The Deepest Living Animal Ever Found ― The Devil Worm

How far down in the crust of Earth can animals survive? There are some tiny worms in the dark, hot depths of several South African gold mines that may hold the key to answering that question.

When researchers found a worm deep in the aquifer, more than 2 km (1.2 mi) below the Earth's surface, they hailed it as the discovery of the deepest living animal ever discovered. Because no other multicellular organism has ever been detected beyond 2 km (1.2 mi) below the Earth's surface.

In 2008, Gaetan Borgonie and Tullis Onstott from the University of Ghent and the University of Princeton accidentally discovered live Mephisto worms nearly 2.2 miles (3.6km) underground in South African gold mines; Borgonie's research team nicknamed it "The Devil Worm."

It came from the deep, a mile below the Earth's surface, in a place where only bacteria were thought to exist. It's Halicephalobus Mephisto, a new roundworm species with a length of 0.5 to 0.56 mm, radically extends the potential of animal life on this planet and perhaps on others.

They were surprised to see the complex, multicellular organism surviving in an environment of high temperature, high concentration of methane, and low oxygen levels, which was thought to be livable only by microbes.

It's only been two decades since scientists have recognized that any life of any kind could live hundreds or thousands of feet beneath the Earth's surface, a region of extreme pressure, high temperatures, and few nutrients.

The team has found evidence that worms have been there for thousands of years. According to Isotope dating, these worms live in groundwater that is 3,000–12,000 years old — indicating that the animals had evolved to survive the crushing pressure and high heat of the depths.

In fact, devil worms possess about 112 copies of the gene that makes Hsp70 proteins. These proteins help cells deal with high levels of heat — the "HSP" in their name stands for "heat shock proteins" — and they work by repairing other proteins that have been damaged due to heat stress. And that's not the only unusual gene pattern found in devil's worms: there are also about 63 copies of the AIG1 gene, which controls whether a cell lives or dies. 

Scientists scanned genomes of other organisms and identified animals with similar types of Hsp70 and AIG1 genes. Bivalves, some mollusks, such as oysters, mussels, and clans, were identified organisms, suggesting that this genome pattern may be present in organisms trapped in a warm environment. The research was published in the journal of molecular evolution.

Researchers hope that by studying the Devil Worm genome, they can develop new ways of understanding how life is possible beyond the confines of the Earth.