Jellyfish is the common name of a type of sea animal that biologists call a medusa.
Jellyfish get their names from the jellylike material between the two layers of cells that make up the animal's body. This substance serves as a skeleton to support the fragile body wall and to help the jellyfish maintain buoyancy in the water. The jellyfish body looks like a bell or umbrella. A short tube, which contains the mouth, hangs from the center of the body like a bell clapper. The edges of this tube form four frilly projections called oral arms.