GENERAL HISTOLOGY

Detailed explanation-1: -Echinodermata are marine invertebrates comprising starfish, brittle stars, sea cucumbers, sea urchins, and sea lilies. Animals in this phylum lack any centralized brain and instead possess diffuse neural networks known as nerve nets.

Detailed explanation-2: -Echinoderms are named for their spiny skin, which is covered by a thin layer of calcium carbonate plates and spines. Adult echinoderms have radial symmetry, but larvae have bilateral symmetry. Echinoderms have a unique water vascular system, with canals that extend along each body part.

Detailed explanation-3: -The correct answer is (b). Echinoderms do not have gills.

Detailed explanation-4: -Echinoderms have no head or brain. Instead, the nervous system consists of a central ring of nerves with branches extending into each of the arms.