Turritopsis nutricula is a small hydrozoan that once reaching adulthood, can transfer its cells back to childhood. This adaptive trait likely evolved in order to extend the life of the individual. Several different species of the genus Turritopsis were formerly classified as T. nutricula, including the "immortal jellyfish" which is now classified as T. dohrnii.
Hydrozoans have two distinct stages in their life, a polyp stage and a medusa stage. The polyp stage is benthic, with the cells forming colonies, while the medusa stage is a singular, planktonic organism. Generally in hydrozoa the medusa develops from the asexual budding of the polyp and the polyp results from sexual reproduction of medusae. In T. nutricula, planktonic medusa have the capability to bud polyps or medusae which also have the ability to spawn new medusae. Several nominal species have been described for this genus, but most of them had been synonymized and attributed to one cosmopolitan species, Turritopsis nutricula.
