A novel aerobic, heterotrophic, prosthecate bacterium, designated 26III/A02/215(T), was isolated from surface water of the north-western Mediterranean Sea. Cells stained Gram-negative and were straight to slightly curved rods, forming red colonies on agar plates. The strain grew at 15-37 degrees C inclusive (optimum 30 degrees C) and grew optimally at seawater salinity. Growth was observed on organic acids, amino acids and complex organic substrates. The fatty acids (>5 %) detected in strain 26III/A02/215(T) were C(17 : 1)omega6c, C(18 : 1)omega7c and C(17 : 0). The lipid pattern indicated the presence of phosphatidylglycerol, glucuronopyranosyldiglyceride, monoglycosyldiglyceride, an unidentified glycolipid and three unidentified phospholipids. Phosphatidylethanolamine and diphosphatidylglycerol were absent. Ubiquinone Q-10 was the only respiratory lipoquinone. The G+C content of the genomic DNA was 46.8 mol%. Comparative 16S rRNA gene sequence analysis indicated that strain 26III/A02/215(T) belonged to the Hyphomonas-Hirschia-Robiginitomaculum branch of the order Caulobacterales. This affiliation was consistent with the results of polar lipid analyses. Among this group, the novel isolate was most closely related to Robiginitomaculum antarcticum (93.9 % 16S rRNA gene sequence similarity to the type strain). On the basis of genotypic, chemotaxonomic and phenotypic distinctness, we propose a novel genus, Hellea gen. nov., with Hellea balneolensis sp. nov. as the type species. The type strain of Hellea balneolensis is 26III/A02/215(T) (=DSM 19091(T) =CIP 109500(T) =OOB 269(T)).