A Gram-negative, slightly halophilic, strictly aerobic, motile chemoorganotrophic bacterium, strain MED92T, was isolated from a surface water sample from the eastern Mediterranean Sea. Phylogenetic analysis based on its 16S rRNA gene sequence, retrieved from the whole-genome sequence, demonstrated that this isolate is unique, showing <93 % sequence similarity to species of the families Oceanospirillaceae and Alteromonadaceae. The polar lipid profile of the novel strain consisted of phosphatidylethanolamine, phosphatidylglycerol, an unknown aminophospholipid and diphosphatidylglycerol. Major fatty acids are 16 : 1ω7c/15 iso 2-OH (41.2 % relative amount), 18 : 1ω7c (35.9 %), 16 : 0 (16.1 %), 10 : 0 3-OH (5.0 %) and 18 : 0 (1.0 %). Preferred carbon sources are organic acids and amino acids. The DNA G+C content is 46.6 mol%. Based on a phenotypic, chemotaxonomic and phylogenetic analyses, it is proposed that this marine bacterium represents a novel genus and species, for which the name Neptuniibacter caesariensis gen. nov., sp. nov. is proposed. The type strain is MED92T (=CECT 7075T=CCUG 52065T).