Description of two new species of Psilochasmus Lühe, 1909 (Digenea, Psilostomidae), with remarks on the diversity of the genus and a key to its species

Psilochasmus Lühe, 1909 is a small genus of psilostomid digeneans parasitic in birds and characterized by the presence of a retractable tail-like structure at the posterior end of the body. Despite its low diversity, the taxonomic history of the genus is tumultuous, with opinions varying from recognizing only a single species to 11 nominal species. In this study, newly generated and previously available sequences of nuclear ribosomal DNA operon (ITS 1 + 5.8S + ITS 2; 28 S) and partial NADH dehydrogenase (nad 1) mtDNA gene sequences of Psilochasmus spp. from Europe (Palearctic), North America (Nearctic) and South America (Neotropics) were used to assess the diversity of Psilochasmus spp. and explore the phylogenetic interrelationships among members of genus and to distinguish between species.

Based on combined morphological and molecular data, descriptions of two new Psilochasmus species from Europe and North America, Psilochasmus slavaukrainii sp. nov. and Psilochasmus urbeni sp. nov., are provided, as well as the first morphological description of P. oxyurus specimens linked to DNA sequence data. In addition, a key to the identification of Psilochasmus spp. recognized as a result of this study has been constructed.