<jats:p>Three strains of a hitherto unknown, Gram-negative, tiny, anaerobic coccus were collected from human clinical samples originating from skin and soft tissues. The three isolates displayed at least 99.9 % identity in their 16S rRNA gene sequences and more than 99.8 % identity in their <jats:italic>dnaK</jats:italic> gene sequences. The isolates were affiliated to the family <jats:italic>Veillonellaceae</jats:italic>, the coccobacillus <jats:italic>Dialister micraerophilus</jats:italic> being the most closely related species, but there was no more than 91.1 % identity in the 16S rRNA gene sequence between this species and the three isolates. Phylogeny based on the 16S rRNA gene confirmed that the three strains represent a novel and robust lineage within the current family <jats:italic>Veillonellaceae</jats:italic>. A similar genomic structure was demonstrated for the three isolates by PFGE-based analysis. Morphology and metabolic end products, as well as genotypic and phylogenetic data supported the proposal of the novel genus <jats:italic>Negativicoccus</jats:italic> gen. nov., with the novel species <jats:italic>Negativicoccus succinicivorans</jats:italic> sp. nov. [type strain ADV 07/08/06-B-1388<jats:sup>T</jats:sup> (=AIP 149.07<jats:sup>T</jats:sup>=CIP 109806<jats:sup>T</jats:sup>=DSM 21255<jats:sup>T</jats:sup>=CCUG 56017<jats:sup>T</jats:sup>) as type species]. Phylogenetic analyses based on the 16S rRNA gene sequences of members of the phylum <jats:italic>Firmicutes</jats:italic> and other phyla indicated that the family <jats:italic>Veillonellaceae</jats:italic> forms a robust lineage clearly separated from those of the classes ‘<jats:italic>Bacilli</jats:italic>’, ‘<jats:italic>Clostridia</jats:italic>’, <jats:italic>Thermolithobacteria</jats:italic> and ‘<jats:italic>Erysipelotrichi</jats:italic>’ in the phylum <jats:italic>Firmicutes</jats:italic>. Therefore, we propose that this family is a class-level taxon in the phylum <jats:italic>Firmicutes</jats:italic>, for which the name <jats:italic>Negativicutes</jats:italic> classis nov. is proposed, based on the Gram-negative type of cell wall of its members, with the type order <jats:italic>Selenomonadales</jats:italic> ord. nov. In this order, a novel family, <jats:italic>Acidaminococcaceae</jats:italic> fam. nov., is proposed and description of the family <jats:italic>Veillonellaceae</jats:italic> is emended.</jats:p>