GENERAL HISTOLOGY

Detailed explanation-1: -So, the correct answer is ‘Endodermal skeletal system’.

Detailed explanation-2: -Together with other well-known forms such as sea urchins, sea cucumbers and brittle stars, they belong to a major group called the echinoderms, which is characterized by a unique type of symmetry-called fivefold symmetry. This means they can be divided into five roughly equal parts.

Detailed explanation-3: -These include species such as the sand dollar, sea biscuits, and heart urchins, many of which don’t have spines. This adaptation generally allows them to burrow into the sand for protection as an alternative to the protection provided by the long spines of most other urchins.

Detailed explanation-4: -(Purple-spined Sea Urchin) Characteristics: Long slender spines, often purple to brown in color with white bases. Total diameter including spines can reach 100mm. Habitat: shallow waters, under coral rubble, rocky and sandy bottoms. Scientific classification: Kingdom: Animalia. Phylum: Echinodermata. Class: Echinoidea.