This slide contains cycloid, ctenoid, and placoid fish scales. Cycloid and ctenoid scales are found in most bony fishes. Cycloid scales have a smooth posterior margin while ctenoid scales have a spiny posterior margin, resembling the teeth on a comb. Both of these scales increase in size as the fish grows. Placoid scales are found in cartilaginous fish like sharks and rays. Placoid scales vary greatly in appearance and do not increase in size as the fish grows.
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