Methanosagania

This simple microbe, the Methanosagania, evolved from a relic population of Protosagania, and it developed new features through a combination of heavy selective pressure and horizontal gene transfer. It lives deep under the sediment where there is very little oxygen, as well as few other microbes. It derives energy through methanogenesis, where it converts carbon dioxide and hydrogen into methane. Unlike earthly methanogens, it is not quite completely intolerant of oxygen; however, oxygen-rich environments interfere with its own processes enough that it cannot thrive above ground. It has a cell wall.