Meet the mysterious deep-sea 'sock'
The mystery of a deep-sea creature that resembles a discarded purple sock has been solved, scientists report.
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.
But the discovery of four new species in the Pacific has enabled scientists to conclude that this animal belongs to one of the earliest branches of life.
The study is published in the journal Nature.
Prof Greg Rouse, from the Scripps Institution of Oceanography in the US, explains here why these creatures are so odd.
03 Feb 2016