SHARK SKIN (DERMAL DENTICLES)

the following is information from
​Rory Cooper, Animal and Plant Sciences, The University of Sheffield

Sharks, skates and rays (of the subclass Elasmobranchii) possess small, tooth-like scales known as denticles. Evidence from the fossil record Indicates these ‘skin-teeth’ arose roughly 450 million years ago(1).
​

STRUCTURE

Denticles are structurally very similar to the teeth of other vertebrates, consisting of a pulp cavity,
​surrounded by layers of dentine and enamel-like tissue.

Denticles have evolved to FULFILL a diverse range of roles, meaning their shape varies both within and between different species.
Examples of their functions include:

Drag reduction

Shark denticles reduce the backflow of water that results from fast forward motion, thereby limiting drag. This makes swimming more efficient, meaning they can move faster and further using less energy (2).
Alizarin red stained denticles of the small spotted catshark (Scyliorhinus canicula) – Rory Cooper (The University of Sheffield)

aRMOUR

Certain species use these denticles for protection. For example, the female catshark has a region of enlarged denticles on the pectoral fins, which
protects her from the male’s biting behaviour during mating (3).
CT render of the juvenile catshark head – Scanned by Dr. Kyle Martin (Imaging and Analysis Centre, Natural History Museum, London) and rendered by Rory Cooper (The University of Sheffield)

cOMMUNICATION

Denticles of some shark species have evolved to accommodate bioluminescent algae. These glowing organisms enable sharks of the same species to recognize each other and group together (4).​
Scanning electron microscope (SEM) image of juvenile catshark denticles – Rory Cooper (The University of Sheffield) 

HATCHING

Shark embryos possess two rows of enlarged denticles along their back. When ready to hatch, they dig these units into the inside of their egg case and use their body as a ratchet to emerge (5).
CT render of the juvenile catshark head – Scanned by Dr. Kyle Martin (Imaging and Analysis Centre, Natural History Museum, London) and rendered by Rory Cooper (The University of Sheffield)

FEEDING

Juvenile catsharks have enlarged denticles close to their anal fins. This enables them to anchor pray with their tales, whilst simultaneously removing chunks of flesh with their teeth (6).
SEM of hatchling shark teeth (Rory Cooper, The University of Sheffield)

what is piebald?

A piebald or "pied" animal is one that has a pattern of dark spots on an unpigmented (white) background of scales (or hair/feathers, depending the animal). The pigmented spots are usually a black color. 

Shark denticle inspired design

The drag reductive properties of shark denticles are attractive to industries aiming to improve
the efficiency of locomotion. For example, shark skin inspired materials have been
manufactured by Speedo for use in swimming competitions. Scientists and engineers are also
examining whether denticle inspired design could improve the efficiency of aeroplanes and
boats, by reducing fuel costs and increasing speed (2).

references

  1. Sansom, I. J., Smith, M. M. & Smith, P. Scales of thelodont and shark-like fishes from the Ordovician of Colorado. Nature 379, 628–630 (1996).
  2. Dean, B. & Bhushan, B. Shark-skin surfaces for fluid-drag reduction in turbulent flow: a review. Philos. Trans. A. Math. Phys. Eng. Sci. 368, 4775–806 (2010).
  3. Crooks, N., Babey, L., Haddon, W. J., Love, A. C. & Waring, C. P. Sexual Dimorphisms in the Dermal Denticles of the Lesser-Spotted Catshark, Scyliorhinus canicula (Linnaeus, 1758). PLoS One 8, e76887 (2013).
  4. Reif, W.-E. Functions of Scales and Photophores in Mesopelagic Luminescent Sharks. Acta Zool. 66, 111–118 (1985).
  5. Grover, A. C. Juvenile denticles of the swell shark Cephaloscyllium ventriosum: function in hatching. Can. J. Zool. 52, 359–363 (1974).
  6. Southall, E. J. & Sims, D. W. Shark skin: a function in feeding. Proc. R. Soc. B Biol. Sci. 270, S47–S49 (2003).