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The ecological scenario of the evolution of main branches of Neodermata is described. The first neodermateans (= promonogeneans) were parasites of the gill lamellae of Paleozoic jawless vertebrates, which were microphagous suspension-feeding animals. The main apomorphic characters of the primary neodermateans are neodermis, cercomer (posterior hooked attachment organ) and swimming infective larva. All subsequent evolution of Neodermata was related with their acquisition new niches in hosts, which were intensively diverging in that time adapting to new food types and conquering new ecological niches. The acquisition of new microhabitats was accompanied by the development of morphological diversity in Neodermata especially in a structure of attachment and genital organs. Trematoda, Cestoda and Polyopisthocotylea comprise specialized evolutionary lineages and Monopisthocotylea is a basal taxon. Polyopisthocotylea is specialized to the blood feeding on fish gills. The common ancestors of the Trematoda and Cestoda inhabited walls of gills and pharyngeal cavities, from where they penetrated the digestive tract. The aspidogastri-dean multiloculate holdfast appears to be a highly specialized attachment organ of the mo-nogenean ancestor, which inhabited muscular pharyngeal walls of Paleozoic vertebrates. The loss of cercomer hooks probably took place when mollusk-hosts have been involved in the aspidogastridean life cycle. The extinction of many chondrichthiean groups and progress of small plankton fishes (Teleostei) has led to the appearance Digenea. New vertebrate hosts needed a new infestation type and the cercaria appeared. Parthenogenesis has been developed in stages living in mollusks to counterbalance the loss of individuals at two transmission stages in the digenean cycle; this was resulted in a strong specificity to mol-lusk-host. Evolutionary tendencies of Trematoda and Cestoda show noticeable similarities.

Morpho-fuctional causes of the formation of protandrous Cyclophyllidea (tapeworms) have been studied. Two forms of protandry are described. The protandry type I is typical for polymeric (polysegmental) Hymenolepididae. It appears independently in different taxa of this family (Aploparaksis, Echinatrium, Wardium, Diorchis and others) while the narrow-strobila forms with a low prolificacy of proglottids are formed. The development of this living form of hymenolepidids is ecologically caused by the high density of their aggregation in intestines of hosts. The primordium results in the development of genitals in the juvenile strobila proglottids with the limited internal space. Due to this process, parallel morphogenesis of male and female gonads is proved to be impossible. A selection leading to the overtaking development of testicles and copulative apparatus regarding morphogenesis of ovary and vitellarium is based an earlier maturation of testicles and group copulation of proglottids with and underdeveloped ovary that is typical in original euandrogyne forms. The group insemination of proglottids from a polysegmented strobila reduces the number of copulation and improves an efficiency of cross-copulation of tapeworms and. As a result, morpho-functional zones of male proglottids characterized by an immature ovary and those of fertile female segments losing their testicles are differentiated in the strobila. The protandry type II is typical of mesomeric tapeworms (Dilepididae, Schistotaeniidae, Anoplocephalidae). It is also resulted from a limited space of proglottids for developing the hermaphroditic genital apparatus. This is caused by the shift of genital morphogenesis process into juvenile proglottids and also by the enlargement of gonad sizes as the result of a selection for a higher prolificacy of proglottids. The dissociation of the development of male and female gonads takes place because of the retardation of ovary morphogenesis.

A comparative analysis of indices of peroxidation lipids in tissues of Ligula intestinalis plerocercoids and in the intermediate fish host, the bream Abramis brama, was performed for the content of common lipids (CL), malonate di-aldehyde (MDA), which is a product of lipid peroxidation (POL), and common antioxidate activity (CAA). The dependence of indices upon size of parasites is recovered. The long-sized parasites had higher rate of MDA and intense CAA. The higher rate of MDA and low one of CAA was observed in the infected fishers comparing to the healthy ones.

The first generation of Echinostoma caproni partenitae is represented maternal sporocysts developing in the cardium of the Biomphalaria mollusk. During all their life, they produce rediae of maternal generation. Rediae of Echinostoma caproni of all generations are similar. The first generation consists of maternal rediae forming only redoid embryos. Due to this process, the number of partenitae increases very fast. The next generations are represented by daughter rediae. In the beginning of their life they produce redoid embryos but later begin forming cercariae. The number of rediae produced before this shift of production depends on the population density. Further, the partenitae retain their potential ability to form rediae but realize it in exceptional cases. Generative organs of all generations are germinal masses. Proliferation of generative elements and beginning stages of redia and cercaria development take place within these masses. The infrapopulation of E. caproni belongs to the "prolonged type", because it is a complete microhemipopulations; its existence is limited by a lifespan of the mollusk host.

In contrasts to formerly known data, it is found that two species of the Parasymphilodora trematodes, Parasymphilodora japonica (Yamaguti, 1938) and P. markewitschi (Kulakowskaja, 1947) are actually distributed in the territory of Primorye land. The first intermedial hosts of the former species are snails of the genus Parafossarulus; in the second species, these hosts are snails of Boreoelona. A life cycle and stages of development of both trematodes are described.

A new species of the genus Microsomacanthus Lopez-Neyra, 1942 is described. The material was collected from eider ducks (Somateria mollissima, S. fischeri, and S. spectabilis) in the Chaunskaya lowland (North-Western Chukotka). Microsomacanthus parasobolevi sp. n. differs from the closest species of this genus (M. polystictae Regel, 1988, M. sobolevi Spassky et Jurpalova, 1964; M. strictophalius Tolkatchieva, 1966) by the structure and size of the copulatory organ. Wide distribution of the new species was detected based on the cestodes collections from eider ducks of the Eastern Chukotka, Lena River mouth (in the museum of the Institute of the Parasitology RAS) and Iceland (Karl Skirnisson's cestode collection of the common eider). Furthermore, this species was reported once of the common eider in Newfoundland and Labrador, but erroneously identified as Hymenglejns (Microsomacanthnis) formosoides Spasskaja et Spassky, 1961 by Bishop and Threlfall (1974).

Estimation of the standard metabolic rate (SMR), maximal oxygen consumption (MOC) and thermoregulation ability in males of red-backed vole (Clethrionomys rutilus Pallas, 1779) have shown that individuals infected with nematodes Heligmosomum mixtum, regardless of intensity of worm infection, had an increased level of oxygen consumption in the cold exposition, while the individuals infected with the cestodes Arostrilepis horrida, had a lover oxygen consumption than non-invaded individuals. Worm burden of A. horrida correlated negatively with MOC value in the hosts. Thermo-conductance of individuals infected with A. horrida was significantly lower than in ones infected with H. mixtum. Opposite effects of these two helminthes seems to be determined by the specificity of pathogenesis and different body mass of parasites. Total body mass of nematodes are usually less than 0.2% of the host body mass whereas the total body mass of cestodes may exceed 5% of the host body mass.

The ciliary transition zone is described in the orthonectid Intoshia variabili. The ciliary transition zone in this species corresponds to the long type of transition zones. Close proximity of orthonectids to Spiralia is discussed.

Summary is absent.

Summary is absent.