Lake Tanganyika s biodiversity and endemicity sparked considerable scientific interest. Its monogeneans, minute parasitic flatworms, have received renewed attention. Their host-specificity and simple life cycle 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. Three representatives of Bathybatini (Bathybates minor, B. fasciatus, B. vittatus), endemic predatory non-littoral cichlids, host a single dactylogyridean monogenean species. It is new to science and described as Cichlidogyrus casuarinus sp. nov. This species and C. nshomboi and C. centesimus, from which it differs by the distal end of the accessory piece of the male apparatus and the length of its heel, are the only Cichlidogyrus species with spirally coiled thickening of the penis wall. In Cichlidogyrus, this feature was only found in parasites of endemic Tanganyika tribes. The seemingly species-poor Cichlidogyrus community of Bathybatini may be attributed to meagre host isolation in open water. The new species infects cichlids that substantially differ phylogenetically and ecologically. This may be an adaptation to low host availability. Cichlidogyrus species infecting African Great Lake cichlids are summarized and proposed as model for the influence of host ecology on disease transmission.