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Hypothesis on the origin of Sporozoa from Spiromonadida ancestors is discussed on the basis of the data on their ultrastructure. The phylum Sporozoa comprises three large distinct groups of organisms as follows: Perkinsemorpha, Gregarinomorpha and Coccidiomorpha. Advanced Coccidiomorpha have not descended directly from Gregarinomorpha. Gregarinomorpha and Coccidiomorpha have commom ancestors, Protospiromonadida. Heteroxeny is quite common among Coccidiomorpha. The formation of heteroxeny in Coccidiomorpha proceeded in different ways and at different time in different groups. Cystoisospora, Toxoplasma, Aggregata, Atoxoplasma, Schellackia have primary definitive hosts while Sarcocystis, Karyolysus, Haemogregarina, Hepatozoon, Plasmodium, HaemaproteuSy Leucocytozoon, Akiba, Babesiosoma, Theileria, Babesia have primary intermediate hosts.

Cercaria unidiverticulata sp.n. (Trematoda, Echinostomatidae) from Lymnaea auricularia and L. fontinalis is described.

2 species of the genus Dirhabdilaimus were recorded from the weevil Hylobius albosparsus. D. macroonchatis sp. n. was found in the Kolyma river basin. It differs from D. carolinensis Massey, 1967 and D. nacogdochensis Massey, 1974 by the number of caudal papillae of male and from D. leuckarti (Fuchs, 1915) Paramonov et Turlygina, 1955 by the presence of a large three-cornered tooth (onchus) on the dorsal segment of the metastoma, by the form of gubernaculum and by the localization of latent larvae on the host's larva. Dirhabdilaimus sp. were found in the basins of the rivers flowing into the northern part of the Sea of Okhotsk. Since all examined specimens had stoma with deformed rhabdions we failed to identify their species belonging.

A detailed description of morphology of the trematode Haplosplancluius pachysomus from Black Sea mullets is given for the first time.

The morphology of the cestode Proteocephalus percae, a typical parasite of Perca fluviatilis, from Lake Rindozero has been studied. The variability of 8 age groupings has been revealed and the connection of their morphological parameters with the specificity of host-parasite relationships at different developmental stages of the population has been shown.

Studies of the fine structure of the adult acanthocephalan Echinorhtynchus gadi have given a new information on the structure and organization of the body wall of these parasitic helminths. Their body surface is covered by glucocalics of mucopolysaccharide nature. Just under it there is the surface membrane which has numerous invaginations forming a network of branching canals from which membrane vesicles are isolating. In their turn these canals pass through "the cytoplasmic canals" of the cortical matrix. Between the surface membrane and cortical matrix there is the base plate. These three structures form the striped layer underlain by the felt layer. It is formes by three layers of fibrous strands (one circular and two longitudinal), which are parallel to the body surface. These strands consist of loosely laid fibrils. The lowest layer is a radial one which occupies 2/3 of the body wall. It consists of the radial strands beginning from the cortical matrix and ending at the basement membrane. Numerous lipid droplets and glicogen granules are formed here. Two types of fibrils with 0.26 and 0.05 diameter have been detected for the first time. The radial layer in the cytoplasm was found to have crystalline structures and poly membrane bodies, numerous nuclei with light caryoplasm and distinct nucleoli. The location of the nuclei is of two types: either in the cytoplasm or in the "lacunae". We have shown that the "lacunae" are specialized sites of the cytoplasm whose boundaries are marked by the fibres of two types. Besides, this type of the acanthocephalan was found to have two "giant lacunae" extending along the body. The lowest site of the radial layer, formed by the invaginations of the basement membrane, was named alveolar.

Three species of the genus Anomalohimalaya Hoogstraal, Kaiser et Mitchell, 1970, A. lama Hoog., Kaiser et Mitch., 1970, A. lotozkyi Fil. et Pan., 1978 and A. cricetuli Teng et Huang, 1981, known at present, are distributed on the periphery Central and in the mountains of Middle Asia. A. cricetuli is known from two localities: Xinjiang (China) and eastern spurs of the Kirghiz ridge in northern Tien Shan. Data are given on 6 new findings of A. cricetuli in separate localities in the mountains of Middle Asia: 3 from Tien Shan (1 female, 7 nymphs, 7 larvae) and 3 from the western Pamirs (1 female, 6 nymphs, 1 larva). The species was found in talli and rock biotopes at a hight of 1600 to 3200 m above sea level. Cricetulus migratorius is a primary host. The presence of the three species in the colection of Zoological Institute RAS (Saint Petersburg) has enabled the authors to make the generic diagnosis of Anomalohimalaya and differential diagnosis of A. cricetuli more precise. Female of A. cricetuli has pointed posteriorly scutum and U-shaped genital opening while two other species have rounded posteriorly scutum and V-shaped genital opening. A. cricetuli differs from A. lotozkyi by less pointed and shorter lateral projections of the gnathosoma basis, apexes of which are moved forward from the posterior margin, and by concave laterally porous area. It differs from A. lama by the absence of the dorsal process on the peritrema and a short tooth on coxae IV. Nymph of A. cricetuli has a smooth nitidous scutum with closely moved lateral and cervical grooves, forming a narrow deep short furrow, while in two other species the scutum is dull, the furrow between the lateral and cervical grooves is short and nearly reaches posterolateral margins of the scutum. Shape and location of the lateral projections of the gnathosoma basis corresponds to those of female. Anal valves equally get narrow forward and backward while in A. lotozkyi they are more narow anteriorly. Contrary to Chinese authors (Teng, Huang, 1981; Teng, Jiang, 1991) larva has no eyes.

A new species, Ctenophthalmus (Euctenophthalmus) parthicus sp. n., is described from social vole (Microtus socialis Pallas) from four localities of the West Kopetdag Mountains of Turkmenia. The new species is close to C. (E.) secundus Wagner and C. (E.) congener nadimi Farhang-Azad. It differs from males of the other known species by the following characters. The movable process has an infra-acetabular process whose length is the same as the height of its supra-acetabular portion. The movable process has the straight front margin, right anterior apical angle. The anterior part of the dorsal margin of the movable process is elevated, the hins part is slightly concave. The posterior apical angle of the movable process is cut. The hind margin of the movable process is convex. The apex of the distal arm of sternum IX is straight, not oblique. The female differs by the following peculiarities. Sternum VII has a well developed dorsal lobe below which there is a smaller rounded lode abd a distinct small ventral process. Unciform sclerotization of tergum VIII (or the place of connection between tergum VIII and its internal lobe) resembles an arc. The front margin of the internal lobe of tergum VIII is not sclerotized. The bursa copulatrix is as long as the dorsal spines of pronotum.

Experimental interspecific hybridization between males and females of Nosopsyllus fasciatus and N. mokrzeckyi was carried out. Most abundant progeny was obtained after hybridization between N. fasciatus females and N. mokrzeckyi males. Hybrid descendantsinherited, in general, the characters of the maternal species and in less number the paternal characters and those of both parents. The fecundity of hybrid progeny of N. fasciatus females and N. mokrzeckyi males in two generations was studied. A conclusion is made concerning close affinity of the species and their relative evolutionary youth.

In the pupae of three populations of Testisimulium kondici (Bar.) the variations of nine quantitative characters are determined. The discrepancies between these populations are analyzed. With the help of statistical indices the specific distinctions of one of the studied populations from two others, which are not essentially different, is established. Earlier (Kachvorian, 1989; Kachvorian and Tonojan, 1990) caryological and phenotypical differences between the larvae of these populations were found. Considering that the isolated population develops under anthropogenic influence a link between the above discrepancies and this influence is assumed to exist.

In order to estimate the absolute number of Stomoxys calcitrans subpopulation in housings of a dairy farm the capture-mark-recapture method has been used. It has been established that the absolute number of S. calcitrans subpopulation can be as high as 100 000 specimens per a farmyard. The possibilities of using indices of the relative number of flies (caught on fly-paper) for estimation of the absolute number of these insects in the housings of farms have been found out.

IIId-stage larva of Thubunea baylisi was obtained and described as a result of experimental infection of Trigonoscelis gigas (Tenebrionidae), an intermediate host, with eggs of nematodes. The morphology of the imago of this species has been described more precisely.

The finding of eggs of the nematode Eustrongylides excisus has been reported from true sturgeons of the Caspian Sea. The nematode is in the capsule with an opening into the cavity of the alimentary canal. In addition to birds, true sturgeons are expected to be under certain conditions definitive hosts of this nematode.

The method of cultivation of Blastocystis galli from hens and Blastocystis sp. from ducks was worked out. Blastocystis grow on nutrient medium at pH 7.0 to 7.2 in a wide range of temperatures from 30 to 45°C. Optimum temperatures for cultivation are 41 to 42°C. The growth of cultures was obtained on biphase egg medium. Solid phase of the medium presents coagulated contents of the hen's egg. Liquid phase can be made of Henk's solition with the addition of 30% of fresh or lyophilizinic hen serum or horse serum. Henk's solution can be replaced by medium 199 (we observed the growth of culture on medium 199 without addition of blood serum). In all variants of medium we added antibiotics on a per — 1 ml of medium basis: ampicillini — 4 thousand units, streptomycini — 1 thousand units. After 2 to 3 passages antibiotics can be excluded from the medium. Optimum medium is that with the addition of 30% of fresh hen serum. Passages go well at the transfer of 15—20% culture after 72 to 96 hours. The size of cultural stages varied within the limits of 2.5—56.2 x 2.5—56.2 µm and 2.5—110 x 2.5—110 µm for Blastocysts sp. and B. galli, respectively, the number of nuclei in one individual varied from 1 to 64, seldom over 100.