Placoid scales are found in sharks and rays, and can vary greatly in external appearance. Unlike the scales of bony fishes, placoid scales do not increase in size as the fish grows, instead new scales are added between older scales.

What are Placoid cells?

Placoid scales are the tiny, tough scales that cover the skin of elasmobranches, or cartilaginous fish—this includes sharks, rays, and other skates. While placoid scales are similar in some ways to the scales of bony fish, they are more like teeth covered with hard enamel.

What is Placoid scale in fish?

Placoid scales (or denticles) are spiny, toothlike projections seen only in cartilaginous fishes. Ganoid scales, sometimes considered a modification of the placoid type, are chiefly bony but are covered with an enamel-like substance called ganoin.