An orange-pigmented, Gram-staining-negative, rod-shaped bacterium, designated 96_Hippo_TS_3/13(T) was isolated from the brood pouch of a diseased seahorse male of the species Hippocampus barbouri from the animal facility of the University of Giessen, Germany. Phylogenetic analyses based on the nearly full-length 16S rRNA gene sequence placed strain 96_Hippo_TS_3/13(T) into the monophyletic cluster of the genus Mesonia within the family Flavobacteriaceae. However, the strain shared only 92.2-93.8% sequence similarity to type strains of species of the genus Mesonia, with highest sequence similarity to the type strain of Mesonia aquimarina. Cellular fatty acid analysis showed a Mesonia-typical fatty acid profile including several branched and hydroxyl fatty acids with highest amounts of iso-C15 : 0 (40.9%) followed by iso-C17 : 0 3-OH (14.8%). In the polyamine pattern, sym-homospermidine was predominant. The diagnostic diamino acid of the peptidoglycan was meso-diaminopimelic acid. The quinone system contained exclusively menaquinone MK-6. The only identified compound in the polar lipid profile was phosphatidylethanolamine present in major amounts. Additionally, major amounts of an unidentified aminolipid and two unidentified lipids not containing a phosphate group, an amino group or a sugar residue were detected. The genomic G+C content of strain 96_Hippo_TS_3/13(T) was 30 mol%. Based on genotypic, chemotaxonomic and physiological characterizations we propose a novel species of the genus Mesonia, Mesonia hippocampi sp. nov., with strain 96_Hippo_TS_3/13(T) ( = CIP 110839T = LMG 28572(T) = CCM 8557(T)) as the type strain. An emended description of the genus Mesonia is also provided.