Most fish are protected by scales, overlapping bony plates that cover all or part of the body. Scales come in four forms: placoid, cycloid, ctenoid, and ganoid. Ctenoid scales have small points on the surface and are rough to the touch. These and smooth, rounded cycloid scales are most common among modern fishes. Some less highly developed fishes have tough ganoid scales, while sharks and many rays have placoid scales, sharp and toothlike.