How Does a Jellyfish Move?

jellyfish-move Credit: Ilan Ejzykowicz/Flickr/CC-BY-2.0

Jellyfish move by floating with the ocean's currents, jet propulsion or by using cilia. Jellyfish typically move deep in the water, though some move in shallow water. Man-o'-wars float on top of the water.

Most jellyfish utilize the ocean's currents as their prime mode of movement. However, they use jet propulsion if they need to move themselves. They squeeze their bodies to push jets of water from the bottom of their bodies. The displaced water creates a vortex. This propels them through the water. Jellyfish pause in between contractions, so that the vortex gives them more push, allowing them to travel 30 percent farther with each contraction. Most jellyfish can move this way. The comb jellyfish has tiny cilia in rows on its body. These cilia beat against the water to propel the jellyfish through the water.

Jellyfish do not use their long tentacles for movement. The tentacles contain the stinging cells that jellyfish use to stun their prey or as protection from predators.

Jellyfish aren't animals. They're plankton, which means their movement is limited by the currents. They are related to sea anemones and coral. Jellyfish have simple anatomies that include an inner and outer layer, jelly, organs, an orifice and tentacles. They range in size from under an inch to almost 7 feet in length.