A Gram-stain-negative, non-flagellated, non-gliding and rod-shaped bacterial strain, designated KEM-8 T , was isolated from seawater in the Korean peninsula. Strain KEM-8 T was found to grow optimally at pH 7.0-8.0, at 30 8C and in the presence of 2-3 % (w/v) NaCl. A neighbourjoining phylogenetic tree based on 16S rRNA gene sequences showed that strain KEM-8 T falls within the clade comprising species of the genus Gaetbulibacter, clustering with the type strains of Gaetbulibacter marinus and Gaetbulibacter lutimaris with which it exhibits 98.4 and 97.2 % 16S rRNA gene sequence similarity, respectively. Sequence similarities to Gaetbulibacter saemankumensis SMK-12 T and Gaetbulibacter aestuarii KCTC 23303 T were 95.4 and 95.2 %, respectively. Strain KEM-8 T was found to contain MK-6 as the predominant menaquinone and iso-C 15 : 0 , iso-C 17 : 0 3-OH, iso-C 16 : 0 3-OH and iso-C 15 : 1 G as the major fatty acids. The major polar lipids were identified as phosphatidylethanolamine and an unidentified lipid. The DNA G+C content of strain KEM-8 T was 36.0 mol% and mean DNA-DNA relatedness values with G. marinus KCTC 23046 T and G. lutimaris D1-y4 T were 27.6¡0.9 and 10.3¡1.4 %, respectively. Differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, revealed that strain KEM-8 T is distinguishable from species of the genus Gaetbulibacter with validly published names. On the basis of the data presented, strain KEM-8 T represents a novel species of the genus Gaetbulibacter, for which the name Gaetbulibacter aquiaggeris sp. nov. is proposed. The type strain is KEM-8 T (5KCTC 42198 T 5NBRC 110553 T ).The genus Gaetbulibacter, a member of the family Flavobacteriaceae (phylum Bacteroidetes), was established by Jung et al. (2005) with the description of Gaetbulibacter saemankumensis, isolated from seawater of the Yellow Sea in South Korea. Subsequently, three further species of the genus, Gaetbulibacter marinus, Gaetbulibacter aestuarii and Gaetbulibacter lutimaris, were described from marine environments in Korea (Yang & Cho, 2008;Park et al., 2012;Yoon et al., 2013).The standard dilution plating technique was used for isolation of bacterial strains from seawater from Geumgang Estuary Bank (368 009 48.960 N 1268 449 23.9990 E) in South Korea. Strain KEM-8 T was isolated on marine agar 2216 (MA; Becton Dickinson) at 25 8C and cultivated routinely on MA at 30 8C. Strain KEM-8 T was maintained on MA at 4 8C for short-term preservation and as a glycerol suspension (20 %, w/v in distilled water) at 280 8C for long-term preservation. G. marinus KCTC 23046 T and G. lutimaris D1-y4 T were used as reference strains for DNA-DNA hybridization, phenotypic characterization (except for some characters) and fatty acid analysis. G. saemankumensis (type species of the genus Gaetbulibacter) SMK-12 T and G. aestuarii KCTC 23303 T were used as reference strains for phenotypic characterization (except for some characters) and fatty acid analysis. G. saemankumensis SMK-12 T and G. lutimaris D1-y4 T were obta...