The body of a medusa is composed of two different layers, the ectoderm, and the endoderm.
They have an umbrella shape, the aboral zone (the pole opposite to the mouth) is convex and is called the exumbrella. The concave oral zone is called the subumbrella, at the end of which the mouth opens. From the edge of the exumbrella hang several tentacles provided with numerous cnidocytes, the typical stinging cells of cnidarians.
The tissue that makes up their bodies is called mesoglea and unlike polyps, it is normally very thick and gelatinous, but may attain cartilaginous consistency in some species.