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Morphological inversions during the ontogenesis of the ixodid ticks consist in the deranges of species-specific tendencies in the development of some external structures by the female line. The inversions, which included a wide range of organs and their fine structures, have been described for the first time in 14 species of 4 from 7 Palearctic ixodid genera. Emphasis is placed on the study of the structures, which serve as differential characters for closely related species. It is shown, that the using of the structures subjected to inversions is unavoidable in systematics because of the great similarity of closely related species, especially in immature stages. It is established by the data on the variability of all active stages in the species distribution ranges, that the degree of the inversions manifestation may somewhat fluctuate in different subspecies or geographic morphotypes of the same species, but the peculiarity of the inversions always remains a species-specific character. The cause of inversions origin is the evolution of the Ixodidae by the way of morpho-ecological specialization, namely hypertrophic, giantism, the growth of teguments in the period of nutrition act by pasture ambushing, which led to the derange of the development coordination of the organs during ontogenesis. Biological implication of the inversions is a guarantee of the adaptive potential of species during the process of microevolution. Even though the inversions make identification of closely related species difficult, their substantial importance is that they form integral species-specific character for the whole active part of the species ontogenesis.

Intraspecific morphological variation of the chigger mite species Montivagum dihumerale (Traub et Nadchatram, 1967) is studied. Eco-geographic rules of the variation are revealed. General size of mites is found to be increased along with the rise of the high-mountain character of the landscape in the collection localities. The numbers of idiosomal setae are varied independently from the size parameters and geographically close populations are proved to be the most similar by these characters. At the same time, numbers of the setae of different types play the leading role in the discrimination of closely related Montivagum species, while the eco-geographical rules have not been found in this genus at the level of interspecific differences. As a result, the hypothesis is set up, that a significant degree of isolation of local populations separated from each other by high mountain ranges of the Central Asia is the main factor of speciation in the genus Montivagum. Regional character of this speciation mode is confirmed by the comparison with other chigger mites taxa.

New data on the migration and development of Echinostoma caproni mother sporocysts in two mollusk species of the genus Biomphalaria are obtained. It is confirmed, that the formation of primary and second generative cells takes place only as a result of undifferentiated cells' proliferation and following differentiation of some of them. These processes in miracidium, as well as in the parasitic stage of mother sporocyst, take place in a special organ, germinal mass, which occupies caudal position in both cases. The supposition of the role of germinal mass as the universal centre of multiplication and development of generative elements in all generations of Echinostoma caproni parthenites is confirmed. It is established, that mother sporocysts do not relize their reproductive potential completely, and the degree of its realization depends on the conditions arising in the host organism.

A new genus and species of cestodes from the great-crested grebe Podiceps cristatus collected in the Eastern Europe is described. The genus Mircia gen. n. in addition to the type species M. shigini gen. n. includes the following species formerly being included in the genus Joyeuxilepis Spassky, 1947: M. decacantha (Fuhrmann, 1913) comb. n., M. decacanthoides (Borgarenko et Gulyaev, 1991) comb. n., M. fimbriata (Borgarenko, Spasskaja et Spassky, 1972), comb. n., and M. uralensis (Gulyaev, 1989) comb. n. Brief revision of the genus Joyeuxilepis is provide.

A microsporidian species producing octospores in sporophorous vesicles is found in Aeshna viridis larvae from intermittent streams situated in the vicinity of Novosibirsk City. Size of the spores measured on fresh smears was 6.9 ± 0.09 цт x 4.1 ± 0.08 µm (6.0—7.6 x 3.5—4.9). Each spore have single elongated nucleus and an anisofllar polar filament composed of 10—11 anterior and 10—11 posterior coils. The infection was restricted to adipose tissue. According to spore morphology the Siberian isolate can be attributed to the species Systenostrema alba described from Aeshna grandis in Sweden (Larsson, 1988). This is the first description of Microsporidia infecting Odonata from Siberia.

The effect of the microsporidian Vairimorpha ephestiae Matted (Microsporidia: Burenellidae) on nonspecific esterases was studied in hemolymph, fat body and midgut of the larvae of Galleria mellonella L. (Lepidoptera: Pyralidae). Esterase patterns were analyzed by the polyacrylamide gel electrophoresis, the total esterase activity was detected spectrophotometrically. The increase of total esterase activity was registered in hemolymph of inflected larvae. An overexpression of esterase isozyme in hemolymph was already detected at the 3rd day post infection. No changes in esterases pattern were observed in the fat body's homogenates of the G. mellonella larvae possessing the symptoms of microsporidiosis. The degradation of esterase isozymes and the decrease of total esterase activity in the pattern of the midgut homogenates of infected larvae were registered during parasite sporogony. The greatest esterase activity in hemolymph and midgut tissues was registered during vegetative reproduction of parasite, but the least level of esterase activity was observed during mass sporogony of microsporidia.

On the base of literature and the original data in has been established that acanthocephalan species known as Acanthocephaloides kostylewi Meyer, 1933, and described from the Black Sea sole Solea lascaris nasuta (Pallas) is to be transferred to the genus Solearhynchus with new species name Solearhynchus rhytidotes nov. comb. (syn. Echinorhynchus rhytidotes Monticelli, 1905; E. aurantiacus Monticelli, 1887; E. corrugatus Monticelli, 1887; Acanthocephaloides kostylewi Meyer, 1933; A. rhytidotes (Monticelli, 1904) Belofastova et Korniychuc, 2000; Solearhynchus soleae (Porta, 1905) de Buron et Moillard, 1985). Detailed descriptions, measurements and original figures are given.

The description of a new species Cnetha itelmenica Chubareva et Yankovsky, sp. n. is given. Only 6 species of the genus Cnetha have the simple lobes of rectal organ (C.fontia, C. garniensis, C. gejgelensis, C. costata, C. subcostata and C. karzhantavica). These species distribute only in Southern Europe, Northern Africa and Transcaucasia, excluding C. subcostata distributed in NE China, Korea and Japan. C. itelmenica differs from C.fontia and C. garniensis in having a deep inlet of the head capsula, from C. costata, C. subcostata and С. karzhantavica in the different number of hook rows in the posterior circlet (86—90 versus 96—100 in C. gejgelensis and C. costata, 68 in C. karzhantavica). The new species differs from other Siberian and Far Eastern species of the genus (C. cornifera, C. paracornifera, C. patrushevae, C. pugetensis, C. shutovae) in having simple lobes of the rectal organ, from C. gejgelensis in having another pattern of setae arrangement on the submentum (by 1 line, versus 2 lines in C. gejgelensis), from C. shutovae, C. pugetensis and C. patrushevae in the different number of hook rows in the posterior circlet (86—90 versus 60—62 in C. shutovae and 62—66 in remains), and from C. pugetense and C. patrushevae in the number of primary fans (36—40 versus 41—52). C. itelmenica differs from C. vernum (as base standard), as well as from other studied species of the genus, in having a species-specific disk pattern, three wide homozygous inversions in IS, IL, IIIL, and a little homozygous inversion in IIS. It differs from C.fontia, C. garniensis, C. costata and C. zakhariensis in the absence of chromocenter and presence of additional heterochromatic B-chromosomes.