Scale (zoology)
In
Scales are generally classified as part of an organism's integumentary system. There are various types of scales according to shape and to class of animal.
Fish scales
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Ganoid scales on a carboniferous fish Amblypterus striatus
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Placoid scales on a lemon shark (Negaprion brevirostris)
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Cycloid scales on a common roach (Rutilus rutilus)
Fish scales are dermally derived, specifically in the mesoderm. This fact distinguishes them from reptile scales paleontologically. Genetically, the same genes involved in tooth and hair development in mammals are also involved in scale development.[1]
Cosmoid scales
True
has modified cosmoid scales that lack cosmine and are thinner than true cosmoid scales.Ganoid scales
Placoid scales
Leptoid scales
- .
- .
Reptilian scales
Reptile scale types include: cycloid, granular (which appear bumpy), and keeled (which have a center ridge). Scales usually vary in size, the stouter, larger scales cover parts that are often exposed to physical stress (usually the feet, tail and head), while scales are small around the joints for flexibility. Most snakes have extra broad scales on the belly, each scale covering the belly from side to side.
The scales of all reptiles have an epidermal component (what one sees on the surface), but many reptiles, such as
Avian scales
Birds' scales are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. The scales and scutes of birds were thought to be homologous to those of reptiles,[4] but are now agreed to have evolved independently, being degenerate feathers.[5][6]
Mammalian scales
An example of a scaled mammal is the
On the other hand, the musky rat-kangaroo has scales on its feet and tail.[7] The precise nature of its purported scales has not been studied in detail, but they appear to be structurally different from pangolin scales.
Anomalures also have scales on their tail undersides.[8]
Foot pad epidermal tissues in most mammal species have been compared to the scales of other vertebrates. They are likely derived from cornification processes or stunted fur much like avian reticulae are derived from stunted feathers.[9]
Arthropod scales
Some types of spiders also have scales. Spider scales are flattened setae that overlay the surface of the cuticle. They come in a wide variety of shapes, sizes, and colors. At least 13 different spider families are known to possess cuticular scales, although they have only been well described for jumping spiders (Salticidae) and lynx spiders (Oxyopidae).[10][11]
Some crustaceans such as Glyptonotus antarcticus have knobbly scales.[12] Some crayfish have been shown to use antennal scales that are activated in rapid response movements.[13]
See also
- Armour (zoology)
- Psoriasis: a long-lasting autoimmune disease characterized by patches of thin pieces of hard skin like scale.
References
- S2CID 18868124.
- .
- ISBN 978-1-118-92421-1.
- ^ Lucas AM (1972). Avian Anatomy - integument. East Lansing, Michigan, USA: USDA Avian Anatomy Project, Michigan State University. pp. 67, 344, 394–601.
- S2CID 206544531.
- PMID 12949769.
- ^ "Musky Rat Kangaroo". Rainforest-Australia.com. Archived from the original on 2013-10-30. Retrieved 2014-03-08.
- ISBN 0-87196-871-1.
- ISBN 978-0-521-20048-6.
- JSTOR 3227034.
- ^ Hill, David E. (22 October 2022). "Jumping spider scales (Araneae: Salticidae)" (PDF). Peckhamia. 279 (1): 1–83.
- S2CID 9216365.
- . Retrieved 5 January 2024.
Further reading
- Kardong KV (1998). Vertebrates: Comparative Anatomy, Function, Evolution (second ed.). USA: ISBN 978-0-697-28654-3.