An international team, led by Princeton University, has found the new species, Halicephalobus mephisto, 2.2 miles below the surface. It had previously been thought that only single-celled bacteria could survive at such depths.
The worm -- a bacteria-feeding nermtode that is just 0.5mm long -- was found at various depths of between 0.6 miles and 22 miles; it lives in the 48C water which seeps between cracks that are deep below the surface, the `Daily Mail` said.
Writing in the `Nature` journal, the scientists said this is the deepest living multicellular organism ever found in "fracture water".
Lead researcher Dr Tullis Onstott said: "The lack of oxygen, temperature and food is a big dissuader. It`s like finding Moby Dick in Lake Ontario. It scared the life out of me when I first saw them moving. They look like black little swirly things."
The worms were discovered in three gold mines in the Witwatersrand basin near Johannesburg. They are capable of surviving in an environment where there is almost no oxygen, just 1 per cent of the level found in oceans.
Carbon dating of the water they were found in suggests that they have been living at such depths for between 3,000 and 10,000 years, Dr Onstott said.
The team believes that the worms originated from the surface but were washed down into the cracks of Earth`s crust by ancient rainwater. They are of similar appearance to the worms that live in rotting fruit on the surface, although much smaller.