The immortal jellyfish: between truth and legend
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Is there really an immortal jellyfish that can live almost forever? Turritopsis nutricula, called immortal jellyfish, is the only known form of jellyfish to have developed the ability to return to the polyp state, through a transdifferentiation process that requires the presence of certain types of cells.
These undergo a sort of regression to a totipotent phase, from which they can then multiply and differentiate into different cells. Laboratory experiments have revealed that all T. nutricula jellyfish, both newborn and fully mature jellyfish, are capable of transforming back into polyps.
The transformation of the jellyfish is characterized by a deterioration of the bell and tentacles, with the subsequent growth of the perisarch and stolons, and finally of the polyps. These multiply further forming a colony.
This ability to reverse the life cycle in response to adverse conditions is likely unique in the animal kingdom and allows the jellyfish to circumvent or at least delay death, making T. nutricula potentially immortal. Laboratory studies have shown that 100% of specimens can return to the polyp stage, but so far the process has not been observed in nature, in part because it is very rapid and field observations at the right time are difficult.
In theory, the cycle could repeat itself indefinitely, even if in nature most individuals, like other jellyfish, are exposed to the normal dangers of planktonic life, risking becoming prey to other animals or dying of disease without having the possibility of return to the polypoid stage.
The genus Turritopsis is believed to be native to the Pacific, but has spread around the world through trans-arctic migrations and has distinguished itself in numerous populations that are sometimes difficult to morphologically identify.
T. nutricula is geographically located in the western Atlantic and the Caribbean. It is morphologically distinguished from T. dohrnii, purely Mediterranean, and from T. polycirrha of the European coasts of the eastern Atlantic. The medusoid stage of T.
nutricula has a bell shape that reaches a maximum diameter of 4-5 mm. Bell jelly is uniformly thin, with some thickening at the top. The relatively large gastro-vascular cavity is bright red and cruciform. The young specimens have only 8 tentacles, regularly spaced along the edge, while the adults reach 80-90 tentacles.