Even so, most sharks must swim constantly or they will sink. Teeth and scales. A shark's mouth is on the underside of the head among all species except the angel, megamouth, whale, and wobbegong sharks. The mouth of these sharks is at the front of the head. A shark has several rows of teeth.
Some sharks have molarlike grinding teeth.
Others have razorlike cutting teeth, and still others have pointed teeth. Some people believe that sharks must turn over on their back to bite, but this is not true. Small, toothlike scales cover a shark's body. These placoid scales make the skin of a shark very rough. Dried sharkskin, called shagreen, was once used as sandpaper.