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The results of comparative analysis of two phylogenetic trees of the trypanosomatids based on morphological and molecular characters are discussed. The morphological dendrogram was based on 33 ultrastructural characters, 6 light microscope characteristics and 8 biological characters. Molecular UPGMA dendrogram depicting differences (Dice distance) between examined trypanosomatids is based on the universally primed PCR polymorphisms. The general topology of both dendrograms are similar, with the Trypanosoma at the base. The genus Wallaceina appears to be monophyletic. In a contrary, the genera Leptomonas, Crithidia and Herpetomonas look like artificial groups according to both methods used. The cyst-forming homoxenous trypanosomatids from insects represent a monophyletic clade, which seems to be a separate genus. Two species of within genus Wallaceina are arranged as a separate subgenus.

The coccidian nature of the genus Cryptosporidium was undoubedly accepted by Tyzzer who was the first to describe this sporozoan parasite in 1907. Electron microscopic studies made in 70—90s demonstrated the intracellular, although extracytoplasmic localization of Cryptosporidium spp. The pattern of Cryptosporidium life cycle fits well that of other intestinal homoxenous coccidian genera of the suborder Eimeriina: macro- and microgamonts develop independently, a microgamont gives rise to numerous male gametes, oocysts serving for parasite's spreading in the environment. Along with these characters, Cryptosporidium spp. demonstrate some secondary peculiarities (an endogenous phase of development in microvilli of epithelial surfaces, two morphofunctional types of oocysts, the smallest number of sporozoites per oocyst, a multimembranous «feeder» organelle etc.), which may be due presumably to their early acquisition of specialization in the course of evolution. The recent studies based on molecular sequence data (18S rRNA) applied to 8 eimeriid and isosporid coccidian genera (Morrison, Ellis, 1997), suggested that the subclass Coccidia (class, according to Morrison and Ellis) be considered monophylic if Cryptosporidium were excluded, and this genus was regarded as the sister group to the rest of the Apicomplexa, or as the sister to the suborder (class) Hematozoa within the Apicomplexa. Either of these placements of Cryptosporidium definitely conflicts with both the generally accepted taxonomic scheme by Levine (1982) and the phenotypically based phylogeny of the phylum Apicomplexa (Barta e. a., 1990). The author's opinion is that the differences between the examined eimeriid and isosporid coccidia, on the one hand, and Cryptosporidium, on the other hand, provided by molecular sequence data, may testify primarily to the well known morphofunctional dissimilarities between the compared organisms, rather than cast doubt on the coccidian nature of Cryptosporidium. Again, these data can hardly prove that Cryptosporidium does not belong to the coccidia. Thus, the modern molecular sequence data, despite their obvious scientific value, would make sence for phylogeny estimation only, if they are critically analysed and considered in combination with results of the relevant basic research.

Phoxinus phoxinus being a widely distributed through Palaearctic and ecologically specialised species is a good model to study parasite communities. 72 specimens of P. phoxinus from 5 localities of the Siberia and Mongolia has been studied by the author and 651 specimens — from 5 localities in Kola Peninsula by the other researches. 595 specimens were studied by B.S. Shulman (1983) year around. To describe infra- and component parasite communities the Brillouin, Shannon, Berger—Parker indexes were used. Communities within individual fish were compared within, and between localities with quantitative percentage similarity index (Esch e. a., 1988). The Brillouin, Shannon and Berger—Parker indexes can be calculated based on abundance or total number of parasites of each species for component or compound communities. Intensity cannot be used. Significant negative correlation was observed between the Brillouin and Berger—Parker dominance indexes (r = -0.984, p<0.01, n = 66) in infracommunities. The Brillouin index was significant positive correleted with the number of parasites in infacommunity (r = 0.407, p<0.01, n = 66) and with the number of species in infracommunity (r = 0.92, p < 0.01, n = 66). Berger—Parker dominance index was significant negative correlated with the number of parasite in infacom-munity (r = -0.815, p < 0.01, n = 66) and with the number of species in infracommunity (r = -0.268, p < 0.05). Total number of parasites and the number of species in infracommunity was positive correlated significantly (r = 0.565, p<0.01, n = 66). These correlations remain the same at the component community level for the Shannon / Berger—Parker indexes (r = -0.965, p < 0.01, n = 10) and total number of parasites / number of species (r = 0.789, p < 0.01, n = 10) only. Similarity index was not correlate with any other indexes and parameters. No significant correlation was found between the Brillouin, Berger—Parker indexes and geographical characters of localities (longitude, latitude, altitude above sea-level). Weak correlation (r = 0.551, p < 0.098, n = 10) was observed only between the Berger—Parker dominance index and the latitude. 37 metazoan parasites have been found in all localities (specialists — 40 %, allogenic species — 22 %, rare species — 40 %). Allogenic generalist species of the genus Diplostomum (D. phoxini in most cases) were dominant in 60 % of the component communities and 36 % of infracommunities on average. 20 % of the component communities were dominant by autogenic specialists Gyrodactylus magnificus and only 12 % of the infracumminutues were dominated by this species. Trematode and nematode larvae were core species in most localities. Frequency distribution of infracommunity richness varied from locality to locality being overdispersed in combine sample. Parasite communities at least on the infracommunity level demonstrate high variability of all parameters. Some tendecy to decrease the diversity seems to be present depending on remoteness from prospective centre of origin of the genus Phoxinus.

The study of ultrastructure of Philophthalmus rhionica miracidium was carried out. Update the ultrastructures of miracidium were studied in a restricted number of species belonging to the families Notocotylidae, Paramphistomatidae, Sanguinicolidae, Fasciolidae, Schistosomatidae (Galaktionov, Dobrovolsky, 1998). The ultrastructure of representatives of two latter families, Fasciola hepatica and Schistosoma mansoni respectively, have been examened most carefully. The family Philophthalmidae differs from the families Fasciolidae and Schistosomatidae by the aberrant pedogenetic miracidium.

The infusoria fauna was examined in 495 speciemens of 9 fish species living in different water basins of the Minusinsk depression. Data on host associations and location of all found infusoria species are given.

In the result of parasitological researches of reptiles of the Volga delta, 17 species of trematodes belonging to 10 families and 5 orders have been recovered. The dynamics of trematodes in reptiles is regulated by transformations of biocenoses of the delta depending on fluctuations of the Caspian sea level.

Borrelia burgdorferi s. lato in naturally infected females of tick Ixodes persulcatus were examined by transmission electron microscopy. The Borreliae were found in midgut and ovary. Location and ultrastructure of bacteriae indicate extracellular migration through the midgut epithelium as a preferential way. In gonad, the borreliae intracellular situate in ovarial epithelium and oocytes before and at the beginning of vitellogenesis. The demonstration of numerous spirochetes in the oocytes provides the support for transovarial transmission of the agent. Two morphological types of borreliae were observed.

Four new species of blackflies (Diptera: Simuliidae) are described. Helodon rezidentsii Yankovsky, sp. n., Khabarovsk Region, differs from all known species of the genus with morphology of eyes consisting only of microommatidii in male; from related species H. kamtshaticus (Rubzov, 1940) with large triangular posteromedial lobes of branches of genital fork in female; with number of rays of primary fan of premandibles (20—22, when in H. kamtshaticus 30—32) in larva. Helodon submulticaulis Yankovsky, sp. n., Transbaikalia, differs from related species H. multicaulis (Popov, 1968) with number of rays of primary fan of mandibles (36—40, when in H. multicaulis 26—28), narrow anterior branches of anal sclerite, number of rows of hooks in posterior attachment organ (88—92, when in H. multicaulis 78—80) in larva; with morphology of respiratory organ, consisting of 5—8 lobes bearing 40—60 tune filaments (in H. multicaulis 3—4 lobes bearin more than 150 filaments) in pupa. Sch. samarkandica Yankovsky, sp. n., Uzbekistan, differs from related species Sch. pseudopusilla Rubzov, 1956 with 3 (not 2 as in Sch. pseudopusilla) hooks in parameres, bifurcated lateral branches of X sternite, long projection of gonostyles in male. Schoenbaueria ivdelensis Yankovsky, sp. п., Middle Ural, differs from related species Sch. rangiferina (Rubzov, 1956) with prolonged gonostyles bearing narrow projection in male; with number of rays of secondary fan of premandibles (20—28, when in Sch. rangiferina 44—48), deep ventral groove of cephalic capsule, number of rows of hooks in posterior attachment organ (80—82, when in Sch. rangiferina 70—72) in larva; with morphology of respiratory organ (very long stems of 2 and 3 pairs of filaments) in pupa.

Relations of PKX [vector of Proliferative kidney disease (PKD)] of reared and wild Salmonoidea and Tetraspora bryozoides, the only genus and species of Myxozoa found in fresh water Bryozoa, is discussed using recent publications. Both organisms were found in several European countries as well as in North America. It seems that PKX is a Bryozoa parasite which do not undergo full cycle of sporulation in fish.

One of 14 dovekeys (Alle alle) investigated in August 1993 on Hooker Island (Franz Joseph Land) was found to harbour a single specimen of an early immature dilepidid cestode attributed as Alcataenia sp. The rostellum bears a double crown of 22 hooks, 0.025—0.027 mm in length. Except Threlfall (1971) there was no information concerning dovekey's parasites.

Three new species of the monogeneas of the genus Dionchus are described: Dionchus paruchini sp. n. from Rachicentron canadus and D. trachuri sp. n. from Trachurus trachurus from Indian Ocean, D. major sp. n. from R. canadus from the North-Vietnamese gulf. All species are located on gills.

Summary is absent.

Summary is absent.