A Gram-stain-negative, non-flagellated, aerobic and coccoid, ovoid or rod-shaped bacterium, designated AM-4T, was isolated from seawater collected from the East Sea, South Korea and subjected to a taxonomic study using a polyphasic approach. The novel strain grew optimally at 30-35 °C, at pH 7.0-8.0 and in the presence of 1.0-3.0 % (w/v) NaCl. Phylogenetic trees based on 16S rRNA gene sequences showed that strain AM-4T forms a distinct evolutionary lineage independent of other taxa of the family Rhodobacteraceae. Strain AM-4T exhibited 16S rRNA gene sequence similarities of 95.1-95.5 % to the type strains of Aestuariihabitans beolgyonensis, Donghicola eburneus and Pseudooctadecabacter jejudonensis, and of less than 94.9 % to the type strains of other taxa. Strain AM-4T contained Q-10 as the predominant ubiquinone and C18 : 1ω7c and C16 : 0 as the major fatty acids. The major polar lipids detected in strain AM-4T were phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, one unidentified lipid, one unidentified aminolipid and one unidentified glycolipid. The fatty acid and polar lipid profiles of strain AM-4T were distinguished from those of the phylogenetically related taxa. The DNA G+C content of strain AM-4T was 57.2 mol%. On the basis of the phylogenetic, chemotaxonomic and other phenotypic properties, strain AM-4T represents a novel species of a new genus in the family Rhodobacteraceae, for which the name Marivivens donghaensis gen. nov., sp. nov., is proposed. The type strain of the type species is AM-4T ( = KCTC 42776T = CECT 8947T).