First detection of <i>Psilotrema limosum</i> in muskrat in East Asia and a description of <i>Psilotrema elegans</i> n. sp.

The East Asian region has seen the first discovery of trematodes of the genus <i>Psilotrema</i> in the muskrat <i>Ondatra zibethicus.</i> When studying the morphology of the trematodes, two morphotypes were identified among individuals of <i>Psilotrema</i> spp., the differences between which at the morphological level are equivalent to those between species. The affiliation of one of these morphotypes with the bird parasite <i>Psilotrema limosum</i> was established based on partial sequences of genes coding for 28S ribosomal RNA, <i>nad1</i>, and <i>cox1</i> mitochondrial DNA. Based on the analysis of these three markers, we classified individuals with this morphotype as <i>P. limosum</i>, despite some morphological features of worms infecting birds. At the same time, the worms with second morphotype had no interspecies differences based on the first two markers, while the <i>cox1</i> gene confirmed the separation of these samples on a species level. These trematodes were described as a new species, <i>Psilotrema elegans</i> n. sp., based on both morphological and molecular data.