Scale (zoology)

In zoology, a scale is a small, rigid plate that grows out of an animal's skin to provide protection. Scales are present in a variety of animals, primarily vertebrates, but also in some invertebrates. They serve multiple functions including physical protection from predators, abrasion, and desiccation, as well as aiding in locomotion in some species.

Scales are typically composed of bone, dentine, enamel, or keratin, depending on the group of animal. Fish scales are commonly made of bone or dentine, while reptile scales are primarily composed of keratin.

Different types of scales exist, and their classification varies depending on the animal group being studied. However, some common types include:

• Placoid scales: Found in cartilaginous fishes such as sharks and rays. They are tooth-like in structure and composed of dentine and enamel.

• Ganoid scales: Found in some primitive bony fishes. These are thick, rhomboid-shaped scales covered with a layer of ganoin, a hard, enamel-like substance.

• Cycloid scales: Thin, flexible, and circular scales found in many bony fishes. They have smooth edges.

• Ctenoid scales: Similar to cycloid scales but with comb-like serrations along their posterior edge. These are also found in many bony fishes.

• Reptilian scales: Composed of keratin and may be granular, keeled, or smooth depending on the species. They often overlap, providing flexible armor.

The arrangement and morphology of scales can be important characteristics for identifying and classifying different animal species. Scale patterns and coloration can also play a role in camouflage and species recognition. The study of scales is called lepidology, particularly when dealing with fish scales.