Mitochondrial respiration is an ancient characteristic of eukaryotes. However, it was lost independently in multiple eukaryotic lineages as part of adaptations to an anaerobic lifestyle. An international team of researchers has found a multicellular animal with no mitochondrial DNA, making it the only known animal to exist without the need to breathe oxygen. In their paper published in Proceedings of the National Academy of Sciences [1], the group describes their study of Henneguya salminicola, a microscopic, parasitic member of the group Myxozoa and its unique physiology.