Question

Placoid scales are found in
A. Reptiles
B. Bony fishes
C. Cartilaginous fishes
D. Amphibians

Answer 1

The outer body of the fishes and reptiles are covered with scales. They are small, thin horny, or bony plates that act as a protection layer to the external body of fishes and reptiles. Scales are typically overlapping each other.

Complete answer: The external body of the fish is covered by a small rigid plate called fish scale. These scales grow out of the skin of the fishes. They are smooth and form a protective layer on the external body of fishes. They also provide effective camouflage through the use of coloration and reflection. The external body of reptiles is covered with epidermal scales. The horny harsh extensions of the stratum corneum form the epidermal scales.
-Bony fishes also have scales on the external body which are in the form of tiny flat disc set-in pockets. They form the transverse ridges on the skin.
-Placoid scales are found in cartilaginous fishes. Placoid scales are tooth-like scales that are distinct from the scales of other fishes. Some of the examples of cartilaginous fishes are sharks, rays, and other skates. -Amphibians do not possess scales on their external body.
So, option C is the correct option.

Note: Placoid scales do not grow after the organism is completely matured. Placoid scales grow from the dermis layer and hence are referred to as dermal denticles. Placoid scales are hard and rough to touch and form a structure that is nearly impossible to penetrate.