Abstract
Mycteronastes undulatae gen. nov., sp. nov. (Monogenea: Monocotylidae) is described from the nasal cavities of Raja undulata caught off Arcachon in France and off Lisbon (Tagus estuary) and Sines in Portugal. Merizocotyle icopae Beverley-Burton & Williams, 1989, be-comes Mycteronastes icopae n. comb., the type species of Mycteronastes gen. nov. Similarities between M. icopae and M. undulatae include the arrangement of the haptor loculi and hooks, the general disposition of the reproductive system, the presence of eyespots and the habitat (the nasal cavities of the host). However, a distinctive feature is the absence of a copulatory sclerite and bulb in M. undulatae. The diagnoses of the following taxa are amended: Monocotylidae, Merizocotylinae and Merizocotyle.