This is the only known animal that doesn’t need oxygen to survive

Breathing is essential for animals to stay alive. Or so we thought. In a study published Monday in the Proceedings of the National Academy of Sciences , researchers have now identified the first animal that doesn’t use oxygen to breathe: Henneguya salminicola, an 8-millimeter white parasite that infects the flesh of Chinook salmon. Multicellular organisms use oxygen to produce energy, a process that happens in the mitochondria. This organelle has its own genes for this process, but when scientists looked for them in the parasite, they were completely absent, New Scientist reports. The reason why this animal­­ lost the genes to breathe is unclear, but it’s possible it gets its energy from its host.