A novel anaerobic, Gram-stain-negative, endospore-forming bacterium, designated strain MLFW-2T, was isolated from anoxic sediments collected from the drainage area of a geothermal spring near Mono Lake, CA, USA. Optimal growth was achieved at 34 °C and pH 8.25-8.50 in medium containing 0.75 % (w/v) NaCl. Catalase, but not oxidase, was produced. Strain MLFW-2T was an obligate anaerobe capable of respiring with nitrate, nitrite, DMSO, arsenate, antimonate, selenate and selenite as terminal electron acceptors. Lactate, pyruvate, formate and H2 could serve as electron donors to support growth. The isolate was incapable of fermentation. The predominant fatty acids were C16 : 0, C16 : 1ω9c, C16 : 1ω7c, C18 : 1ω9c and C18 : 1ω7c. The major polar lipids were phosphatidylglycerol and phosphatidylethanolamine. The only isoprenoid quinone detected was menaquinone 7 (MK-7). The DNA G+C content was 38.2 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence demonstrated that strain MLFW-2T was a member of the order Bacillales and was most closely related to Desulfuribacillus alkaliarsenatis AHT28T (93.9 % similarity). On the basis of phenotypic and phylogenomic evidence, strain MLFW-2T represents a novel species of the genus Desulfuribacillus, for which the name Desulfuribacillus stibiiarsenatis sp. nov. is proposed. The type strain is MLFW-2T (=DSM 28709T=JCM 30866T). An emended description of the genus Desulfuribacillus is also provided.