A whitish Gram-negative, motile, aerobic bacterium, designated strain H 14(T), was isolated from seawater collected at St Kilda beach in Port Phillip Bay, Melbourne, Australia. Analysis of 16S rRNA gene sequences revealed that the organism belonged to the Roseobacter lineage of the class Alphaproteobacteria, forming a distinct evolutionary lineage at the genus level. Strain H 14(T) was distantly related to the genera Nautella, Ruegeria and Pseudoruegeria (family Rhodobacteraceae). Strain H 14(T) was unable to degrade gelatin, casein, chitin, agar and starch, did not produce any carotenoids, did not possess bacteriochlorophyll a and had a limited ability to utilize carbon sources. Strain H 14(T) grew with concentrations of 1-8 % (w/v) NaCl and over a temperature range of 5-35 degrees C. Phosphatidylglycerol was the major phospholipid (90 %); phosphatidylcholine (7.9 %) and phosphatidylethanolamine (2.0 %) were present in minor quantities. The predominant fatty acids were C(18 : 1)omega7c (82.4 %), C(18 : 1)omega9c (5.1 %) and C(18 : 0) (3.8 %). The DNA G+C composition for strain H 14(T) was 59.1 mol%. Based on the results of physiological, biochemical, chemotaxonomic and phylogenetic investigations, a new genus, Celeribacter gen. nov., with the type species Celeribacter neptunius sp. nov. is proposed. The type strain of the type species is H 14(T) (=KMM 6012(T)=CIP 109922(T)).