A Gram-stain-negative, facultatively anaerobic, dark-yellow-pigmented bacterium, named SSR2A-4-2T, was isolated from coastal water in the East China Sea. Cells were ovoid or short rods with peritrichous flagella and contained carotenoid in addition to bacteriochlorophyll a pigment. A phylogenetic dendrogram based on 16S rRNA gene sequences showed that strain SSR2A-4-2T formed a distinct clade with members of the genus Blastomonas, with Blastomonasnatatoria EY 4220T (=DSM 3183T) (similarity 95.6 %), Blastomonasursincola KR-99T (=DSM 9006T) (95.5 %) and Blastomonasaquatica PE4-5T (=JCM 30179T) (94.8 %) as its closest phylogenetic relatives. Q-10 was the predominant respiratory quinone. The major fatty acids were summed feature 8 (C18 : 1ω6c and/or C18 : 1ω7c), summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), C17 : 1ω6c and C18 : 1ω7c 11-methyl. The polar lipids contained diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, sphingoglycolipid, four unknown glycolipids and one unknown lipid. The DNA G+C content was 65.1 mol%. On the basis of the evidence presented in this study, strain SSR2A-4-2T represents a novel species of the genus Blastomonas, for which the name Blastomonas marina sp. nov. is proposed, with strain SSR2A-4-2T (=CGMCC 1.15297T=DSM 103453T) as the type strain.