Deep below the surface of the earth lives the devil worm. A new study says that this nematode or worm (among the most abundant animals on earth) species, called Halicephalobus mephisto, is the deepest-living creature to be discovered so far. This worm has been found at a depth of 3.6 kilometres. Before this, it was believed that nematodes survived only till some dozen feet beneath the surface of the earth. Beyond that, only microbes — on which these worms feed — could be found. The team which made this discovery has evidence that these worms have been around for thousands of years.