<jats:p>A mesophilic, obligately anaerobic, carbohydrate-fermenting bacterium, designated 8KG-4<jats:sup>T</jats:sup>, was isolated from an upflow anaerobic sludge blanket reactor treating high-strength organic wastewater from salted vegetable production processes. Cells of strain 8KG-4<jats:sup>T</jats:sup> were non-motile, spherical and 0.7–1.5 µm in diameter (mean, 1.0 µm). Spore formation was not observed under any culture conditions tested. The strain grew optimally at 37 °C (range for growth 25–40 °C) and pH 7.0 (range, pH 6.5–7.5), and could grow fermentatively on glucose, ribose, xylose, galactose and sucrose. The main end products of glucose fermentation were acetate, ethanol and hydrogen. Organic acids, alcohols and amino acids were not utilized for growth. Yeast extract was not required for growth. Nitrate, sulfate, thiosulfate, elemental sulfur, sulfite and Fe(III) nitrilotriacetate were not used as terminal electron acceptors. The G+C content of the genomic DNA was 61.1 mol%. 16S rRNA gene sequence analysis revealed that the isolate represented a previously uncultured lineage at the subphylum level within the phylum <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="class" xlink:type="simple"> <jats:ext-link ext-link-type="uri" xlink:href="http://dx.doi.org/10.1601/nm.8953" xlink:type="simple"> <jats:italic>Lentisphaerae</jats:italic> </jats:ext-link> </jats:named-content> known as ‘WWE2 subgroup I’. The major cellular fatty acids were anteiso-C<jats:sub>15 : 0</jats:sub>, iso-C<jats:sub>16 : 0</jats:sub>, C<jats:sub>16 : 0</jats:sub> and anteiso-C<jats:sub>17 : 0</jats:sub>. Respiratory quinones were not detected. The most abundant polar lipid of strain 8KG-4<jats:sup>T</jats:sup> was phosphatidylethanolamine. A novel genus and species, <jats:italic>Oligosphaera ethanolica</jats:italic> gen. nov., sp. nov., is proposed to accommodate strain 8KG-4<jats:sup>T</jats:sup> ( = JCM 17152<jats:sup>T</jats:sup> = DSM 24202<jats:sup>T</jats:sup>  = CGMCC 1.5160<jats:sup>T</jats:sup>). In addition, we formally propose <jats:italic>Oligosphaeria</jats:italic> classis nov. and the subordinate taxa <jats:italic>Oligosphaerales</jats:italic> order nov. and <jats:italic>Oligosphaeraceae</jats:italic> fam. nov.</jats:p>