Examination of gill parasites from Ophthalmotilapia ventralis (Boulenger, 1898) in Lake Tanganyika (Africa) revealed the presence of four new species of Monogenea, all members of Cichlidogyrus Paperna, 1960 (Ancyrocephalidae). In view of the systematic importance of haptoral structure, the fish host shows a remarkable diversity of morphological groups. Cichlidogyrus vandekerkhovei sp. nov. and C. makasai sp. nov. are especially characterized by the unusual length of the dorsal transverse bar auricles, while C. sturmbaueri sp. nov. is distinguished by the unique shape of the accessory piece of its male copulatory organ. Importantly, C. centesimus sp. nov. displays a number of features new to the genus, namely a spirally coiled thickening at the end of the penis, the absence of an accessory piece in the genital apparatus, and a hitherto unknown uncinuli configuration in the haptor. This is the first record of ancyrocephalid parasites from the Tanganyika basin. Some mechanisms possibly contributing to this yet unknown diversity are discussed, identifying topics deserving further scientific scrutiny.