Simple SummaryMonogenean flatworms are mainly parasitic in lower aquatic vertebrates including fish, anurans and chelonians.Gyrodactylusis one of the 23 genera of Gyrodactylidae. With only 41 species described, the total number ofGyrodactylusspecies described from African freshwater fish still remains low. The known species represent only a fraction of the expected species richness ofGyrodactylusin Africa. In this study, we examined the gills of 738 cyprinid specimens. We isolated 26 individuals belonging toGyrodactylusfrom these hosts. Twelve of these from two host species were morphologically characterized and proposed to belong to one single newly described species. In view of the importance of the cyprinid–monogenean system in studying the aquatic biodiversity and biogeography of North Africa, the present study is a substantial contribution to the parasite species inventory of these fishes.AbstractTo date, 41 species ofGyrodactylushave been described from Africa. However, none of these have been reported in Morocco. After identifying and examining 738 cyprinid host specimens, 26 specimens belonging toGyrodactyluswere found to parasitize the gills of nine species ofLuciobarbus,Carasobarbus, andPterocapoeta. The current study provides new information about the presence of a new parasitic species in Morocco, the first to be characterized on a species level in the Maghreb region. It describes in detail 12 specimens ofGyrodactylusisolated from the gills ofLuciobarbus pallaryi(Pellegrin, 1919) andLuciobarbus ksibi(Boulenger, 1905). Based on morphoanatomical observations, the characterization of the specimens collected indicates a species ofGyrodactylusthat is new to science, described here asGyrodactylus nyingiaen. sp. The new species is different from previously described gyrodactylids infecting African cyprinid hosts because it has a longer hamulus total length, a longer hamulus root, a downward projecting toe of the marginal hook, and a trapezium-shaped ventral bar membrane with a slightly striated median portion and small rounded anterolateral processes. This study increases the total number ofGyrodactylusspp. found in African cyprinids to four.