A taxonomic study was carried out on strain SCSWE24(T), isolated from a seawater sample collected from the South China Sea. Cells of strain SCSWE24(T) were Gram-negative, rod-shaped, non-motile, moderately halophilic and capable of reducing nitrate to nitrite. Growth was observed at salinities from 1.5 to 4.5% and at 4-37 °C; it was unable to degrade gelatin. The dominant fatty acids (>15%) were summed feature 3 (C16:1ω7c and/or C16:1ω6c; 50.4%) and C16:0 (21.1%). The G+C content of the chromosomal DNA was 58.8 mol%. 16S rRNA gene sequence comparisons showed that strain SCSWE24(T) was most closely related to an uncultured bacterium clone Tun3b.F5 (98%; GenBank accession no. FJ169216), and showed 92% similarity to an endosymbiont bacterium from the bone-eating worm Osedax mucofloris (clone Omu 9 c4791; FN773233). Levels of similarity between strain SCSWE24(T) and type strains of recognized species in the family Oceanospirillaceae were less than 93%; the highest similarity was 92%, to both Amphritea japonica JAMM 1866(T) and 'Oceanicoccus sagamiensis' PZ-5. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain SCSWE24(T) formed a distinct evolutionary lineage within the family Oceanospirillaceae. Strain SCSWE24(T) was distinguishable from members of phylogenetically related genera by differences in several phenotypic properties. On the basis of the phenotypic and phylogenetic data, strain SCSWE24(T) represents a novel species of a new genus, for which the name Sinobacterium caligoides gen. nov., sp. nov. is proposed. The type strain of Sinobacterium caligoides is SCSWE24(T) (=CCTCC AB 209289(T) =LMG 25705(T) =MCCC 1F01088(T)). An emended description of Amphritea japonica is also provided.