Résumé
What are monogenean parasitic flatworms? In general, parasitic lifestyles, with their exploitation of host resources, necessitate profound evolutionary changes in behaviour, morphology, and genomes. Underlying patterns and mechanisms are fragmentarily understood at best. Monogenean parasitic flatworms are less publicly known or scientifically studied than helminths of well-known clinical concern, like tapeworms and flukes. Nonetheless, the World Register of Marine Species lists 5,706 accepted species of monogeneans in 76 families. These flatworms are mainly ectoparasites (infecting external body parts) of ectothermic aquatic vertebrates. Although several flatworm lineages live in or on a host, most flatworm species belong to a single clade, Neodermata, all representatives of which are parasites. Classically, next to the typically endoparasitic (i.e. living inside a host) tapeworms and flukes, most of which have a complex life cycle involving multiple host species, Monogenea is listed as a third neodermatan group, having a single-host life cycle.