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If a human loses a limb, chances are it will have to rely on a prosthetic device to do the job its former limb did. But a number of less-complicated organisms, like the moon jellyfish have evolved some interesting ways of regenerating lost body parts. When the moon jellyfish loses a limb, for example, it moves around its remaining limbs until it's all set. A recent study published in the Proceedings of the National Academy of Sciences found that this process is called symmetrization. Since jellyfish need to be perfectly symmetrical in order to swim, researchers found that the jellyfish push apart their arms as widely as possible in order to regain symmetry. The whole process is quick, too: it can take between 12 hours to 4 days.
While these jellyfish use symmetrization to compensate for lost limbs, other animals are capable of regrowing missing body parts: starfish, salamanders, zebrafish, and even insects like cockroaches. Some animals can go a step further: they are capable of regrowing their heads! The Hydractinia, which grows on the shells of snails and crabs, regrows its entire head if it gets bitten off by a predator. But they aren't the only animals capable of this seemingly amazing feat: Planaria can reproduce asexually and just make copies of themselves, including newly regrown heads. A study published in the Journal of Experimental Biology found that worms with regrown heads had the same memories as before! Researchers aren't sure how this happens, but think their memories are stored in other cells in the body and then get imprinted into the new brain when it grows.
The Animal that regrows its head! (BBC)
"Many animals can regenerate body parts, from starfish to salamanders. But primitive snail fur is unusual, not least because its abilities are so extreme."
Why Can't Humans Regenerate Body Parts? (Discovery News)
"The snail fur is a pinkish mass of spines, tentacles and polyps just 20 to 30 millimeters in length. The snail fur would seem unremarkable, except for one quality: According to Uri Frank, a scientist at the institute, the creature "in theory -- lives forever."
Limb regeneration: do salamanders hold the key? (University College London)
"The secret of how salamanders successfully regrow body parts is being unravelled by UCL researchers in a bid to apply it to humans."