[living organisms] see Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
   Superkingdom Prokaryota Margulis 1974 nom. nud.
     Kingdom Bacteria Cavalier-Smith 2002 stat. inval. - bacteria see Domain Bacteria Woese et al. 1990 stat. inval.
       Subkingdom Posibacteria Cavalier-Smith 1987 see Domain Bacteria Woese et al. 1990 stat. inval.
         Phylum Firmicutes (Gibbons and Murray 1978) Garrity and Holt 2001 stat. inval. see Phylum Bacillota Gibbons and Murray 2021
           Class Clostridia Rainey 2010
             1 Order Clostridiales Prévot 1953 (Approved Lists 1980) see Order Eubacteriales Buchanan 1917 (Approved Lists 1980)
             2 Order Halanaerobiales corrig. Rainey and Zhilina 1995
             3 Order Natranaerobiales Mesbah et al. 2007
             4 Order Thermoanaerobacterales Wiegel 2010