BackgroundLake Tanganyika harbours the most diverse cichlid assemblage of the Great African Lakes. Considering its cichlid flocks consist of approximately 250 endemic species, we can hypothesize a high species-richness in their often quite host-specific monogenean ectoparasites belonging to Cichlidogyrus Paperna, 1960. Yet, only 24 species were described from Tanganyikan hosts and some host tribes have never been investigated for monogeneans. This study presents the first parasitological examination of species of the tribes Cyprichromini (Cyprichromis microlepidotus (Poll, 1956)), Eretmodini (Eretmodus marksmithi Burgess, 2012 and Tanganicodus irsacae Poll, 1950) and Ectodini (Aulonocranus dewindti (Boulenger, 1899)). Specimens of the ectodine Ophthalmotilapia nasuta (Poll & Matthes, 1962) from which four Cichlidogyrus spp. have been previously described from more southern localities were also studied. Further, we discuss the haptor configuration in Tanganyikan Cichlidogyrus spp. and highlight the morphological diversity of the vagina, and that of the heel, a sclerotized part of the male copulatory organ, absent in some species of Cichlidogyrus.Methods Cichlidogyrus spp. were isolated from gills and fixed using GAP. Haptoral and genital hard parts were measured and drawn by means of a phase contrast microscopic examination.ResultsWe describe eight new species: Cichlidogyrus milangelnari n. sp. on C. microlepidotus; C. jeanloujustinei n. sp. on E. marksmithi; C. evikae n. sp. on T. irsacae; C. aspiralis n. sp., C. glacicremoratus n. sp. and C. rectangulus n. sp. on O. nasuta; and C. pseudoaspiralis n. sp. and C. discophonum n. sp. on A. dewindti. Three haptoral morphotypes were recognized among the new species. Species of Cichlidogyrus from closely related hosts exhibited the same morphotypes. Geographical variation in Cichlidogyrus spp. fauna as observed in O. nasuta and three morphotypes were distinguished. Finally, we listed 111 Cichlidogyrus species, of which 27 and three Tanganyikan species lack sclerotized vagina and heel, respectively, just like 19 and seven species outside of the lake.ConclusionsHaptoral and genital features in the Tanganyikan Cichlidogyrus fauna reflect the phylogenetic relationships of their cichlid hosts. It seems that several lineages of Cichlidogyrus spp. exist in Lake Tanganyika but further studies are necessary to confirm this hypothesis and answer questions related to Lake Tanganyika and its cichlids.Electronic supplementary materialThe online version of this article (10.1186/s13071-017-2460-6) contains supplementary material, which is available to authorized users.

Seven new species of Cichlidogyrus Paperna, 1960 (Monogenea: Dactylogyridae) isolated from the gills of six cichlid host species belonging to four tribes and sampled from the Congolese coastline of Lake Tanganyika (LT) are described: Cichlidogyrus adkoningsi sp. nov. from Cyphotilapia frontosa (tribe Cyphotilapiini); C. koblmuelleri sp. nov. from Cardiopharynx schoutedeni (Ectodini); C. habluetzeli sp. nov. from C. schoutedeni and C. frontosa; C. antoineparisellei sp. nov. from Interochromis loocki (Tropheini); C. masilyai sp. nov. from Petrochromis orthognathus (Tropheini); C. salzburgeri sp. nov. from P. trewavasae, and C. sergemorandi sp. nov. from Tylochromis polylepis (Tylochromini). This study represents the first parasitological examination of cyphotilapiine cichlid hosts. Representatives of the Tanganyikan ectodine, tropheine, and tylochromine cichlids previously sampled from various localities in the lake yielded nine, twelve, and two described species of Cichlidogyrus, respectively. The study further includes a morphological characterization of the male copulatory organ of six undescribed species of Cichlidogyrus found on the gills of the tropheines I. loocki and P. orthognathus, and on those of Callochromis melanostigma and Xenotilapia flavipinnis (both Ectodini). Geographical variation in the monogenean fauna of I. loocki was observed. The most closely related cichlid species investigated in this study harboured Cichlidogyrus spp. exhibiting some similarities in their sclerotized structures. Thus, our paper provides additional evidence of the high species richness of Cichlidogyrus and the link with their hosts’s phylogenetic affinities in LT.

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Ectoparasites face a daily challenge: to remain attached to their hosts. Polyopisthocotylean monogeneans usually attach to the surface of fish gills using highly specialized structures, the sclerotized clamps. In the original description of the protomicrocotylid species Lethacotyle fijiensis, described 60 years ago, the clamps were considered to be absent but few specimens were available and this observation was later questioned. In addition, genera within the family Protomicrocotylidae have either clamps of the “gastrocotylid” or the “microcotylid” types; this puzzled systematists because these clamp types are characteristic of distinct, major groups. Discovery of another, new, species of the genus Lethacotyle, has allowed us to explore the nature of the attachment structures in protomicrocotylids. Lethacotyle vera n. sp. is described from the gills of the carangid Caranx papuensis off New Caledonia. It is distinguished from Lethacotyle fijiensis, the only other species of the genus, by the length of the male copulatory spines. Sequences of 28S rDNA were used to build a tree, in which Lethacotyle vera grouped with other protomicrocotylids. The identity of the host fish was confirmed with COI barcodes. We observed that protomicrocotylids have specialized structures associated with their attachment organ, such as lateral flaps and transverse striations, which are not known in other monogeneans. We thus hypothesized that the clamps in protomicrocotylids were sequentially lost during evolution, coinciding with the development of other attachment structures. To test the hypothesis, we calculated the surfaces of clamps and body in 120 species of gastrocotylinean monogeneans, based on published descriptions. The ratio of clamp surface: body surface was the lowest in protomicrocotylids. We conclude that clamps in protomicrocotylids are vestigial organs, and that occurrence of “gastrocotylid” and simpler “microcotylid” clamps within the same family are steps in an evolutionary sequence, leading to the absence of these attributes in species of Lethacotyle.

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