Anna Karnkowska from the Czech Republic found a eukaryotic cell that lacks mitochondria, recently (granted more studies will have to support the finding to ensure that this is actually the case). Found within the gut of a chinchilla, a species in the genus Monocercomonoides seems to lack genes and key proteins related to mitochondria. The suggestion that it lacks mitochondria goes against the current definition that eukaryotes has mitochondria. It seems that the nutrient rich gut environment may have driven oxymonad Monocercomonoides to direct itself in a way where it has no need for mitochondria to produce energy for it. Oxygen is scarce in the gut and it seems to be relying on enzymes found in the cytoplasm to provide energy. I will be very interested to see what pans out for this eukaryote without a mitochondria.
"A Eukaryote without a Mitochondrial Organelle"