prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Archaea" Woese et al. 1990
     Phylum "Euryarchaeota" Garrity and Holt 2001
       1 Class "Methanomicrobia"
       2 Class Archaeoglobi Garrity and Holt 2002 [monotypic]
       3 Class Halobacteria Grant et al. 2002
       4 Class Methanobacteria Boone 2002 [monotypic]
       5 Class Methanococci Boone 2002 [monotypic]
       6 Class Methanopyri Garrity and Holt 2002 [monotypic]
       7 Class Thermococci Zillig and Reysenbach 2002 [monotypic]
       8 Class Thermoplasmata Reysenbach 2002 [monotypic]