After losing a limb, some animals, such as lizards and salamanders, can regenerate the missing body part. Jellyfish deal with amputation in a different way: They simply rearrange their bodies to compensate for the limb they lost. This unique strategy involves reorganizing existing body parts to reestablish symmetry, a group of researchers from the California Institute of Technology report in PNAS

From left to right, the process of symmetrization, starting with the amputated state. Image Credit:Michael Abrams, Ty Basinger, and Christopher Frick, California Institute of Technology

After anesthetizing moon jellies in the lab, researchers amputated multiple limbs to see how they would regain symmetry, which is essential for their ability to move through the water. The jellyfish did so by rearranging their remaining arms and muscles, and moving their mouths to the new center of their bodies. 

The process commenced within minutes,” the researchers write. “The wound at the cut site closed within the first hours. The arms gradually spread further apart, as the manubrium [the jellyfish equivalent of a throat] relocated to the center of the body.” The jellyfish typically regained their bodily symmetry within 12 hours, whether they were placed in light or dark conditions, upside down, in groups or alone. 

To shed light on the process behind these contortions, the scientists next put muscle relaxants in the water with the jellyfish. By preventing the jellyfish's muscles from contracting, they succeeded in stopping the symmetrization process, suggesting that the action of healing after an injury is triggered by movement.

The way jellies move through the water—alternating powerful propulsive muscle contractions with more elastic movement of their jelly-like bodies—may steadily move the remaining body parts into position. “This is akin to squeezing an elastic ball at one end and producing a protrusion on the other side,” the researchers postulate. “With each cycle of compression and elastic repulsion, the arms may then relax to a new stable state.”

The true lesson here: don't try to hack a jellyfish to pieces, because they will come back to haunt you.