A Gram-negative, heterotrophic, marine bacterium, designated strain TT1T, was isolated from seawater collected from the shallow coastal region of Anping Harbour, Tainan, Taiwan. Cells grown in broth cultures were straight rods that were motile by means of a single polar flagellum. The isolate required NaCl for growth and exhibited optimal growth at 30-35 �XC, 2-4 % NaCl and pH 7-8. Strain TT1T grew aerobically and was not capable of anaerobic growth by fermentation of glucose or other carbohydrates. Q-10 was the sole major isoprenoid quinone. Cellular fatty acids were dominated by C18 : 1�s7c (47.5 %), C18 : 1 2-OH (16.3 %) and C19 : 0�s8c cyclo (10.6 %). The DNA G+C content was 56.4 mol%. Phylogeny based on 16S rRNA gene sequences showed that strain TT1T formed a distinct genus-level lineage in the family Rhodospirillaceae of the class Alphaproteobacteria and exhibited the highest sequence similarity with species of the genera Thalassobaculum (89.9-90.0 % 16S rRNA gene sequence similarity), Oceanibaculum (89.4-89.9 %) and Nisaea (89.1-89.7 %). Strain TT1T could be distinguished from species of these phylogenetically closest genera based on differences in DNA G+C contents (56.4 mol% vs 60.0-68.0 mol%), fatty acid profiles and some physiological characteristics. On the basis of the polyphasic taxonomic data from this study, strain TT1T is considered to represent a novel species of a new genus in the family Rhodospirillaceae, for which the name Tagaea marina gen. nov., sp. nov. is proposed. The type strain of the type species is TT1T (= JCM 18659T = BCRC 80493T).