Systematic position and phylogenetic relationships of the family Omphalometridae (Digenea, Plagiorchiida) inferred from partial lsrDNA sequences

The phylogenetic relationships and systematic position of the digenean genus Omphalometra Looss, 1899 and several other closely related genera, have always been controversial and opinions of different authors on the systematic rank and content of this group have varied greatly. Molecular analysis based on the partial sequences of the large subunit ribosomal DNA gene of representatives of the genera Omphalometra, Rubenstrema and Neoglyphe as well as previously published sequences of members of five families of Plagiorchioidea, has demonstrated: (1) close phylogenetic relationships between these three genera, and (2) a strong support of their position within the family Plagiorchiidae as a well-defined separate clade considered here as a subfamily Omphalometrinae. Molecular data do not support the close affinities of the members of Omphalometrinae and genus Opisthioglyphe as has been suggested by majority of previous authors. Among Omphalometrinae, Omphalometra flexuosa (a parasite of moles, Talpidae) occupies a basal position in relation to Rubenstrema exasperatum and Neoglyphe locellus (both parasitic in shrews, members of the more evolutionary advanced family Soricidae). An extremely low level of lsrDNA sequence divergence between Neoglyphe and Rubenstrema suggests very close phylogenetic relationships of these two genera. Results of the molecular analysis are briefly discussed in comparison with the previously published systems.