Come away O' human child, with a fairy hand in hand, for the world's more full of weeping, than you can understand...

Do coelenterates have a coelom

No. A coelenterate is an animal such as a jellyfish, whose main body cavity is also its alimentary canal gut. Most animals, on the other hand, have a body cavity called a coelom that is separate from the gut.

For instance, inside your own body, you have an alimentary canal your esophagus, stomach and intestines and a separate body cavity that contains your heart, lungs, liver, etc. In a coelenterate, there is only one cavity.