Snakeskin

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Snakeskin may either refer to the skin of a live snake, the shed skin of a snake after molting, or to a type of leather that is made from the hide of a dead snake. Snakeskin and scales can have varying patterns and color formations, providing protection via camouflage from predators. [1] The colors and iridescence in these scales are largely determined by the types and amount of chromatophores located in the dermis of the snake skin. [2] The snake's skin and scales are also an important feature to their locomotion, providing protection and minimizing friction when gliding over surfaces. [3] [4] [5] [6]

Contents

Skin of a living snake

In a living snake, its skin often deals with various forms of abrasion. To combat rough substrates, snakes have formed specialized and multilayered organizational epidermal structures to provide a safe and efficient sliding locomotion when maneuvering over rough surfaces. [7]

Display

The large scutes on the right side cover the ventral, or belly side of the snake. The smaller scales cover the rest of the snake. Note how the scales overlap. Iridescence on Garter Snake Scales.tif
The large scutes on the right side cover the ventral, or belly side of the snake. The smaller scales cover the rest of the snake. Note how the scales overlap.

Pattern formation

Snakes can be ornately patterned. They can be striped, banded, solid, green, blue, yellow, red, black, orange, brown, spotted, or have a unique pattern all their own. These color schemes can serve many functions, including camouflage, heat absorption or reflection, or may play other, less understood roles. Melanin cells in the skin often overlap and form complex patterns and sheets that are highly recognizable. [8] Sometimes the soft integument of a snake is colored differently than their hard scales. This is often utilized as a method of predator determent. [1]

Color and iridescence

The variation of scale colors as caused by different chromatophores, located on the dorsal (top) surface of a Garter snake. Dorsal View of Snake Scales.jpg
The variation of scale colors as caused by different chromatophores, located on the dorsal (top) surface of a Garter snake.

Coloration of snakes is largely due to pigment cells and their distribution. Some scales have lightly colored centers, which arise from regions with a reduced cuticle. A thinner cuticle indicates that some sensory organ is present. [2] Scales in general are numerous and coat the epidermis, and come in all shapes and colors. They are helpful in identification of snake species. Chromatophores in the dermis yield coloration when light shines through the corneal layer of the epidermis. [2] There are many kinds of chromatophores. Melanophores yield brown pigmentation, and when paired with guanophores, yield grey. When paired with guanophores and lipophores, yellow results. When guanophores and allophores are added to melanophores, red pigment results. [2] Carotenoids also help produce orange and red colors. [8] Dark snakes (dark brown or black in color) appear as such due to melanocytes that are active in the epidermis. When melanin is absent, albino individuals result. Snakes do not possess blue or green pigments, instead these arise from guanophores, which are also called iridocytes. Iridocytes reside in the dermis, and are responsible for the iridescent appearance of many dark-colored snakes. Males and females may show varied coloration, as might hatchlings and adults of the same species. [2]

Structures and function

Exposed integument of the garter snake after the overlying scales have been removed. Exposed Garter Snake Integument.tif
Exposed integument of the garter snake after the overlying scales have been removed.

Snakeskin, or integument, is more than just patterns and scales. Scales and patterning are features of snakeskin, and they are derived from a soft and complex integument. These scale patterns are unique to species, and the scales themselves help in locomoting by providing a friction buffer between the snake and the ground [1] [9]

Organization

Reptiles, including snakes, possess extensive keratinization of the epidermis in the form of epidermal scales. [10] A snake's epidermis is composed of four layers. The outer layer of a snake's skin is shed periodically, and is therefore a temporary layer, and is highly keratinized. Beneath the outer layer is the corneal layer (stratum corneum), which is thickened and flexible. Under the corneal layer is intermediary zone (stratum granulosum) and the basal layer (stratum basale), respectively. The dermis of a snake resides beneath the epidermis. [2] The dermis of snakes is generally fibrous in nature, and not very prominent. [10] The dermis houses pigment cells, nerves, and collagen fibers. Nerve fibers extend into the snake epidermis and anchor near scales, generally at the rostral, or head, end of the snake. Specifically, nerves anchor to sensory spines and pits, which are touch and thermal detection organs, respectively. The hypodermis is below the dermis, this layer mainly stores fat. [2]

Friction reduction and protection

Snakeskin is composed of a soft, flexible inner layer (alpha-layer), as well as a hard, inflexible outer surface (beta-layer). Snake bodies are in contact with a surface at all times, causing a large amount of friction. As a result, they have to both minimize friction in order to move forward, and generate their own friction in order to create enough propulsion to move. Scale and skin orientation accomplish this, as it has been demonstrated by studies of the nanostructures on their scales. Specifically, the inner alpha-layer contains alpha-keratins which serve as cytoskeletal proteins for a mechanical form of resistance against traction. [4] [7] [5] Additionally, to reduce friction some snakes polish their scales. They secrete an oil from their nasal passage, and then rub the secretion over the scales. This is done at varying intervals depending on the species of snake, sometimes frequently, other times only after shedding or molting. It is thought that scale polishing is used as a method of waterproofing, and it may also play a role in chemical messaging or friction reduction. [11] Lastly, scales and snake skin provide protection in the form of keratin. [4] It has been found, that beta-keratins aid in formation of scales, as the keratin proteins produce a pre-corneous layer of densely packed epidermal scales creating a thick corneous protective layer. [4] Parts of this keratin covering are shaved back to make the snake's scales, the less restricted portion of each scale overlapping the scale behind it. Between scales lies shaved back connecting material, also of keratin, also part of the epidermis. This material allows for the poised glide of the snake over rough stones or gritty sand. [12] [3] [5]

Exposed integument from the underside of a scute of a garter snake. Exposed Integument Under a Garter Snake Scute.tif
Exposed integument from the underside of a scute of a garter snake.

Permeability

Skin permeability may change seasonally in snakes to help with the problem of drying out. It is known that desert snakes have generally impermeable skins, and that aquatic snakes have a more permeable skin that can sometimes trap water to prevent drying out. Some snakes may change their environment throughout the year, and may subsequently change their skin's permeability as a result. For instance, aquatic snakes may latch on to more water if they are in an environment that is drying out by attracting a layer of water under their scales. [11]

Glands

Not many glands are present in snake skin. Most snake glands are holocrine glands, meaning that the gland's cells are secreted along with the substance the gland makes. These holocrine glands in snakes do not have their own blood supply, and thus lie closely with vascularized connective tissue. Snakes also possess glands that aid in attracting mates, and some marine snake species possess a salt gland that helps remove excess salt that they have consumed. [2] Most glands in reptiles are poorly understood due to their scarcity. [10]

Movement and flexibility

The skin that lies beneath snake's scales is also responsible for snakes' flexibility. [2] The regions between snake scales is made of soft integument called an alpha-layer, which is composed of alpha-keratin that allows for flexibility and movement. [10] [7] [4] Snake mobility is dependent on the skin's contact to a friction surface, the tribological behavior of the snake skin allows for quick and precise changes in direction. [6] For smooth gliding to occur, snakeskin is composed of sharp spines and interlocking longitudinal ridges. The snakeskin also contains highly organized 'micro-hairs' along the ventral (underneath) surface, oriented in a caudal (towards the back) direction. With both of these features, the snake is able to efficiently slide forward on surfaces of low friction, and create high friction when needing to retreat backwardly. [6]

Phylogeny

Snakes belong to a group of reptiles called the Lepidosauria, which are reptiles with overlapping scales. They further are grouped down into the Squamata, which includes all snakes and lizards, and all but two species of Lepidosauria that belong to the Rynchocephalia (the tuatara). The species belonging to both of these subgroups likewise share similar skin features with snakes, with unique adaptations and features, respectively. [10]

Shed skin

Close up of garter snake scales. Note the presence of soft integument, or skin, between the scales and how they overlap. Garter Snake Scales.tif
Close up of garter snake scales. Note the presence of soft integument, or skin, between the scales and how they overlap.

The molting of the skin occurs regularly in snakes. [1] Molting is common, and results in the entire outer layer of epidermis being lost. [10] In the case of snakes, it is called shedding or ecdysis. A new layer of epidermis is grown beneath the old. When it is finished, the snake secretes a fluid between the new skin and the old. The fluid gives the skin a silvery cast. Snakes will work their heads against rough surfaces until the old skin breaks. After which the snake can work itself out of it. A shed skin is much longer than the snake that shed it, as the skin covers the top and bottom of each scale. If the skin is shed intact, each scale is unwrapped on the top and bottom side of the scale which almost doubles the length of the shed skin. While a snake is in the process of shedding the skin over its eye, the eye may become milky. Scales over the snakes eyes harden, to be shed with the rest of the old skin. When the process is complete the snake emerges with its color deepened, the scales polished, the surfaces bright and undulled by contact with scratching brush, a total loss of vision completely restored. [1] [12]

Leather

Close-up of a patterned beige and brown snakeskin leather used to make a cigarette case Cigarette Case MET DP291213.jpg
Close-up of a patterned beige and brown snakeskin leather used to make a cigarette case

Snakeskin is used to make clothing such as vests, belts, boots or shoes or fashion accessories such as handbags and wallets, and is used to cover the sound board of some string musical instruments, such as the banhu, sanxian] or the sanshin.

Snake leather is regarded as an exotic product alongside alligator, crocodile, lizard, ostrich, emu, camel, among others. With crocodile and lizard leathers, it belongs to the category of reptile leathers, with a scaly appearance. There is evidence that the harvest in at least some species of snakes killed for the leather industry is unsustainable and carried out in violation of national legislation in source countries. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Skin</span> Soft outer covering organ of vertebrates

Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.

<span class="mw-page-title-main">Scale (zoology)</span> Small rigid plate that grows out of an animals skin

In zoology, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopterans, 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.

<span class="mw-page-title-main">Keratin</span> Structural fibrous protein

Keratin is one of a family of structural fibrous proteins also known as scleroproteins. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, and the outer layer of skin among vertebrates. Keratin also protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals. Excessive keratinization participate in fortification of certain tissues such as in horns of cattle and rhinos, and armadillos' osteoderm. The only other biological matter known to approximate the toughness of keratinized tissue is chitin. Keratin comes in two types, the primitive, softer forms found in all vertebrates and harder, derived forms found only among sauropsids.

<span class="mw-page-title-main">Integumentary system</span> Skin and other protective organs

The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the skin and its appendages, which act as a physical barrier between the external environment and the internal environment that it serves to protect and maintain the body of the animal. Mainly it is the body's outer skin.

<span class="mw-page-title-main">Chromatophore</span> Cells with a primary function of coloration found in a wide range of animals

Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast, have a class of cells called melanocytes for coloration.

<span class="mw-page-title-main">Keratinocyte</span> Primary type of cell found in the epidermis

Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer of the skin are sometimes referred to as basal keratinocytes. Keratinocytes form a barrier against environmental damage by heat, UV radiation, water loss, pathogenic bacteria, fungi, parasites, and viruses. A number of structural proteins, enzymes, lipids, and antimicrobial peptides contribute to maintain the important barrier function of the skin. Keratinocytes differentiate from epidermal stem cells in the lower part of the epidermis and migrate towards the surface, finally becoming corneocytes and eventually being shed, which happens every 40 to 56 days in humans.

<span class="mw-page-title-main">Epidermis</span> Outermost of the three layers that make up the skin

The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.

<span class="mw-page-title-main">Dermis</span> Layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues

The dermis or corium is a layer of skin between the epidermis and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided into two layers, the superficial area adjacent to the epidermis called the papillary region and a deep thicker area known as the reticular dermis. The dermis is tightly connected to the epidermis through a basement membrane. Structural components of the dermis are collagen, elastic fibers, and extrafibrillar matrix. It also contains mechanoreceptors that provide the sense of touch and thermoreceptors that provide the sense of heat. In addition, hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels, nerves and blood vessels are present in the dermis. Those blood vessels provide nourishment and waste removal for both dermal and epidermal cells.

<span class="mw-page-title-main">Skin condition</span> Any medical condition that affects the integumentary system

A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment.

<span class="mw-page-title-main">Stratum corneum</span> Outermost layer of the epidermis

The stratum corneum is the outermost layer of the epidermis. Consisting of dead tissue, it protects underlying tissue from infection, dehydration, chemicals and mechanical stress. It is composed of 15–20 layers of flattened cells with no nuclei and cell organelles.

<span class="mw-page-title-main">Crocodilian armor</span>

Crocodile armor consists of the protective dermal and epidermal components of the integumentary system in animals of the order Crocodilia.

Beta-keratin (β-keratin) is a member of a structural protein family found in the epidermis of reptiles and birds. Beta-keratins were named so because they are components of epidermal stratum corneum rich in stacked beta sheets, in contrast to alpha-keratins, intermediate-filament proteins also found in stratum corneum and rich in alpha helices. Because the accurate use of the term keratin is limited to the alpha-keratins, the term "beta-keratins" in recent works is replaced by "corneous beta-proteins" or "keratin-associated beta-proteins."

<span class="mw-page-title-main">Scute</span> Type of scale

A scute or scutum is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior portion of the mesonotum in insects as well as some arachnids.

<i>Loxocemus</i> Genus of snakes

Loxocemus bicolor, the sole member of the monotypic family Loxocemidae and commonly known as the Mexican python, Mexican burrowing python and Mexican burrowing snake, is a species of python-like snake found in Mexico and Central America. No subspecies are currently recognized. Analyses of DNA show that Loxocemus is most closely related to the true pythons and the sunbeam snakes.

<span class="mw-page-title-main">Stratum basale</span> Deepest layer of the five layers of the epidermis

The stratum basale is the deepest layer of the five layers of the epidermis, the external covering of skin in mammals.

<span class="mw-page-title-main">Gastrodermis</span> Layer of cells that line the gastrovascular cavity of Cnidarians

Gastrodermis is the inner layer of cells that serves as a lining membrane of the gastrovascular cavity in Cnidarians. It is distinct from the outer epidermis and the inner dermis and is primarily associated with the ventral side of Cnidarians. It is composed of specialized cells responsible for several vital physiological processes. The term is also used for the analogous inner epithelial layer of Ctenophores.

<span class="mw-page-title-main">Snake scale</span> Scales covering the skin of snakes

Snakes, like other reptiles, have skin covered in scales. Snakes are entirely covered with scales or scutes of various shapes and sizes, known as snakeskin as a whole. A scale protects the body of the snake, aids it in locomotion, allows moisture to be retained within, alters the surface characteristics such as roughness to aid in camouflage, and in some cases even aids in prey capture. The simple or complex colouration patterns are a property of the underlying skin, but the folded nature of scaled skin allows bright skin to be concealed between scales then revealed in order to startle predators.

<span class="mw-page-title-main">Stratified squamous epithelium</span> Tissue type

A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Although this epithelium is referred to as squamous, many cells within the layers may not be flattened; this is due to the convention of naming epithelia according to the cell type at the surface. In the deeper layers, the cells may be columnar or cuboidal. There are no intercellular spaces. This type of epithelium is well suited to areas in the body subject to constant abrasion, as the thickest layers can be sequentially sloughed off and replaced before the basement membrane is exposed. It forms the outermost layer of the skin and the inner lining of the mouth, esophagus and vagina.

<span class="mw-page-title-main">Human skin</span> Organ covering the outside of the human body

The human skin is the outer covering of the body and is the largest organ of the integumentary system. The skin has up to seven layers of ectodermal tissue guarding muscles, bones, ligaments and internal organs. Human skin is similar to most of the other mammals' skin, and it is very similar to pig skin. Though nearly all human skin is covered with hair follicles, it can appear hairless. There are two general types of skin, hairy and glabrous skin (hairless). The adjective cutaneous literally means "of the skin".

<span class="mw-page-title-main">Reptile scale</span> Scales covering the skin of Reptiles

Reptile skin is covered with scutes or scales which, along with many other characteristics, distinguish reptiles from animals of other classes. They are made of alpha and beta-keratin and are formed from the epidermis. The scales may be ossified or tubercular, as in the case of lizards, or modified elaborately, as in the case of snakes.

References

  1. 1 2 3 4 5 Mattison, Christopher (2007). The New Encyclopedia of Snakes. Princeton: Princeton University Press.
  2. 1 2 3 4 5 6 7 8 9 Bauchot, Roland (1994). Snakes: A Natural History. New York: Sterling Publishing Company.
  3. 1 2 Parker, H.W. (1977). Snakes - A Natural History Talks. London: Cornell University Press.
  4. 1 2 3 4 5 Toni, Mattia; Alibardi, Lorenzo (2007-02-01). "Alpha- and beta-keratins of the snake epidermis". Zoology. 110 (1): 41–47. doi:10.1016/j.zool.2006.07.001. ISSN   0944-2006. PMID   17169542.
  5. 1 2 3 Filippov, Alexander E.; Gorb, Stanislov N. (23 March 2016). "Modelling of the frictional behaviour of the snake skin covered by anisotropic surface nanostructures". Scientific Reports. 6: 23539. Bibcode:2016NatSR...623539F. doi:10.1038/srep23539. PMC   4804221 . PMID   27005001.
  6. 1 2 3 Yang, Zhe; Zhu, Liangliang; Li, Botong; Sun, Shuocheng; Chen, Youlong; Yan, Yuan; Liu, Yilun; Chen, Xi (2016-09-01). "Mechanical design and analysis of a crawling locomotion enabled by a laminated beam". Extreme Mechanics Letters. Nanomechanics: Bridging Spatial and Temporal Scales. 8: 88–95. doi: 10.1016/j.eml.2016.03.014 . ISSN   2352-4316.
  7. 1 2 3 Klein, Marie-Christin G.; Gorb, Stanislav N. (2012-11-07). "Epidermis architecture and material properties of the skin of four snake species". Journal of the Royal Society Interface. 9 (76): 3140–3155. doi:10.1098/rsif.2012.0479. ISSN   1742-5689. PMC   3479930 . PMID   22896567.
  8. 1 2 Mattison, Christopher (1995). The Encyclopedia of Snakes. London: Blandford.
  9. ↑ Martinez, Alejandro; Nguyen, Damon; Basson, Mandeep S.; Medina, Josh; Irschick, Duncan J.; Baeckens, Simon (2021). "Quantifying surface topography of biological systems from 3D scans". Methods in Ecology and Evolution. 12 (7): 1265–1276. doi:10.1111/2041-210X.13603. hdl: 10067/1774180151162165141 . ISSN   2041-210X. S2CID   235521715.
  10. 1 2 3 4 5 6 Kardong, Kenneth V. (2015). Vertebrates: Comparative Anatomy, Function, Evolution (7th ed.). New York: McGraw Hill. ISBN   9780078023026.
  11. 1 2 Mattison, Christopher (2007). The New Encyclopedia of Snakes. Princeton: Princeton University Press.
  12. 1 2 Campbell, Sheldon; Shaw, Charles E. (1974). Snakes of The American West. New York: Alfred A. Knopf. ISBN   978-0-394-48882-0.
  13. ↑ Nijman, Vincent (2022). "Harvest quotas, free markets and the sustainable trade in pythons". Nature Conservation. 48: 99–121. doi: 10.3897/natureconservation.48.80988 . ISSN   1314-3301.
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