The three types of archaea are the crenarchaeota, the euryarchaeota and the korarchaeota. Archaea is a group of single-celled microorganisms that come in a variety of shapes and survive extreme conditions. Some of them require oxygen, while others do not.
The crenarchaeota are able to endure both extreme temperatures and extreme acidity. They come in rod, cocci, filamentous and unique shapes. Thermophiles, those preferring high temperatures, and psychrophiles, those preferring frigid temperatures, fall into this category. The euryarchaeota include methanogens, which produce methane, and halophiles, which favor environments high in salt. The korarchaeota is a hodge-podge of other archaea that do not fit into the other categories.