Question

Calcareous ossicles form the

• A. exoskeleton of echinoderms
• B. endoskeleton of echinoderms
• C. endoskeleton of cnidarians
• D. exoskeleton of sponges

Answer 1

The correct option is B endoskeleton of echinoderms

The calcareous ossicles make up the endoskeleton of echinoderms. They do not have an exoskeleton.

The exoskeleton of sponges is made of spicules or spongin fibres.

In cnidarians, mesoglea acts like an endoskeleton. The water in the gastrovascular cavity acts as a hydrostatic skeleton. Some cnidarians secrete calcium carbonate which forms the exoskeleton. Eg: Sea anemones.