Lepidotes pankowskii

Ganoid scale of Actinopterygian fish.

Ganoid scales are hard, shiny, diamond-shaped scales found in primitive fish such as sturgeons and gar. They are large plates that cover the body of the fish with a layer of hard enamel called ganoin, instead of the dentin and cosmine of the older cosmoid scales from which they are derived. These scales do not overlap like others, but rather fit together using peg-and-socket joints, forming armor that protects the fish from predators.