An extensive variety of single-celled organisms that live anaerobically, or without oxygen, had been found in the past, regularly deep underwater or deep underground. But investigators had not recovered a multi-cellular or metazoan animal that did so until now- the giant tube worms that live by hydrothermal vents, for example, rely on dissolved oxygen.
The investigators were only expecting to see viruses, bacteria & other microbes. The bodies of multi-cellular animals had previously been exposed in these sediments, "but were thought to have sunk there from upper, oxygenated, waters," they said.
The turning point of the study "offers the tantalizing promise of metazoan life in other anoxic settings for case, in the subsurface ocean underneath hydrothermal vents, or subduction zones, or in other anoxic basins," Levin said, referring to the subduction zones where one slab of Earth called a tectonic plate dives beneath another & occasionally leads to earthquakes.