A novel anaerobic, mesophilic, amino-acid-fermenting bacterium, designated strain CL-84(T), was isolated from the swine intestinal tract on mucin-based media. Cells were curved rods (0.8-1.2 × 3.5-5.0 µm), stained Gram-negative and were non-motile with no evidence of spores. Strain CL-84(T) produced acetate, propionate, formate and butyrate as the end products of metabolism when grown on serine. Optimum growth occurred at 39 °C and pH 6.5. The major cellular fatty acids were iso-C15:0, iso-C15:0 3-OH, iso-C17:0 and C16:0, distinguishing strain CL-84(T) from closely related species. The DNA G+C content of strain CL-84(T) was 55.1 mol%. 16S rRNA gene sequence analysis showed that strain CL-84(T) shared 90-95% similarity with characterized genera within the phylum Synergistetes, family Synergistaceae. Phylogenetic analysis showed that strain CL-84(T) was related to, but distinct from, Cloacibacillus evryensis. Based on these findings, we propose that strain CL-84(T) represents a novel species of the genus Cloacibacillus. We further propose the name Cloacibacillus porcorum sp. nov. be designated for this species. The type strain is CL-84(T) (=DSM 25858(T)=CCUG 62631(T)). An emended description of the genus Cloacibacillus is provided.