[3] The name "Firmicutes" was derived from the Latin words for "tough skin," referring to the thick cell wall typical of bacteria in this phylum.

[5] The currently accepted taxonomy based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[6] and the National Center for Biotechnology Information (NCBI).

[citation needed] "Thermodesulfobiales" ♦ Peptococcales Proteinivoracales Eubacteriales Limnochordales "Capillibacteriales" Sulfobacillales Symbiobacteriales Thermaerobacterales Dethiobacterales Natranaerobiales Gelria Koleobacterales Caldicellulosiruptorales "Caldanaerobiales" Thermacetogeniales Carboxydothermales Desulfovirgulaceae Ammonificales "Brockiales" Dictyoglomerales Thermosediminibacterales Thermoanaerobacterales Tissierellales 1 Tissierellales Peptostreptococcales Thermolithobacterales Carboxydocellales Desulfitibacterales Desulfitisporales Calderihabitantales Moorellales Zhaonellaceae Syntrophomonadales "Thermanaerosceptrales" Thermincolales "Heliobacteriales" Desulfitobacteriales Desulfotomaculales Halanaerobiales "Hydrogenisporales" Selenomonadales Gracilibacteraceae Lutisporales Clostridiales Christensenellales Aristaeellaceae Mahellales Caldicoprobacterales Monoglobales Acetivibrionales "Oscillospirales" Lachnospirales Hydrogenibacillus Thermicanales Alicyclobacillales Paenibacillales Thermoactinomycetales Novibacillaceae Caldalkalibacillales Caldibacillaceae Calditerricolales Microaerobacter Desulfuribacillales Tepidibacillales Oxalophagaceae Aneurinibacillales Brevibacillales "Bacillus thermozeamaize" Bacillales Listeriaceae Exiguobacteriales Staphylococcales Gemellaceae Culicoidibacterales Turicibacteraceae Haloplasmatales Acholeplasmatales Erysipelotrichales Mycoplasmatales Lactobacillales ♦ Paraphyletic Firmicutes Mollicutes [incl.

Alicyclobacillia; Desulfuribacillia; Culicoidibacteria] "Selenomonadia" [Negativicutes] Peptococcia "Dehalobacteriia" Desulfitobacteriia "Moorellia" Thermacetogeniales {DSM-12270} Syntrophomonadia "Carboxydocellia" Thermincolia "Carboxydothermia" Desulfotomaculia "Proteinivoracia" "Dethiobacteria" Natranaerobiia "Halanaerobiia" Thermosediminibacteria "Thermoanaerobacteria" "Clostridiia" s.s. [incl.

[15][failed verification] The phylum Bacillota as part of the gut microbiota has been shown to be involved in energy resorption, and potentially related to the development of diabetes and obesity.

[23] The presence of Christensenella (Bacillota, in class Clostridia), isolated from human faeces, has been found to correlate with lower body mass index.