Dictionary:

scale¹

  (skāl)

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1. 1. One of the many small platelike dermal or epidermal structures that characteristically form the external covering of fishes, reptiles, and certain mammals.
   2. A similar part, such as one of the minute structures overlapping to form the covering on the wings of butterflies and moths.
2. Pathology. A dry thin flake of epidermis shed from the skin.
3. A small thin piece.
4. Botany. A small, thin, usually dry, often appressed plant structure, such as any of the protective leaves that cover a tree bud or the bract that subtends a flower in a sedge spikelet.
5. 1. A scale insect.
   2. A plant disease or infestation caused by scale insects.
6. 1. A flaky oxide film formed on a metal, as on iron, that has been heated to high temperatures.
   2. A flake of rust.
7. A hard mineral coating that forms on the inside surface of boilers, kettles, and other containers in which water is repeatedly heated.

1. To clear or strip of scale or scales: Scale and clean the fish.
2. To remove in layers or scales: scaled off the old paint.
3. To cover with scales; encrust.
4. To throw (a thin flat object) so that it soars through the air or skips along the surface of water.
5. Dentistry. To remove (tartar) from tooth surfaces with a pointed instrument.
6. Australian.
   1. To cheat; swindle.
   2. To ride on (a tram or train, for example) without paying the fare.

1. To come off in scales or layers; flake.
2. To become encrusted.

[Middle English, from Old French escale, of Germanic origin.]

The fundamental unit of the primary scaled integument of vertebrates, of which the epidermal or dermal component may be the more conspicuous or elaborated. Although there is great diversity in detailed structure among vertebrate groups, scaled integuments may be interpreted as the most effective way of producing a physically strong external body surface, with maximum flexibility necessitated by the fundamental pattern of vertebrate locomotion relying on lateral sinusoidal movements of the body.

In the majority of extant fish the epidermis is extremely thin. The term “scale” when used in an ichthyological context usually refers to the relatively large, prominent, dermal ossification, on the outer surface of which lie so-called dental tissues. The latter—enamel or enamellike mineralizations and dentine—are therefore present at the dermoepidermal boundary. The scaled integument of fish shows a definite pattern which is governed by the orientation of the underlying myomeres and by changes in body depth and length. The general evolutionary tendency toward thinning, or size reduction, of integumentary sclerifications seen in various fish lineages is probably associated with weight reduction and increased locomotor efficiency.

Scaled integuments are absent from modern amphibians, although nonoverlapping dermal ossifications are seen in some apodans. It seems probable that the absence of scales in other modern species is associated with the secondary utilization of the integument as a respiratory surface. In most reptilian lineages, there is a ubiquity of scaled integuments, with or without dermal ossifications, but always with elaboration of epidermal tissues. The distribution of keratinaceous protein types varies in different groups of reptiles, and in this respect modern crocodilian scales exactly resemble the leg scales of birds. Scaled integuments prompted the subclass name for lepidosaurs—the tuatara, lizards, and snakes, the last two constituting the order Squamata. Lepidosaurian scales may or may not possess dermal ossifications. Among extant reptiles the extraordinary development of the dermal skeleton in turtles forms the characteristic carapace.

v. A technique by which the scales are removed from the skin of a fish, generally using a dull knife or a special kitchen tool called a fish scaler.

verb

To remove the skin of: decorticate, pare, peel, skin, strip¹. See put on/take off.

The removal of calcareous deposits from the teeth using suitable instruments.

1. removal of tartar from teeth. See also ultrasonic tooth scaling, tartar scraper.
2. in statistical terms the changing of the scale on which a variable is measured, usually to match the scaling of another lot of data and simplify comparison.

1. A small, often dry, leaf or bract.
2. A small inconspicuous sucking insect. There are hundreds of kinds of scale insects. They are serious pests of trees and shrubs, especially in mild climates.

Keeled scales of a colubrid snake

In most biological nomenclature, a scale (Greek lepid, Latin squama) 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. Scales are quite common and have evolved multiple times with varying structure and function.

There are various types of scales according to shape and to class of animal.

Structure

Scales are generally classified as part of an organism's integumentary system.

Fish scales

Scales of Rohu - Labeo rohita

Cosmoid scales

True cosmoid scales can only be found on the extinct Crossopterygians. 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 dentinelike 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

Ganoid scales can be found on gars (family Lepisosteidae) and 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. They are diamond-shaped, shiny, and hard

Placoid scales

Placoid scales are found on cartilaginous fish and sharks. These scales, also called denticles, are similar in structure to teeth.

Leptoid scales

Leptoid scales are found on the higher bony fishes and come in two forms, ctenoid and cycloid scales.

Cycloid scales

Cycloid scales have a smooth outer edge, and are most common on more primitive fish with soft fin rays, such as salmon and carp.

Ctenoid scales

Ctenoid scales have a toothed outer edge, and are usually found on more derived fishes with spiny fin rays, such as bass and crappie.

As they grow, cycloid and ctenoid scales add concentric layers. The scales of bony fishes are laid so as to overlap in a head-to-tail direction, a little like roof tiles, allowing a smoother flow of water over the body and therefore reducing drag.

Reptilian scales

Main article: snake scales

Reptile scale types include: cycloid, granular (which appear bumpy), and keeled (which have a center ridge).

Arthropod scales

Butterfly and moth species of the order Lepidoptera (Greek "scale-winged") have membranous wings covered in delicate, powdery scales. Each scale consists of a series of tiny stacked platelets of organic material. 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.

Bibliography

• Kardong, Kenneth V. (1998). Vertebrates: Comparative Anatomy, Function, Evolution, second edition, USA: McGraw-Hill, 747 pp.. ISBN 0-07-115356-X/0-697-28654-1. 

References

Integumentary system
structures	Skin • Sweat glands • Sebaceous glands • Hair (Hair follicle) • Nails • Scale
layers	Epidermis (Stratum corneum, Stratum lucidum, Stratum granulosum, Stratum spinosum, Stratum germinativum/basale) • Dermis • Subcutis

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