, but bull sharks, tiger sharks and several large requiem sharks take rays as well. Buried rays are still detectable through the ampullae of Lorenzini, which read the electric field of a hidden animal.
Is a stingray's barb poisonous or venomous?
Venomous. Poison has to be eaten or absorbed; venom is injected, and a stingray's tail spine is a serrated barb backed by glandular tissue that delivers toxin into a wound. The spine points backwards and is used against something pressing down from above, which is why shuffling rather than stepping matters in shallow water.
References
A small team focused on researching sharks and making marine biology easy to understand. Every page is reviewed against current species records and the SharkSider attack database, and updated when new incidents or research appear.
Published September 19, 2016 · Last updated September 23, 2026 · Filed under Cool Shark Facts.
