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Denticles are body surface structures found on some fish and insects.

Denticles or placoid scales are small outgrowths
Scale (zoology)

In most biology nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration....
 which cover the skin of many cartilaginous fish including shark
Shark

Sharks are a type of fish with a full Cartilage skeleton and a highly Streamlines, streaklines and pathlinesd body. They respire with the use of five to seven gill slits....
s. They are similar in structure to teeth, and teeth may have evolved from denticle-like structures in primitive fish. The placoid scales in sharks are formed of dentine with dermal papillae located in the core.






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Denticles are body surface structures found on some fish and insects.

Denticles or placoid scales are small outgrowths
Scale (zoology)

In most biology nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration....
 which cover the skin of many cartilaginous fish including shark
Shark

Sharks are a type of fish with a full Cartilage skeleton and a highly Streamlines, streaklines and pathlinesd body. They respire with the use of five to seven gill slits....
s. They are similar in structure to teeth, and teeth may have evolved from denticle-like structures in primitive fish. The placoid scales in sharks are formed of dentine with dermal papillae located in the core. These scales develop from the dermal layer of the skin, which is in contrast to the epidermal development seen in the elasmoid scales of tetrapods. 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
Sandpaper

Sandpaper is a form of paper where an abrasive material has been fixed to its surface.Sandpaper is part of the "coated abrasives" family of abrasive products....
; some societies have in fact used it as such for many years (see Oroshigane
Oroshigane

Oroshigane , also known as oroshiki are graters for use in the Cuisine of Japan.These oroshigane differ significantly from Western world-style graters, as they produce a much finer grating....
). Most point backward, so stroking a shark from head to tail produces a smooth feeling. However, stroking the skin in the opposite direction reveals the rough texture. An exception is the Basking Shark
Basking shark

The basking shark, Cetorhinus maximus, is the second largest living fish, after the whale shark. It is a cosmopolitan species ? it is found in all the world's temperate oceans....
 (Cetorhinus maximus), which is unique amongst sharks in having denticles which point every which way, rather than uniformly towards the tail. Sharks have been observed to use their skin to inflict wounds on prey.

Studies have found that the denticles create tiny vortices
Vortex

A vortex is a Rotation, often Turbulence,flow of fluid. Any spiral motion with closed Streamlines, streaklines and pathlines is vortex flow....
 that reduce drag to make swimming more efficient. Denticles also allow sharks to swim silently compared to other fish that generate considerable noise when they ply the water.

In Japan
Japan

Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south....
, traditional swordsmiths used shark skin for the hand-grips of swords
Katana

A Japanese sword, or , is one of the traditional bladed weapons of Japan. These are categorised in several types according to size and method of manufacture....
, to make them less likely to slip in the hand. By applying the skin so that the denticles point toward the blade, the wielder will be able to quickly grip the sword even loosely and still get a grip.

See also

  • Odontode
    Odontode

    Odontodes, or dermal teeth, are hard structures found on the external surfaces of animals or near internal openings. They are comprised of a soft pulp surrounded by dentine and covered by a mineralized substance such as tooth enamel, a structure similar to that of tooth....
  • Hedgehog (cell signaling)
  • Dentin
    Dentin

    Dentin is a calcified tissue of the body, and along with tooth enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp....


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