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The dependence of indices of the larvae number and their biomass upon characte-ristics of the immune response in ELISA at organism and population levels of the Oestris ovis parasitic system is discussed. It was determined, that the majority of larvae distribution excerptions in the host population and the distribution of specific antibodies level indices in the serum blood of animals correspond to the model of the negative binomial distribution. The straight dependence of the parasitic larvae number on the specific anti-bodies level in the serum blood of host at the organism level of the parasitic system was not determined. The high correlative dependences of the mean number indices and of the distribution of larvae upon the mean value of extinction in the immunity enzyme reaction and upon the mean level of specific antibodies in the serum blood of the host population at the population level were determined. The control of the sheep bot fly larvae number is possible by the determination of the mean specific antibodies level in host population in ELISA.

Results of the seventy year long study of a species composition of fishes' parasites in basins of the Dvina river, Mesen' river and Pechyora river are summed up. During this time the 57 ichtioparasitic protozoan species have been recorded in the first basin, 21 species - in the second basin and 31 species - in the third basin. The total species number of ichtioparasitic protozoans of fishes in the examined region is 66 species.

While a long term observation of the Nosema mesnili infections in the Pieris brassicae natural populations in the North-Western Russia a regular massive occurrence (once in 4-8 years) of another microsporidia, Thelohania mesnili, was revealed. It is supposed, that the life cycle of Nosema mesnili consists of 2 sequences of a development dispalying in the foration of either Nosema-like binuclear single spores or Thelohania-like mononuclear octospores enclosed in sporophorous vesicles. Merogony-sporogony stages of the Nosema form and sporogony stages of the Thelohania form were studied. An ultrastructural analysis of the octosporal sequence showed its resemblance to the respective stage of the life cycle in Vairimorpha species. The light and electron microscopic data together with immunological tests conducted earlier give a basis for a transferring of Nosema mesnili to the genus Vairimorpha. An occasional appearance of octospores, that is not typical for the Vairimorpha, indicates a possible way of the origin of the genus Nosema from genera posessing two types of sporogony.

In 2353 specimens of 8 molluscs species and subspecies of the family Unionidae (Unio timidus falcatus, U. rostratus rostratus, U. r. gentilis, U. conus borysthenicus, U. pictorum, Colleptopterum ponderosum rumanicum, C. piscinale falcatum, Anodonta piscinalis) we detected two trematode species, Bucephalus polymorphus and Cercaria duplicata, with an occurrence rate in water basins 100 and 20% respectively. The average infection rate of molluscs was 4% with a variation from 0.8 to 10%. The trematode infection is observed on mature specimens only (gonads are formed in moluscs since the age of 2 years), and its intensiveness grows up with the age of hosts. The infection in males is higher than in females. Peack of infection were observed in spring, eariy sumrrier and autumn. In all Unionidae the trematode parthenits are located in genital glands. The pathogenic influence of parasites manifests in a constriction of the connective tissue, which fastens genital gland tubes. If the infection is extremely grave, the parasites perforate an integument and migrate into the hepatopancreas and mantle. In this case the germinal epithelium of gonads degenerates up to parasitosis castration.

An ectoparasitic suctorian Pottsia parasitica Nozawa, 1939 inhabits periphytonic peritrichs in the Selenga estuary of the Baikal lake; ist morphological discription is presented. Previous records of this species includes Japan, Germany and Ukraine. Formerly, it was included into the genus Manuelophrya, but it must be regarded as a type species Mistarcon parasiticus (Nozawa, 1939) of the monotypic genus Mistarcon Jank., 1986. Manuelophrya is a valid monotypic genus with M. hannae as a type species, because it lacks an adhesive plate unlike in Mistarcon. The designation of Pottsia parasitica as the type of Manuelophrya is unacceptable as an anonymuos publication disregard a previous indication (Jankovski, 1986) of this species as the type of the new genus Mistarcon. The author does not follow the Wenzel's principle and retains an authorship of Matthes for the genus Manuelophrya.

By means of an electron microscopic study of the intestine in young rats infected with Cryptosporidium parvum we observed a mass migration of immunocompetent cells of the host (eosynophils, neutrophils and macrophages) into the lumen of intestine. Some lymphocytes were also observed. Immunocompetent cells (except lymphocytes) included inside phagosomes with different endogenic states of C. parvum. Macrophages with typical extracytoplasmatic parasitophorous vacoules formed by C. parvum were also observed in the intestine lumen. Almost all stages of C. parvum could be observed on a surfface of such macrophages. However, we did not find in lamina propria of intestine villi any macrophages with parasites. The place of macrophages infection is unknown. We suggest that surviving of C. parvum in macrophages is principally possible.

An occurrence of the parasitic dinoflagellate Ellobiopsis chattoni in the dominant copepod species Calanus finmarchicus was studied in 1990-1991 and 1993 in the Norwegian Sea and in the Arctic Ocean. The infection rate of C. finmarchicus with parasitic dinoflagellates was highest in the Norwegian Sea, reaching 20.0% in the Viking Bank and 45.5% in the Sklinn Bank. In the Spitsbergen waters the copepodes with parasites occur seldom and in the northest waters of Spitsbergen their occurrens was below 1.0%. There is a suggestion that the observed distribution of C. finmarchicus infected with the dinoflagellates is due to the large-scale formation of the copepod area within the Northest Atlantic and adjacent waters. The possible role of the parasitic dinoflagellate E. chattoni as a biological tag of host local populations is discussed.

A new species, Blastocystis lemuri sp. n., was found in the Lemur catta. Size of blastocysts in a culture is 10.25-35.25 mkm, the number of nuclei varies from 1 to 2. The optimun temperature for cultivation is + 39°.

935 specimens of small mammals (21 species) from the Transcarpathian region of the Ukraine were examined to check a helminth infection. 666 animals (71.2%) were infected with 44 parasite species belonging to 22 families of 4 classes: Trematoda (7 species), Cestoda (18), Nematoda (18) and Acanthocephala (1). A carried out analysis of the distribu-tion of parasite species among their host took in account a host biology and their landscape zone.

Epimastigotes of a homoxenous trypanosomatid of the genus Blastocrythidia were found in a gut of the bug Gerris lacustris. An unusual type of the cyst-like stage formation and an ultrastructure of these stages are described.

The Palaearctic fauna of the Dactylogyridae consists of 6 genera (180 species) parasitizing on 127 species and subspecies of fishes. 168 palaearctic species of the genus Dactylogyrus Dtesing, 1850 are divided into 20 monophyletic groups. 14 species are included into D. varicorhini group spp.; D. pulcher Bychowsky, 1957 belongs to D. pseudanchoratus group spp., and D. barbioides Gussev et al., 1993 belongs to D. ruahae group spp. These three groups have the African or Indo-African origins. The four representatives of D. longicopula group spp. have apparently the Indian origin. Three spesies from gudgeons are included into D. cryptomeres group spp.; and D. bicornis Malewitskaya, 1941 belongs to the same name group spp. These two groups have the Amuro-Chinese origin. For D. meridionalis group spp. (3 spp.from Nemachilus) an origin is not clear. The other 13 monophyletic species groups of Dactylogyrus spp. are typical palaearctic ones. These groups are as follows: monotypical D. yinwenyingae group spp.; D. anchoratus group spp. (21 spp., 7 subgroups) mainly from Cyprininae; D. amphibothrium group spp. from Gymnocephalus and Abyssocottus; D. borealis group spp. (7 spp., 3 subgroups) mainly from Phoxinus; D. fraternus group spp. (22 spp., 9 subgroups) from Leuciscinae; D. rosyckyi group spp. (6 spp., 2 subgroups) from lakes of the Balkan Peninsula; D. tuba group spp. (17 spp., 8 subgroups) being parasites of Leuciscinae; D. crucifer group spp. (6 spp.) from Rutilus; D. fallax group spp.; D. malleus group spp. (34 spp., 7 subgroups), parasites of Barbus; D. auriculatus group spp. (4 spp.); D. sphyrna group spp. (5 spp.); D. capoetobrama group spp. (2 spp.). The genera Dogielius Bychowsky, 1936 and Pellucidhaptor Price et Mizelle, 1964 are represented in the Palaearctica by 4 spp. each one. Three dactylogyrid genera without anchors occur in the Palaearctica: Markewitschiana Allamuratov et Koval, 1966 (2 spp.), Acolpenteron Fischthal et Allison, 1940 (2 spp.) and Pseudacolpenteron pavlovskii Bychowsky et Gussev, 1955. The polyphylesis of the genus Acolpenteron is shown.

Summary is absent.

Summary is absent.