Host-specificity patterns are not well-defined for trematodes of the genus Phyllodistomum Braun, 1899. The Eurasian ruffe, Gymnocephalus cernuus L., has been recorded as a definitive host for Phyllodistomum folium (Olfers, 1816), P. angulatum Linstow, 1907 and P. megalorchis Nybelin, 1926 and as the type-host for P. pseudofolium Nybelin (1926). A wide range of other host fishes have been recorded for these species as well. All present host records have been based on light microscopy and the life-cycles of P. pseudofolium, P. angulatum and P. megalorchis are unknown. The validity of P. pseudofolium and P. megalorchis require verification. In this study, rDNA sequences generated from adult Phyllodistomum spp., as well as from larval stages developing in Pisidium amnicum Müller, were analysed to establish the real number of Phyllodistomum species utilizing G. cernuus, and to associate larvae with the corresponding adult forms. Phylogenetic analyses of adult and larval stages of Phyllodistomum spp. based on ITS2 and partial 28S rDNA data allowed the confirmation of the validity of P. pseudofolium. A macrocercous cercaria, known as Phyllodistomum sp. from P. amnicum is genetically identical to adult P. pseudofolium. Phyllodistomum megalorchis obtained from its type-host, Lota lota L., showed no genetic differences from P. angulatum parasitizing Sander lucioperca L. In our analysis, P. pseudofolium, P. angulatum and P. macrocotyle formed a highly supported clade despite the fact that these species appear to be associated with distinct patterns of first intermediate host identity and cercarial morphology. Some morphological differences between gravid specimens of P. pseudofolium and P. angulatum were observed and their SEM tegumental surface topography is described. The results lead us to the perception that macroevolutionary host switching in the genus Phyllodistomum is independent of host phylogeny. This study suggests strict host-specificity (oioxeny) for P. pseudofolium using one first intermediate host species (P. amnicum) and one definitive host species (G. cernuus). Phyllodistomum megalorchis is to be regarded as a synonym of P. angulatum. The close phylogenetic relatives, P. pseudofolium and P. angulatum, can be differentiated by morphological traits, the micromorphology and tegumental surface topography of these two species is intended to provide useful data for their identification and support the use of such features as a valuable taxonomic criterion. Molecular data showed that G. cernuus is a definitive host for two species: the oioxenous P. pseudofolium and the euryxenous P. folium.

The results of original research and published data on the number of alien parasite species of fish recorded in the Volga River basin are generalized. At present, 47 alien species of fish...

Background: European species of the large genus Phyllodistomum Braun, 1899 had historically been erected based solely on morphological characters. Unfortunately, many of them are still poorly known and inadequately described. Molecular approaches are critical to delineate species which were impossible to differentiate based on morphology alone. Methods: New samples of adult Phyllodistomum spp. were collected from the urinary bladder and/or ureters of European freshwater fishes and fixed to conduct a light and scanning electron microscopy study, and to obtain sequences of nuclear (ITS2 spacer and 28S rRNA gene), to be analysed in the context of a molecular phylogeny. Results: Based on new findings, a new species of Phyllodistomum from the urinary bladder of the European perch, Perca fluviatilis, in Volga River basin, Russia, is described. Additionally, new data on the morphology and tegumental surface topography of P. macrocotyle (Lühe, 1909) Odhner, 1911 from ureters of the common rudd, Scardinius erythrophthalmus, is presented. The host range of P. folium, confirmed by DNA analysis, is extended to other cyprinid fish species. Conclusions: The present study has again shown that species of the genus Phyllodistomum are in dire need of revision based on both molecular analysis and detailed morphological redescriptions of the forms attributed to the genus. Morphologically, P. kupermani n. sp. most closely resembles P. pseudofolium, a highly host-specific parasite of Gymnocephalus cernuus (L.), but molecular phylogenetic analyses based on ITS2 and 28S rDNA sequences showed that these species are distantly related. Phyllodistomum kupermani n. sp. was found to be phylogenetically most closely related to the type-species of Phyllodistomum, P. folium. Phylogenetic analyses revealed that Phyllodistomum kupermani n. sp. and P. folium formed a clade with other freshwater species for which cystocercous cercariae develop in bivalves of the family Sphaeriidae. The micromorphology and tegumental surface topography of P. macrocotyle revealed in the present study provide a valuable taxonomic criterion for congeneric species differentiation.

This study is devoted to the investigation of Azygia (Digenea: Azygiidae) species diversity using classical morphological, recent molecular tools (28S rRNA and cox1 mtDNA for genetic-based inference) and robust statistical techniques (Principal component analysis, PCA). The analysis revealed that the genus Azygia included four valid species: A. lucii, A. longa, A. hwangtsiyui, and A. sibirica n. sp. The distribution of the type species A. lucii was confirmed in the largest Russian rivers: the Volga and the Ob. The worms isolated from Perccottus glenii were determined as the Chinese species A. hwangtsiyui, according to the genetic data for the cox1 mtDNA gene, at 1.32–1.56%. The new species, Azygia sibirica n. sp, was described from Esox lucius in the Ob River and differentiated from the type species A. lucii by the smaller ovary, testes and prostatic sac, wider body, very narrow pharyngeal lumen and form of anterior margin of ovary. In addition, multivariate analysis and three methods for species delimitation (ABGD, GMYC, bPTP) showed the subdivision of A. lucii and A. sibirica n. sp. into two separate groups, one from the Volga River and another from the Ob River, respectively. To conclude, A. lucii infects Esox lucius in the western (European part of Russia, the Volga River basin), and northern (Western Siberia, the Ob River basin) parts of Russia; A. sibirica n. sp. has also been found to infect Esox lucius in the Ob River, while A. hwangtsiyui infects Perccottus glenii in the South of the Russian Far East (the Artymovka River basin).

The metazoan parasites of the invasive goby species Proterorhinus semilunaris were studied in August 2015. In total, 101 specimens sampled at four sites of Rybinsk Reservoir were analyzed. Six parasite species were found: Unionidae gen. sp., Paracoenogonimus ovatus, Diplostomum sp., Ichthiocotylurus platycephalus, Posthodiplostomum cuticola, and Camallanus lacustris. Trematode metacercariae were the dominant parasites in all the studied samples. The specific parasites, monogenean Gyrodactylus proterorhini and cestode Proteocephalus gobiorum, were not recorded. The study summarizes the published and original data on the parasite faunae of P. semilunaris and P. marmoratus in Eurasia. The parasite fauna of P. marmoratus comprises 40 species (Microspora—1 species, Ciliophora—4, Myxozoa—4, Monogenoidea—1, Cestoda—4, Trematoda—17, Nematoda—4, Acanthocephala—4, Arthropoda—1). The parasite fauna of P. semilunaris has 92 species (Kinetoplastida—1, Sporozoa—2, Microspora—4, Ciliophora—11, Myxozoa—2, Monogenoidea—2, Cestoda—8, Trematoda—35, Nematoda—12, Acanthocephala—5, Annelida—1, Mollusca—4, and Arthropoda—5).

In summer and autumn 2016–2017, the parasitic fauna in four anemonefish species (Amphiprionclarckii (53 ind.), A. polymnus (58 ind.),A. perideraion (15 ind.), and A. frenatus (10 ind.) (Pomacentridae)) from the areas close to Nha Trang, South China Sea, Vietnam, were studied. In total 11 parasite species were found in the studied fish with 3–8 parasite species per fish species. The survey revealed two species of copepods (Hatschekia sp. 1 and Hatschekia sp. 2), six digeneans (Macvicaria sp. 1, Macvicaria sp. 2, Aponurus piriformis,Aponurus laguncula, Hysterolecitha nahaensis, Bivesicula sp. metacercariae), two nematodes (Spirocamallanus istiblenni and Hysterothylacium sp. J4), and one acanthocephalan (Echinorhynchus sp.). The trematode Hysterolecitha nahaensis and the nematode Spirocamallanus istiblenni were the most abundant and prevalent parasites. These parasites reached a prevalence of 64% and 90% with an intensity of infection of 1–6 ind. and 1–37 ind., respectively. Two ectoparasite taxa were found: Hatschekia sp. 1 (a single specimen found in A.clarckii) and Hatschekia sp. 2. Among them, Hatschekia sp. 2 was the most frequent and abundant species in A. polymnus (prevalence 96.6%, intensity of infection 0–51).