But marine biologists seem open to the idea that multicellular animals can live without oxygen though the evidence is indirect. Three species of loriciferan appear to go their whole lives without oxygen, researchers report in BMC Biology. Pulled out of a briny, sulfurous hellhole 3.5 kilometers below the surface of the Mediterranean Sea, the newly found creatures look like tiny cups with tentacles sticking out. Loriciferans are real, multicellular animals though, so different from other creatures that the tiny marine oddballs have their own phylum on a par with mollusks and arthropods. Following molecular tests and microscope work, the scientists who found the three species propose that the loriciferans in the muck aren’t just visiting down there but are full-time residents.
Three research expeditions — in 1998, 2005 and 2008 — have found loriciferans in core samples from the basin. When researchers first found the animals, they thought they were cadavers. To see if the loriciferans had just wafted down after dying elsewhere, researchers brought up more sediment cores and tested them on ship in nitrogen-filled incubators protected from oxygen. In molecular tests, the animals appeared to be alive and metabolizing. The presence of cast-off skins also suggests that the loriciferans are growing on location. They may be reproducing there too -Two individuals had eggs. Also, the loriciferans aren’t even a millimeter long and have limited mobility, so it’s unlikely that they’d move through the 50 meters of oxygen-free water above them. Thus, the researchers argue, it’s most likely the basin is their full-time home. Their cells don’t appear to have mitochondria, which use oxygen to generate energy. Instead, images of loriciferan tissue reveal what look like hydrogenosomes, organelles that power some anaerobic single-celled creatures.
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