Immortal Jellyfish

• GeneralIt can run its life cycle backwards to the polyp stage, and so avoid dying of old age.
• biologíaIt can run its life cycle backwards to a juvenile state (a polyp) after reaching maturity, and so avoid dying of old age.
• Faced with hunger, injury or stress, the adult medusa settles on the bottom, reabsorbs itself and turns back into a polyp, the juvenile stage, through a process of transdifferentiation in which already specialised cells change identity.
• That reversal can be repeated many times over, so that an individual has no lifespan set by ageing — though it can still be eaten or fall ill: immortal does not mean invulnerable.
• It is an extremely rare case among animals, and for that reason is intensively studied in research on regeneration and ageing.
• It is the only animal known whose adults can reverse their development to avoid death. When damaged, diseased or in poor condition, the medusa contracts into a cyst of undifferentiated tissue and turns back into a polyp, restarting the cycle.
• The process is called transdifferentiation: already specialised cells change identity and become another cell type. It takes between 48 and 72 hours.
• Related species can do it when young but lose the ability on maturing. This one keeps it once sexually mature, with rejuvenation rates of up to 100%.
• It was described in the Mediterranean in 1883, but its ability was not recognised until the 1990s.
• A 2022 study compared its genome with that of a non-immortal relative and found duplicated genes for DNA repair and protection, along with the silencing of repressor complexes and the activation of pluripotency factors during reversal.
• The adult medusa is barely 4.5 millimetres across and has a bright red stomach.

Skeleton type

Invertebrate - no skeleton (gelatinous cnidarian)

Habitat and environment

Shallow coastal waters

Sources consulted: https://es.wikipedia.org/wiki/Turritopsis_dohrnii