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While aging is a universal biological process, a few remarkable species appear to sidestep it. The immortal jellyfish (Turritopsis dohrnii) famously reverts to a juvenile stage when threatened, a discovery that sparked widespread interest in biological immortality. Recent research has uncovered a similar, though distinct, phenomenon in the comb jelly (Mnemiopsis leidyi), a ctenophore found in the photic zone.
Published in the October 2024 issue of the Proceedings of the National Academy of Sciences, the study documents the accidental observation that an adult comb jelly had disappeared from its tank, replaced by a larva. Researchers Pawel Burkhardt and Joan J. Soto‑Angel subsequently replicated the event in 65 specimens, inducing reversal by removing gelatinous tissues and withholding food.
Under these stressors, the organisms shed their adult lobate form and regressed to the cydippid larval stage, shrinking visibly over several weeks. When food was reintroduced, 13 individuals resumed growth, ultimately reaching reproductive maturity. “Witnessing them shift back in time, reshaping morphology and feeding behavior, was simply fascinating,” Soto‑Angel remarked in a press release.
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The comb jelly’s reverse development is a unique model for aging research, but it operates via a different cellular pathway than the immortal jellyfish’s transdifferentiation. When an adult medusa of Turritopsis dohrnii is starved or injured, it reabsorbs its tentacles and converts into a benthic polyp. The cells then merge, losing individual identities and forming a cyst that initially resembles neither polyp nor medusa.
Within two days, the cyst develops polyp‑like traits and reenters the jellyfish’s normal life cycle, a process known as transdifferentiation. This rare metamorphosis allows the animal to evade senescence. “It’s not the exact same creature that transforms back to a preceding stage,” Soto‑Angel explained to Science. “Understanding the underlying molecular mechanisms could have profound implications for human health.”
