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Scale (anatomy)

December 02, 2023

For other uses, see Scale.

In most biological nomenclature, a scale (Ancient Greek: λεπίς, romanized: lepís; Latin: squāma) is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran (butterfly and moth) species, scales are plates on the surface of the insect wing, and provide coloration. Scales are quite common and have evolved multiple times through convergent evolution, with varying structure and function.

Keeled scales of a colubrid snake (banded water snake; Nerodia fasciata)

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 edit

Main article: Fish scale

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 edit

True cosmoid scales can only be found on the Sarcopterygians. The inner layer of the scale is made of lamellar bone. On top of this lies a layer of spongy or vascular bone and then a layer of dentine-like material called cosmine. The upper surface is keratin. The coelacanth has modified cosmoid scales that lack cosmine and are thinner than true cosmoid scales.

Ganoid scales edit

Ganoid scales can be found on gars (family Lepisosteidae), bichirs, and reedfishes (family Polypteridae). Ganoid scales are similar to cosmoid scales, but a layer of ganoin lies over the cosmine layer and under the enamel[clarification needed]. Ganoin scales are diamond shaped, shiny, and hard. Within the ganoin are guanine compounds, iridescent derivatives of guanine found in a DNA molecule.[2] The iridescent property of these chemicals provide the ganoin its shine.

Placoid scales edit

Placoid scales are found on cartilaginous fish including sharks and stingrays. These scales, also called denticles, are similar in structure to teeth, and have one median spine and two lateral spines. The modern jawed fish ancestors, the jawless ostracoderms and later jawed placoderms, may have had scales with the properties of both placoid and ganoid scales.

Leptoid scales edit

Leptoid scales are found on higher-order bony fish. As they grow they add concentric layers. They are arranged so as to overlap in a head-to-tail direction, like roof tiles, allowing a smoother flow of water over the body and therefore reducing drag.[3] They come in two forms:

  • Cycloid scales have a smooth outer edge, and are most common on fish with soft fin rays, such as salmon and carp.
  • Ctenoid scales have a toothed outer edge, and are usually found on fish with spiny fin rays, such as bass and crappie.

Reptilian scales edit

 
Brightly colored scales on a gold dust day gecko
Main article: Reptile 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 crocodilians and turtles, have osteoderms underlying the epidermal scale. Such scales are more properly termed scutes. Snakes, tuataras and many lizards lack osteoderms. All reptilian scales have a dermal papilla underlying the epidermal part, and it is there that the osteoderms, if present, would be formed.

Avian scales edit

 
Scales on talons of a Steller's sea eagle (Haliaeetus pelagicus)
Main article: Bird anatomy § 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 edit

 
Scale-covered Indian pangolin

An example of a scaled mammal is the pangolin. Its scales are made of keratin and are used for protection, similar to an armadillo's armor. They have been convergently evolved, being unrelated to mammals' distant reptile-like ancestors (since therapsids lost scales), except that they use a similar gene.

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 edit

 
Scales on a luna moth (Actias luna)
 
Generalized structure of a keeled, lanceolate scale from a jumping spider

Butterflies and moths - the order Lepidoptera (Greek "scale-winged") - have membranous wings covered in delicate, powdery scales, which are modified setae. Each scale consists of a series of tiny stacked platelets of organic material, and butterflies tend to have the scales broad and flattened, while moths tend to have the scales narrower and more hair like. Scales are usually pigmented, but some types of scales are iridescent, without pigments; because the thickness of the platelets is on the same order as the wavelength of visible light the plates lead to structural coloration and iridescence through the physical phenomenon described as thin-film optics. The most common color produced in this fashion is blue, such as in the Morpho butterflies.

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]

See also edit

References edit

  1. ^ Sharpe PT (September 2001). "Fish scale development: Hair today, teeth and scales yesterday?". Current Biology. 11 (18): R751–2. doi:10.1016/S0960-9822(01)00438-9. PMID 11566120. S2CID 18868124.
  2. ^ Levy-Lior A, Pokroy B, Levavi-Sivan B, Leiserowitz L, Weiner S, Addadi L (2008). "Biogenic guanine crystals from the skin of fish may be designed to enhance light reflectance". Crystal Growth & Design. 8 (2): 507–511. doi:10.1021/cg0704753.
  3. ^ Ballard B, Cheek R (2 July 2016). Exotic Animal Medicine for the Veterinary Technician. John Wiley & Sons. ISBN 978-1-118-92421-1.
  4. ^ Lucas AM (1972). Avian Anatomy - integument. East Lansing, Michigan, USA: USDA Avian Anatomy Project, Michigan State University. pp. 67, 344, 394–601.
  5. ^ Zheng X, Zhou Z, Wang X, Zhang F, Zhang X, Wang Y, Wei G, Wang S, Xu X (March 2013). "Hind wings in Basal birds and the evolution of leg feathers". Science. 339 (6125): 1309–12. Bibcode:2013Sci...339.1309Z. doi:10.1126/science.1228753. PMID 23493711. S2CID 206544531.
  6. ^ Sawyer RH, Knapp LW (August 2003). "Avian skin development and the evolutionary origin of feathers". Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 298 (1): 57–72. doi:10.1002/jez.b.26. PMID 12949769.
  7. ^ . Rainforest-Australia.com. Archived from the original on 2013-10-30. Retrieved 2014-03-08.
  8. ^ Fleming T, Macdonald D, eds. (1984). The Encyclopedia of Mammals. New York: Facts on File. p. 632. ISBN 0-87196-871-1.
  9. ^ Spearman RI (1973). The integument: a textbook of skin biology. Cambridge University Press. ISBN 978-0-521-20048-6.
  10. ^ Townsend, Victor R.; Felgenhauer, Bruce E. (1998). "Cuticular Scales of Spiders". Invertebrate Biology. 117 (4): 318. doi:10.2307/3227034. JSTOR 3227034.
  11. ^ Hill, David E. (22 October 2022). "Jumping spider scales (Araneae: Salticidae)" (PDF). Peckhamia. 279 (1): 1–83.

Further reading edit

December 02, 2023
scale, anatomy, other, uses, scale, most, biological, nomenclature, scale, ancient, greek, λεπίς, romanized, lepís, latin, squāma, small, rigid, plate, that, grows, animal, skin, provide, protection, lepidopteran, butterfly, moth, species, scales, plates, surf. For other uses see Scale In most biological nomenclature a scale Ancient Greek lepis romanized lepis Latin squama is a small rigid plate that grows out of an animal s skin to provide protection In lepidopteran butterfly and moth species scales are plates on the surface of the insect wing and provide coloration Scales are quite common and have evolved multiple times through convergent evolution with varying structure and function Keeled scales of a colubrid snake banded water snake Nerodia fasciata 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 Contents 1 Fish scales 1 1 Cosmoid scales 1 2 Ganoid scales 1 3 Placoid scales 1 4 Leptoid scales 2 Reptilian scales 3 Avian scales 4 Mammalian scales 5 Arthropod scales 6 See also 7 References 8 Further readingFish scales editMain article Fish scale nbsp Ganoid scales on a carboniferous fish Amblypterus striatus nbsp Placoid scales on a lemon shark Negaprion brevirostris nbsp 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 edit True cosmoid scales can only be found on the Sarcopterygians The inner layer of the scale is made of lamellar bone On top of this lies a layer of spongy or vascular bone and then a layer of dentine like material called cosmine The upper surface is keratin The coelacanth has modified cosmoid scales that lack cosmine and are thinner than true cosmoid scales Ganoid scales edit Ganoid scales can be found on gars family Lepisosteidae bichirs and reedfishes family Polypteridae Ganoid scales are similar to cosmoid scales but a layer of ganoin lies over the cosmine layer and under the enamel clarification needed Ganoin scales are diamond shaped shiny and hard Within the ganoin are guanine compounds iridescent derivatives of guanine found in a DNA molecule 2 The iridescent property of these chemicals provide the ganoin its shine Placoid scales edit Placoid scales are found on cartilaginous fish including sharks and stingrays These scales also called denticles are similar in structure to teeth and have one median spine and two lateral spines The modern jawed fish ancestors the jawless ostracoderms and later jawed placoderms may have had scales with the properties of both placoid and ganoid scales Leptoid scales edit Leptoid scales are found on higher order bony fish As they grow they add concentric layers They are arranged so as to overlap in a head to tail direction like roof tiles allowing a smoother flow of water over the body and therefore reducing drag 3 They come in two forms Cycloid scales have a smooth outer edge and are most common on fish with soft fin rays such as salmon and carp Ctenoid scales have a toothed outer edge and are usually found on fish with spiny fin rays such as bass and crappie Reptilian scales edit nbsp Brightly colored scales on a gold dust day geckoMain article Reptile 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 crocodilians and turtles have osteoderms underlying the epidermal scale Such scales are more properly termed scutes Snakes tuataras and many lizards lack osteoderms All reptilian scales have a dermal papilla underlying the epidermal part and it is there that the osteoderms if present would be formed Avian scales edit nbsp Scales on talons of a Steller s sea eagle Haliaeetus pelagicus Main article Bird anatomy 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 edit nbsp Scale covered Indian pangolinAn example of a scaled mammal is the pangolin Its scales are made of keratin and are used for protection similar to an armadillo s armor They have been convergently evolved being unrelated to mammals distant reptile like ancestors since therapsids lost scales except that they use a similar gene 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 edit nbsp Scales on a luna moth Actias luna nbsp Generalized structure of a keeled lanceolate scale from a jumping spiderButterflies and moths the order Lepidoptera Greek scale winged have membranous wings covered in delicate powdery scales which are modified setae Each scale consists of a series of tiny stacked platelets of organic material and butterflies tend to have the scales broad and flattened while moths tend to have the scales narrower and more hair like Scales are usually pigmented but some types of scales are iridescent without pigments because the thickness of the platelets is on the same order as the wavelength of visible light the plates lead to structural coloration and iridescence through the physical phenomenon described as thin film optics The most common color produced in this fashion is blue such as in the Morpho butterflies 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 See also editScale insect anatomy Armour anatomy Psoriasis a long lasting autoimmune disease characterized by patches of thin pieces of hard skin like scale References edit Sharpe PT September 2001 Fish scale development Hair today teeth and scales yesterday Current Biology 11 18 R751 2 doi 10 1016 S0960 9822 01 00438 9 PMID 11566120 S2CID 18868124 Levy Lior A Pokroy B Levavi Sivan B Leiserowitz L Weiner S Addadi L 2008 Biogenic guanine crystals from the skin of fish may be designed to enhance light reflectance Crystal Growth amp Design 8 2 507 511 doi 10 1021 cg0704753 Ballard B Cheek R 2 July 2016 Exotic Animal Medicine for the Veterinary Technician John Wiley amp Sons 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 Zheng X Zhou Z Wang X Zhang F Zhang X Wang Y Wei G Wang S Xu X March 2013 Hind wings in Basal birds and the evolution of leg feathers Science 339 6125 1309 12 Bibcode 2013Sci 339 1309Z doi 10 1126 science 1228753 PMID 23493711 S2CID 206544531 Sawyer RH Knapp LW August 2003 Avian skin development and the evolutionary origin of feathers Journal of Experimental Zoology Part B Molecular and Developmental Evolution 298 1 57 72 doi 10 1002 jez b 26 PMID 12949769 Musky Rat Kangaroo Rainforest Australia com Archived from the original on 2013 10 30 Retrieved 2014 03 08 Fleming T Macdonald D eds 1984 The Encyclopedia of Mammals New York Facts on File p 632 ISBN 0 87196 871 1 Spearman RI 1973 The integument a textbook of skin biology Cambridge University Press ISBN 978 0 521 20048 6 Townsend Victor R Felgenhauer Bruce E 1998 Cuticular Scales of Spiders Invertebrate Biology 117 4 318 doi 10 2307 3227034 JSTOR 3227034 Hill David E 22 October 2022 Jumping spider scales Araneae Salticidae PDF Peckhamia 279 1 1 83 Further reading editKardong KV 1998 Vertebrates Comparative Anatomy Function Evolution second ed USA McGraw Hill p 747 ISBN 978 0 697 28654 3 Retrieved from https en wikipedia org w index php title Scale anatomy amp oldid 1181888235, wikipedia, wiki, book, books, library,

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