Lake Tanganyika harbours the most diverse cichlid species assemblage of all African Great Lakes, is home to several non-cichlid fish species flocks, and numerous invertebrate taxa underwent radiation in the lake. This makes it an exquisite study system in the fields of biodiversity and evolution. Since a few years, research on Lake Tanganyika parasites, previously severely overlooked, has intensified. The ecological, behavioural and phylogenetic diversity of Tanganyika cichlids makes them an ideal natural experiment to investigate parasite speciation mechanisms. We use ectoparasitic flatworms belonging to Cichlidogyrus (Monogenea, Dactylogyridae) as model parasites, because of their simple lifecycle, rendering them prime candidates to study the influence of host ecology and evolution on parasite biodiversity. Whereas in littoral Tanganyika cichlids, the host specificity of Cichlidogyrus is relatively strong, preliminary morphological observations suggest this parasite to have a broader host range when infecting deepwater cichlids (e.g. Bathybatini). This may be an adaptation to lower host availability in the deepwater realm, as has been suggested regarding marine fishes. Using multivariate statistic approaches of morphological characters, and genetic characterisation by means of established markers with different rates of molecular evolution, we will assess this apparent lack of host-specificity, by checking for cryptic speciation or host preference. Goals: 1) The student will study the relevant literature, with a focus on the biodiversity of Lake Tanganyika and on evolution of monogeneans infecting cichlid fishes. 2) The student will acquire the skills to isolate parasites, identify them and characterize them using morphological (measurements of hard parts under phase contrast microscopy) and molecular approaches (DNA amplification and sequencing). 3) The student will learn to analyze the morphological and molecular data collected from the target parasites, using multivariate statistics and molecular phylogenetic methodology. 4) The student will practice English writing skills in writing the diploma thesis, with the aim of writing a paper on the obtained results together with the supervisors/collaborators.