When you cut your finger, you (hopefully!) develop a scab.
When a sea star loses an arm, he grows it back!
So what happens when a moon jelly loses a limb, or is cut in half?
Scientists hypothesized that the jellies would also grow back missing arms, but instead something very interesting happened.
Moon jellies bodies rearranged themselves to become symmetrical again. So if they lost 4 of their 8 arms, the remaining four would spread out to become the most efficient.
Further experiments found that no matter how many limbs went missing, a jelly would make itself symmetrical again.
These jellies were healing themselves by swimming! As they pulsed through the water in search of food, the contraction and release of the muscles forced the limbs back into symmetry. Why? Moon jellies must be absolutely symmetrical in order to survive.
Although jellies do have methods of moving through the water and of righting themselves if they are upside down, they are often at the whim of the currents of the sea. This means that being radially asymmetrical is a huge liability and can prevent proper movement and feeding.
Check this cool video of a moon jelly utilizing his perfect symmetry to deftly capture his tasty morsels.
So, in an extremely efficient way, they save their existence by using what they’ve got. Could be a good lesson for us all, I suppose.