Question

What is difference between placoid and cycloid scales?

Answer 1

Placoid scales:

1. These are triangular, rough structures on the fish cartilage.
2. These are seen in cartilaginous fish like sharks.

Cycloid scales:

1. These are round flexible structures present in bony fish.
2. These are commonly found in bony fishes.

Placoid scales	Cycloid scales
1. These are found only in Elasmobranch fishes	1. These are found in bony fishes.
2. Placoid itself suggests they are tiny, sharp like structures.	2.They did not have sharp pointed structures
3. These are present in sharks, rays, etc	3. Theses are seen in fishes like salmon and carp
4.They are hard and tough.	4. They are flexible.
5. They protect injury and can kill prey	5. They give protection against predators.