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This is Scientific American's 60-Second Science. I'm Cynthia Graber. This'll just take a minute.

As scientists delve¹ deeper beneath the ocean’s surface, they find bizarre creatures that have adapted to harsh and extreme environments. Now comes a new one—the discovery of the first multicellular animals that survive and reproduce entirely² without oxygen.

Researchers had thought that only single-celled organisms such as prokaryotes and protozoa could live in the oxygen-deprived environments of the deepest ocean. When scientists did find multicellular organisms, they assumed that they’d sunk from oxygen-enriched waters.

But over the past decade, scientists in Italy and Denmark sent three expeditions to fetch samples from sediment³ in what’s known as a deep hypersaline anoxic basin in the Mediterranean⁴. And in these sediments⁵, from almost two miles below the ocean’s surface, they found three distinct species of a tiny multicellular animal phylum called Loricifera.

They don’t have mitochondria. Instead, they seem to have organelles that resemble hydrogenosomes—similar to mitochondria, but that use anaerobic⁶ chemistry. Scientists don’t yet fully⁷ understand the biochemistry—but the discovery opens the possibility of complex life forms on oxygen-free planets.

Thanks for the minute for Scientific American's 60-Second Science. I'm Cynthia Graber.