Jellyfish have a complex life cycle that includes both a sexual stage and an asexual stage.

In the sexual stage, the body (called a medusa) produces gametes (eggs and sperm). Then the eggs fertilized by sperm develop into a free-swimming larval form called planula.

After a brief period floating about in surface waters, the larvae settle to the sea floor, attaching themselves to a rock or the seafloor. They develop into a polyp (asexual stage) and begin to feed and grow.

In spring, some of the polyps start to bud off immature jellyfish known as ephyra larvae. These grow into mature jellyfish.