Body Plan
Fact Sheet


Picture by Tom Volk

Movement of Moon Jellyfish is truly beautiful to watch.  They begin their lives as larvae which swim by use of cilia.  Polyps and medusae have a very simplistic muscle-like tissue created from their ectoderm or endoderm.  Polyps use their gastrovascular cavity as a sort of hydrostatic skeleton which, with the assist of the muscle-like cells, contracts and extends the body.  They can also move by creeping along their substrate using the muscle cells in their base.  Medusa move in a somewhat different way.  The base of their bell-like upper body is composed of a ring of muscle-like cells called coronal muscle.  The impulse for these muscles to contract is received from the subumbrellar nerve net.  When the cells contract in a rhythmic pattern, movement by jet propulsion occurs.  Water flows in the opposite direction of the medusa's movement.  Propulsions are controlled by the rhopalial centers.  Swimming is usually more of a way to keep the jellyfish near the surface of the water than a means of travel through the water.  Often, movement of jellyfish from place to place is simply a result of water currents. 

Visit http://www.youtube.com/watch?v=duWdlP7VJV4 to view a video by Steve Mannian of Moon Jellyfish swimming in an aquarium at the Horniman Museum in South London.