EVERYDAY SCIENCE

Detailed explanation-1: -Placoid scales (or denticles) are spiny, toothlike projections seen only in cartilaginous fishes. Ganoid scales, sometimes considered a modification of the placoid type, are chiefly bony but are covered with an enamel-like substance called ganoin. These rather thick scales, present in some primitive bony fishes, …

Detailed explanation-2: -Placoid denticles are found on sharks, rays, and chimaeras. Not really a true “scale, ” like ctenoid or cycloid scales, placoid denticles are actually modified teeth. They have an inner tissue component, which contains both blood vessels and nerves, that is covered by a layer of dentin and an outer enamel.

Detailed explanation-3: -Scales are small plates that form part of the skin of certain animals. They provide protection from the environment and from predators. Sharks have placoid scales, bony, spiny projections with an enamel-like covering.

Detailed explanation-4: -Cartilaginous fishes (sharks and rays) are covered with placoid scales. Some species are covered instead by scutes, and others have no outer covering on part or all of the skin.