60秒科学:多细胞生物不需要氧气（在线收听）

As scientists delve 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 entirely 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 sediment in what’s known as a deep hypersaline anoxic basin in the Mediterranean. And in these sediments, 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 anaerobic chemistry. Scientists don’t yet fully understand the biochemistry—but the discovery opens the possibility of complex life forms on oxygen-free planets.

—Cynthia Graber