The species of jellyfish that is immortal is called Turritopsis dohrnii, also known as the immortal jellyfish. It is a small jellyfish found worldwide in temperate to tropical waters and is one of the few known cases of animals capable of reverting completely to a sexually immature, colonial stage after having reached sexual maturity as a solitary individual. This means that when it is injured or faces environmental stress, it can hit the reset button and revert to an earlier developmental stage, essentially starting its life cycle over again. This process can be repeated, and in perfect conditions, it may be that these jellyfish would never die of old age.