[1] Although several neighbouring Clostridia species (firmicute bacteria) also stain gram-negative, the proteins responsible for the unusual diderm structure of the Negativicutes may have actually been laterally acquired from Pseudomonadota (formerly Proteobacteria).

[7] Historically, the Negativicutes consisted of a single order, the Selenomonadales, and two families, Veillonellaceae and Acidaminococcaceae based on 16S rRNA gene sequence similarity.

The current taxonomic view is inclusive of these members who have been validly assigned to the families Selenomonadaceae and Sporomusaceae within the emended Selenomonadales order.

[7] Molecular markers in the form of conserved signature indels (CSIs) and proteins (CSPs) justify the present taxonomic divisions.

[7] The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[13] and National Center for Biotechnology Information (NCBI)[14] Succinispira Acidaminococcus Phascolarctobacterium Phascolarctobacterium wakonense Shigeno et al. 2019 Succiniclasticum Anaeromusa Anaeroarcus Anaerosporomusa Pelorhabdus Acetonema Pelosinus Methylomusa Sporomusa Lucifera Sporolituus Thermosinus Propionispora Anaerospora Dendrosporobacter Anaerosinus Strömpl et al. 1999 Veillonella Megasphaera [incl.