Most living creatures are bound by the fact of birth, aging and death. A few, however, have evolved to interrupt the typical life cycle.

The immortal jellyfish (Turritopsis dohrnii) is one such animal—and in a surprising discovery now published in the Proceedings of the National Academy of Sciences, scientists have added its cousin, the comb jellyfish (Mnemiopsis leidyi), to the coveted forever young. club.

Researchers at the University of Bergen in Norway realized they had an aging specimen in their lab when they found a larval ctenophore in a tank that should have housed a mature comb jellyfish.

The unintended discovery raises the question: how many more animals can age in reverse.

“The work challenges our understanding of early animal development and body plans, opening new avenues for the study of plasticity and life cycle rejuvenation. “The fact that we found a new species that uses this specific ‘time travel machine’ raises fascinating questions about how widespread this ability is in the tree of animal life,” study co-author Joan J. Soto-Angel said in a statement. on Phys.org.

Soto-Angel and her team conducted experiments in an attempt to recreate the circumstances that caused the comb jellyfish to return to begin with, identifying extreme stress as the trigger.

“To witness how they slowly transition to a typical cidipid larva, as if going back in time, was just fascinating,” Soto-Angel said. “Over several weeks, they not only remodeled their morphological features, but also had a completely different feeding behavior, typical of a cidipid larva.”

Previous research suggests that comb jellyfish may have been the first animal species to appear on Earth 700 million years ago, and may indeed owe their longevity to their ability to reverse growth and development.

“This is a very exciting time for us,” said Paul Burkhardt, who co-authored the study. “This fascinating discovery will open the door to many important discoveries. It will be interesting to unravel the molecular mechanism that leads to reverse development and what happens to the animal’s nervous network during this process.

In the future, similar discoveries could lead scientists to understand how humans too could harness the aging process.