Jellyfish force themselves to be symmetrical

When a team of biologists studied jellyfish that had lost parts of their bodies they couldn’t believe how they healed themselves

Many marine invertebrates are able to regrow limbs they lose during their lives. That’s exactly what the team from the California Institute of Technology (Caltech) expected jellyfish to do if it lost an arm. The jellyfish in question, a moon jellyfish (Aurelia aurita), was missing two arms at the beginning of the experiment.

Unexpected results

Rather than grow two replacement arms as the study team expected, the jellyfish did something the world had never seen before. The jellyfish moved its six remaining arms into a symmetrical pattern. This process has been termed ‘symmetrisation’, and is controlled by the muscles in the jellyfish’s bell.

Taking between 12 hours and four days, this incredible process is the ultimate quick fix. Rather than using time and energy growing entirely new arms they simply force the remaining arms to shift until they are evenly spaced. Muscle relaxant halted the process entirely, but increasing the muscular pulses sped the movement up significantly.

Why they do it

Symmetry is essential to movement in moon jellyfish, and without the ability to move they are easy targets for prey. The long, trailing arms of a jellyfish are delicate and can be damaged easily. This process to restore symmetry can mean the difference between life and death to a jellyfish, and has helped them survive for thousands of years.

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