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The ultrastructural features of the vitelline follicles of ectoparasitic monogenean Chimaericola leptogaster Leuckart, 1830 (Polyopisthocotylidea, Chimaericolidae) and endoparasitic Calicotyle affinis Scott, 1911 (Monopisthocotylidea, Monocotylidae), parasites of the gills and cloaca of a holocephalan fish, Chimaera monstrosa L., are described. The vitelline follicles of the studied monogenean species are composed of the cells of a single type, vitellocytes at various stages of development. Special isolation of the vitellarium from the surrounding tissue in C. leptogaster is absent. Instead, a close relationship between bordering vitelline cells and intestinal cells of numerous branches of the caecum diverticula is observed. However, vitelline follicles of C. affinis are enclosed in a thin fibrous sheath. Some differences in the composition of the vitelline material in mature vitellocytes of C. leptogaster and C. affinis are revealed, these include the presence of different number of vitelline globules within a cluster, up to 30 globules in C. leptogaster cluster and up to 50 globules in C. affinis, and the presence of moderately electrondense homogeneous lipid droplets in C. affinis and heterogeneous droplets in C. leptogaster. The mature vitelline cells of C. leptogaster are recognised by the presence of clusters with granular bodies inside them, these bodies have the same size as vitelline globules. In developing vitellocytes of C. affinis, the glycan vesicles about 3.5 µm in diameter are present; in mature vitellocytes, these vesicles are destructed; this process is accompanied by liberation of glycogen rosettes and agglomerate of the dark material. Morphological variations of vitelline cytoarchitecture in the Neodermata are discussed.

225 minnow specimens of the 2+—3+ age were collected and studied using the standard technique of the total parasitological dissection. The component parasite community in a period of studies was well-established. This state is characterized by maximum species richness and biomass values. The results showed that probable differences in the infection by parasites of minnow females and males could not be ignored and underestimated. Indeed, the differences in minnow of different sex's infestation by parasites may be absent or present. In some reservoirs females are stronger affected by the same kinds of parasites, in other reservoirs, males are affected stronger. In comparison to males, in females parasites are more commonly represented by single individuals. Discussed differences may manifest themselves only in a certain seasonal condition of a fish. The structure of parasitic communities in hosts of different sex is equal and almost identical to that obtained in mixed host samples.

Comparative analysis of the taxonomic position of microsporidians from mosquitoes of the family Culicidae, for which SSU rDNA sequences data were obtained, demonstrates partial contradiction of systems based on morphological and phylogenetic characteristics. Representatives of the genera Annсаlliа Issi et al., 1993 and Vavraia Weiser, 1977 constitute separate evolutionary branches of the phylogenetic tree of microsporidians of blood-sucking mosquitoes. Representatives of other genera, for which the SSU rRNA sequences data were obtained (Amblyospora Hazard, Oldacre, 1975, Andreanna Simakova et al., 2008, Culicospora (Kudo, 1921), Weiser, 1977, Culicosporella Hazard, Savage, 1970, Edhazardia (Kudo, 1930), Sprague, Fucuda, 1989, Hazardia Weiser, 1977, Hyalinocysta Hazard, Oldacre, 1975, Novothelohania Andreadis et al., 2012, Parathelohania Codreanu, 1966, Senoma Simakova et al., 2005, and Trichoctosporea Larsson, 1994), form a separate, monophyletic group in the tree of Microsporidia. They are closely related and probably possess a common ancestor. The genera Amblyospora, Culicospora, Edhazardia, and Trichoctosporea were placed in the family Amblyosporidae with the revision of the diagnosis. On the basis of the obtained data on morphology and molecular phylogeny we placed Intrapredatorus barri Chen et al., 1998 into the genus Amblyospora as Amblyospora barri, comb. nov., and also the species Amblyospora bakcharia Andreadis et al., 2012, A. kazankia Andreadis et al., 2012, A. mocrushinia Andreadis et al., 2012, and A. rugosa Simakova, Pankova, 2005 into the genus Trichoctosporea as Trichoctosporea bakcharia comb. nov., T. kazankia comb. nov., T. mocrushinia comb. nov., and T. rugosa comb. nov. Microsporidians of blood-sucking mosquitoes originally possessed complicated life cycles with transovarial and oral transmissions and with the presence of intermediate hosts (lower crustaceans). Later, some microsporidians had lost a part of their life cycle, either during disorganization of habitats of main and intermediate hosts, or as a result of adaptation to environmental and (or) physiological characteristics of hosts. Changes in the life cycle occurred rather rapidly in comparison with the duration of evolutionary development and had an adaptive character. Differences in the life cycle of parasites of the genera Amblyospora,Culicospora, Culicosporella, Edhazardia and Hyalinocysta possibly represent an adaptation increasing the probability of host-parasite meeting. In the process of evolution, spores formed stronger spore wall with thick exospores and endospores. The appearance of thick spore walls in mature spores promoted the development of the apparatus of extrusion process, namely the flattening of the polaroplast chambers and the emergence of long anisofilar polar filament.

In the territory of St. Petersburg, 26 sites situated in areas with 4 types of forest vegetation, were examined. Fleas of 16 species were collected from small mammals belonging to 13 species. The flea Ctenophthalmus agyrtes was the most abundant species. Two types of flea communities can be distinguished, including communities of fleas of forests and forest parks and communities of fleas of urban parks and cemeteries.

New findings of ectoparasites from the eastern water bat Myotis petax Hollister, 1912, belonging to the Siberian-Russian Far Eastern complex and earlier attributed as a subspecies of the Daubenton's bat Myotis daubentonii s. lato, is given. Fourteen species of bloodsucking arthropods feed on M. petax; these species include 4, 3, and 7 species of gamasid mites, fleas, and bloodsucking flies, respectively.

Metacercariae of Crepidostomum metoecus (prevalence 2.0%), procercoids of Cyathocephalus truncatus (2.9%), and nematodes of the family Cystidicolidae (17.6%) were found in the body cavity of amphipods Gammarus lacustris from the Kronotskoe Lake (Kamchatka). The nematodes were presented by Cystidicola farionis (third-stage juvenile) and Ascarophis sp. (adult and fourth-stage juvenile).