What is the type of fish scales?

1. Cosmoid Scales: These are found in extinct fish like coelacanths and lungfish. They are thick and bony, covered by a layer of enamel-like substance called "cosmine."

2. Placoid Scales: These are the scales found in sharks, rays, and chimaeras. They are small, tooth-like structures embedded in the skin, with a pointed tip and a base that is attached to the skin.

3. Ganoid Scales: These are found in sturgeons, bichirs, and gar. They are rhombus-shaped, hard, and bony, and they overlap like roof tiles.

4. Cycloid and Ctenoid Scales: These are the most common types of scales found in bony fishes (teleosts). They are thin, flexible, and overlapping, and they are made of bone-like material called "ganoin."

* Cycloid scales are smooth and rounded, while ctenoid scales have small, comb-like teeth along their edges.

The type of scale a fish has can be a helpful characteristic for identifying the fish. For example, sharks have placoid scales, while most bony fishes have cycloid or ctenoid scales.