A new species of the genus Petalophthalmus (Crustacea: Mysida: Petalophthalmidae) is described, based on one specimen collected from the Bismarck Sea (Papua New Guinea, Western Pacific Ocean). This species can be distinguished from the other species of the genus Petalophthalmus by the globular cornea and the armature of the telson. This new species lives between 800 and 1065 m depth. A discussion on the geographic and bathymetric distribution and an identification key to world species of Petalophthalmus are provided.