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, were 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, i.e. a newly coined taxon), it was placed in the order Selenomonadales (ordo novus) in the class Negativicutes (classis novus) of the phylum Firmicutes.