The exoskeleton is sometimes absent but generally consists of overlapping cycloid or ctenoid scales.
The distinctions between cycloid and ctenoid scales, between placoid and ganoid fishes, are vague, and can hardly be maintained.
ctenoid scales have a comb-edge of fine prickles or cilia; cycloid scales have the edges smooth.
Louis Agassiz distinguished four kinds of scales—placoid, ganoid, cycloid and ctenoid.
A ctenoid scale differs in having its posterior margin pectinate.
There are two principal types of Teleostean scales, the cycloid and ctenoid.
In general, prickly points on the skin are modifications of ctenoid scales.
The cycloid and ctenoid scales of Teleosteans (see p. 105) are thin plates coated with epidermis.