According to a study published on Tuesday in Proceedings of the National Academy of Sciences, researchers have come across an animal that doesn't need oxygen to survive. That makes it the only one of its kind that can get by like that. Must be nice.
The animal is the parasite Henneguya salminicola. It's commonly found preying upon salmon, though those fish don't appear to be "adversely affected" by it, nor would any human eating such a fish. Due to the fact that it establishes residency within these salmon, it has adapted to survival without adequate oxygen.
Henneguya salminicola neither breathes nor has mitochondrial DNA, giving it the distinction of also being the first multicellular animal discovered in the wild to not have DNA within its mitochondria. In scientific parlance, researchers believed that they had goofed when they initially failed to locate that DNA. But further studies confirmed that they, in fact, did not.
The researchers add that the parasite no longer has "the ability to perform aerobic cellular respiration." This is where the "multicellular" designation is of note, since some single-celled organisms can survive without respiration.
Previous studies have speculated that other multicellular animals can live without oxygen, but those studies lack full confirmation. Analysis is currently being conducted to fix that.
H. salminicola shed it's need for oxygen as it evolved over time. It's not clear why that is, and the mystery is further clouded since its relatives still have a need for oxygen.
"[H. salminicola has] lost their tissue, their nerve cells, their muscles, everything," said evolutionary biologist/study co-author Dorothée Huchon to Live Science. "And now we find they have lost their ability to breathe."
As for how it does survive, well that's not entirely clear. But Huchon speculates it may be leeching off its host.