Two gram-negative, aerobic, non-pigmented, non-motile, rod-shaped bacteria, strains KMM 9015 and KMM 9018(T), were isolated from a sample of shallow sediment collected from the Sea of Japan. An analysis of the nearly complete 16S rRNA gene sequences showed that the isolates were very close to each other phylogenetically (99.9 % sequence similarity) and their close relatives were Marinovum algicola FF3(T) (95.8 and 95.9 %, respectively) and members of the genera Leisingera (95.7-95.1 and 95.8-95.2 %), Phaeobacter (95.0-94.2 and 95.1-94.2 %) and Thalassobius (96.3-94.8 and 96.2-94.7 %) of the class Alphaproteobacteria. In phylogenetic trees based on 16S rRNA gene sequences, strains KMM 9015 and KMM 9018(T) were positioned as a distinct phylogenetic line adjacent to Marinovum algicola. The major isoprenoid quinone was Q-10, the polar lipids consisted of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and an unknown lipid and the major fatty acid was C(18 : 1)ω7c, followed by 11-methyl C(18 : 1)ω7c, in both strains. The DNA G+C contents of strains KMM 9015 and KMM 9018(T) were 60.2 and 61.9 mol%, respectively. Based on distinctive phenotypic characteristics and phylogenetic analysis, strains KMM 9015 and KMM 9018(T) represent a novel species in a novel genus, for which the name Primorskyibacter sedentarius gen. nov., sp. nov. is proposed. The type strain of Primorskyibacter sedentarius is strain KMM 9018(T) ( = NRIC 0784(T) = JCM 16874(T)).