Shark skin feels like sandpaper because it is covered in tiny tooth-like scales called denticles.

The longer version

Tiny scales cover nearly every part of the body, each shaped like a small curved tooth with a hard enamel-like outer layer. Their ridges lie in ordered lines that channel flow along the flanks, trimming drag and quieting turbulence, so swimming costs less than it otherwise would.

The surface feels smooth in one direction and rough in the other, which is why stroking forward and back gives such different results. The same texture discourages settlers from gripping. Unlike the plates of bony fish, these units are never shed but instead wear and are replaced continuously.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.