Nanoarchaeum

Discovered as being tiny dots on another organism, Nanoarchaeum was published as being an organism in need of a new phylum among the Archaea. They have not been able to grown on their own and while a parasitic lifestyle cannot be excluded at present, there have been several observations that promote a symbiotic mode of life. Since the original publication, there have been nanoarchaeotal 16 S rDNA sequences found in high temperature biotopes all over the world that are related to Nanoarchaeum but need to be classified in different families.
See Ignicoccus for detailed descriptions.