Most species of jellyfish live for less than one year. Some smaller species may only live for a few days. However, a type of jellyfish called Turritopsis is technically immortal, as it can age backwards into a polyp form and then produce hundreds of genetically identical adult forms.
Jellyfish have a complex life cycle. The form commonly known as jellyfish is the adult form, or medusa form. The adults breed and release eggs. The eggs hatch into larvae called planulae. The planulae eventually form into polyps that attach to the sea floor. The polyps bud off tiny jellyfish called ephyrae that rapidly grow into adult medusa jellyfish.