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Two variants of intraspecific morphological differentiation of 7 palearctic species of Ixodidae and respectively two variants of their intraspecific taxonomic pattern have been revealed on the basis of the study of geographic variation of each species. Three species — Ixodes pavlovskyi Pom., 1946, Haemaphysalis erinacei Pavesi, 1884, Hyalomma asiaticum Sch. et Schl., 1929, are subdivided into subspesies, and four ones — I. ricinus (L., 1758), I. persulcatus Sch., 1930, I. crenulatus Koch, 1844, Dermacentor marginatus (Sulzer, 1776), — into morphotypes by the degree of distinction of the whole complex of active stages in ontogenesis. Acknowledginy the conventional character of the categories of subspesies and morphotype their criteria have been formulated for ixodid ticks. Paleogeographic and ecological grounds are given. Some data of geographic variation of immature stages favour the identification of closely related spesies in concrete localities. The research was supported by the Russian Fund of Fundamental Investigations (Grant 97-04-50094) and in part by FIRCA, USA (Grant N 1 R03-TW0027-01A1).

A morphological expression of quiescent nymphal instars (calyptostases) in trombiculid mites (Trombiculidae) is analysed. The analysis takes into consideration ontogenetic functions of different instars during the individual development of these mites, which includes an alternation of active and regressive quiescent instars. Cyclic start and blocking of different integumental differentiation programs in Trombiculidae is caused by the cyclic reduction and renewal of particular functions of respective instars, whereas internal organs of these mites do not transform significantly during the life cycle. The reduction of some functions, particulary the locomotion and feeding, in the quiescent nymphal instars with changed integumental function has an inevitable result in a complication and prolongation of the moulting process. The moulting of these instars begins at once after finishing the prevoius moulting cycle, i. e. it is realized in "automatical pattern" without the intermoult phase. In general, the organization of both quiescent proto- and tritonymph is the same, because it expresses concordant morphological correlations and synchronous reductions of certain functions and structures in these instars during the evolutionary process. At the same time, the trombiculid mites and, perhaps, other representatives of Parasitengona reveal the most generalized type of ontogenesis in Acariformes within the "alterating calyptostasy" phenomenon.

The development of Ichthyocotylurus variegatus from metacercariae to ovigerous adults in the natural definitive host (Larus ridibundus) was examined at 24 h intervals. The metacercariae develope to the adults through a somatic growth of hindbody; the gametogeny and vitellogenesis take 4—6 days. During the first day of development the pair of testes are separated from the genital anlage. The ovary differentiates one day later. Genital ducts are completely differentiated on 4 th day after the beginning of spermatogenesis and cogenesis. The vitelline cells developed from 2nd to 5th day. They take an origin from the subtegumental cells of hindbody. The hind part of uterus in strigeoid adults is identical to the metraterm of other trematodes. The spermaduct along all its length works as a spermatic bladder.

The data on an occurence of capsalines in marine fishes are analized. 33 capsaline species among 55 recently known species are monoxienous, that points to the high specialization of these monogeneans. The majority of species are recorded from three subfamilies of perciform fishes: Scombridae, Istiophoridae, Xiphiidae. Possible factors causing the high specificity in monogeneans are discussed.

The european smelt Osmerus eperlanus had been accidentally introduced into the ecosystem of the Syamozero lake (Karelia). The population of this species has achieved a high density and caused serious changes in the structure and trophic relationships of fish community of the Syamozero ecosystem. The microsporidia Glugea hertwigi Weisenberg, 1921 has become a new and superdo-minant parasite of the european smelt in this ecosystem. The invasion of microsporidia has caused a mass death of fishes, that has led to changes in population structure of the smelt and lowered a fishe catch. The present study suggests to show a role of parasites in the ichtiocenosis structure regulation in freshwater ecosystem.

Different cited and author's data on the ultrastructural morphology of tegument in Acanthocephala are analyzed and discussed.

The mosquitos collected in the Smolensk and Kaluga regions in 1985 by the expedition team of the D.I. Ivanovsky Institute of Virusology were identified by V.N. Danilov in 1986. Among the females of mosquitos collected in the Smolensk region four genera and 16 species were recorded; two genera (Culiseta, Mansonia) and 9 species were new ones for this region. Taking in account the reference data (excluding Anopheles hircanus and Aedes behningi, the presence of which here is doubtful) there 22 species of mosquitos of five genera (Anopheles — 3, Aedes — 16, Mansonia, Culiseta, Culex — one of each) are recently known in the Smolensk region. Among the females of mosquitos collected in the Kaluga region, two genera and 8 species were found including one genus (Mansonia) and three species being a new ones for this region. Together with the reference data, there 17 species of mosquitos of four genera (Anopheles — 2, Aedes — 13, Mansonia, Culex — one of each) are known now for the Kaluga region.

Letal cases of valiporosis in the silver carps of the age 3 and 4 years are described. The resistence of hybrids between different forms of Cyprinus carpio to the infection with Valipora campylancristrota is discussed.

The total number of eggs (absolute fecundity) and the number of eggs per 1 gr of body weight (relative fecundity) of Echinorhynchus borealis Linstow, 1901, E. salmonis salmonis Muller, 1784, E. s. baicalensis Bogolepova, 1957 and E. truttae Schrank, 1788 from the Baikal lake was examinide. The absolute fecundity decreases in the rpw or species: E. borealis (26 200 eggs), E. s. salmonis (110 113), E. truttae (8123), E. s. baicalensis (6087). The fecundity of acanthocephalans depends on the host species. The dependence of the whole number of larvae upon the body length of females (r = 0.804) is shown.

It is found out, that the life cycle of the trematode Glyphthelmins rugocaudata (Yoshida, 1916) in the Primorye region includes two intermedial hosts (mollusc Lymnaea pacifampla and dragonfly larvae of the genera Cordulia and Lestes) and a final host, frog species Rana migrimaculata and R. semiplicata.

A new species, Gyrodactylus onegensis sp. n., is described from gills of the freashwater sculpin Cottus gobio.

The report contains the results of faunistic study of parasitic Hirudinea, Mollusca, Crustacea and Arachnida occurring on fishes in the region of the S. Dvina, Mezen' and Pechyora river basins. The parasite fauna in the first basin is represented by 3 species of leechs, 4 species of molluscs, 13 species of crustaceous and 1 species of water mites, in the second basin — 4, 1, 11, 0; in the third basin — 2, 7, 7, 1 species respectively. Total number of parasites in the region investigated: 4 leech species, 5 molluscs species, 16 cruscaceous species and 1 water mite species.

Summary is absent.