Question

Exoskeleton in Echinoderms is
A. Calcareous
B. Siliceous
C. Tunicin
D. Chitinous

Answer 1

Hint: Echinoderms are known as the spiny-armed animals as their bodies are covered with spicules. Few examples of echinoderms are starfish, sea urchins, brittle fish, etc. A special water vascular system is a characteristic feature of echinoderms.

Complete answer:In Option A, Calcareous – The calcareous exoskeleton is found in the phylum Mollusca and Echinodermata. The word Echinodermata is made up of two words, Echino which means spines, and Dermata meaning skin. Thus, echinoderms have spiny texture skin. Echinoderms have an exoskeleton made up of spicules. These spicules are spiny structures that are made up of Calcium carbonate minerals. They are very hard and provide a tough and protective skeleton for the body. The calcareous covering is to protect them against predators.
In Option B, Siliceous – The siliceous covering or exoskeleton is found in the diatoms. Diatoms are a member of the phylum Protista. They are found deposited on the sea bed and are known as the diatomaceous earth.
In Option C, Tunicin – Tunicin is a protective covering that is found in the members of the phylum Urochordata. It is a covering made up of cellulose-like organic substances. Due to the presence of this Tunicin covering they are also known as Tunicates and the phylum is known as Tunicata.
In Option D, Chitinous – The chitinous exoskeleton is found in Arthropods. It is believed to be very hard. It is made up of chitin.
Thus, the exoskeleton of echinoderms is made up of a calcareous substance.
Hence, the correct answer is option (A).

Note: The spicules of the Echinodermata form its exoskeleton. The Exoskeleton is the outermost, hard, protective covering of the body. However, in the case of the echinoderms, it is developed from the mesodermal germinal layer. The Echinoderms are triploblastic animals, so they have three germinal layers in their body.