Abstract | The first metazoa living in permanently anoxic conditions.
Three species of multi-cellular eukaryote, phylum Loricifera, have been found in totally anoxic conditions. They have no mitochondria, instead replacing those oxygen-burning energy generators with endosymbionts that look a lot like hydrogenosomes, an organelle seen in unicellular lifeforms in anoxic conditions. Thus ‘complex’ life can live without oxygen – a proof of principle discovery. Only a millimetre long, so maybe oxygen-free life isn’t suited to big lifeforms, but who knows? In the right conditions – a hydrogen and sulfur rich environment – larger forms might evolve.
