ABSTRACT. – Solostamenides iraqensis n. sp. (Microcotylidae), a monogenean parasite on the gill filaments of the freshwater mullet fish Liza abu (Heckel, 1843) in the Tigris River in Iraq, is described. The present specimens assigned to Solostamenides because they have a penis head armed with hook-like spines, atrial rim muscular unarmed, with single mid-dorsal vaginal pore. The new species is distinguished from the other four Solostamenides species previously recorded, namely, Solostamenides mugilis (Vogt, 1878), S. pseudomugilis (Hargis, 1956), S. platyorchis Zhang & Yang, 2001 and S. paucitesticulatus Kritsky & Öktener, 2015. Absence or presence of longitudinal septum in the ventral view of buccal organ, the size, shape and number of clamps, the arrangement, size and number of testis, the size and shape of spines of the copulatory organ, and the absence or presence and shape of the proximal filament in the egg were the main characters for differentiation between the species. All species of Solostamenides have been described from gills of grey mullets (Mugilidae), three of them (S. mugilis, S. pseudomugilis, S. platyorchis) occur on Mugil cephalus L. in marine habitats, whereas S. paucitesticulatus and S. iraqensis n. sp. have been found on L. abu in freshwater habitats. These data suggest some degree of host specificity of Solostamenides spp.