The mystery of a deep-sea creature that resembles a discarded purple sock has been solved. The animal, called Xenoturbella, is so bizarre that for 60 years researchers could not work out what it was - or where it fitted into the family tree.

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The mystery of a deep-sea creature that resembles a discarded purple sock has been solved. The animal, called Xenoturbella, is so bizarre that for 60 years researchers could not work out what it was - or where it fitted into the family tree.