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The indigenous symbiotic microflora associated with the tegument of proteocephalidean cestodes and the intestines of their fish hosts has been investigated in morphological and ecological aspects. The indigenous microflora associated with the cestode tegument consists of the nannobacteria population, which was present obligatorily on the surface of tegument, and the "deep microflora". The deep microflora associates with some few species of parasites only. Each individual host-parasite micro-biocenosis includes specific indigenous symbiotic microorganisms, with the differing microfloras of host intestine and parasite. Physiology, biochemistry and/or diet of hosts apparently influence on the symbiotic microflora's structure of parasites. The least bacteria abundance and diversity of their morphotypes were observed in the parasites from baby fishes. The diversity and abundance of bacteria were increased with the fish host ageing and the formation of the definitive structure of its intestine. It is an evidence of the gradual invading of the intestinal parasites (cestodes) tegument by bacterial cells. The invading is realized on the base of the microflora that was present in the food of fish host. The symbiotic microflora has specific morphological features, can regulate the homeostasis of the cestodes and fish hosts and also can maintain equilibrium of alimentary and immune interrelations in the host-parasite system.

A checklist of the Monogeneans and Coelenterates parasitizing fishes in the Volga River basin is given. The list of hosts with the data on their occurrence in different areas of the Volga River basin is provided for each parasite species. The data on the parasites from 46 fish species are presented. The checklist includes 139 species and 6 taxa of subspeci-fic rank. 9 species (Dactylogyrus aristichthys, D. ctenopharyngodonis, D. hypophthalmichthys, D. lamellatus, D. nobilis, D. suchengtaii, Pseudodactylogyrus bini, P. microrchis, and Eudiplozoon nipponicum) were introduced into the Volga River basin accidentally together with the Far Eastern fish species during the process of their naturalization.

Faunistic and some morphological data, as well as nomenclature notes on dracunculoid nematodes parasitising fishes in the Volga River delta, are presented. The author replaced a preoccupied generic name Molnaria Moravec, 1968 (Skijabillanidae) by the new name Kalmanmolnaria nom. nov. The validity of Philometroides lusii (Vismanis, 1962) comb. nov. as a senior objective synonym of Philometroides lusiana (Vismanis, 1967) Ivaschkin et al., 1971 is restored.

The changes of the midgut in the females of the tick species Ixodes persulcatus and I. ricinus during the second and third immunizing feeding on rabbits were studied by the histological technics. The alternation of one generation of the digestive cells of nymphal stage and two generations of the digestive cells of adult stage was observed. The generation of secretory cells is absent. The tick completes feeding and drop off when the last generation of the digestive cells is on the initial activity stages. The amount of the blood consumed is not enough for the rhythmical functioning of the midgut. The feeding of tick is broken on the second phase and full satiation does not take place. It is apparently an effect of the interruption of the blood entrance into the midgut cavity of feeding tick as a probable result of anti-ticks resistance of unnatural hosts.

New conception of the anthropo-parasitic system has been elaborated. Spatial and temporal structure of the infections diseases incidence in the Primorye Territory has been analysed on the base of this conception.

The longevity of the tick Ixodes ricinus has been studied on 27 samples from a wild population of the Moscow Region. Ticks were kept in small cages and glass tubes under conditions close to natural. About 2/3 of the specimens collected in spring survived till the next spring and later died out gradually during the second season of their activity. Very few specimens reached the beginning of the third winter in their life, but apparently none of them survived the end of the winter. The life span of males was the same as that of females. No mass activation of adult ticks was recorded in the autumn of the year of their molting. It seems that the rise of the autumnal density of adult ticks depends mainly on the increased activity of the females which molted from nymphs last year.

A count of the tick species Ixodes persulcatus Schulze, 1930 was carried out in the «Denezhkin Kamen» Nature Reserve and adjacent territories (the Severoural'sk and Ivdel' Districts of the Sverdlovsk Region, the Northern Urals geographical province) in the 2005. The abundance and distribution of unengorged adults has been evaluated on an area of 22.5 square kilometers (N 60°27'—60°30' E 059°38'-059°42'). The area includes proportionally main landscape and vegetation elements of the region studied, from mountain analogues of the middle and northern taiga up to tundra. One tick species, I. persulcatus, has been collected by flagging with the abundance from 0.4 up to 6.8 (average 1.6 ± 0.9) specimens per flag-hour. The observed values of abundance are classified into three classes (I — ticks are absent, II — 1—2 specimens, and III — 3—7 specimens per flag-hour). The class I amounts 20, II — 75, and III — 5% of the area examined. It has been revealed by the expert evaluation of the 2003—2004 and counts of the 2005 that ticks occur stably in the Northern Ural, reaching N 61° and 400 m above sea level. The level of the species abundance remained constant till the middle of summer. In this period the activity of ticks dependent on the weather optimum only.

Summary is absent.