This study of monogenean species of Ligophorus Euzet & Suriano, 1977 from Liza spp. (Mugilidae) from the Northwestern African coast identifies the occurrence of four new species. Ligophorus gabrioni n. sp. on Liza falcipinnis (Valenciennes, 1836) is characterized by a small antero-median protuberance and two lateral and symmetrical expansions on the ventral transverse bar; a tubular accessory piece distally expanded; and a vagina that is not sclerotised (not visible). Ligophorus benhoussai n. sp. on Liza grandisquamis (Valenciennes, 1836) is characterized by a very long sickle-shaped accessory piece, which is wide at the base and tapering at the end, and a α-shaped vagina. Also found on Liza grandisquamis were Ligophorus bazairii n. sp. and Ligophorus hamzati n. sp. The former is characterized by a tubular bottle-opener shaped accessory piece; whereas the latter is characterized by a tubular accessory piece with a bifurcated distal extremity whose branches are also bifurcated. No Monogenea were found on the endemic Liza bandialensis Diouf, 1991. In our opinion, the differences in monogenean species richness that exist among the various hosts may be due to fluctuations of host populations as the result of bottleneck or vicariant events.