Hydrogenosome

A hydrogenosome is a membrane-enclosed organelle of some anaerobic ciliates, trichomonads, fungi and a few metazoa. The hydrogenosomes of trichomonads (the best studied) produce ATP by a complex metabolic cycle. Unlike mitochondria, this cycle does not use oxygen. It is thought that hydrogenosomes evolved from mitochondria; their structure is rather similar.
In 2010, scientists reported their discovery of the first known anaerobic metazoans with hydrogenosome-like organelles. These organisms were Loricifera living in sediments under deep-water brine pools like the L'Atalante basin. These brine pools are completely without any oxygen (anoxic).