Turritopsis nutricula, a species of jellyfish found in oceans worldwide, typically undergoes sexual reproduction and dies. However, during periods of environmental stress it has been observed that solitary members of this species do something amazing: they transform their cells back to into their younger state, and it is thought, do not die.
Additionally, through a process called transdifferentiation, the muscle cells of the jellyfish can morph into nerve cells or even sperm or eggs. To date, this is the only known animal species that undergoes this type of transformation. Some scientists believe that this jellyfish may hold the keys to cellular repair mechanisms that allow organisms to age without the breakdowns that are associated with aging.