The turritopsis nutricula species of jellyfish … [as it is] capable of cycling from a mature adult stage to an immature polyp stage and back again, there may be no natural limit to its life span. … The key lies in a process called transdifferentiation, where one type of cell is transformed into another type of cell. Some animals can undergo limited transdifferentiation and regenerate organs, such as salamanders, which can regrow limbs. Turritopsi nutricula, on the other hand, can regenerate its entire body over and over again.
The world’s only immortal animal | Yahoo! Green