MSc (Environmental Sciences), North-West University, Potchefstroom Campus Amphibians serve as hosts to all the major parasite groups including polystomes (Monogenea). Although Madagascar has more than 350 frog species of which all but two are endemic, the known polystome (Monogenea: Polystomatidae) diversity parasitising Malagasy frogs is restricted to three species of Madapolystoma Du Preez, Raharivololoniaina et al., 2010, one species of Kankana Du Preez, Raharivololoniaina et al., 2011 and one Metapolystoma Combes, 1976. Investigating the anuran parasite diversity at selected Malagasy localities led to the discovery of polystomes unknown to science. Two Madapolystoma species were discovered from respectively Blommersia domerguei Guibé, 1974 and Mantella expectata Busse and Böhme. For Metapolystoma, two new host genera are reported with the description of six new species from Boophis Tschudi, 1838 treefrogs, Boophis albilabris (Boulenger, 1888), Boophis doulioti (Angel, 1934), Boophis luteus (Boulenger, 1882), Boophis madagascariensis (Peters, 1874), Boophis occidentalis Glaw & Vences, 1994, and Aglyptodactylus madagascariensis (Duméril, 1853). These descriptions are supported with morphology and, where possible, with phylogenetic analyses and genetic divergences. For Madapolystoma, advanced in utero development was reported following the observation of well-developed hamuli and two pairs of haptoral suckers in developing embryos of the newly described species. Inside some of these in utero embryos an early F2 generation embryo was also observed. This is the first report of true viviparity among polystomatid flatworms. Twenty-six percent of the 311 Malagasy frogs for which red listing assessment has been completed are classified as Endangered and 7% as Critically Endangered. Consequently, it will be difficult to describe further polystomes that were retrieved from frogs now listed as Threatened. For some of these only a single specimen is available, and the Threatened conservation status would prohibit any further collection. The full extent of the effect that polystomes have on their hosts is not fully understood. In numerous anuran species the parasite-host interactions are at best poorly documented. Polystomes provide insights into the biogeographical origin of their amphibian hosts and ultimately aid in their conservation. The need for parasite surveys in Madagascar is, therefore, emphasised to better conserve its biodiversity. Using the criteria proposed by Smyth and Wakelin (1994) for ‘ideal parasites’, amphibian polystomes have been found to meet all the listed requirements necessary to be considered ‘ideal parasites’. Masters