A new nematode species, Philometra johnii sp. nov. (Philometridae), is described from male and female specimens found in the ovary of the sin croaker, Johnius dussumieri (Cuvier) (Perciformes, Sciaenidae), in the Arabian Gulf, off the southern coast of Iraq. Based on light and scanning electron microscopical examination, the new species differs from all other gonad-infecting Philometra spp. with dorsal lamella-like structures on the distal tip of the gubernaculum in having a dorsal bipartite protuberance formed by two subdorsal lamellated parts separated from each other by a smooth longitudinal field. This gubernaculum structure is unique among all philometrids. Other distinguishing features include the structure of the male tail, number (6 pairs) and arrangement of genital papillae and the length of spicules (102-153 μm). From eight congeneric, gonad-infecting species with unknown males, the new species can be distinguished by some morphological and biometrical features found in gravid females (absence of caudal projections, length of oesophagus, moderately developed anterior oesophageal inflation, length of first-stage larvae) by the host type (fish family) and geographical distribution. Philometra johnii sp. nov. is the fourth known philometrid species recorded from marine waters of Iraq.
