Sharks have a special valve inside their intestine that looks like a spiral staircase on its side. Spiral valves help sharks digest food by slowing its passage through their short, compact intestines. Large, oily livers give sharks some buoyancy. Shark skin looks and feels as though it is covered with tiny teeth. Shark skin is sometimes used as sandpaper.
Water flows out of the gill slits after passing over their gills.
The largest pelagic sharks are filter-feeders. These sharks strain small fishes, krill, larvae and other types of plankton out of the water. They eat huge quantities of tiny animals. Sharks are internal fertilizers. That means their eggs are fertilized in the female's body.