A Gram-negative, aerobic, slightly halophilic, rod-shaped bacterium was isolated from black sand in Soesoggak, Jeju island, Korea. The strain, designated J63(T), was oxidase- and catalase-positive and arginine dihydrolase-negative. The isolate required Na(+) for growth and differed from phenotypically related species by being able to utilize sucrose and d-galactose as a carbon source. Phylogenetic analysis based on the sequence of the 16S rRNA gene revealed that strain J63(T) belongs to the genus Marinomonas. It exhibited 16S rRNA gene sequence similarities of 97.6-98.7 % to the closely related species Marinomonas communis, Marinomonas ostreistagni, Marinomonas aquimarina and Marinomonas vaga. The phylogenetic analysis revealed that strain J63(T) comprised a relatively long subline of descent, shared a branch point with the outlying species Marinomonas communis and occupied a phylogenetically distant position on the main Marinomonas branch. Based on DNA-DNA hybridization, the levels of relatedness between strain J63(T) and M. communis NBRC 102224(T), M. aquimarina CIP 108405(T) and M. vaga JCM 20774(T) were 56.2, 45.1 and 51.3 %, respectively. On the basis of the phenotypic, genetic and phylogenetic data, strain J63(T) should be placed in the genus Marinomonas as representing a novel species, for which the name Marinomonas basaltis sp. nov. is proposed. The type strain is J63(T) (=KCTC 22118(T)=JCM 14948(T)).