Comet Enthusiast

Danovaro and his colleagues conducted three expeditions during the past decade off the south coast of Greece looking for signs of life in samples of mud from deep, hyper-salty basins in the Mediterranean Sea more than 3,250 meters deep. These basins are completely anoxic, or oxygen-free, and loaded with toxic levels of sulfides.

The creature, shown above, has specialized organelles so that it can survive without oxygen and gives a hint at possible types of lifeforms awaiting discovery in off-planet habitats such as Jupiter's Europa. A wide variety of single-celled organisms that live anaerobically, without oxygen, have been discovered in the past, usually deep underwater or deep underground. But researchers had not found a multi-cellular or metazoan animal that did so until now — the giant tube worms that live by hydrothermal vents, for instance, rely on dissolved oxygen.

In these extremes, the investigators were only expecting to see viruses, bacteria and other microbes. The bodies of multi-cellular animals had previously been discovered in these sediments, "but were thought to have sunk there from upper, oxygenated, waters," explained Danovaro. "Our results indicate that the animals we recovered were alive," Danovaro said. "Some, in fact, also contained eggs." 

These new animals could shed light on what life might have looked like before the rise of oxygen levels in the deep ocean and the appearance of the first large animals in the fossil record roughly 550 million to 600 million years ago, the scientists noted.

Danovaro and his colleagues presented their findings online April 6 in the journal BMC Biology.

Casey Kazan