The jellyfish that can reverse its life cycle

Turritopsis dohrnii is only about 4.5 millimetres across, yet its life history has earned it an enormous reputation. Under stresses such as physical injury or starvation, an adult medusa can shrink, reabsorb its tentacles and settle as a cyst-like mass. From there it can develop into a polyp, an earlier stage that can eventually produce new medusae. [1]

The Natural History Museum describes the cellular process as transdifferentiation: specialised cells are reprogrammed into different specialised cells, helping rebuild the animal in another body plan. Life-cycle reversal can happen repeatedly. This is not merely an adult producing ordinary offspring through fertilisation; the striking feature is the return from the swimming medusa stage to the polyp stage. [1]

“Immortal” is therefore a shorthand for a remarkable developmental capacity, not a promise that an individual cannot die. The museum presents freedom from death through old age as a possibility under perfect conditions, rather than a demonstrated guarantee of endless survival in the sea. Nothing here requires resurrection or paranormal intervention. Nor does the animal provide an established treatment for human ageing. Its scientific importance lies in what its cells can change into, not in a literal exemption from every cause of death. [1]

Editorial note: This feature summarises the published sources listed below; it is not a new archive investigation. The accompanying image is AI-generated illustration, not an archival photograph or evidence of the event.