Q What are the major classes into which the phylum is divided? What are the few examples of each and in which form (polyp or medusae) are they found?

Coelenterates are divided into three major classes: hydrozoans, anthozoans and scyphozoans. In hydrozoans the polypoid form predominates and examples are by-the-wind- sailors, hydras and Obelia. In scyphozoans the major phase is the medusoid and the best known instance is the common jellyfish (Aurelia). In anthozoans there is only the polypoid form and sea anemones and corals are notable in this group.