The immortal jellyfish, Turritopsis nutricula, was discovered a few years ago by researchers at the University of Lecce. Its prerogative depends on the fact that it is capable of reversing its biological cycle and thus escaping death.

(Where does the name Medusa come from? - Are jellyfish useless?)

Double cycle
Of small dimensions, it has a diameter of just 4 millimeters, it develops following two stages: in the first it is similar to a small octopus, in fact it is equipped with tentacles useful for underwater hunting, in the second it turns into jellyfish, with the development of more tentacles (from ten to over 80). Once sexual maturity is reached and after reproducing, it does not die. It descends to the bottom of the sea and returns to the juvenile stage from which it developed.
For scientists, this rejuvenation is made possible, at the cellular level, due to a phenomenon known as "transdifferentiation".
The change is due to the action of cells that from highly specialized are re-transformed into non-specialized cells, typical of the juvenile phase. Cells, such as muscle cells, which are able to lose their morphological specialization and return to a totipotent stage through which new cells with different characteristics can be produced. What makes this jellyfish special, however, is not the cells in and of themselves, but the process that brings back the biological clock. Partial processes of this type are also present in other animals, such as newts and lizards that can regenerate some parts of their body.
(Chills in jelly: jellyfish arrive)