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To date, three genera of dactylogyridean parasites have been recorded on African characiform fishes: Afrocleidodiscus (3 species), Annulotrema (46 species) and Characidotrema (10 species). Annulotrema represent the most species-rich genus, while 39 species are parasitizing hosts from the family Alestidae. Alestidae, often called African tetras are distributed in freshwaters almost throughtout Africa, and belong to the most speciose family of the African characiform fishes. During field trips in Kenya (2008, 2009) and Sudan (2010, 2014) a total of five species of the Alestidae (Alestes baremoze, Alestes dentex, Brycinus nurse, Hydrocynus forskahlii, Micralestes elongatus) have been examined and 16 Annulotrema species were found: Annulotrema ansatum Kičinjaová and Řehulková, 2015; A. pontile Kičinjaová and Řehulková, 2015; A. bipatens Kičinjaová, Řehulková and Gelnar, 2015; A. cucullatum Kičinjaová, Řehulková and Blažek, 2015; A. besalis Řehulková, Musilová and Gelnar 2014; A. sangmelinensis Birgi, 1988; A. nili Paperna, 1973; A. alestesnursi Paperna, 1973; A. delta Paperna, 1973; A. elongata Paperna & Thurston, 1969; A. spiropenis Paperna, 1969, and five others probably represent species new to science. The main objectives of the present study are to: 1) investigate species diversity of Annulotrema species from alestids in Lake Turkana, Kenya and Blue and White Nile, Sudan; 2) evaluate the relative taxonomic importance of the characters of the reproductive organs and those of the haptoral sclerites in accordance with molecular data; and 3) build, for the first time, the molecular phylogeny of dactylogyrids infecting African tetras based on partial sequences of the 28S rDNAgene. Morphological analysis of sclerotized structures of the Annulotrema species indicates that the most important feature for species determination within this genus is the morphology of the male copulatory organ (abbreviated below as MCO). Our survey of monogeneans found on the gills of five species of tetras suggests that there are at least four morpho-groups within these parasites, with regard to the basic structure of the MCO. The division into the groups based on morphological criterions was also supported by molecular data. Results of the phylogenetic analysis show the monophyletic nature of the Annulotrema species.
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