Two novel Gram-negative bacterial strains, designated CL-GR15(T) and CL-GR35, were isolated from coastal seawater of the east coast of Korea. Identical 16S rRNA gene sequences were found in the two strains, and it was found that the strains represented a distinct and deep evolutionary lineage of descent in the order Rhizobiales, and clustered with yet-uncultured marine bacteria. This lineage could not be associated with any of 12 known families in the order Rhizobiales. The most closely related established genus was Ochrobactrum (90.7-92.5% sequence similarity) in the family Brucellaceae. Cells of the strains were facultatively anaerobic, weakly motile rods which occasionally exhibited cohesion with each other. The strains were catalase-, oxidase- and gelatinase-positive, and accumulated intracellular poly-beta-hydroxybutyrate granules. Ubiquinone 10 was the major quinone. The major polar lipids comprised phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, an unidentified aminolipid and an unidentified glycolipid. The cellular fatty acids mainly consisted of C(18:1)omega7c, summed feature 3 (C(15:0) iso 2-OH and/or C(16:1)omega7c) and C(20:1)omega7c. The DNA G+C content was 52.8-53.0 mol%. DNA-DNA hybridization experiments revealed high values (>97%) for relatedness between strains CL-GR15(T) and CL-GR35 and suggested that these two strains constituted a single species. The distinct phylogenetic position and combinations of genotypic, phenotypic and chemotaxonomic characteristics support the proposal of Cohaesibacter gen. nov., with the type species Cohaesibacter gelatinilyticus sp. nov. (type strain, CL-GR15(T)=KCCM 42319(T)=DSM 18289(T)). Cohaesibacteraceae fam. nov. is also proposed.