placoid scale

fish anatomy

Also known as: denticle

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July 1, 2026

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Placoid scales are a type of scale found on cartilaginous fishes, such as sharks. These scales are bony, spiny projections that originate from the deeper layer of the skin (dermis) and are covered with an enamel-like substance. They are toothlike in appearance and structure, with a pulp cavity and layers of dentine and enamel. It is believed that true teeth may have evolved from placoid scales.123

In contrast, other fish have different types of scales: ganoid scales are bony with a ganoin covering, while cycloid and ctenoid scales are typical overlapping scales found in advanced bony fishes. Some fish, like certain eels and catfishes, lack scales altogether.12

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clupeiform
Distinguishing characteristics
The development of denticles (toothlike skin projections) and teeth represents another specialization of evolutionary importance. The most primitive clupeiform fishes have an enormous number of dermal denticles (on the head and in the mouth), which have been replaced in evolutionarily more-advanced forms by teeth, which are larger and…
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The development of denticles (toothlike skin projections) and teeth represents another specialization of evolutionary importance. The most primitive clupeiform fishes have an enormous number of dermal denticles (on the head and in the mouth), which have been replaced in evolutionarily more-advanced forms by teeth, which are larger and…
Read More

scale
, sharks) have placoid scales, which are bony, spiny projections with an enamel-like covering. Ganoid scales, which are found on such fishes as gars and the bowfin, are similar to placoid scales but are covered with a peculiar enamel-like substance called ganoin. It is thought that true teeth…
Read More
, sharks) have placoid scales, which are bony, spiny projections with an enamel-like covering. Ganoid scales, which are found on such fishes as gars and the bowfin, are similar to placoid scales but are covered with a peculiar enamel-like substance called ganoin. It is thought that true teeth…
Read More

integument
Fishes
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. These rather thick scales, present in some primitive bony fishes,…
Read More
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. These rather thick scales, present in some primitive bony fishes,…
Read More