A species of a previously unknown Gram-positive-staining, anaerobic, coccus-shaped bacterium recovered from a swine manure storage tank was characterized using phenotypic, chemotaxonomic, and molecular taxonomic methods. Comparative 16S rRNA gene sequencing studies and biochemical characteristics demonstrated that this organism is genotypically and phenotypically distinct, and represents a previously unknown sub-line within the order Clostridiales, within the phylum Firmicutes. Pairwise sequence analysis demonstrated that the novel organism clustered within the genus Peptoniphilus, most closely related to Peptoniphilus methioninivorax sharing a 16S rRNA gene sequence similarity of 95.5%. The major long-chain fatty acids were found to be C14:0 (22.4%), C16:0 (15.6%), C16:1ω7c (11.3%) and C16 : 0 ALDE (10.1%) and the DNA G +C content was 31.8 mol%. Based upon the phenotypic and phylogenetic findings presented, a novel species Peptoniphilus stercorisuis sp. nov. is proposed. The type strain is SF-S1(T) ( = DSM 27563(T) = NBRC 109839(T)). In addition, it is proposed to accommodate the genera Peptoniphilus, Anaerococcus, Anaerosphaera, Finegoldia, Gallicola, Helcococcus, Murdochiella and Parvimonas in a new family of the order Clostridiales, for which the name Peptoniphilaceae fam. nov. is proposed; the type genus of the family is Peptoniphilus.