Placoid scales

 

 

Placoid scales are found in the cartilaginous fishes . They are also called dermal denticles. Placoid scales are structurally homologous with vertebrate teeth, having a central pulp cavity supplied with blood vessels, surrounded by a conical layer of dentine, all of which sits on top of a rectangular basal plate that rests on the dermis. The outermost layer is composed of vitrodentine, a largely inorganic enamel-like substance. Placoid scales cannot grow in size, but rather more scales are added as the fish increases in size.

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