Wikipedia
Monocercomonoides is a genus of flagellated protozoa belonging to the order Oxymonadida. Monocercomonoides species have been discovered living in the guts of small mammals, snakes and insects. It has been characterized as the first example of an Eukaryotic organism devoid of mitochondria. The total genome of Monocercomonoides incorporates around 75 million base pairings (75 Mb) with 16629 predicted protein-coding genes. The genome does not contain any mitochondrial genes (mtDNA), or any genes for cardiolipin, a lipid for energy-transducing membranes.
In 2016, Monocercomonoides sp. PA 203, a Monocercomonoides species which resides in the intestines of the chinchilla, was found to possess no mitochondria at all. Monocercomonoides sp. PA 203 obtains its energy by enzymatic action on nutrients absorbed from the environment. It has also acquired, by lateral gene transfer, a cytosolic sulphur mobilisation system to provide essential clusters of iron and sulfur required for protein synthesis. The quintessential mitochondrial iron-sulphur cluster pathway is considered to have been lost secondarily.