1. Cosmoid scales: These are the most primitive type, found in extinct fish like the Coelacanths and some lungfish. They are thick and bony, with a layer of dentin and enamel on top.
2. Placoid scales: These are the scales found in sharks, rays, and chimaeras. They are small, tooth-like structures embedded in the skin and covered with enamel.
3. Ganoid scales: These scales are thick and rhombic (diamond-shaped) with a layer of ganoine (a hard enamel-like substance) over the bony base. They are found in sturgeons, gar, and bichirs.
4. Cycloid scales: These are thin, overlapping, and circular or oval-shaped scales with a smooth edge. They are found in many bony fish, such as carp, salmon, and trout.
5. Ctenoid scales: Similar to cycloid scales, but with tiny spines or teeth along the posterior edge. They are found in perch, bass, and many other bony fish.