Explainer: What is a shark?

Picture a shark. You mightiness deliberation of a large achromatic stalking beachgoers successful a movie. Or possibly a hammerhead, with its distinctive T-shaped noggin. Or the extinct megalodon, the largest shark known to ever exist. But that’s conscionable a tiny illustration of the splendid diverseness of sharks swimming Earth’s oceans.

There are much than 500 surviving taxon of sharks, notes Heidy Martinez. She’s a freelance shark scientist and subordinate of Minorities successful Shark Sciences. Sharks scope successful size from the gentle elephantine whale shark — which tin scope up to 18.8 meters (61.7 feet) agelong — to the dwarf lantern shark, which is tiny capable to cradle successful the thenar of your hand. Most sharks are lone astir a metre (three to 4 feet) agelong oregon less.

One of Martinez’s favorites is the cooky cutter shark. This astir foot-long shark takes round, cookie-shaped bites retired of ample food similar tuna, marlin and adjacent different sharks. “They’re truthful tiny and they look truthful antithetic from … what you would think,” she says. Another shark she likes is the tiger shark, which volition devour beauteous overmuch thing and tin crook its tummy wrong retired to get escaped of the inedible bits.

“They’re each truthful antithetic from each other,” Martinez says. Yet galore radical don’t cognize astir the fascinating quirks of assorted shark species. They conscionable spot sharks arsenic scary.

Part of sharks’ fearsome estimation is earned. Sharks bash termination a fewer radical each twelvemonth (though you’re much apt to get deed by lightning than eaten by a shark). Media similar the classical movie Jaws — which depicted a large achromatic shark terrorizing a New England formation — has added to the animals’ atrocious rap.

But radical are a acold greater menace to sharks than the food are to people. Sharks, says Martinez, are “misunderstood.” Don’t deliberation of them arsenic killers but arsenic truly absorbing food with tons of crisp teeth.

A antithetic kettle of fish

Sharks beryllium to a people of food called Chondrichthyes. Fish successful this people person skeletons made not of bony but of cartilage. This cartilage, akin to the worldly that your receptor is made of, is little dense and much flexible than bone. This helps sharks not descend and aquatics faster. An oil-filled liver besides helps to support them afloat. (Fish with bones usage a gas-filled organ called a aquatics bladder for buoyancy.)

Beyond cartilage, 1 of the defining features of Chondrichthyes is having 5 to 7 pairs of gills. Bony food lone person 4 pairs. And, dissimilar bony fish, sharks indispensable ever beryllium moving to support oxygen-filled h2o moving implicit those gills truthful that they tin breathe.

Among Chondrichthyes, sharks are acceptable isolated by a fewer features. For one, each sharks stock a akin assemblage type: streamlined similar the assemblage of an airplane. A shark has astatine slightest 1 dorsal fin connected the apical of its body. This fin, on with pectoral fins connected its sides, assistance it maneuver done the water.

Sharks besides person keen senses that assistance marque them effectual predators. These see crisp eyes and a bully consciousness of smell. And sharks tin sense electrical fields. This quality is called electroreception. Sharks usage it to find prey and navigate murky waters.

If you were to favored a shark, “it feels similar sandpaper,” says Martinez. That’s due to the fact that shark tegument is covered with denticles. Denticles — which are besides recovered connected sharks’ cousins, skates and rays — are tiny, overlapping scales. As a shark swims forward, these scales flatten and trim drag, helping the shark aquatics with little energy. Denticles besides assistance forestall barnacles from attaching to a shark.

Skates and rays are besides members of Chondrichthyes. They are distinguished by their flat, wide bodies...