A facultatively anaerobic marine gammaproteobacterium, designated strain M46(T), was isolated from Mediterranean seawater at Malvarrosa beach, Valencia, Spain. The strain was characterized by using a polyphasic approach and was found to be situated within the genus Photobacterium in the family Vibrionaceae. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain M46(T) was closely related to P. rosenbergii CECT 7644(T), P. halotolerans CECT 5860(T) and P. ganghwense CECT 7641(T), showing sequence similarities of 96.8, 96.4 and 96.2 %, respectively. According to the results of phylogenetic analyses based on recA and gyrB gene sequences, the most closely related taxon was P. ganghwense CECT 7641(T) with 87.4 and 85.0 % sequence similarity, respectively. Regardless of the gene used in phylogenetic analysis, strain M46(T) always formed a separate and stable clade containing these three species of the genus Photobacterium. Strain M46(T) was not luminescent and produced a diffusible brown pigment. It required NaCl to grow, reduced nitrate to nitrite and oxidized a small number of substrates in Biolog GN plates. Strain M46(T) was positive for arginine dihydrolase (ADH), β-galactosidase, aesculin hydrolysis and DNase activity. In API ZYM tests, the novel strain was positive for alkaline phosphatase, leucine arylamidase and acidic phosphatase activities. The major cellular fatty acids were unsaturated C(18) and C(16), as in other members of the genus Photobacterium, but their relative amounts and the presence or absence of other fatty acids differentiated strain M46(T) from its closest relatives. Based on the results of this polyphasic taxonomic study, strain M46(T) represents a novel species of the genus Photobacterium, for which the name Photobacterium aphoticum is proposed. The type strain is M46(T) ( = CECT 7614(T) = KCTC 23057(T)).