Question

Shark skin has a protective coating of a calcareous deposit called

• A. Calcium carbonate
• B. Calcium silicate
• C. Calcium phosphate
• D. Shagreen

Hint:

Shagreen is prized in the leather industry for its unique "beaded" appearance. In biology, always remember that shark scales are "Dermal Denticles" (Placoid scales), which give the skin its characteristic "sandpaper" feel.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the name of the protective coating or the finished leather product derived from shark skin. Shark skin is unique among fishes due to its specialized scales and texture.
Detailed Explanation:

• Placoid Scales: Sharks (Elasmobranchs) possess placoid scales, also known as dermal denticles. These scales are structurally similar to vertebrate teeth, consisting of a central pulp cavity, a layer of dentine, and a hard outer layer of vitrodentine (enamel-like substance primarily made of calcium phosphate).

• Shagreen: The term "Shagreen" refers to the untanned or untaxed skin of sharks and rays which is covered in these sharp, abrasive dermal denticles. Historically, shagreen was used as an abrasive (like sandpaper) for polishing wood and metal, and also as a decorative covering for sword hilts and luxury boxes because of its non-slip properties and durability.

• Evaluation of Options: While the scales themselves contain calcium phosphate, the question asks for the name of the "coating" or the layer as a whole. "Shagreen" is the recognized term for this specialized, rough, protective shark skin coating. Options (A), (B), and (C) refer to chemical compounds, not the name of the anatomical/commercial structure.

Step 2: Final Answer:
The protective coating of shark skin is called Shagreen.