Prosogonotrema iraqiense n. sp. (Sclerodistomidae: Prosogonotrematinae) is described in the flathead grey mullet, Mugil cephalus Linnaeus (Mugiliformes: Mugilidae), collected from the Arabian Gulf off Iraq during June and October 2019. Currently there are 11 species of Prosogonotrema Vigueras, 1940 commonly accepted: Prosogonotrema arabica Yadav, 1980; Prosogonotrema bilabiatum Vigueras, 1940 (type species); Prosogonotrema caesionis Gu and Shen, 1979; Prosogonotrema diacanthi Bilqees and Durrani, 1980; Prosogonotrema karachiense Bilqees and Durrani, 1980; Prosogonotrema pavasi Lokhande, 1990; Prosogonotrema piscicola (Srivastava, 1949) Gibson, 2002 (Syn. Bhaleraoia piscicola Srivastava, 1949); Prosogonotrema plataxum Gu and Shen, 1979; Prosogonotrema posterouterina Yadav, 1980; and Prosogonotrema symmetricum Oshmarin, 1965 originally described from marine fishes, and Prosogonotrema nickoli Bilqees and Khan, 1992 described from a freshwater cyprinid. Six additional species that have been considered synonyms of P. bilabiatum are also considered. Prosogonotrema diacanthi is considered a junior synonym of P. piscicola and Prosogonotrema carangi Hussain and Rao, 1980 nec Velasquez, 1961 is determined to be a species distinct from P. bilabiatum and is reassigned herein as Prosogonotrema aluteri nomen novum per the ICZN. Prosogonotrema iraqiense differs from all currently recognized species in the genus by having the width of the ventral sucker approach or exceed the width of the body and from all except P. pavasi (body length/width ratio 1:1.4–1:1.5) by having a distinctive narrower, more elongate body profile with a larger body length/width ratio (1:5.8–1:6.1 vs. 1: 2.0–1:4.1). A key to the 18 species we recognize in Prosogonotrema is included.