A novel bacterium, designated strain F028-2(T), was isolated from seawater at Damupo beach in Pohang, Korea, and investigated in a taxonomic study using a polyphasic approach. This novel strain was strictly aerobic, non-motile, Gram-stain-negative and rod-shaped, and occasionally formed aggregates. The temperature, pH and NaCl ranges for growth were 4-30 °C, pH 6.5-9.0 and 1-7% (w/v), respectively. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain F028-2(T) formed a lineage within the family Rhodobacteraceae of the class Alphaproteobacteria, and was closely related to members of the genera Sagittula and Antarctobacter with 96.3-96.4% sequence similarities. The polar lipid profile of strain F028-2(T) comprised diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminolipids, one unidentified phospholipid and six unidentified lipids. The predominant cellular fatty acids were C18:1ω7c and C12:1 3-OH. The genomic DNA G+C content of strain F028-2(T) was 61.6 mol% and the major respiratory quinone was Q-10. Based on phenotypic, phylogenetic and genotypic data, strain F028-2(T) is considered to represent a novel species in the genus Sagittula, for which the name Sagittula marina sp. nov. is proposed. The type strain is F028-2(T) (=KCTC 23543(T)=JCM 17627(T)). An emended description of the genus Sagittula is also proposed.