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The eyes or ocelli of trombidioid mite larvae of Euschoengastia rotundata, Hirszutiella zachvatkini and Camerotrombidium pexatum, and larvae and adults of Platytrombidium fasciatum were studied by means of transmission electron microscopy. These species together with larvae of Odontacarus efferus, Ericotrombidium hasgelum, Walchia chinensis and adult E. rotundata and H. zachvatkini were also studied under scanning electron microscope. The eyes of larvae are not inverted and characterized by an epicuticular lamellar lens. The group of phoreceptor cells with rhabdomeres arranged typically of Chelicerata is underlaid by a pigment cup. The eyes of adult mites are inverted, perikarions of photoreceptor cells are situated between the lens and rhabdomeres; tapetum occupies the space between the pigment cup and rhabdomeres. Sensitivity of eyes to light is similar to that of primary eyes of spiders dwelling on soil surface.

Fine structure of the subepidermal tissue was investigated in the adult predatory mite Hypoaspis miles (Gamasina: Laelapidae) and bloodsucking mite Dermanyssus gallinae (Gamasinae: Dermanyssidae) of both sexes. This tissue is analogous to the fat body of other arthropodes. The subepidermal tissue of females consists of two types of cells: cells containing a synthetic apparatus and secretory granules; cells containing storage substances. In the subepidermal tissue of H. miles, cells being similar to hemocytes were also observed. As the males of both species have only one cell type in this tissue — the storage one and the females have the secretory cells, it is suggested that the subepidermal tissue of females could probably take part in the vitellogenesis.

Morphological characters of immature stages of three closely related tick species, Hyalomma asiaticum Schulze et Schlottke, 1929, H. dromedarii Koch, 1844 and H. schulzei Olenev, 1931, collected mainly in areas of their sympatry (Fig. 1) were investigated. The larvae and nymphs of these three species were collected in Egypt, Iran, Turkmenistan, Uzbekistan, Afghanistan and Tadjikistan: 159 larvae and 137 nymphs of H. asiaticum from 12 localities; 78 larvae and 167 nymphs of H. dromedarii from 5 localities; 30 larvae and 6 nymphs of H. schulzei from one locality. Both qualitative morphological features and measured character (in mkm) were used to discriminate these species. Main discriminant characters for larvae. H. asiaticum (Fig. 3). Scutum: length < 246, width < 389; base of capitulum: width < 158, dorsally hexagonal, apices of lateral projections directed forward; palpae (II and III segments): length < 106, width < 42; hypostome: length < 87, width < 25; the spur of coxa I small, equilateral triangular; patella: length < 154. H. dromedarii (Fig. 4). Scutum: length >236, width >379; base of capitulum: width > 158, dorsally almost triangular, apices of lateral projections directed laterally or backward; palpae: length > 110, width < 46; hypostome: length > 87, width < 26; the spur of coxa I large, isosceles triangular; patella: length > 115. H. schulzei (Fig. 5). Scutum: length >249, width >407; base of capitulum: width > 162, dorsally hexagonal, apices of lateral projections directed forward; palpae: length > 114, width > 44; hypostome: length > 89, width > 28; the spur of coxa I large, isosceles triangular; patella: length > 164. Main discriminant characters for nymphs: H. asiaticum (Fig. 3). Scutum: small, width < 650, length and width subequal, posterior margin widely rounded, lateral incisions weakly developed; spiracular plates with distinct, pointed dorsal projection, marginal row of perforations distant from the base of dorsal projection, submarginal row with a gap; base of capitulum: lateral projections situated in posterior half of capitulum; palpae (II segment) short and narrow; hypostome short and narrow, width < 69; pore of coxae I—III present. H. dromedarii (Fig. 4). Scutum: large, width > 650, length shorter than width, posterior margin widely rounded, lateral incisions moderately developed; spiracular plates: with distinct and wide dorsal projection, marginal row of perforations distant from the base of dorsal projection, submarginal row present, without gap; base of capitulum: lateral projections situated in the middle part of capitulum; palpae long and narrow; hypostome long and wide, width > 69; coxal pore lacking. H. schulzei (Fig. 5). Scutum: small, width < 630, length larger than width, posterior margin narrow rounded, lateral incisions weakly developed; spiracular plates: with weakly developed dorsal projections, marginal row of perforation situated just behind the base of dorsal projection, submarginal row with a gap; base capitulum: lateral projections situated in posterior half of capitulum; palpae short and wide; hypostome long and narrow, width < 73; coxal pore lacking.

A technique of temporal factor prognosis of the tick born encephalitis infection during in real time has been elaborated and tested. High adequacy of prognosis for certain regions of the Maritime territory with the tick borne encephalitis foci has been achieved. This approach has a methodological and applied importance and may be used in medico-ecological and epidemiological investigations.

A new homoxenos trypanosomatide, Leptomonas repentinus sp. n., is described from the digestion tract of the water strider Gerris rufoscutellatus. The laboratory culture of L. repentinus has been obtained. Cultural stages of L. repentinus have been studied with ТЕМ. The mitochondrion and kinetoplast have unusual structure. Large symbiont-like spherical bodies have been found in the mitochondrial matrix.

The cumulating of heavy metals (Cu, Cd, Pb, Zn) by the pond snail Lymnaea stagnalis from river and pond populations in a norm and under the trematode infection was examined. The copper and cadmium were accumulated by all specimens, mainly in the mantle and leg, in less content — in the hepatopancreas, and in the least content — in the shell and haemolymph. The lead was accumulated most intensively by the river specimens in the shell and mantle, while in the pond specimens it was accumulated in the mantle and leg. The greatest content of zink was found in the mantle, leg, and hepatopancreas. According to the ratio of cumulation the heavy metals by the river and pond populations the following series of ions were obtained respectively: Pb > Zn > Cu > Cd and Zn > Pb > Cu > Cd. The difference between uninfected specimens and one infected with trematodes was recorded in the ratio of cumulated heavy metals, in the ratio of benthic biological accumulation, and also based on bending force between metals compared in pairs. An intensity of differences was directly proportional to the intensity of the trematode infection.

The helminth fauna from amphibians inhabiting open channels of different meliorated territories of the Belorussian Polesie was investigated in 1986—2000. 31 species of helminthes were found in these animals. Total infection rate with helminthes is 89.1%. A role of amphibians in a formation of natural foci of helminthoses of medical and veterinary importance is discussed.

The presence of some glacial species in the parasite fauna of the Onega Lake and relict representatives of the Litorinic sea in the Ladoga Lake leads to the suggestion, that the first water basin did not undertake a strong influence of sea transgression and did not have an extensive connection with the sea.

Vertical dispersion of the cercariae Renicola thaidus in the water layer was examined in experiments. Dispersion of larvae of 1 and 6 hours old were investigated in different conditions of illumination. It was found out that in the first hour of life the larvae both in light and dark conditions display a negative geotaxis. 6 hours later, the reaction alternates. Both in light and dark condition, the larvae show a positive geotaxis. This changes of vertical dispersion is the result of inversion of the reaction onto the gravitation, that depends on biology of cercariae examined.

An ecological analysis of parasite fauna occurring in the Amur sickleback in different water basins of the Maritime Territory is carried out. Possible pathways of distribution of this fish within the Maritime Territory is discussed.

Two new species of Myxosporidia, Henneguya bayerii sp. n. and Myxobolus korjakovii sp. n. from the kidney of the Comephorus baicalensis (Pallas, 1776) and C. dybowskii Korotneff, 1905 from the Baikal lake are described.

A device for collecting eggs produced by monogeneans parasitizing on fish is described. The device may be used in different natural conditions, i. e. lake, river, pond, sea, ocean.