A Gram-stain-negative, non-motile, aerobic and ovoid or rod-shaped bacterium, designated MA4-5T, was isolated from ark shell (Scapharca broughtonii) collected from the South Sea, South Korea. The novel strain grew optimally at 25 °C, at pH 7.0-8.0 and in the presence of 2.0 % (w/v) NaCl. Neighbour-joining and maximum-likelihood phylogenetic trees based on 16S rRNA gene sequences showed that strain MA4-5T forms a coherent cluster with the type strains of Roseovarius albus, Roseovarius aestuarii and Roseovarius nubinhibens, sharing 97.0-99.2 % sequence similarity. It exhibited 16S rRNA gene sequence similarity of 93.1-96.1 % to the type strains of other Roseovarius species. Strain MA4-5T contained Q-10 as the predominant ubiquinone and C18 : 1ω7c as the major fatty acid. The major polar lipids of strain MA4-5T were phosphatidylcholine, phosphatidylglycerol, one unidentified aminolipid and one unidentified lipid. The DNA G+C content of strain MA4-5T was 53.8 mol% and its mean DNA-DNA relatedness values with the type strains of R. albus, R. aestuarii and R. nubinhibens were 11-26 %. Differential phenotypic properties, together with phylogenetic and genetic distinctiveness, indicated that strain MA4-5T is separate from recognized species of the genus Roseovarius. On the basis of the data presented, strain MA4-5T is considered to represent a novel species of the genus Roseovarius, for which the name Roseovarius scapharcae sp. nov. is proposed. The type strain is MA4-5T ( = KCTC 42703T = NBRC 111226T).