What makes shark skin so good?
Shark skin is made of a matrix of tiny, hard, tooth-like structures called dermal denticles or placoid scales. These structures are shaped like curved, grooved teeth and make the skin a very tough armor with a texture like sandpaper. They have the same structure as a tooth with an outer layer of enamel, dentine and a central pulp cavity. Unlike the scales of scales of bony fish (ctenoid scales) that get larger as the fish grows, placoid scales stay the same size. As the shark grows, it just grows more placoid scales. These scales also help the shark swim more quickly because their streamlined shapes helps decrease the friction of the water flowing along the shark’s body, by channeling it through grooves. Also, the shark’s skin is so rough that contact with it can injure prey. All of the spines of the denticles point backwards (towards the tail), so it would feel relatively smooth it you moved your hand from head to tail (but rough the other way). Sharks are mostly drably countershaded.
