BACKGROUND: Lake Tanganyika is the world's second deepest lake. Its diverse cichlid assemblage offers a unique opportunity for studying a deep-water host-parasite model in freshwater. Low host specificity and a broad host range including representatives of the Bathybatini tribe in the only monogenean parasite described from this habitat, Cichlidogyrus casuarinus Pariselle, Muterezi Bukinga & Vanhove, 2015 suggest a link between lower specificity and lower host density. Conversely, high host specificity and species richness are reported for monogeneans of the lake's littoral cichlids. We further investigated whether the deep-water environment in Lake Tanganyika is really monogenean species-depauperate by investigating the monogenean fauna of Trematocara unimaculatum (a representative of the tribe Trematocarini, the sister lineage of the Bathybatini) and Benthochromis horii, a member of the tribe Benthochromini, found in the same deep-water habitat as the already known hosts of C. casuarinus. METHODS: Sclerotised structures of the collected monogenean individuals were characterised morphologically using light microscopy and morphometrics. RESULTS: Both examined cichlid species are infected by a single monogenean species each, which are new to science. They are described as Cichlidogyrus brunnensis n. sp., infecting T. unimaculatum, and Cichlidogyrus attenboroughi n. sp., parasitising on B. horii. Diagnostic characteristics include the distal bifurcation of the accessory piece in C. brunnensis n. sp. and the combination of long auricles and no heel in C. attenboroughi n. sp. In addition C. brunnensis n. sp. does not resemble C. casuarinus, the only species of Cichlidogyrus thus far reported from the Bathybatini. Also Cichlidogyrus attenboroughi n. sp. does not resemble any of the monogenean species documented from the pelagic zone of the lake and is among the few described species of Cichlidogyrus without heel. CONCLUSIONS: As two new and non-resembling Cichlidogyrus species are described from T. unimaculatum and B. horii, colonisation of the deep-water habitat by more than one morphotype of Cichlidogyrus is evident. Based on morphological comparisons with previously described monogenean species, parasite transfers with the littoral zone are possible. Therefore, parasites of pelagic cichlids in the lake do not seem to only mirror host phylogeny and the evolutionary history of this host-parasite system merits further attention.

Department of Botany and Zoology Faculty of Science Masaryk University Kotlářská 2 611 37 Brno Czech Republic

Department of Botany and Zoology Faculty of Science Masaryk University Kotlářská 2 611 37 Brno Czech Republic Biology Department Royal Museum for Central Africa Leuvensesteenweg 13 B 3080 Tervuren Belgium Laboratory of Biodiversity and Evolutionary Genomics Department of Biology University of Leuven Ch Deberiotstraat 32 B 3000 Leuven Belgium Present address Capacities for Biodiversity and Sustainable Development Operational Directorate Natural Environment Royal Belgian Institute of Natural Sciences Vautierstraat 29 B 1000 Brussels Belgium

Institute of Zoology University of Graz Universitätsplatz 2 A 8010 Graz Austria Institute of Vertebrate Biology Academy of Sciences of the Czech Republic Květná 8 603 65 Brno Czech Republic

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