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Denticles are body surface structures found on some fish and insects.
Fish
Denticles or placoid scales are small outgrowths which cover the skin of many cartilaginous fish including sharks. They are similar in structure to teeth, and teeth may have evolved from denticle-like structures in primitive fish. The shape of denticle varies from species to species and can be used in identification.
Shark skin is covered in denticles, and can therefore be as rough as sandpaper; some societies have in fact used it as such for many years (see Oroshigane). Sharks have been known to use their skin to inflict wounds on prey.
Insects
Denticles on insects are cuticular spikes projecting from body surface epithelial cells. The denticles of Drosophila larvae are present in bands on each body segment. During embryonic development, cells are directed to either make or not make a denticle depending on the pattern of expression of morphogens. The Wingless protein is produced by a stripe of cells (w, in the figure to right) in each segment. It is released from those cells and acts on nearby cells where it prevents denticle production resulting is a band of "naked cuticle".
See also
External links
Animal anatomy | ichthyology | Entomology
"Dermal denticle"