Two　Gram-stain-negative　bacterial　strains,　15-R06ZXC-3T　and　R06B22T,　were　isolated　from　the　surface　sediment　of　the　Arctic　Ocean.　Phylogenetic　analyses　based　on　the　16S　rRNA　gene　and　genome　sequences　indicated　that　strain　15-　R06ZXC-　3T　belongs　to　the　genus　Thioclava,　while　strain　R06B22T　belongs　to　the　genus　Zhongshania.　Strain　15-R06ZXC-3T　showed　the　closest　relationship　to　Thioclava　indica　DT23-4T.　The　digital　DNA-DNA　hybridization　(dDDH)　and　average　nucleotide　identity　(ANI)　values　between　strain　15-R06ZXC-3T　and　all　of　the　type　strains　of　the　genus　Thioclava　ranged　from　20.8　to　30.4%　and　79.1　to　85.7%,　respectively.　Strain　R06B22T　was　most　closely　related　to　Zhongshania　marina　DSW25-10T.　The　dDDH　and　ANI　values　between　strain　R06B22T　and　all　of　the　type　strains　of　the　genus　Zhongshania　ranged　from　18.6　to　20.4%　and　77.5　to　79.4%,　respectively.　These　dDDH　and　ANI　values　were　all　below　the　standard　cutoff　criteria　for　the　delineation　of　bacterial　species,　indicating　that　the　two　strains　may　represent　novel　species　within　their　respective　genera.　Furthermore,　their　phenotypic　and　chemotaxonomic　characteristics　also　differentiated　them　from　closely　related　species.　Based　on　the　polyphasic　analyses,　strains　15-R06ZXC-3T　and　R06B22T　separately　represent　novel　species　of　the　genera　Thioclava　and　Zhongshania,　for　which　the　names　Thioclava　arctica　sp.　nov.　(type　strain　15-　R06ZXC-　3T　=　MCCC　1A07434T=　KCTC　8342T)　and　Zhongshania　arctica　sp.　nov.　(type　strain　R06B22T　=　MCCC　1A08273T=　KCTC　8343T)　are　proposed.　Additionally,　phylogenomic　analyses　showed　that　the　strain　Marortus　luteolus　ZX-21T　was　clustered　with　the　strain　Z.　marina　DSW25-10T　and　all　other　type　strains　of　the　genus　Zhongshania.　Furthermore,　the　ANI　and　dDDH　values　between　strains　ZX-　21T　and　DSW25-　10T　were　97.6%　and　78.8　+/-　2.5%,　respectively,　strongly　indicating　that　they　represented　a　single　species.　Therefore,　it　is　proposed　that　M.　luteolus　Yu　et　al.　2019　be　recognized　as　a　later　heterotypic　synonym　of　Z.　marina　On　et　al.　2019.