Moon jellies muscle their way to recovery

Symmetrization
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Rapid pulsing to regain body symmetry after an injury in some jellyfish.

Scientists have long studied jellies’ ability to regrow body parts. But it turns out that some of these creatures, including the diaphanous Aurelia aurita, or moon jelly, forgo sprouting new arms after an injury, researchers report online June 15 in the Proceedings of the National Academy of Sciences. Instead, these animals use their muscles to move their existing arms into a symmetrical arrangement. (As youngsters, moon jellies have arms. Later, they grow into the canonic bell shape.)

Researchers sliced off some of the eight arms in young moon jellies to see how the animals heal. Rather than regrow limbs, the team discovered that the young moon jellies used symmetrization, an exercise that resembles a fist opening and closing rapidly. The pulsing redistributed each jelly’s mouth and muscles as well as existing limbs: Within four days, the creatures were symmetrical again.

Symmetry is important to young moon jellies: Without it, swimming would become awkward. The researchers think regaining symmetry after losing a limb might be even more important than having the correct number of body parts. 

SYMMETRY IN MOTION  Young moon jellies don’t sprout new arms after losing limbs, new research shows. Instead, the animals use their muscles to reorganize their existing arms to regain body symmetry. This “symmetrization” lets the jellies swim and develop normally.
Courtesy of M.J. Abrams et al/PNAS 2015.