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A new species of virgulate cercaria is described. The morphology and chaetotaxy of cercariae are studied. The new type of virgule organ is described. Every description is illustrated by drawings.

Two new species of virgulous cercariae are described. Morphological descriptions and differential diagnoses are given. Each description is supplemented with a detailed picture.

Deepwater fishes from the Amundsen Sea, d'Urville Sea, Ross Sea, Cooperation Sea, Weddell Sea, and open waters of the South-West part of the Pacific sector of the Antarctic were examined. Fourteen species of trematodes were found. Muraenolepitrema magnatestis Gaevskaya et Rodjuk, 1988 and Helicometrina sp. were found in the Antarctic for the first time. Muraenolepitrema magnatestis was redescribed and basing on this, diagnosis of the genus Muraenolepitrema was amended. Muraenolepitrema magnatestis possesses the uroproct and glandular cells that are loosely arranged around the external seminal vesicle (without a membranous sac).

New data on Ospey parasites in Karelian Republic are given. One specimen was investigated. Two parasite species--Nematostrigea serpens and Diplostomum pseudospathaceum were found. Trematoda D. pseudospathaceum was recorded in Osprey parasite fauna for the first time.

Data on trematodes of the order Plagiorchiida from 11 species of amphibians from the Middle Volga region are given. Literary data of the last 30 years, combined with the results of our own research are presented together for the first time. Finds of 17 trematode species are reliable. From them, metacercaria of Astiotrema monticelli is recorded from amphibians of the fauna of Russia for the first time; Dolichosaccus rastellus and Paralepoderma cloacicola are recorded for the first time from amphibians of the Middle Volga region. New hosts are mentioned for 8 species of parasites. Trematodes of edible frog Rana esculenta Linnaeus, 1758, a new species to the region, are described for the first time. The following characteristics are given for each trematode species: its taxonomic position, set of hosts, localization, places of detection, biology, geographical distribution, and the degree of host specificity. Morphological descriptions and original figures are given for 12 trematode species.

Data on trematodes of the orders Fasciolida, Hemiurida, Paramphistomida and Strigeida from 11 amphibian species of the Middle Volga region are given. Literature data for the last 30 years are reviewed for the first time; these data are supplemented by our own material. Reliable recordings are confirmed for 23 trematode species. Two of these species are new for amphibian trematode fauna of Russia. New hosts were revealed for 12 trematode species. Trematodes of the new for the region amphibian species, the edible frog Rana esculenta Linnaeus, 1758, are recorded for the first time. Two trematodes from freshwater fishes are shown to be temporary or occasional parasites of amphibians. The following characteristics are given for each parasite: it's systematic position, the spectrum of hosts, localization, collecting site, biology, geographical range, and the degree of host specificity. The morphological description and original figures are given for 9 species of parasites.

Trematode fauna of waterfowl birds of Karelia comprises 23 species; 8 of them are described from the region for the first time. Descriptions and figures of Urogonimus macrostomus, Neoeucotyle zakharovi, Hypoderaeum conoideum, Echinostoma robustum, Orchipedum tracheicola, Prostogonimus cuneatus P. ovatus, and P. rarus are given.

Two new microcotylous cercariae are described. Their morphology is described and the differential diagnoses is given. All description are allustrated. For the first time, taxonomy of some microcotylous cercariae is discussed on the basis of their basic morphology.

The morphology and chetotaxia of Cercaria metagonimus sp. Manafov, 1991 of the Azerbaijan have been studied. The structure of glandular apparatus is of especial importance for the description of this group of cercariae. On the basis of the original and literary data the taxonomical significance some morphological characters of Heterophyidae cercariae are discussed.

Pictures and descriptions of morphology and differential diagnosis of two new species of cyathocotylid cercariae--Cercaria agstaphensis 37 and Cercaria agstaphensis 38 are given. Special attention is paid to the structure of the glandular apparatus, excretory system, tegument armature, and other individual peculiarities of cercariae.

The results of the study of typical specimens of the trematode G. amoena from blood vessels of the crocodile Crocodylus johnstoni in Australia are provided. The data obtained on the morphology of this parasite did not confirm the statement of Platt et al. (1991) that this species belongs to the family Schistosomatidae. Morphological data on G. amoena enable attributing it to the genus Vasotrema of the family Spirorchidae as a new species. In this connection, the monotypical genus Griphobilharzia (justified by Platt et al., 1991) becomes a synonym of the genus Vasotrema, while the subfamily Griphobilharziinae becomes a synonym of the subfamily Hapalotrematinae.

The structure (illustrated by pictures) and differential diagnoses of 3 new closely related forms of stylet cercaria (Cercaria agstaphensis 8, Cercaria agstaphensis 21 and Cercaria agstaphensis 16) are given. Special attention was paid to the armament of the glandular apparatus, to the excretory and digestive systems, and to other taxonomically important structural peculiarities.

Two closely related forms of virgulate cercaria, Cercaria agstaphensis 9 and C. agstaphensis 10 of the superfamily Lecithodendroidea from water bodies of Azerbaijan are described. Morphological data, including chaetotaxic traits, fugures, and differential diagnoses are provided. Descriptions of armature, glandular apparatus, excretory and digestive systems, inclusions of parenchyma, and other structures of the cercaria, characteristic for the superfamily, are presented.

The pygmaeus-species group is composed of close related species from the genus Microphallus in which metacercariae develop inside daughter sporocysts without encystment. Infection of periwinkles Littorina (Neritremna) spp. with intramolluscan stages of a new species of this group (Microphallus kurilensis sp. nov.) was recorded on the coasts of Sakhalin and Kuril islands, north of the Sea of Okhotsk and Chukchi Peninsula (the Bering Sea). Application of molecular methods allowed us to establish that M. kurilensis metacercariae are conspecific with one of the morphotypes of microphallid adults obtained from the intestine of the Pacific common eider (Somateria mollissima v-nigrum), which was shot in the north of the Sea of Okhotsk (Galaktionov, Olson, and Blasco-Costa, in press). The adults of the same morphotype were recorded in the Pacific common eider from the northwestern part of the Bering Sea (Chukchi Peninsula). In the course of experimental infection of the slaty-backed gull Larus schistisagus chicks with metacercariae of M. kurilensis, few microphallid adults were obtained. These adults were identical in their morphology with specimens of the microphallid morphotype from the Pacific common eider, which had been identified as M. kurilensis based on molecular data. Morphological description of metacercaria and adult of M. kurilensis and list of their differences from the same developmental stages of other species from pygmaeus-group are provided. It is concluded that M. kurilensis is transmitted in the host system including periwinkle Littorina (Neritrema) and seaducks (predominately, Pacific common eider). Most probably, distribution of M. kurilensis is not limited by the north Asiatic coast but expanded to the North American coast of the Pacific Ocean.

The musculature of body wall, attachment organs (oral and ventral suckers), and internal organs (alimentary tract, excretory bladder, and ducts of reproductive system) of the Microphallus pygmaeus metacercaria are described. An unusual arrangement of longitude and diagonal muscles was found in the hind part of the metacercaria body. Longitude fibers of dorsal and lateral body surfaces are bow-shaped and bend round the excretory pore along its ventral margin. An additional group of diagonal fibers is situated in the hind part of ventral body surface.

Microphallus pseudopygmaeus belongs to the "pygmaeus" microphallids, a group of closely related species with homotypic two-host life cycle. This cycle involves one intermediate host (littoral or sublittoral gastropods, mostly of the genus Littorina), and bird-invading metacercariae develop within daughter sporocysts. In spite of the fact that the name Microphallus pseudopygmaeus is widespread in special literature, the original description of this species (Galaktionov, 1980) was performed in contravention of the International Code of Zoological Nomenclature. This article is aimed to correct the above defect. The maritae of Microphallus pseudopygmaeus were obtained from the common eider ducklings which were infected experimentally with metacercariae of Microphallus sp. I Galaktionov, 1980. These metacercariae were extracted from the naturally infected mollusks Littorina saxatilis collected at the Barents Sea coast. The valid description of the species M. pseudopygmaeus, its comparison with other representatives of the "pygmaeus" microphallids and synonymy are provided. Detailed analysis of digeneans from marine and coastal birds preserved in the collections of the Zoological Institute RAS (St. Petersburg, Russia) and the Natural History Museum (London, UK) showed that in some cases M. pseudopygmaeus was misidentified as M. pygmaeus. It has been shown that M. pseudopygmaeus has an amphiboreal-arctic distribution and the spectrum of its first intermediate hosts is unequally wide for digeneans. It includes 15 species of north-Atlantic and north-Pacific mollusks belonging to different families and even orders of Prosobranchia. At the same time, the range of final hosts of M. pseudopygmaeus is limited by benthophagous marine ducks, first of all the common eider.

Data on all known currently trematodes, revealed in insectivores and muride rodents from the Middle Volga region are generalised and analysed in article. The description and original drawings of 10 parasites species are given. 2 helminth species (Brachylecithum rodentini, Corrigia vitta) were specified for micromammals from Volga basin for the first time. The new hosts were marked for 2 parasites (B. rodentini, Quinqueserialis wolgaensis).

The new species of virgulate cercariae, Cercaria agstaphensis 6 and C. agstaphensis 14, were described from the freshwater mollusc Melanopsis praemorsa in the Kura River basin, Azerbaidjan. Secretory apparatus, excretory system, arming of tegument, and other structures of virgulate cercariae are characterized.

Metacercariae of the genus Diplostomum Nordmann, 1842 from fishes of Lake Ladoga were investigated. Sixteen trematode species of this genus were found. The species D. parviventosum Dubois, 1932, known previously only in Lithuania, was for the first time recorded in Lake Ladoga. The description and figure of its metacercaria are provided. Data on the infestation of different fish species by diplostomids are also given. Changes in the infestation of fishes by the Diplostomum metacercariae for a long-term period are analysed.

Morphology of the Helicometra fasciata Rud., 1819 parthenogenetic generation from the Black Sea gastropods Gibbula adriatica (Phil.) was studied for the first time. Data on seasonal dynamics of the hemipopulation of daughter sporocysts are given. Daughter sporocysts of H. fasciata infest 10 +/- 0.2 % of G. adriatica (mainly specimens of larger size and elder age classes). As a rule, local microhemipopulations of daughter sporocysts castrate mollusc hosts. Reproduction of H. fasciata daughter sporocysts is asynchronous: daughter sporocysts born specimens of next sporocyst generation during autumn and winter, and then they begin producing cercaria. In winter development of the cercaria embryo is blocked. Second change of the character of the each sporocyst' posterity is impossible because of the annual life cycle of G. adriatica. Endogenous agglomeration of the H. fasciata daughter sporocysts is extremely little: individuals of next sporocyst generation develop from no more than 2 % of embryonic balls. Energy resources of the mollusc host are used by the H. fasciata daughter sporocysts mainly for producing cercaria; this fact can be interpreted as an adaptation of H. fasciata to using medium-sized, short-living mollusc hosts.

According to our research there are two species of trematoda of genus Aporocotyle: A. simplex and A. theragrae in the far eastern seas.

As a result of experimental and faunistic investigations it is established that the development of the trematode species Azygia hwangtsiytii Tsin, 1933 in Primorsky Territory is realized in the first intermediate host, snail Cipangopaludina ussuriensis, and in second hosts, fishes Perccottus glehni and Channa argus warpachowskii, which can serve as transit, as well as final hosts. For Azygia robusta Odhner, 1911 terms of the development in the first intermediate host, snail Anisus centrifugus are established.

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.

The genus Corpiatestes Crowcroft, 1948 is revised. It is shown that Corpiatestes filiferus (Leuckart, in Sars, 1885), Syncoelium cypseluri Yamaguti, 1970 and S. regulaci Villarreal and Dailey, 1993 are junior synonyms of the type species C. thyrsitae Crowcroft, 1948. The genus Copiatestes is monotypical.

A redescription and comparative diagnosis of Gyrodactylus atherinae Bychowsky, 1933 is made based on the material collected of B. E. Bychowsky from Atherina boyeri pontica caught near Karadag (Black Sea) in summer of 1947.

A morphological description of Sanguinicola armata cercaria is given. This larva belongs to the group of brevifurcate and apharingeal cercariae. Mouth opening is on ventral surface of the anterior organ. The body and branches of the furca bear a membrane. The body/tail ratio is much more than in other cercariae of the family Sanguinicolidae. The gland apparatus of the larva is represented by several types of secretory cells. The penetration glands form a group of 5 pairs of cells on the ventral side. Their ducts form a single bunch directed anterior, go through the anterior organ and open terminally on the proboscis, which is able to turn outside. Other gland cells apparently represent specialized cytones of the tegument. Excretory formula: 2[(1 + 1) + (1 + 1)] = 8. The external surface of the larva bears a small number of sensilla. Some similarities of the families Sanguinicolidae and Schistosomatidae in the cheatotaxy of cercaria have been noticed.

The hypothesis of the origin and evolution of the hamuli in monogeneans is proposed. It is suggested that the hamuli originated as the adult attachment organs of protomonogeneans inhabited the gills of the first vertebrates. Primarily they were represented by two lateral pairs of large hooks disposed anterior to the larval haptor. The fundamental direction in the evolution of monogeneans was the concentration of all attachment structures on the growing haptor. It the course of this evolutionary process, the hamuli onchoblasts migrated to the haptor, in which they had reached the position in the hind part of the haptor. The neotenic evolution of the Dactylogyridea and Gyrodactyloidea resulted in the forming new hamuli pairs. The hooks of opposite sides of the haptor are joined in a single complex within each side by the transverse plates (bars). So the presence of 4 hamuli is plesiomorphy for all the monogeneans and the presence of the transverse bars and new hamuli pairs are apomorphy for the Dactylogyridea and Gyrodactyloidea, whose evolution was linked with that of the Teleostei. The origin of the new hamuli pairs and transverse bars in the Dactylogyridea and Gyrodactyloidea appears to be a convergence.

Metacercariae of Cyathocotyle bushiensis Khan, 1962 (Digenea) were found in populations of seven species of gastropod snails collected from lakes and rivers in the south of West Siberia (Russia). This is the first record of C. bushiensis in Russia. Five species of snails, Lymnaea stagnalis, L. palustris, L. tumida, Planorbis planorbis (Pulmonata) and Viviparus viviparus (Prosobranchia) were recorded as new hosts for the metacercariae of C. bushiensis. The infection rate of Bithynia tentaculata and Opisthorchophorus (= Codiella) troscheli (Prosobranchia), the main hosts of C. bushiensis metacercariae, was analyzed in regard to the sex and shell length of molluscs. It was revealed that infection rate and mean intensity of metacercariae increases with the shell lengths. Drawings and descriptions of excysted metacercariae from naturally infected snails and adult worms from experimentally infected domestic ducklings are given.

Two species of dactylogyrids, Dactylogyrus barbatuli Ermolenko, 1992 and D. tonii Ermolenko, 1992, occurring in the Siberian stone-loah in Primorye are redescribed. These species are distinguished from others monogenean of the genus Dactylogyrus, that are found in fishes of the genus Nemachilus, by the size of anchor structures and complexes of copulatory organs.

Description of a life cycle and development stages of a trematode Holostephanus nipponicus Yamaguti, 1939 is given. Experimental studies have shown that in Primorye, the first intermediate host is commonly a snail Parafossarulus spiridonovi, and the second hosts are freshwater fishes Rhodeus sericeus sericeus and Pseudorasbora parva. Adult worms H. nipponicus were reared in a chicken.

Drawings, description and size characteristics are given for Tetraonchus awakurai, which is registered for the first time from Brachymystax tumensis in the Ussury river (Primorye). The T. awakurai from the Ussury river differs from the typical forms living in water reservoirs of Japan by the measurements of external and internal lengths of anchors and copulatory complex.

The trematiode Lecthodolfusia anatina Kchotenovsky, 1967 is redescribed. Experimental study has shown, that in the Primorye land, the first intermedial host of this trematode is a mollusk Boreoelona contortrix ussuriensis, and the second ones are larvae of the may fly Ecdyonurus aurarius and caddis flies Semblis phaenoides and Groerodes sp. Adult worm were reared in chickens.

Polyclithrum ponticum sp. n. is described and P. mugilini Rogers, 1967 is redescribed. Both monogenean species are parasites of Mugil cephalus in the Black Sea. The new species differs from P. mugilini, P. alberti and P. boegeri by the lesser size of anchors, while it is distinguished from P. corallense by the larger size of these structures. P. ponticum sp. n. differs from all formerly described species by the greater length of dorsal connective bar. In both species from the Black Sea, "ear-like" structures situated near the external roots of anchors are described for the first time. It is suggested, that these structures take part in longitudinal, two-lobe folding of the haptor. The process of opening the haptor is probably performed by the additional bars of the haptor (bars 2 and 3 after: Rogers, 1967), joined to each other and with the anchors. The fifth pair of additional bars (Ernst e. a., 2000) derives from the "beard" of ventral connective bar and is united with its basal part. The sixth pair of additional bars (Ernst e. a., 2000) is considered as a typical "ribs" of the haptor, and therefore the "ribs" are represented by three pairs. Differences between marginal hooks of P. ponticum sp. n. and P. mugilini are insignificant, that probably depends on the presence of "ribs" of the haptor. Based on the subdivision of marginal hooks into two groups, the presence of additional supporting structure in the haptor, and the presence of the seminal receptacle, it is suggested that the subfamily Polyclithrinae Rogers, 1967 should include the genera Polyclithrum Rogers, 1967, Swingleus Rogers, 1969, Macrogyrodactylus Mamlberg, 1959, and probably Fundulotrema Hargis, 1955. Based on such characters as the lack of the anchors, the presence of suckers in the haptor, and ovipositing of eggs, it seems to be expedient to use the following taxa in systematics of gyrodactylids: Isancistrinae Fuhrmann, 1928 (genera Isancistrum, Anacanthocotyle); Gyrdicotylinae Vercammen-Grandjean, 1960 (Gyrdicotyle) and Ooegyrodactylinae Harris, 1983 (genera Phanerothecium, Ooegyrodactylus, Nothogyrodactylus, Hyperopletes).

The additions concerning the morphological characters and measurements of Anomalotrema koiae, Helicometra fasciata, Accacladocoelium macrocotyle, A. petasiporum, and Paraccacladium jamiesoni have been made. Podocotyle atomon (Rud., 1802) in Gaevskaya, Umnova, 1977 described from Sebastes marinus from the northwest Atlantic is considered as Anomalotrema koiae. Helicometra fasciata is found in Mugilidae for the first time. Accacladocoelium macrocotyle and A. petasiporum are found in the new region--the Azores.

It is considered that in Anacanthorinae, Markewitschiana and Pseudacolpenteron pavlovskii (Dactylogyridae s. s.) the anchors are absent originally. In the other dactylogyrids (s. l.) 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. l.) 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. l.) 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. l.) 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 unit all dactylogyrids (s. l.) having 0-4 anchors and 18-14 hooks into Dactylogyridae sensu Boeger et Kritsky, 1993.

Morphology of schistosomatid cercariae of the genus Trichobilharzia (ocellata group) is described based on original and reference data. The material (Trichobilharzia cercariae) was collected in 1999-2000 from naturally 'infected snails Lymnaea stagnalis from Moscow and Saint-Petersburg megalopolises. The more accurate flame cell formula for these cercariae, as well as some aspects of chaetotaxy and eye morphology are given. The differences between cercariae from these regions were found. Based on a comparison of nef data with the reference data, it was found that the cercariae examined differ from those from the Central Europe.

The haptors Dactylogyrus spp., Anacanthorus sp., Trianchoratus sp. and Schilbetrematoides pseudodactylogyrus are investigated. On the base of the morphology, transfer of the domus, etc. a homology of the hooks in dactylogyrids (s. s.) and the pin-like structures (4 "A") in the haptor of Anacanthorinae and Dactylogyridae sensu Bychowsky et Nagibina, 1978 is demonstrated. The vestiges of the anchors in the haptor of dactylogyrids (s. l.), according to morphological data, correspond to the point of anchor formed during the ontogenesis. In S. pseudodactylogyrus the pins are redescribed as typical vestiges of the anchors.

A new cryptobiid flagellates, Cryptobia udonellae sp. n., is described from the excretory channels of Udonella murmanica. The body of flagellates is spindle-shaped. The flagellar pocket is subapical. Two flagella emerge from the pocket. One flagellum turns anterior and is forward-directed; the other flagellum is directed posterior and close to the ventral cell surface. The ventral groove is well developed. The cytostome opens just anterior to the flagellar pocket. The cytostome leads to the short cytopharynx. In the excretory channel of worms the flagellates C. udonellae sp. n. are attached to microvilli of epithelium or lay free in the lumen. Both flagellates have been studied with TEM. The unusual parasite system which involves organisms of four different phylums of animals has been described for the first time.

Some new data on the expansion, host-animals, biology and morphology of different developmental stages of the trematode Exorchis oviformis in the southern Prymorye are given. It was revealed, that the first intermediate host of that species is Stenothyra (S.) recondita. Different species of freshwater fishes play a role of a second intermediate host. The definitive host of E. oviformis is a bullhead (Parasilurus asotus).

The host variability of adults of Phyllodistomum umblae and P. folium in fishes of the Baikal region has been studied. The absence of considerable geographical variability of P. umblae in Coregonus lavaretus (Lake Baikal, Lake Storsjön in Sweden) has been shown. The complexes of most stable (the size of acetabulum and eggs, location of acetabulum, ovary and vitelline bodies) and variable (the distance from oral sucker to intestinal bifurcation, distance from intestinal back edge to body end, width of seminal vesicle) features of trematodes of the genus Phyllodistomum have been determined.

The historical account and recent taxonomic consideration of the monogenean subfamily Encotyllabinae are given. Main criteria used for diagnostics of the subfamily and its genera are discussed.

The experimental study of life cycles of the trematodes Nenimandijea kashmirensis Kaw, 1950 and Pleurogenoides medians Olsson, 1876 was carried out. It was found out, that their life cycles include: the first intermediate host--the mollusc Boreoelona contortrix ussuriensis, the second intermediate host--dragonfly larvae of the genus Cordulia, and the final host--the frogs Rana nigrimaculata and R. semiplicata. Based on obtained data it is suggested, that Pleurogenoides japonicus (Yamaguti) should not be considered as a separate species.

Three new species of the monogeneans of the genus Dionchus are described: Dionchus paruchini sp. n. from Rachicentron canadus and D. trachuri sp. n. from Trachurus trachurus from Indian Ocean, D. major sp. n. from R. canadus from the North Vietnamese Gulf. All species are located on gills.

A monogenean Entobdella hippoglossi (Capsalidae: Entobdellinae), a common parasite of the flat fishes (Pleuronectidae), is recorded for the first time from an ocean perch Sebastes glaucus (Scorpaenidae) in the north-east part of Pacific ocean. New data on hosts and location of Sessilorbis limopharynx (Capsalidae: Trichopodinae) are also given.

The muscle fascicles of the haptor in Tetraonchus monenteron have been described. The muscle connection of the fan-shaped dorsal bars with dorsal anchors is shown. When these muscle fascicles are contracted the dorsal anchors works as pincers. The division of tetraonchids into two genera based on types of copulatory organs, morphology of bars and haptor ans associations with different groups of fishes is restored. Different authors based on ciliated cells and chaetotaxy of the oncomiracidium and comparative spermiogenetic of T. monenteron include the tetraonchids with 16 marginal hooks into the order Dactylogyroidea. In the same time, based on the analysis of the onthogenesis of the dactylogyrid's haptor they postulate, that the haptor of these worms originally had 2 pairs of anchors and only 14 marginal hooks. The present paper contains data indicating that different representatives of the Dactylogyridea have 14-18 marginal hooks. Author put forward a suggestion, that some group of dactylogyrids originally did not have the anchors.

Three fish trematode species are found from the new hosts: Pseudobacciger harengulae in Sardina pilchardus and Sardinella aurita; Diphterostomum brusinae in Parapristipoma octolineata, Pagellus acarne and Umbrina canariensis; Lecithocladium angustiovum in Pomadasys incisus caught in the East Atlantic. All species were found in the new localities. Some characters of D. brusinae morphology are detailed. Measurements of trematode species from different hosts are given. Key to species of genus Pseudobacciger in proposed.

Taxonomy values of morphological features used for differential diagnostics of different taxa is considered for cercariae of the genus Diplostomum. It was shown that, as a rule, taxa criteria of superspecies ranks had a qualitative nature and were easily detected in live cercaria studies. In contrast, cercariae species diagnostics (CSD) is based exclusively on less significant, from a taxonomy point of view, quantitative features presenting absolute and relative body dimensions and that of cercariae organs as well as peculiarities of their cuticular armament. All this compels a taxonomist to use for CSD a whole range of diagnostic features of groups mentioned and increase their taxonomy values owing to standardization of cercariae collection, fixation and subsequent processing techniques, as well as broader application of variation-statistic methods of analysis that is possible only in cercariae studies through a use of permanent slices. A complex of methodical devices, which observance will ensure reliable CSD of the genus mentioned, is proposed. It encompasses cercariae collection and fixation as well as mounting of permanent balsame slides with preceding cercariae treatment with acetic-acid carmine (morphometric analysis), acid fuxine Sekki (cuticular armament staining) and silver nitrate (sensory apparatus detection). The reagents mentioned may form a real base for a creation of cercariae museum collections being not inferior in scientific value to existing trematode maritae and metacercariae stocks.

Topographic anatomy of the nervous systems of the trematodes Azygia lucii and Phyllodistomum angulatum was studied by the histochemical method of cholinesterase detection. The cholinergic part of the nervous system of A. lucii is represented by the brain, the ventral, dorsal and lateral longitudinal cords, by rather long complementary anterior branch of the ventral cord and by very short anterior branch of the dorsal cord. All cords are connected with numerous commissures. In the anterior region of the body, between the brain and the ventral sucker there are distributed 9 ring commissures. Behind the ventral sucker there has been revealed up to 18 commissures, 10 of which are ring ones. The regularity of the distribution of commissures is disturbed only in the region of the ventral sucker. The nervous system of such type can be regarded as a regular frequent orthogon. In Ph. angulatum has been revealed another type of the nervous system--an uneven orthogon. It is represented by the brain, 3 pairs of longitudinal nerve cords, small complementary anterior branches of ventral and dorsal cords, 5 ring commissure between the oral--and ventral suckers and one ventral commissure behind the ventral sucker. The origin of regular frequent orthogon in A. lucii and the irregular orthogon in Ph. angulatum is explained by certain morphological peculiarities of their structure; the body shape, musculature development and the reprodactive system localization. The morphological diversity being a characteristic for the trematode nervous system allows to relate them with Neorhabdocoela suborder Typhloplanoida.

Basing on materials collected from the fishes of the south part of the Indian and Pacific oceans, 2 new species of trematodes are described: Liliaoralis cataluphi gen. n., sp. n., Steganodermatoides notocanthi sp. n. The diagnosis of the new genus and discrimination are given. The detailed anatomo-morphological descriptions, illustrations and differential diagnoses are given for each of new species.