Barring a few known species of single-celled bacteria, scientists have maintained that all living organisms need oxygen to survive. Now, some marine biologists believe that they may have discovered a species of metazoa or multi-celled animals, that can survive without O2!

The three species of Loricifera, were discovered by a team of Italian researchers in the marsh sediments of the L'Atlante basin in the Mediterranean Sea. Considered to be one of the harshest and most extreme environments on Earth, the area, which lies 10,000 feet below the surface, is comprised of salt brines so dense that it does not mix with the oxygen-containing waters. While the researchers have known and pulled some single-celled organisms from the region during prior expeditions, this is the first evidence of a living multi-cell organism surviving in an anoxic or oxygen-free environment.

The sub-millimeter long animals that resemble tiny cups with tentacles sticking out, are similar to mud dragons, except that they lack mitochondria, the cellular structures responsible for converting sugar and oxygen into energy. Instead, their cells are rich in hydrogenosomes, structures that can do a similar job in an oxygen-free environment.

While the researchers do not know how these little creatures evolved to survive in such a harsh environment, they provide a great insight into what the environment under the Earth's ocean used to be like, about 600 million years ago, when the ocean waters did not contain oxygen and, the creatures were much smaller.

The expedition that found these fascinating creatures, is the third one carried out in the last 10 years to look for living organisms in this salty basin, that lays 200km from the Greek Island of Crete.

sources: sciencemag.org,www.cbc.ca,www.wired.com