cosmoid scale

In zoology, scales are small plates or shields that form part of the outer skin layers of certain animals, primarily offering protection from the environment and predators.1

Types of Scales in Fishes

• Cosmoid scales: Characteristic of extinct lungfishes, these scales have a hard, enamel-like outer layer, an inner layer of dentine called cosmine, and a layer of vascular bone. They are related to ganoid scales.234
• Placoid scales: Found in cartilaginous fishes like sharks, these are spiny, tooth-like projections made of bone with an enamel-like covering.13
• Ganoid scales: Present in fishes such as gars, these are bony scales covered with a substance called ganoin.13
• Cycloid scales: Typical of fishes like carp, these are thin, round or oval scales with visible growth rings.13
• Ctenoid scales: Similar to cycloid scales but with comblike teeth on their edges, found in fishes like perch.13

Some modern teleost fishes have scales made of bone, which are thinner and allow for more movement. Certain fish, like some catfishes and eels, lack scales altogether. Scales are a significant evolutionary feature in fishes, with their structure varying across different groups.23