abstract:Turritopsis nutricula, the immortal jellyfish, is a hydrozoan whose medusa, or jellyfish, form can revert to the polyp stage after becoming sexually mature. It is the only known case of an animal capable of reverting completely to a sexually immature, colonial stage after having reached sexual maturity as a solitary stage.
The animals that canpossiblyachieveimmortality under idealconditions, such asseasquirts, certaincorals, Hydra, and Turritopsis nutricula (the immortaljellyfish), often activate telomerase.