Answer:
- The body is radially symmetrical (usually pentaradial), triploblastic and coelomate, and is covered with calcareous spines and a hard endoskeleton.
- They have a water-vascular system with tube feet, which is used for locomotion, capturing prey and respiration.
- They are exclusively marine, have separate sexes, and show great power of regeneration; the larva is bilaterally symmetrical.
Examples: starfish, sea urchin, brittle star, sea cucumber.