Sergei A. Vlasenkov

Geographic distance is often recognized as a leading factor structuring the diversity of parasite communities. However, specific ecological and biogeographic mechanisms underlying the influence of this factor are not always evident. We used the material on the helminths of Fulica atra Linnaeus, 1758 (Rallidae) from seven areas in the Palaearctic to study geographic differentiation of the parasite communities at the level of both component communities and infracommunities. The analysis of spatial patterns of the parasite communities included (i) a reconnaissance study exploring the directions of variability of the communities using principal component analysis (PCA), and (ii) a careful disentanglement of the relationships identified in the reconnaissance study using metric scaling in Euclidean space. The component communities showed a clearer differentiation associated with geographic factors as compared to the infracommunities. The differences in the species composition of the parasite component communities of F. atra. increased consistently with increasing longitudinal distance between the localities, while the differences in prevalence increased with increasing latitudinal distance. The longitudinal trend of similarity decay of species composition of the component communities is probably determined by the directions of the seasonal migrations of F. atra. , which promote or prevent the exchange of parasite species between geographically isolated areas. The latitudinal gradient in the variability of the component communities in terms of prevalence may be associated with the latitudinal patterns in the temperature regime of the water bodies and their impact on the species composition and biomass of the food objects of F. atra.

The myxozoan genus Triangula Chen & Hsieh, 1984 has a strong morphological similarity with the genus Cardimyxobolus Ma, Dong, & Wang, 1982, and their distinction presents a complex taxonomic problem that cannot be resolved without molecular data. Here we first provided phylogenic reconstructions of Triangula spp. and Cardimyxobolus spp. using molecular data from Triangula perccotti (Dogiel & Achmerov in Achmerov, 1960). Polysporic plasmodia of T. perccotti were collected from the skin of P. glenii caught in the Lake Bolon basin (Amur system) and molecularly characterized based on the 18S rRNA gene. In the phylogenetic tree, T. perccotti appeared as a sister species to Cardimyxobolus donkoi (Ishizaki, 1955). The T. perccotti + C. donkoi clade was nested within one clade with other of species of Triangula Chen & Hsieh, 1984 and Cardimyxobolus Ma, Dong, & Wang, 1982. It was shown that neither Triangula spp. nor Cardimyxobolus spp. appeared as monophyletic groups.

Hyptiasmus Kossack, 1911 is a genus of cyclocoelid digeneans infecting the body cavity, air sacs, and lungs of mainly anseriform and gruiform birds. Some species of this genus have extensive ranges, spanning more than one continent. Therefore, this taxon is potentially of interest for studying patterns of genetic diversity and the associated problems of taxonomic delimitation of species. We focused on the examination of Hyptiasmus specimens initially identified as Hyptiasmus oculeus Kossack, 1911. These digeneans were collected from the nasal sinuses of specimens of Eurasian Coot Fulica atra Linnaeus, 1758 taken in both European and Asian parts of Russia. Phylogenetic analyses based on 28S rRNA, nd1, and cytb markers, in combination with morphological data, indicate that the newly collected digeneans are in fact members of H. oculeus complex represented by true H. oculeus and a putative new species Hyptiasmus sp. The morphological differences between these species appear to be the length of the postovarian space and the position of the genital pore. A detailed morphological study revealed the presence of rudimentary ventral and oral suckers in gravid specimens of H. oculeus complex. We did not find any geographic structuredness of the haplotype diversity in true H. oculeus. Our findings do not support the recent proposal to resurrect H. singilum Witenberg, 1923 and H. brumpti Dollfus, 1948. In addition, we hypothesise that Paracyclocoelum Vainutis, Andreev & Voronova, 2024 is a synonym of Cyclocoelum Brandes, 1892.

Notocotylidae is a family of digeneans with some aberrant morphological features (absence of ventral sucker), which as sexual adults parasitise herbivorous and molluscivorous birds and mammals. The phylogenetics and taxonomy of this family have many unresolved problems concerning the relatedness of genera and species and the reliability of identification of specimens for which molecular data are available. The aim of this study is morphological and molecular characterisation of the type species of Notocotylus Diesing, 1839 ( Notocotylus triserialis Diesing, 1839) and its two congeners, Notocotylus pacifera (Noble, 1933) and Notocotylus sp., and verification of the monophyly of the genus Notocotylus within the taxonomic boundaries established in the recent revision. Notocotylus triserialis was collected from a Greater White-fronted Goose Anser albifrons (Scopoli, 1769) taken down in the Russian Karelia, and the other two digenean species were derived from European Coots Fulica atra Linnaeus, 1758, from different locations in Eurasia (Eastern Europe and the Far East). We provide detailed morphological descriptions of the examined digeneans, supplemented with original line drawings. Notocotylus sp. is morphologically similar to N. pacifera but differs in cirrus sac length. Phylogenetic inference based on the 28S rRNA gene dataset places N. triserialis within a well-supported clade comprising several congeners, whereas N. pacifera is recovered outside this assemblage, forming a closer phylogenetic association with Pseudocatatropis dvoryadkini Izrailskaia, Besprozvannykh, Tatonova, Nguyen and Ngo, 2019. Thus, our data do not support the monophyly of the genus Notocotylus.

Faustulidae sensu lato is a polyphyletic assemblage of digeneans that parasitise marine or euryhaline fish as adults in the gastrointestinal tract. In previous phylogenetic reconstructions, this family appeared to be represented by two groups nested within the Gymnophalloidea and Microphalloidea. However, the choice of a correct name for these groups was impossible without assessing the phylogenetic position of the type genus of the Faustulidae, Faustula Poche, 1925. In the current study, we provide morphological and molecular data on Faustula gangetica (Srivastava, 1935), which represents the first molecular data for the genus Faustula. Specimens of F. gangetica were found in Tenualosa ilisha (Hamilton) from Shatt Al-Arab River, southern Iraq. We report the presence of discernible muscle fibres between the pharynx and the oral sucker, as well as a zone of distinctly differentiated transversely oriented muscle fibres located anterior to the common genital pore in this species for the first time. All molecular markers used in our study (ITS2 region, 28S rRNA gene) indicated that the genus Faustula is nested within the clade of gymnophalloid faustulids. Thus, Faustulidae sensu stricto is confirmed to belong to the Gymnophalloidea.

Cyathocotyle Mühling, 1896 is a genus of primitive diplostomoid digeneans parasitising birds. The results of recent studies suggest that this taxon is paraphyletic, which means that further phylogenetic assessment of species assigned to Cyathocotyle is necessary. In this study, two species, C. bithyniae Sudarikov, 1974 and C. fulicae Ginetzinskaja, 1952, from the Eurasian Coot (Fulica atra Linnaeus, 1758) are characterised based on morphological and molecular data. For C. fulicae, the size of the testes and the cirrus sac are clarified, and the presence of a poorly developed ventral concavity and the tegumental scale-like spines is noted. This study is the first report of infection of a bird host by C. bithyniae in nature. The new molecular data confirm the paraphyletic status of Cyathocotyle. The obtained results suggest that C. bithyniae is conspecific with an isolate of C. bushiensis Khan, 1962 molecularly characterised by Achatz et al. in 2019, and C. fulicae is conspecific with cyathocotylid cercariae previously found in Bithynia tentaculata (Linnaeus, 1758) from Central Europe.