Domain Bacteria Woese et al. 1990
   Phylum Firmicutes corrig. Gibbons and Murray 1978 (Approved Lists 1980)
     Class "Clostridia" Garrity et al. 2001 nom. ined. see Class Clostridia Rainey 2010
       1 Order Clostridiales Prévot 1953 (Approved Lists 1980)
       2 Order "Thermoanaerobacteriales" see Order Thermoanaerobacterales Wiegel, 2010
       3 Order Haloanaerobiales Rainey and Zhilina 1995 see Order Halanaerobiales corrig. Rainey and Zhilina 1995