Sharks have Placoid scales, also known as dermal denticles (skin teeth). This type of scale is unique to cartilaginous fishes. The scales themselves are like miniature teeth, each having dentine layer, a plum cavity, and an enamel. As the animal grows it gets more scales, the scale themselves don’t grow ( like with most bony fish). This is one reason that it is difficult to age a shark. The placoid scales on a shark all point the same direction (toward the tail), this makes the animal very hydrodynamic. This design is now being emulated in the swim suits for Olympic swimmers. The scales also protect the shark like a suit of armor. If you tough a shark head to tail it will feel relatively smooth, but if you touch it in the opposite direction it will feel very rough and sand paper-like, doing this on some species you may even cut your hand. Because of this quality shark skin was used as sandpaper in the past. Nurse shark skin was also used as leather due to its thickness and durability.
Writing by: Liesl Schindler