A bacterial strain designated SW15(T) was isolated from a sample of the reef-building coral Isopora palifera, collected in southern Taiwan. The novel strain was characterized using a polyphasic taxonomic approach. Cells of strain SW15(T) were Gram-negative, aerobic, light yellow, rod-shaped and motile by means of a single polar flagellum. In phylogenetic analyses based on 16S rRNA gene sequences, strain SW15(T) appeared to belong to the genus Idiomarina in the class Gammaproteobacteria and to be most closely related to Idiomarina homiensis PO-M2(T) (97.6% sequence similarity). Strain SW15(T) exhibited optimal growth between 20 and 30 �XC, with NaCl between 3% and 4% (w/v) and at a pH value between 7 and 8. Predominant cellular fatty acids were iso-C(15:0) (31.1%), iso-C(17:0) (15.4%), iso-C(17:1)�s9c (10.0%) and C(16:0) (8.8%). The major respiratory quinone was ubiquinone Q-8. The polar lipid profile consisted of a mixture of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylserine, an uncharacterized aminolipid and several uncharacterized phospholipids. The DNA G+C content was 51.1 mol%. The level of DNA-DNA relatedness between strain SW15(T) and Idiomarina homiensis PO-M2(T) was 42.6-56.5%. The results of physiological and biochemical tests allowed the clear phenotypic differentiation of the novel strain from established species of the genus Idiomarina. Based on the genotypic, phenotypic and chemotaxonomic data, strain SW15(T) represents a novel species in the genus Idiomarina, for which the name Idiomarina aquimaris sp. nov. is proposed, with SW15(T) (=LMG 25374(T)=BCRC 80083(T)) as the type strain.