Gyrodactylus aff. mugili Zhukov, 1970 (Monogenoidea: Gyrodactylidae) is recorded and described from the gill lamellae of 11 of 35 greenback mullet, Chelon subviridis (Valenciennes) (minimum prevalence 31%), from the brackish waters of the Shatt Al-Arab Estuary in southern Iraq. The gyrodactylid was also found on the gill lamellae of one of eight Speigler's mullet, Valamugil speigleri (Bleeker), from the brackish waters of the Shatt Al-Basrah Canal (minimum prevalence 13%). Fifteen Klunzinger's mullet, Liza klunzingeri (Day), and 13 keeled mullet, Liza carinata (Valenciennes), collected and examined from southern Iraqi waters, were apparently uninfected. The gyrodactylids from the greenback mullet and Speigler's mullet were considered to have affinity to G. mugili Zhukov, 1970, and along with G. mugili may represent members of a species complex occurring on mullets in the Indo-Pacific Region. A single damaged gyrodactylid from the external surfaces of the abu mullet, Liza abu (Heckel), was insufficient for species identification. Previously identified species of Gyrodactylus recorded on L. abu in Iraq by various authors were considered possible misidentifications or accidental infections.