🔬 The sea walnut (Mnemiopsis leidyi), a comb jelly the size of a mango, can reverse its own aging. When starved or injured, it shrinks from an adult lobed form back into a tentacled larval stage. Once conditions improve, it matures again into a reproductive adult. Unlike the "immortal jellyfish" which becomes a different individual through cell transformation, this comb jelly stays the exact same creature — literally going back in time. The finding was published in PNAS in 2024 and suggests reverse development may be an ancient animal trait.
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