A novel anaerobic, alkaliphilic, Gram-positive, spore-forming bacterium was isolated from a carbonaceous hydrothermal chimney in the Prony Bay, New Caledonia. This bacterium designated strain 3bT grew at temperatures from 30 to 43 °C (optimum 37°C) and at pH between 7.8 and 10.1 (optimum 9.5). Added NaCl was not required for growth (optimum 0-0.2%), but was tolerated up to 4%. Yeast extract was required for growth. Strain 3bT utilized crotonate, lactate, and pyruvate, but not sugars. Crotonate was dismutated to acetate and butyrate. Lactate was disproportionated to acetate and propionate. Pyruvate was degraded to acetate, and traces of hydrogen. Growth on lactate was improved by addition of fumarate, which was used as electron acceptor and converted into succinate. Sulfate, thiosulfate, elemental sulfur, sulfite, nitrate, nitrite, FeCl3, FeIII-citrate, FeIII-EDTA, chromate, arsenate, selenate, and DMSO were not used as terminal electron acceptors. The G+C content of the genomic DNA was 33.2 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the isolate is a member of the family Clostridiaceae, order Clostridiales within the phylum Firmicutes. Strain 3bT was most closely related to Alkaliphilus hydrothermalis FatMR1T (92.2% 16S rRNA gene sequence identity), and was positioned approximately equidistantly between the genera Alkaliphilus, Anaerovirgula, and Natronincola. On the basis of phylogenetic, genetic, chimiotaxonomic, and physiological properties, strain 3bT is proposed to represent the first species of a novel genus, for which the name Serpentinicella alkaliphila gen. nov., sp. nov. is proposed (type strain 3bT = DSM 100013T = JCM 30645T).