A new aerobic, Gram-negative, chemo-organotrophic, euryhaline bacterium, designated strain JL2009(T), was isolated from surface water of the Caribbean Sea. The strain formed flaxen colonies on marine ager 2216 (MA; Difco) medium. Cells were dimorphic, with stalks or a polar flagellum, and reproduction occurred by means of binary fission. Growth occurred at 15-45 A degrees C (optimum at 35 A degrees C), 0-15 % (w/v) NaCl (optimum at 1-10 %) and pH 5-9 (optimum at pH 7-8). Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain formed a distinct evolutionary lineage within the family Hyphomonadaceae. Strain JL2009(T) was most closely related to Maricaulis parjimensis MCS 25(T) (92.2 % DNA sequence similarity), Woodsholea maritime CM2243(T) (90.9 %), and Oceanicaulis alexandrii C116-18(T) (90.9 %). The major respiratory quinone was Q-10. The dominant cellular fatty acids were summed feature 8 (C-18:1 omega 7c), C-18:0 and 11-methyl C-18:1 omega 7c. The polar lipid pattern indicated the presence of phospholipid, phosphatidyl glycerol and glycolipids. The G + C content of the genomic DNA was 70.5 mol%. On the basis of the chemotaxonomic and phenotypic characteristics and the phylogenetic evidence, strain JL2009(T) represents a novel genus and species in the family Hyphomonadaceae, for which the name Euryhalocaulis caribicus gen. nov., sp. nov. is proposed. The type strain of Euryhalocaulis caribicus is JL2009(T) (=CGMCC 1.12036(T) = JCM 18163(T)).