A Gram-negative, rod-shaped and motile strain, designated CL-AS9(T), was isolated from polar seawater of the Arctic. Analysis of the 16S rRNA gene sequence of the strain showed an affiliation with the genus Spongiibacter, sharing 93.9% and 93.7% sequence similarities with the type strains of Spongiibacter tropicus CL-CB221(T) and Spongiibacter marinus HAL40b(T), respectively. Phylogenetic analyses revealed that strain CL-AS9(T) formed a separate branch that was distinct from a clade comprising Spongiibacter marinus HAL40b(T), Spongiibacter tropicus CL-CB221(T) and Melitea salexigens 5IX/A01/131(T). Cells of the strain grew optimally at 20-25 �XC and pH 6.6-8.0 in the presence of 3-4% (w/v) sea salts. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unidentified aminophospholipid. The major quinone was ubiquinone 8. The major cellular fatty acids were C(16:1)�s7c and/or iso-C(15:0) 2-OH (23.1%), C(17:1)�s8c (22.1%) and C(18:1)�s7c (15.6%). The genomic DNA G+C content was 53.6 mol%. Based on the phylogenetic, chemotaxonomic and phenotypic data presented, we propose the name Spongiibacter borealis sp. nov. with the type strain CL-AS9(T) (=KCCM 90094(T) =JCM 17304(T)) and the reclassification of Melitea salexigens as a later heterotypic synonym of Spongiibacter marinus. We also provide emended descriptions of the genus Spongiibacter and Spongiibacter marinus.