# Phylogenetic Position and Morphological Characteristics of the Plagiorchioid Trematode, Skrjabinoplagiorchis polonicus (Soltys, 1957), a Parasite of Rodents

## TL;DR

This study clarifies the classification of a parasitic flatworm, Skrjabinoplagiorchis polonicus, and its placement within a new subfamily based on morphology and DNA analysis.

## Contribution

The study provides the first molecular data for these helminths in Russia and reclassifies the genus into a new subfamily.

## Key findings

- Skrjabinoplagiorchis polonicus is reassigned to the subfamily Omphalometrinae based on morphological and molecular data.
- This is the first molecular phylogenetic analysis of these helminths in mammals from Russia.

## Abstract

The taxonomic position of the genus Skrjabinoplagiorchis, represented by the sole species Skrjabinoplagiorchis polonicus, remains unclear. Our paper presents the morphological and morphometric features of two trematode species parasitizing small mammals in the Middle Volga region (European Russia): S. polonicus from the liver of the herb field mouse (Apodemus uralensis) and Rubenstrema exasperatum from the small intestine of the common shrew (Sorex araneus). For the first time, we provide molecular data on these species of helminths in mammals from Russia. Our results establish the taxonomic affiliation of S. polonicus within the subfamily Omphalometrinae. Previously, parasitic flatworms of this subfamily were known only as parasites of insectivorous mammals belonging to the order Eulipotyphla.

The genus Skrjabinoplagiorchis is monotypic, with Skrjabinoplagiorchis polonicus parasitizing rodents in the Western Palaearctic. This genus is classified within the family Plagiorchiidae; however, its taxonomic position remains unclear. In the present study, two species of digeneans, S. polonicus and Rubenstrema exasperatum, found in small mammals in the Middle Volga region (European Russia), were examined. We provide morphological descriptions of the studied trematodes complemented with a molecular phylogenetic analysis of partial sequences of the 28S rDNA gene, obtained for these helminths of mammals in Russia for the first time. Based on morphological data and the results of molecular phylogenetic analysis, we reassign the genus Skrjabinoplagiorchis from the subfamily Plagiorchiinae to the subfamily Omphalometrinae. Previously, digeneans of the subfamily Omphalometrinae were known only as parasites of insectivores of the order Eulipotyphla.