<jats:p>A novel facultatively anaerobic bacterium, strain HC45<jats:sup>T</jats:sup>, was isolated from sediment of a brackish meromictic lake in Japan, Lake Harutori. Cells were pleomorphic, and filamentous bodies were 5–100 μm in length. For growth, the optimum pH was 7.0 and the optimum temperature was 45–50 °C. The G+C content of the genomic DNA was 71 mol%. iso-C<jats:sub>15 : 0</jats:sub>and anteiso-C<jats:sub>15 : 0</jats:sub>were the major components in the cellular fatty acid profile. The predominant respiratory quinone was MK-7. Strain HC45<jats:sup>T</jats:sup>shared very low 16S rRNA gene sequence similarity with cultivated strains ( ≤ 85 %). Phylogenetic analysis based on 16S rRNA gene sequences revealed that the isolate was distantly related to members of the family<jats:italic>Symbiobacteriaceae</jats:italic>and family XVII<jats:italic>Incertae Sedis</jats:italic>in the class<jats:italic>Clostridia</jats:italic>, and they formed a cluster separate from canonical species of the phylum<jats:italic>Firmicutes</jats:italic>. These results indicated that strain HC45<jats:sup>T</jats:sup>should not be placed in any existing class of the phylum<jats:italic>Firmicutes</jats:italic>. On the basis of phylogenetic and phenotypic characterization,<jats:italic>Limnochorda pilosa</jats:italic>gen. nov., sp. nov. is proposed with HC45<jats:sup>T</jats:sup>( = NBRC 110152<jats:sup>T</jats:sup> = DSM 28787<jats:sup>T</jats:sup>) as the type strain, as the first representative of novel taxa,<jats:italic>Limnochordales</jats:italic>ord. nov.,<jats:italic>Limnochordaceae</jats:italic>fam. nov. in<jats:italic>Limnochordia</jats:italic>classis. nov.</jats:p>