Yet, in nature there exists a species which, instead of galloping toward its third age, heads back to the beginning once it matures. And, unlike the tragic fictional character Benjamin Button, it doesn’t even die as a baby. On the contrary, once a baby, it grows up again, and the cycle repeats itself. This creature is the Turritopsis dohrnii, more commonly known as the “immortal” jellyfish—an animal that has no brain, no heart, no bones, and no eyes, but does have the ability to never die from natural causes.
The process goes like this: the jellyfish eggs grow into small, free-swimming larvae called planula larvae; these morph into polyps, tiny anemones whose stalks attach to coral reefs; and polyps bud off into immature baby jellies, which mature into medusae, the familiar umbrella-shaped, tentacled creatures that pulse along the oceans and mate to spawn eggs. Push a medusa enough, though, and it can skip the fertilization and larval stages, changing straight into a polyp—like a butterfly reverting back to a caterpillar.
Many other species of jellyfish can pull off this reverse aging trick and return to the larval stage, but only once and rarely after sexual reproduction, according to Reuters. The immortal jellyfish is unique in its ability to do this a seemingly infinite number of times.
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