I distinctly remember being 10 or 11 and asking my father about how jellyfish age, and whether jellyfish ever die if they do not encounter severe destructive conditions. Well, that's what I was thinking, but I probably phrased it a little differently at the time. The question regarded jellyfish only. My dad told me not to be silly, and that all organic matter, sooner or later, breaks down and dies. Tonight, while waiting for something to happen that never did, I was enlightened. While standing in line, I googled life-spans (first of hummingbirds, then that of pigeons) and eventually came upon the turritopsis nutricula. "Jellyfish usually die after propagating; however, the turritopsis nutricula has developed the ability to return to a polyp state after becoming sexually mature. It does this through the cell development process of transdifferentiation (occurs when a non-stem cell transforms into a different type of cell or when an already differentiated stem cell creates cells outside its already established differentiation path). This is done through a cell change in the external screen (exumbrella). The medusa is transformed into a stolon and the polyps into a hydroid colony. The umbrella turns inside out; middle section and tentacles are reabsorbed before the polyp spawns. Stolons form two days before the polyps differentiate. Lab tests showed that 100% of specimens reverted to the polyp stage. The ability to reverse the life cycle is probably unique in the animal kingdom, and allows the jellyfish to bypass death. Theoretically, this cycle can repeat indefinitely, rendering endering the Turritopsis nutricula biologically immortal, until its nerve center is removed from the rest of the body."
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