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Obtained data strongly suggest that stability of the system A. paradoxus (Monogenea, gills parasite) — host S. lucioperca on the first year of the host life is based on the parasite migration from the gills on the isthmus and back, the variability of the host abundance and on the intensivity of invasion within the different periods of the host life.

The male reproductive system of Prosthodendrium ascidia and P. mirabile has much in common. It includes two testes, two vasa efferentia, vas deferens, seminal vesicle, ejaculatory duct with pars prostatica and cirrus tube, and accessory glands. Seminal vesicle, ejaculatory duct and prostate glands are embodied in cirrus sac in both species. The wall of cirrus sac consists of basement lamina and one muscle layer. In P. ascidia this layer is very thin, but in P. mirabile it is rather well developed. The existence of cirrus sac in trematodes of the genus Prosthodendrium was denied many times in literature. The absence of cirrus sac was fixed in diagnosis of the genus Prosthodendrium and even in some diagnosis of the family Lecithodendriidae and subfamily Lecithodendriinae (Odening, 1964; Хотеновский, 1975). Thus, the obtained data raise the question about the review of taxonomic significance of this morphological feature. Testes contain two types of cells: germinal ones and very few somatic supporting cells, located in peripheral region of gonades under thin basement lamina, surrounded by sparse muscle layer. The male reproductive ducts except cirrus tube are lined with flat epithelial cells, joined by septate desmosomes, cirrus tube is lined with thin aspinose tegument. Basement lamina around duct epithelium is underlined by the only circular muscle layer in vasa efferentia, vas deferens and seminal vesicle; and by circular and longitudinal muscle layers in ejaculatory duct and cirrus tube. In vas deferens and seminal vesicle the luminal surface of epithelium forms elongate lamellae. In vas deferens epithelial cells have also cilia, that congregate in a bundle, directed towards seminal vesicle. P. mirabile possesses three types of unicellular prostate glands. The glands of one type open into seminal vesicle, the glands of two other types open into pars prostatica. In P. ascidia only two groups of prostate glands were found: the first one connected with seminal vesicle and the other one — with pars prostatica. The deep extent of reduction of cirrus sac in P. ascidia is proposed to cause the loss of one type of accessory glands of pars prostatica in this species.

Gastropode molluscs L. saxatilis and L. obtusata were investigated in two sites of the White Sea coast (Ryazhkov Island and Levin Navolok, Kandalaksha Bay). The molluscs in the studied sites were heavily infected with trematodes parasites (about 65% for L. saxatilis and 50% for L. obtusata). The frequency of the shell shape abnormalities in both species were 7—8% in the studied sites. The shell spires of these shells were extremely high with "balloned" whorls probably due to downward displacement of the shell sutures. All snails with abnormal shell were infected by microphallides of "pygmaeus" group (mainly M. piriformes) at the final stage of development. The parasites prevalence of the molluscs with the normal shell was significantly lower. The morphological analysis of shells revealed that the spire height in infected snails increased as compared to uninfected ones. All these data confirm that the shell shape deviations of littorines were caused by the trematodes. However, many of the littorines infected by M. piriformes hadn't got any shell deviations. These cases seemed to de connected with the recent infestation. Here the shell increment was not yet affected by the parasites. This suggestion was supported by the investigation of the shell shape in the molluscs contained the early development stages of the microphallides. The morphometrical analysis also showed that the shell shape of periwinkles was dependent on the type of habitat (intertidal zone and substrate type). The relative spire height was the highest in L. obtusata and L. saxatilis from the upper zone (L. saxatilis especially from the stones). Thus, specific microhabitat may affect on the molluscs shell independently or intensify the influence of trematode infection.

An influence of different concentrations of the ammonium nitrate (200, 700, 1200 mg/l) onto the flat-coil Planorbarius corneus infected with Echinoparyphum aconiatum parthenites and in a control was investigated. The begining of poisoning of molluscs is demonstrated in increasing of moving activity, then their activity decreases and completely disappears. The molluscs loose the water, that appeared in decreasing of the soft body mass (by 12.8—37.7%) and haemolymph volume (by 19— 33.3%). Symptoms of hard poisoning appeared earlier in infected flat-coils.

The ultrastructure of the oncospheral envelopes and embryonic epithelium in Passerilepis crenata has been studied in utero by transmission electron microscopy. It demonstrates peculiarities, which have not been observed in other cyclophillideans studied and seems to be related to the peculiarities of terrestrial life cycle of the species. The oncosphere is surrounded by 3 layers — the shell, the outer envelope and the inner envelope. The uterine wall seems to contribute to shell formation on the early stage of morphogenesis. The outer envelope in the preoncosphere consists of a thin cytoplasmic layer, containing two nuclei (fig. 1), while in the matured oncosphere it is thick, vacuolized and produces granular secret, that thickening the shell (fig. 3, в, г). The inner envelope gives rise to the embryophore. The incomplete embryophore has irregular shape with prominent thickenings in some regions (fig. 3, б; 4, a). The arising of embryonic epithelium preceeds the embryophore formation. This processus begins by invagination of the basal membrane of the inner envelope (figs. 2, a, б). The embryonic epithelium forms two separate plates around the embryo. The nuclei of this plates and the connection with the sunken tegumental cells were not found. The "oncospheral membrane" was not observed. Nevertheless, the thin dense layer covering the basal membrane of embryonic epithelium was observed. The uterine all in P. crenata is syncitial epithelium with deep basal invaginations (fig. 4, б). The cytoplasm of the uterine epithelium during the oncosphere maturation contains extensive granular endoplasmic reticulum while in proglottides containing the matured oncospheres the uterine epithelium does not show high sinthetic activity. It is surrounded by the prominent additional dense lamina beneath the uterine epithelium (fig. 4, в). Thus, the main peculiarities of ultrastructure of oncospheral envelopes in P. crenata are as follows: the secretory activity of the outer envelope in the older oncosphere, incomplete embryophore with thin areas and massive thickenings, absence of "oncospheral membrane" and the separation of the embryonic epithelium by the invaginations of basal membrane of the inner envelope resulting in the presence of two epithelial plates.

The ultrastructure of sensory organs in Triaenophorus nodulosus at all stages of onthogenesis has been examined. There were recovered 6 types of receptors in adult worm and 3 types of receptors in procercoid. The plerocercoid obtains 4 types of receptors, two of them correspond in their structure to those in adult T. nodulosus. Receptors of the type I were observed in all stages of onthogenesis. The development of central and peripheral nervous systems at earlier stages of T. nodulosus onthogenesis has been studied.

The reexamination of a cestode Dicranotaenia globosoides Soltys, 1954 from the water shrew Neomys fodiens was based on the material collected in the eastern part of the National Park "Bialowieza". The neotype of this species has been chosen. Hymenolepis fodientis Vaucher, 1971 is considered a synonym of D. globosoides Soltys, 1954. The latter species is regarded as a palaearctic species of the genus Cryptocotylepis Skrjabin et Mathevossian, 1948. The validity of Pseudobotrialepis mathevossianae Schaldybin, 1957, the type species of the genus Pseudobotrialepis Schaldybin, 1957 is restored. Hymenolepis globosoides sensu Vaucher, 1971 nec Soltys, 1954 is considered a synonym of P. mathevossianae Schaldybin, 1957.

In experiments the fecundity of Leptosylla segnis was depended upon duration of the preliminary contact of the host (white mouse) with fleas of the same species. As the duration of the contact was promoted the daily mean number of eggs per female at first (at time of contact from 1 to 6 days) increased, then (at time of contact 7—12 days) declined and decreased below original level at 13— 30 days of contact. It is supposed that observed changes in fleas fecundity were connected with the immune reactions of the host to the bites of insects.

The study conducted in 1996—1997 has shown that in large town lads there is a steady population of the taiga tick with the maximum number 3 specimens per 1 km of account route. In these lads there are well developed wood and shrub layer, grass cover and thick ground litter layer. Tick larvae often occur on rodents from these territories. In lads and gardens, where the ground litter is ruined and herbal cover is oppressed, the taiga ticks do not occur. In outskirts the number of ticks is higher. Abundance of ticks in these areas has an inverted dependence upon recreational load degree.

A new species Bunocotyle constrictus sp. n. was found in an intestine of the haarder in Molochnyi lagoon (Azov sea). A new host is recorded for B. cingulata. The new species B. constrictus sp. n. differs from a closely related species B. mugilis by characters as follows: a striated cuticle, bindings in posterior part of body, larger gastral suckers, and location in the intestine of hosts.

A parasite fauna of fishes in lakes of distrophic type was studied. Some general aspects of a lake distrophication influence on a parasite fauna are discussed.

One hundred of young starlings were caught in the different time of day on the Courish spit of the Baltic Sea (55°12'N, 20°46'E). The feces of these birds were collected at the time of capture and then examined to find Isospora oocysts. The intensity of infection was higher among the starlings at an early stage of the postjuvinal moult that among those who were at the last stages of the moult. The Isospora oocysts were observed only in feces that were collected in the afternoon. The most number of oocysts were observed in feces collected between 4 p. m. and 7 p. m. In the droppings of one starling, who was sitting in a cage for four days, the oocysts were also observed only in the afternoon. The appearance of Isospora oocysts in the droppings of birds only in the afternoon may have adaptive meaning. For example, it can increase the concentration of invasion oocysts at forage places of the host. It can also preserve the oocysts from drying up immediately because of the straight sunlight and low humidity.

Myxobolus najdenovae is recorded for the first time in Azov sea. It is found in a new host, Neogobius melanostomus. Redescription of the parasite based on material from the new host is given. An assignation of M. najdenovae to the pontocaspian endemic group of fresh water origin is confirmed.

Summary is absent.

Summary is absent.

Summary is absent.

Summary is absent.

Summary is absent.

Summary is absent.