Lake Tanganyika's biodiversity and endemicity sparked considerable scientific interest regarding biodiversity and evolution. Its monogeneans, minute parasitic flatworms, have received renewed attention. Their host-specificity and simple lifecycle render them ideal for parasite speciation research. Because of the wide ecological and phylogenetic range of its cichlids, Lake Tanganyika is a "natural experiment" to contrast factors influencing monogenean speciation. Bathybatini representatives Bathybates minor, B. fasciatus and B. vittatus, endemic predatory non-littoral cichlids, host a single dactylogyridean monogenean species. New to science, it is described as Cichlidogyrus casuarinus sp. nov. This species and C. nshomboi and C. centesimus, from which it is distinguished based on the distal end of the accessory piece of the male copulatory organ and the length of its heel, are the only Cichlidogyrus species with spirally-coiled thickening of the penis wall. In Cichlidogyrus, this was only found in parasites of endemic Tanganyika tribes. The seemingly species-poor Cichlidogyrus community of bathybatines may be attributed to meagre host isolation in their open water habitat. The new species' host range, cichlids substantially differing phylogenetically and ecologically, may be an adaptation to low host availability. Cichlidogyrus infecting Tanganyika cichlids is proposed as model for the influence of host ecology on disease transmission.