Macroderoides luki n. sp. (Trematoda: Macroderoididae) is described from the intestine of spotted gar (Lepisosteus oculatus) collected from multiple locales on the Trinity River in eastern Texas, U.S.A. Members of the new species are most similar to Macroderoides trilobatus in that they possess an ovary composed of 3 lobes rather than an undivided ovary as in the other 6 species in North America. In the new species, the distance between the cirrus sac and ovary is far greater, the eggs are almost twice the size, and the body is longer than in M. trilobatus. This is the eighth species of Macroderoides named in North America and the largest specimens known from this group.