Morphological and molecular characterisation of an intestinal trematode from the marbled lungfish Protopterus aethiopicus in Kenya reveals a new species of Heterorchis (Digenea: incertae sedis)

<i>Heterorchis</i> Baylis, 1915, is a poorly reported genus of parasitic digeneans with ambiguous phylogenetic affinities. Four members of this genus have been described exclusively from Africa, although two of these taxa are regarded as <i>species inquirenda</i>. The material for this study was collected from the intestine of Marbled lungfish, <i>Protopterus aethiopicus</i> Heckel, 1851, in Lake Kanyaboli, Kenya, between May and October 2023. An integrated approach of light microscopy, scanning electron microscopy (SEM), and molecular techniques was employed in the study of the trematode. Morphological analysis revealed a new species characterised by distinctive features, including the extent of the intestinal caeca in the post-excretory vesicle field, a large excretory pore located posterior to the testes, and the cirrus-sac reaching the level of the seminal receptacle. Phylogenetic trees from Bayesian Inference and maximum-likelihood analyses of the <i>28S</i> rDNA dataset formed a separate clade comprising sequences of <i>Heterorchis</i> spp. The interspecific distance of 2 % (25 bp) was calculated between the present sequence and those available on GenBank, MW586924, for <i>Heterorchis</i> cf. <i>crumenifer</i> Baylis, 1915. The infection indices were recorded as prevalence (P) = 46.7 %, mean intensity (MI) = 1.25, and mean abundance (MA) = 0.58.