1) They are characterized by the presence of stinging cells called Cnidoblast and a cavity called coelenterates, justifying the name Cnidaria and Coelenterata.
2) They are exclusively aquatic and marine.
3) They are radially symmetrical and diploblastic animals.
4) The ectoderm of Coelenterates is provided with a special type of cells called cnidoblasts or stinging cells. These cells have hypnotoxin which are used for defense and paralyzing the prey. They are found in large numbers around the mouth and over the tentacles.
5) Two types of body forms are present: asexual polyp and sexual medusa stage.