The Jellyfish go through alterations of two generation. One generation reproduces sexually, this is the medusa, while the next reproduces asexually, this being called the scyphistomae.

Jellyfish are either male or female and reproduce sexually. The male jellyfish release their sperm through their wouth and into the water. The sperm swims into the mouth of the female jellyfish, where the eggs are then fertilized.

The fertilized eggs begin their development in either the female or in brood pouches located on the oral arms.

Once the embryos have developed, they leave the mouth or pouch as small, free swimming larva called Planula. Eventually the larva attaches itself to a hard surface and develops onto a pulyp or scyphistomata. The pulyp stage is also called a sessile stage, meaning that the pulyp is stationary and not free swimming.

The pulyp develop into a hydroid colony that is linked together by feeding tubes. like the original pulyp stage the polyp hydroid colony remains attached to a hard surface.

The hydroid colony reproduce asexually and bud tiny free swimming jellyfish also called ephyra. In a few weeks the ephyra will grow in size and become an adult jellyfish called a Medusa. This completes the life cycle. Jellyfish live normally three to six months.