A taxonomic study was carried out on strains 22Ⅱ1-22F38T and 22Ⅱ-S13e,which were isolated from sea water and sediments from the Atlantic Ocean,respectively.Two strains are Gram negative,oxidase and catalase positive,oval to pear shaped,and motile by a polar flagellum.Phylogenetic analysis based on 16S rRNA gene sequences indicate that both strains belong to the genus Hyphomonas,with highest sequence similarity (98.2%) to the type strain H.jannaschiana DSM 5153T andH.Johnsonii ATCC 43964T.The genomic ANIm values and DNA-DNA hybridization estimate values between strain 22Ⅱ1-22F38T and seven type strains were determined to range from 82.84%to 84.10%and from 18.0%to 19.1%respectively.The isolate 22Ⅱ1-22F38T processes a G+C content of 58.3%and uses Q-11 as the predominant respiratory quinone.The combined phenotypic and genotypic data show that strains 22Ⅱ1-22F38T and 22Ⅱ-S13erepresent a novel species of the genus Hyphomonas,for which the name Hyphomonasatlanticussp.nov.is proposed,with the type strain 22Ⅱ1-22F38T (=LMG 27916T=MCCC 1A09418T).In addition,we conclude that Hyphomonas hirschiana is a later synonym of Hyphomonas neptunium.