The immortal Jellyfish

This immortal species cannot die. It achieves this by aging backward after sexual maturity, going through reverse puberty so it can start the cycle again and if the jellyfish is injured or sick, it returns to its polyp stage over a three-day period, transforming its cells into a younger state that will eventually grow into adulthood all over again.

Turritopsis typically reproduces the old-fashioned way, by the meeting of free-floating sperm and eggs. And most of the time they die the old-fashioned way too.

But when starvation, physical damage, or other crises arise, "instead of sure death, Turritopsis transforms all of its existing cells into a younger state," said study author Maria Pia Miglietta, a researcher at Pennsylvania State University. The jellyfish's cells are often completely transformed in the process. Muscle cells can become nerve cells or even sperm or eggs. It could also applied to human beings because human and jellyfish are not genetically very different.