A gram-negative, motile, coccoid- and amorphous-shaped, non-pigmented chemoheterotrophic bacterium, designated strain $PZ-5^T$, was isolated from sea water of Sagami Bay in Japan and subjected to a polyphasic taxonomic study. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the novel isolate could be affiliated with the class Gammaproteobacteria. Strain $PZ-5^T$ showed below 93.9% similarity with validly published bacteria and demonstrated the highest sequence similarity to Dasania marina KOPRI $20902^T$ (93.9%). Strain $PZ-5^T$ formed a monophyletic group with D. marina KOPRI $20902^T$. The DNA G+C content of strain $PZ-5^T$ was 49.8 mol%. The major isoprenoid quinone was Q-8 and redominant cellular fatty acids were $C_{15:0}$ ISO 2OH (19%), $C_{16:1}$ ${omega}7c$ (17.4%), $C_{17:1}$ ${omega}8c$ (16.2%), $C_{11:0}$ 3OH (7.5%), and $C_{15:1}$ ${omega}8c$ (6.5%). Based on evidence from a polyphasic taxonomical study, it was concluded that the strain should be classified as representing a new genus and species of the class Gammaproteobacteria, for which the name Oceanicoccus sagamiensis gen. nov., sp. nov., (type strain $PZ-5^T$ =NBRC $107125^T$ =KCTC $23278^T$) is proposed.