Immortal Jellyfish

The good news is that you can be immortal. The bad news is that you have to become a floating blob of jelly to do so. Scientists have discovered a jellyfish which can live forever. 

Turritopsis dohrnii is now officially known as the only immortal creature. The secret to eternal life, as it turns out, is not just living a really, really long time. It's all about maturity, or rather, the lack of it. The immortal jellyfish (as it is better known popularly) propagate and then, faced with the normal career path of dying, they opt instead to revert to a sexually immature stage.

It turns out that once the adult form of the 4.5 mm-wide species Turritopsis dohrnii have reproduced, they don't die but transform themselves back into their juvenile polyp state. Their tentacles retract, their bodies shrink, and they sink to the ocean floor and start the cycle all over again. Among laboratory samples, all the adult Turritopsis observed regularly undergo this change.

And not just once: they can do it over and over again.

Thus, the only known way they can die is if they get consumed by another fish or if a disease strikes the jelly. However, there are still many mysteries surrounding the turritopsis dohrnii. While the process of reverting from its adult-phase to a polyp was observed several times, it hasn't been observed yet in nature, only in laboratory environments.

Turritopsis dohrnii, the so-called "immortal jellyfish," can hit the reset button and revert to an earlier developmental stage if it is injured or otherwise threatened.

Fully grown, Turritopsis dohrnii is only about 4.5 mm (0.18 inches) across, smaller than a pinky nail. A bright-red stomach is visible in the middle of its transparent bell, and the edges are lined with up to 90 white tentacles. These tiny, transparent creatures have an extraordinary survival skill, though. In response to physical damage or even starvation, they take a leap back in their development process, transforming back into a polyp. In a process that looks remarkably like immortality, the born-again polyp colony eventually buds and releases medusae that are genetically identical to the injured adult.