Explanation:
C
Sea pen (Pennatula) are soft corals that are under the class Anthozoa and under the phylumcoeleneterata or Cnidaria. Sea urchin, Brittle star and Sea cucumber are echinoderms.
Characteristics of coelenterate -
These are sac-like animals having a radially symmetrical body, A gastrovascular cavity is present having the same inlet and outlet in these organism reproduction mode is asexual e.g. Hydra and sea anemone, corals, Jellyfish.