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A revision of the families Diphyllobothriidae Lühe, 1910 and Ligulidae Claus, 1868, emend. Dubinina, 1959 was conducted. The subfamily Polygonoporinae Delamure et A. Skriabin, 1968 was excluded from the family Diphyllobothriidae and elevated to the status of a distinct family Polygonoporidae fam. n. and a distinct suborder Polygonoporiata subordo n. The subfamily Baylisiinae Jurachno, 1989 was excluded from the family Diphyllobothriidae and elevated to the status of a distinct family Baylisiidae fam. n. The subfamily Schistocephalinae Dubinina, 1962 was excluded from the family Ligulidae and retained as a distinct family Schistocephalidae fam. n. in the superfamily Diphyllobothrioidea Lühe, 1910. The families Baylisiidae and Ligulidae were united into the superfamily Baylisioidea superfam. n. Keys to suborders of pseudophyllids and superfamilies and families of diphyllobothriids are given. Possible ways of their evolution are considered.

In different seasons of 1987— 1988 the quantitative samples of Littorina saxatilis molluscs were collected from several squares (0.1 and 0.25 m2). The samples were collected separately from the open surfaces (stone surfaces, macrophytes, etc.) and from the sheltered microstations (macrophyte thickness, grounds under it) in the middle and lower strata of the intertidal zone of the Yarnyshnaya inlet (the East Murman). The section of molluscs was accompanied by the registration of the invasion with local hemipopulations (= the totality of parasite individuals of the same species within one host individual) of daughter sporocysts of "pygmaeus" microphallids. The following groups were distinguished among them: young sporocysts (YS); sporocysts containing young metacercariae which were invasional for the final host (common eider) (YIM) and sporocysts containing old invasional metacercariae (OIM). Mass death of molluscs containing OIM took place in spring. It was connected with an influence of the whole complex of unfavouratle environmental factors. The number of littorines invaded with YIM increased at the open surfaces in June—July. YS-group invading molluscs in sheltered microstations in April had already matured up to this stage. The behaviour alterations caused by developing parasites forced molluscs to crawl to the surface. In September—October the local YIM-hemipopulations matured up to OIM-stage and the number of littorines invaded with them at the open surfaces increased. Invasion of molluscs with YS was not revealed here but it was rather high in the individuals from sheltered microstations. It was connected with the concentration of "pygmaeus" eggs with miracidia, which were distributed by ducklings and adult common eiders in July—August. In littorines, which had been invaded in summer, the daughter sporocysts matured up to YS-stage till September—October. In winter littorines left the open surfaces and formed aggregations under stones. As compared to the whole population the number of molluscs at the open surfaces was small. As a result, molluscs leaving them in autumn and heavily invaded with OIM were masked by the other part of L. saxatilis population. This fact caused an erroneous idea of the sharp decrease in the invasion of littorines with "pygmaeus" microphallids supposedly owing to mass death of invaded molluscs in that period. During the cold period the further development of YS ceased and renewed only in spring, with the transition of littorines to active life.

A new species of acanthocephals, a parasite of local Naemacheilus stoliczkai, was recorded from Salmo gairdneri after 9 years of its introduction into mountain water bodies of Tien Shan. Gammarus lacustris serves as an intermediate host. Dynamics of infection of trout for 9 years is shown.

Rightfulness of the statistical method application for the analysis of spatial structure of helminth populations is considered. It is stressed that the statistical description does not support the suggested hypothesis. It only permits the tested hypotheses to be rejected since its main aim is to make rules for drawing conclusions on the basis of observation data.

The paper presents the results of studies on the effect of wastes of the Cherepovets iron-and-steel works containing phenol, naphthaline and oil products on fish parasites of the Sheksna part of the Rybinsk water reservoir (the Volga river system). It has been shown that the number of highly sensitive ectoparasites of Abramis brama (Protozoa, Dactylogyrus monogeneans, Ergasilus sieboldi crustaceans and Caspiobdella fadejewi leeches) considerably decreases in the zone of pollution. It has been first suggested to use Diplozoon paradoxum and Caryophyllaeus laticeps, parasites of bream highly resistant to toxic effect, the number of which considerably increases in the zone of pollution, as indicators of anthropogenic pollution and ecological state of a water body. Among diplozoons there have been first discovered individuals having structural anomalies (reduction of the attachment organs, violation in the symmetry of arrangement and number of valves) that serves as evidence of mutagenic effect of toxic substances of polluted waters on morphogenesis of the parasite.

On the basis of analysis of structural characters, peculiarities of distribution and host-parasite relationships a new classification of the family Leptopsyllidae Rothschild, 1915 has been suggested. The family Leptopsyllidae is divided into three subfamilies as follows: Leptopsyllinae (contains the tribes Acropsyllini tr. nov., Amphipsyllini, Caenopsyllini, Cratyniini, Leptopsyllini, Mesopsyllini), Paradoxopsyllinae (Paradoxopsyllini, Ornithopahagini), Dolichopsyllinae (the genus Dolichosyllus). The subfamily Leptopsyllinae is characterized by the presence of 2 bristles in the ocular row while Paradoxopsyllinae and Dolichopsyllinae have 3 bristles. When establiching phylogenetic relations between the tribes of the family such characters as structure of the frontal part of the head, frontal tubercle, interantennal wall, antennal fossae, eye, genal comb, mesonotum and mesosternum, framework of aedeagus, apodemal rod of sternum IX, articulation of crochet and sternum IX, spermatheca of females, 2nd thoracic link-plate have been used. Morphological peculiarities of some tribes are unique not only for the family Leptopsyllidae but also for Siphonaptera as a whole that points to their early isolation that is borne out by the peculiarities of their host-parasite relationships. Thus, Dolichopsyllus fleas parasitize rodents of Aplodontidae, Caenopsylla fleas are parasitic on rodents of Ctenodactylidae, and Mesopsyllini fleas on rodents of Dipodidae known from Eocene. Further evolution of the family Leptopsyllidae was connected with parasitism on rodents of Crecitidae and Muridae.

Two new species of the genus Zachvatkinia are described from the crab plover Dromas ardeola (Charadriiformes: Dromadidae) captured on Providence Island, Madagascar: Zachvatkinia dromae sp. n., Z. oxyloba sp. n.

Simultaneous but separate feeding of ticks on nonviremic animal (guinea pig) has shown that Amblyomminae ticks are practically unable to transmit distantly tick-borne encephalitis virus (ТВЕV) to the specimens of their own subfamily and to Ixodinae as well. Ixodes persulcatus and I. ricinus displayed their ability as donors and recipients of ТВЕV (adults and nymphs) not only for their own subfamily representatives but also as donors for recipients of Amblyomminae subfamily (nymphs and adults of Dermacentor and Rhipicephalus and nymphs of Haemaphysalis). Experimental and literature data analysis permits the authors to conclude that the very important role of TBEV circulation in nature belongs to the distant virus transmission. The absence of such type of virus exchange among Amblyomminae excludes this group of ticks from active virus circulation in TBEV foci.

The fleas of wild and commensal small mammals, domestic animals (dogs, cats) and free-living flea forms in houses have been collected in plague nidi of Tay Nguyen plate, Dak-Lak province, Vietnam. Pulex irritans, Ctenocephalides felis felis, Ct. felis orientis were found in the houses on dogs, cats and on the ground floor. Commensal rats in populated areas were infested by Xenopsylla cheopis and rarely by Lentistivalius klossi. The agricultural zone was inhabited by both home and wild animals such as commensal, savannah and forest-dwelling small mammals. The flea fauna of this zone is presented by X. cheopis and L. klossi. In the tropical forest surrounding villages four of the flea species were found: X. vexabilis, a specific parasite of the forest-dwelling rat Berylmys berdmorei, L. klossi found on six species of forest small mammals, Acropsylla girshami from Berylmys bowersii and Pariodontis subjugis from Hystrix brachyura. The agricultural zone is the most possible place of commensal and forest-dwelling small mammals contact, where the latter can get plague microbe.

The influence of trematodes on the aquatic respiration rate of their gastropod host Littorina obtusata (L.) under different conditions of salinity was investigated. It was found that the respiration rate decreased when salinity declined both in infected and non-infected snails. The oxygen consumption rate was proved to be unaffected by trematode invasion at different (25‰ and 13.6‰) salinities. The possible mechanism of the influence of parasites on the spatial distribution of the host is discussed. It is suggested that changes in the aquatic respiration rate are not involved in this mechanism.

Mature and larval forms of the nematode known under the name Sobolevispirura arali (Schaldybin, 1961) were recorded from Hemiechinus auritus and Diplomesodon pulchellum in Turkmenia. Illustrated descriptions of III and IV stage larvae and imaginal form of the nematode are given. After analysis of the parasite's morphological peculiarities the genus Sobolevispirura Schaldybin, 1961 is considered invalid and its only species S. arali is suggested to transfer to the genus Spirura Blanchard, 1849.

Panagrolaimus orthotomici sp.n. is a nematode associate of the bark beetles Orthotomicus laricis and O. suturalis in north-eastern Asia. From P. peruensis, P. halophilus, P. juditae the nematode differs in the number of its male caudal papillae; from P. aberrans in its stome armature and from the other genus members by the presence of unpaired preanal ventromedial papillae in male. The biology of the nematode is described.

Summary is absent.

Summary is absent.