A newly discovered nematode (roundworm) species has set a new record for a known animal life form living naturally at the greatest depth beneath the Earth’s surface. The worm—named Halicephalobus mephisto by scientists, and nicknamed the “devil worm”—occurs at depths where only microorganisms like bacteria were previously known to live. At 0.5 millimeters long, it is the largest life form known to thrive this deep underground.
Nematodes (like the ones pictured at left) are one of the most abundant groups of animals on Earth, and are found in almost every habitat imaginable. Though some are parasites living in the bodies of humans and other animals and plants, the majority are microscopic or near-microscopic decomposers that feed on dead organic material, or predators that hunt for microbes. 90,000 individual nematodes have been found living in one rotting apple—a statistic that provides a glimpse of how common these creatures are in nature.
In total, about 12,000 nematode species are known to science—but there is little doubt that thousands more await discovery. Some scientists predict as many as 500,000 species of nematodes actually exist, most of them as yet un-described. Because of their role as decomposers and predators, nematodes are important to the functioning of many of the world’s ecosystems.
The devil worm was found 2.2 miles below the Earth’s surface, much deeper than most scientists had previously believed animal life could live. The search that led to finding the new species was prompted in part by the discovery of nematodes in a gold mine in South Africa. At first researchers thought the worms might simply have been transported deep underground on mining equipment or the clothing of miners—but scientists from the University of Ghent in Belgium launched an effort to see if nematodes might occur naturally in deep water veins nearby.
After sampling thousands of gallons of water, the researchers found multiple types of nematodes, including a species already known from shallower depths, and the new species Halicephalobus mephisto. The research team published their findings on June 1st in the scientific journal Nature.
The devil worm probably feeds on bacteria that scientists long known to occur deep beneath the surface of the Earth. However the underground environment poses unique challenges for animals, including extreme heat and pressure. Somehow the worms have adapted to live under such conditions, and it looks as though they have been doing it for a while. Isotope dating techniques suggest the water where devil worms were found is at least 3,000 years old, and perhaps as old as 12,000 years. This means the species has probably already survived in its challenging environment for millennia.
The discovery of the devil worm and other deep-underground nematodes raises the question of whether there might be other animals living underground at depths far greater than researchers have looked for them previously. If so, they are likely to be very small creatures like nematodes and related near-microscopic worms. But their existence miles beneath the planet’s surface could re-shape scientific understanding of the kinds of harsh conditions where some form of animal life can survive.
Scientists are also asking whether animal-like life forms could exist deep underground on other planets. In the search for extraterrestrial life, research teams have usually assumed any life encountered far below the surface of a planet or moon would consist of relatively simple bacteria-like organisms. But if more complex life can survive at such depths on Earth, the same could be true of other planets.
The discovery of the devil worm, which is not only a new species but a representative of animal life found at previously unknown depths, is a reminder of how much remains to be learned about life on Earth. Like the depths of the ocean, the canopies of tropical rainforests, and other comparatively unexplored environments, pockets of water deep beneath the planet’s surface likely hold many other surprises that could re-shape our understanding of life in the world around us.
Photo credit: flickr.com/photos/snickclunk/200926410/sizes/m/in/photostream/