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A method of factor temporal prognosis for the epidemic manifestation of the tick-borne encephalitis foci has been elaborated, based on recognized critical levels of infection. High reliability of possible prognoses and obvious perspectives of the proposed method are noted.

Ultrastructure of the epithelium of adult and juvenile Urastoma cyprinae has been studied. The epithelium of both adult and juvenile worms is cellular, ciliated and bears numerous microvilli. The cytoplasm is rich in large, numerous epitheliosomes of two types — electron-dense and with fibrillated content (fig. 1, a, б; 2, a—в). Besides large secrete granules small membrane-bounded vesicles were observed (fig. 2, a—в). In juvenile worms the dense epitheliosomes are less abundant and the fibrillated content in the second type of granules has a different structure: the fibrils are very thin and more densely packed forming the structures of the less electron density (fig. 3, a, б, б1). The membrane-bounded vesicles in the epithelium of juvenile worms were not observed. All types of secrete are ejected by exocytosis (fig. 2, в; 3, в, г). The ultrastructure of the epithelium in juvenile U. cyprinae is strongly similar to that in parasitic turbellarian Kronborgia, especially to the epithelium in a male and a larva. The basal lamina consists of tree layers and forms numerous deep infoldings into the epithelium (fig. 1, a; 2, a; 3, а, б, д). The basement membrane projects deep and numerous invaginations into the epithelium which may almost reach the apical membrane (fig. 1, a; 2, а, б, г; 3, д). Mitochondria are large and situated mainly near the projections of the basement membrane (fig. 2, б—г; 3, д). Such ultrastructure implies an intensive process of the transmembrane transfer of the dissolved organic substances from the sea water. The same structures were found in the epithelium of Kronborgia. Uptake of organic compounds through the epithelium in the common ancestors of Urastoma and Kronborgia could be the preadaptation to the endoparasitic mode of life in Fecampiida. The differencies in ultrastructure of epithelium in U. cyprinae from the White Sea and from Mediterranean Sea (Noury-Srairi e. a., 1990) may be explained by the differences in the method of fixation or by the parasitizing the another host — the mollusk Mytilus galloprovincialis. The ciliary receptors of five types were revealed in U. cyprinae (fig. 3, e, ж; 4; 5; 6). They differ in the shape and length of the ciliary rootlets and in the content of the nerve processes. All receptors lack of the real collars typical for the receptors of Neodermata. Urastoma is most close to the Neodermata amond parasitic turbellarians studied thus far, and the absence of collars in receptors of this species testifies that the collars are the veritable synapomorphy of the Neodermata. The diversity in the ultrastructure and possible functions of receptors correspond to the complicated adaptations of this species. The modern molecular data as well as the ultrastructural evidence attest that parasitic turbellarians of the genera Urastoma, Genostoma and Ichthyophaga are relatives and cannot be included in any turbellarian order known. Therefore Urastoma, Genostoma and Ichthyophaga have been erected in the separate order Urastomida ord. nov. The diagnosis of the new order is given.

Short-term simultaneous effect of high concentrations (LC₂₅, LC₅₀, LC₇₅) of heavy metal ions (Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺) and infection with trematode partenites Echinoparyphium aconiatum onto haemolymph of mollusk has been investigated. It was noted that low doses of toxicant (2.5 and 10 maximum admitted concentrations) have variable effect. In infected molluscs the concentration of haemoglobin decreases, while in intact ones it increases. In relation to this index, it was found, that the ion Cu²⁺ is highly toxic, Zn²⁺ and Cd²⁺ — toxic, Pb²⁺ — moderately toxic.

Based on the examination of specimens of Aploparaksis crassirostris deposited in the Museum of Zoology in Copenhagen and the Museum of Natural History in Geneva and cestode material from other collections, we have carried out the revision of this species, designated the lectotype and paralectotypes, made its redescriptions, enumerated synonyms, showed the only host of this species in the snipe Gallinago gallinago, and more precisely mapped the distribution range of the parasite. The investigation of the type series of A. sinensis, the parasite of the woodcock Scolopax rusticola, deposited in the Museum of Natural History in Geneva, confirmed the validity of this species, earlier considered as synonym of A. crassirostris. The lectotype and paralectotypes of A. sinensis were designated. Some data on its life cycle have been obtained. It was also found by the experimental invasion that five species of oligochaetes of the family Lumbricidae are intermediate hosts. The metacestodes of this species belongs to the tailed diplocyst modification and posesses a characteristic feature, the bifurcation of tail.

It is shown for the first time that during 50 years of the Rybinsk reservoir's existence the abundance of parasite leeches (Piscicolidae) has increased, and the species composition has become richer. In 70 the leech Caspiobdella fadejewi (Epstein) was registered here as a mass species. This species became a real competitor to Piscicola geometra (L.) inhabiting the Volga river in all times. In early '90s the leech Acipenserobdella volgensis (Zykoff) appeared in the Rybinsk reservoir. Till 1987 this species was not found to the north from the Kuibyschev reservoir. An increase in number of fish leeches and an extension of their specific composition occurred not only in the Rybinsk reservoir but in the other reservoirs of the Volga cascade as well.

Ectoparasites have been investigated on gills of the ruff, perch, white bream, roach, bream, ide, and European cisco from the Pleshcheevo lake. 13 parasite species were found: Dactylogyrus falcatus, D. distinguendus, D. cornoides, D. cornu, D. sphyma, D. robustus, D. amphibothrium, Ancyrocephalus paradoxus, Argulus foliaceus, Ergasilus sieboldi, Achtheres percarum, Ancyrocephalus percae, and Rhipidocotyle companula. A reliable negative correlation between the number of monogeneans An. paradoxus and the copepods Ac. percarum on the perch. D. falcatus, the specific monogenean of the bream, was found on the roach. The comparison of the obtained data with those of 1939 has shown the decrease of oxyphilic copepods E. seiboldi, that prove the increasing eutrophication.

It is considered that in Anacanthorinae, Markewitschiana and Pseudacolpenteron pavlovskii (Dactylogyridae s. s.) the anchors are absent originally. In the other dactylogyrids (s. 1.) without anchors (Pseudacolpenteron ignotus; Acolpenteron; Anonchohaptor—Icelanchohaptor; Kritskyia— Telethecium—Pavanelliela) these structures are lost. In related genera Rhinoxenus and Nanotrema the dorsal pair of anchors is transformed into the "spikes"; in Heteronchocleidinae there is one anchor; in Trinigyrus and Schilbetrematoides are two anchors; and in Urogyrus three anchors are reduced. But in Rhinonaster, Cacatyocotyle, Callceostomella, Neocalseostoma elongatum and Pseudodactylogyridae the presence of one pair of ventral "peduncular" or "haptoral" anchors appear to be the original state. For Anacanthorinae and Dactylogyridae s. s. the presence of 18—16 hooks, original lacking of anchors, appearance of one pair of them, evolutionary development and subsequent reduction of these structures are characteristic. In the dactylogyrids (s. 1.) having two pairs of anchors and 14 hooks, one pair of the anchors is present originally, then usually the second dorsal pair grows up, and finally, the reduction of a part of anchors or all the anchors is possible. In the 16-hooked dactylogyrids (s. 1.) having two pairs of anchors (Tetraonchinea, Amphibdellainea, Neodactylodiscinea) the original lacking or reduction of the anchors is not reported. The author considers, that it is unwarranted to unite all dactylogyrids (s. 1.) without anchors into the superorder Ananchorea Malmberg, 1990 or to postulate the original presence of the two pairs of ventral anchors in this group. It is also impossible to unite all dactylogyrids (s. 1.) having 0—4 anchors and 18—14 hooks into Dactylogyridae sensu Boeger et Kritsky, 1993.

We studied the effects of the parasitic dinoflagellate Ellobiopsis chattoni on the winter mortality of natural population of the calanoid copepod Calanus finmarchicus in the Norwegian Sea (materials was collected in March-April 1989 and September 1990). Dinoflagellate infection occurred during autumn (the infection rates of copepods with E. chattoni was 15%, as average). Average mortality rate in C. finmarchicus was about 0.08% per day, or about one-tenth of total mortality in winter period.

The first case of a mass infection of fish fry with the ciliate Ambiphrya ameiuri (Thompson e. a., 1946) was found during the summer of 1989 in one of spawning zones of the Rybinsk reservoir. In June—July of 2000 after the ten-year interval, the second case of infection with this parasite in the first-year roach Rutilus rutilus has been observed. The prevalence of A. ameiuri was very low. Nine other species of ciliates forming the ectoparasite community were also observed. Parasites were disposed mostly on a surface fish bodies, gills and more densely on fins.

The myxosporidian fauna of the Gadidae from Far Eastern seas have been investigated. 7 species of myxosporidians of two families have been found Redescriptions of myxosporidian species are given.