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Polystomatidae is a monogenean family whose representatives infect mainly (semi)-aquatic tetrapods. Species of SphyranuraWright, 1879 exhibit ectoparasitism on salamander hosts, with molecular work supporting their inclusion within Polystomatidae, at an early diverging, yet unresolved, position in the clade of otherwise endoparasitic polystomatid parasites of batrachian hosts. Records of representatives of Sphyranuraare scarce with genetic data only available for S. oligorchisAlvey, 1933. Based on detailed morphological examination and comparison with type material, we identified worms belonging to Sphyranurainfecting Oklahoma salamander (Eurycea tynerensis) as S. euryceaeHughes & Moore, 1943. Along with an amended diagnosis of Sphyranura, we provide the first molecular data for S. euryceaein the form of a mitochondrial genome and nuclear (18S, 28SrRNA) markers. Close morphological similarity between the two species of Sphyranurais reflected in low genetic divergence. Mitochondrial level comparison reveals instances of tRNA gene rearrangements in polystomatids. Although the phylogenetic reconstruction supports Sphyranuraas early branching in the lineage of polystomatid monogeneans infecting batrachians, certain nodes remain unresolved.

Owing to the largely unexplored diversity of metazoan parasites, their speciation mechanisms and the circumstances under which such speciation occurs – in allopatry or sympatry – remain vastly understudied. Cichlids and their monogenean flatworm parasites have previously served as a study system for macroevolutionary processes, e.g., for the role of East African host radiations on parasite communities. Here, we investigate the diversity and evolution of the poorly explored monogeneans infecting a West and Central African lineage of cichlid fishes: Chromidotilapiini, which is the most species-rich tribe of cichlids in this region. We screened gills of 149 host specimens (27 species) from natural history collections and measured systematically informative characters of the sclerotised attachment and reproductive organs of the parasites. Ten monogenean species (Dactylogyridae: Cichlidogyrusand Onchobdella) were found, eight of which are newly described and one redescribed herein. The phylogenetic positions of chromidotilapiines-infecting species of Cichlidogyruswere inferred through a parsimony analysis of the morphological characters. Furthermore, we employed machine learning algorithms to detect morphological features associated with the main lineages of Cichlidogyrus. Although the results of these experimental algorithms remain inconclusive, the parsimony analysis indicates that West and Central African lineages of Cichlidogyrusand Onchobdellaare monophyletic, unlike the paraphyletic host lineages. Several instances of host sharing suggest occurrences of intra-host speciation (sympatry) and host switching (allopatry). Some morphological variation was recorded that may also indicate the presence of species complexes. We conclude that collection material can provide important insights on parasite evolution despite the lack of well-preserved DNA material.