The Negativicutes is a class of firmicute bacteria, whose members have a peculiar cell wall composition which stains Gram negative, unlike most other members of the Firmicutes. The family Veillonellaceae, formerly known as Acidaminococcaceae, we once considered members of the class Clostridia. The name Selenobacteria also refers to some members of this group. The description of this family was emended in 2010 and, together with the Acidaminococcaceae (familia nova, which means a newly coined taxa), it was placed in the order Selenomonadales (ordo novus) in the class Negativicutes (classis novus) of the phylum Firmicutes.
Members of this family are all obligate anaerobes, and occur in habitats such as rivers, lakes, and the intestines of vertebrates. They range from spherical forms, such as Megasphaera and Veillonella, to curved rods, as typified by the Selenomonads. Selenomonas has a characteristic crescent-shape, with flagella inserted on the concave side, while Sporomusa is similar but non-motile. Their names refer to this distinctive morphology: selene means moon, and musa means banana.
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)  and National Center for Biotechnology Information (NCBI) and the phylogeny is based on 16S rRNA-based LTP release 111 by The All-Species Living Tree Project 
♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature (LPSN)
♪ Prokaryotes where no pure (axenic) cultures are isolated or available, i. e. not cultivated or can not be sustained in culture for more than a few serial passages
- ^ Morotomi M, Nagai F, Sakon H (July 2007). "Genus Megamonas should be placed in the lineage of Firmicutes; Clostridia; Clostridiales; 'Acidaminococcaceae'; Megamonas". Int. J. Syst. Evol. Microbiol. 57 (Pt 7): 1673–4. doi:10.1099/ijs.0.65150-0. PMID 17625216.
- ^ Marchandin, H.; Teyssier, C.; Campos, J.; Jean-Pierre, H.; Roger, F.; Gay, B.; Carlier, J. -P.; Jumas-Bilak, E. (2009). "Negativicoccus succinicivorans gen. Nov., sp. Nov., isolated from human clinical samples, emended description of the family Veillonellaceae and description of Negativicutes classis nov., Selenomonadales ord. Nov. And Acidaminococcaceae fam. Nov. In the bacterial phylum Firmicutes". International Journal of Systematic and Evolutionary Microbiology 60 (6): 1271–1279. doi:10.1099/ijs.0.013102-0. PMID 19667386.
- ^ J.P. Euzéby. "Negativicutes". List of Prokaryotic names with Standing in Nomenclature (LPSN) . Retrieved 2013-03-20.
- ^ Sayers et al. "Negativicutes". National Center for Biotechnology Information (NCBI) taxonomy database . Retrieved 2013-03-20.
- ^ All-Species Living Tree Project."16S rRNA-based LTP release 111 (full tree)". Silva Comprehensive Ribosomal RNA Database . Retrieved 2013-03-20.