The species of jellyfish known as turritopsis nutricula may be the only animal in the world to become immortal. This creature is a hydrozoan (a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater). This hydrozoan’s jellyfish form can revert back to the polyp stage (its first stage of life) after becoming sexually mature. It is the only known case of a metazoan capable of reverting completely to a sexually immature, colonial stage after having reached sexual maturity as a solitary stage. It does this through the cell development process of transdifferentiation. Cell transdifferentiation is when the jellyfish alters the differentiated state of the cell and transforms it into a new cell. During this process the medusa of the jellyfish is transformed into the polyps of a new polyp colony.
When the jellyfish transforms its umbrella first reverts itself and then the tentacles and mesoglea break down. The reverted medusa then attached itself to the substrate by the end that had been at the opposite end of the umbrella and starts giving rise to new polyps to form the new colony. Theoretically speaking, this process could go on forever effectively rendering this particular species of jellyfish biologically immortal. Although in nature, it is very rare for turritopsis to ever revert to the polyp stage as many succumb to predation or disease during the plankton stage.
It has been said that it is currently impossible to estimate the age of an individual jellyfish as no single specimen has ever really been observed for an extended period of time. And even if this species does have the potential for immortality, there is no laboratory evidence of many generations surviving from any individual. Scientists are still trying to study this magnificent creature to discover how it is able to reverse the aging process. Because they are able to escape death, the number of this particular species is continuing to grow and they are now found worldwide in oceans around the globe rather than just their native Caribbean waters.