Cycloid scales are thin, overlap, and flexible. They're found on primitive teleosts (like minnows and carp).

Ctenoid scales have small, backwards pointed scales (known as cterns) make the fish more hydrodynamic and faster. They're found on Advanced Ctenoids (like perch and sunfish).

Ganoid scales are thick, diamond-shaped, and mostly non-overlapping. They're found on Chondrostei (like sturgeons and paddlefish).

Placoid scales are spikey and tooth-like with nerves. These are found on Chondrichthyes (like sharks and rays).