Jellyfish, also known as medusae, then bud off these polyps and continue their life in a free-swimming form, eventually becoming sexually mature.

Theoretically, this process can go on indefinitely, effectively rendering the jellyfish biologically immortal,[3][6] although in practice individuals can still die.

In nature, most Turritopsis dohrnii are likely to succumb to predation or disease in the medusa stage without reverting to the polyp form.

[15] These polyps develop over a few days into tiny 1 mm medusae, which are liberated and swim free from the parent hydroid colony.

Turritopsis is believed to have originated in the Pacific, but has spread all over the world through trans-Arctic migrations, and has speciated into several populations that are easy to distinguish morphologically, but whose species distinctions have recently been verified by a study and comparison of mitochondrial ribosomal gene sequences.

[17] "We are looking at a worldwide silent invasion", said Smithsonian Tropical Marine Institute scientist Maria Miglietta.

Mature eggs are presumably spawned and fertilized in the sea by sperm produced and released by male medusae, as is the case for most hydromedusae.

[19] The medusa of Turritopsis dohrnii is the only form known to have the ability to return to a polyp state, by a specific transformation process that requires the presence of certain cell types (tissue from both the jellyfish bell surface and the circulatory canal system).

[20] Experiments have revealed that all stages of the medusae, from newly released to fully mature individuals, can transform back into polyps under the conditions of starvation, sudden temperature change, reduction of salinity, and artificial damage of the bell with forceps or scissors.

In the experiment, they would eventually transform into stolons and polyps and begin their lives once again, even without environmental changes or injury.

[3] This ability to reverse the biotic cycle (in response to adverse conditions) is unique in the animal kingdom.

[3] Regardless, most individual medusae are likely to fall victim to the general hazards of life as mesoplankton, including being eaten by predators or succumbing to disease.

The species possesses unique mechanisms related to telomere maintenance, which play a significant role in its regenerative abilities.

[23] Genomic analyses such as sequence analysis on mRNA or mitochondria DNA have been employed to investigate its lifecycle.

Currently, only one scientist, Shin Kubota from Kyoto University, has managed to sustain a group of these jellyfish for a prolonged period of time.

[32] Kubota regularly appears on Japanese television to talk about his immortal jellyfish and has recorded several songs about them, often singing them at the end of his conference presentations.