Integrated characterisation of nine species of the Schistorchiinae (Trematoda: Apocreadiidae) from Indo-Pacific fishes: two new species, a new genus, and a resurrected but ‘cryptic’ genus

We report nine species of the Schistorchiinae Yamaguti, 1942 (Apocreadiidae Skrjabin, 1942) from Indo-Pacific marine fishes. Molecular data (ITS2 and 28S rDNA and cox1 mtDNA) are provided for all species and the genus-level classification of the subfamily is revised. For Schistorchis Lühe, 1906, we report the type-species Sch. carneus Lühe, 1906 and Sch. skrjabini Parukhin, 1963. For Sphinteristomum Oshmarin, Mamaev & Parukhin, 1961 we report the type-species, Sph. acollum Oshmarin, Mamaev & Parukhin, 1961. We report and re-recognise Lobatotrema Manter, 1963, for the type and only species, L. aniferum Manter, 1963, previously a synonym of Sph. acollum. Lobatotrema aniferum is phylogenetically distant from, but morphologically similar to, Sph. acollum and Lobatotrema is recognised as a ‘cryptic genus’. We propose Blendiella n. gen. for B. trigintatestis n. sp. and B. tridecimtestis n. sp. These species are broadly consistent with the present morphological concept of Schistorchis but are phylogenetically distant from the type-species; a larger number of testes and some other subtle morphological characters in species of Blendiella serve to distinguish the two genera. We report three species of Paraschistorchis Blend, Karar & Dronen, 2017: P. stenosoma (Hanson, 1953) Blend, Karar & Dronen, 2017 (type-species), P. seychellesiensis (Toman, 1989) Blend, Karar & Dronen, 2017, and P. zancli (Hanson, 1953) Blend, Karar & Dronen, 2017. Lobatotrema aniferum, P. stenosoma, and Sch. carneus each have two distinct cox1 populations either over geographical range or in sympatry. Available evidence suggests that most of these species, but not all, are widespread in the tropical Indo-Pacific.