Medusa - a umbrella or bell shaped body, free living and have a central projection on the inside of the unbrella which supports the mouth and their tentacles around the rim of the umbrella. The medusa form is most commonly associated with adult jellyfish. Although jellyfish pass through planula and polyp stages in their life cycle, it is the medusa form that is most recognized with this group of animals.
Polyp Cnidarians
Polyp - a Cylindrical body with arm like tentacles. In a polyp, the mouth points upward and are usually sessile.
~ Some cnidarians remain a polyp for their entire life, while others pass through the medusa body form.
Cnidariam polyps and medusas each have a body wall that surrounds an internal space called a gastrovascular cavity.