Placoid scales are tiny, hard, tooth-like structures, also called dermal denticles. They have the same structure as a tooth, having an outer layer of enamel, dentine and a central pulp cavity. Sharks' teeth and skin are composed of placoid scales.

(Gk: plax/placos=flat plate) small scales consisting of a hard base and a tooth-like backward projection, embedded in the skin of sharks.

These scales are found on sharks and many rays and chimaeras. They consist of a plate-like base just under the skin, with a spine projecting from the back of the plate onto the surface of the skin. Li [..]