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The flagellate Leptomonas rigidus (Podlipaev e. a., 1991) forms transmission stages in the posterior part of midgut of the bug Salda littoralis (Hemiptera: Saldidae). Solitary promastigotes attach to the surface of the gut epithelium with their widened flagella. In the course of divisions of the flagellates the sub-pellicular microtubules come closer to each other, the cytoplasm condenses and a zone of densely packed ribosomes is formed. Nuclear chromatin transforms into a labyrinth-like structure and the DNA-containing part of the kinetoplast also condenses. The flagellar pocket considerably shortens and its cavity becomes filled with a homogeneous matrix of medium electron density. The flagellum is being reduced, amastigotes are released into the gut lumen. The relation between various types of the formation of transmission stages in the trypanosomatids is discussed.

In the paper are presented the data on revealement of cryptosporidian oocysts (Apicomplexa, Sporozoa) in fecaes of cattle, swine and sheep of different ages and results of the experimental infection of laboratory animals (rats, mice, rabbits, coypus) with the oocysts detected as well. The latters were attributed to Cryptosporidium parvum species. The analysis of the size characteristic in the isolates of naturally and artificially infected hosts has shown that the oocysts dimensions might vary both in different host species and in different individuals of one host species.

There is a group of gymnophallids with the parthenogenetic metacercariae ("germinal sacs") in their life cycle. These metacercariae have been found by many investigators in different species of marine prosobranch molluscs, while the generation of sporocysts remained unknown. In the present study the participation of the first intermediate host in the life cycles of the above mentioned gymnophallids was demonstrated experimentally on the example of Parvatrema sp. For this parasite the part of the first intermediate host is played by the common in the Barents Sea subtidal bivalve Turtonia minuta,where the sporocyst generations develop. The daughter sporocysts produce furcocercariae that have a typical for gymnophallid cercariae shape. They are shed from the molluscan host and penetrate the subtidal prosobranch Margarites helicinus - second intermediate host. Cercaria migrates to the extrapallial cavity of mollusc, drops out their tail and changes into the parthenogenetic metacercaria. This primary metacercaria produces the second generation of metacercariae that leave the mother organism and begin to parasitize independently in the extrapallial cavity of the same specimen of host. They are also parthenogenetic and produce the metacercariae that are invasive for the definitive host - the common eider. If the mollusc containing these metacercariae is eaten by eider the adults will be developed in their intestine.

The morphology of Hymenolepis skrjabiniana Achumian, 1947 from Meriones libicus Lichtenstein, 1823 out of Copetdag (Turcmenistan) is defined and completed. Its characters confess its belonging to the tribe Sudaricovini Spassky, 1991 (an apical glandular pit on the scolex and a labyrinthine uterus within limits of the middle field of proglottid) and its similarity with Paraoligorchis taterae Wason and Johnson, 1977 from Tatera indica. The species is transfered to the genus Paraoligorchis and receives the name P. skrjabiniana (Achumian, 1947) comb. nov. Paraoligorchis spp. are differed by the number of the testes (4-5 in the type species and 3-5 in P. skrjabiniana). The genus Paraoligorchis is considered as an oligonchous genus of the tribe Sudaricovini. The morphological and differential diagnoses of these taxa are given. Sudaricovini are thought to be the hymenolepidid group evolved by the adaptation to parasitize the Gebrillinae. In contrast to Hymenolepidini its representatives preserved some plesiomorphal features proper to Pseudhymenolepidinae which parasitize Insectivoria: an apolysis of gravid proglottids and disposition of excretory canals near the lateral bundles of the internal longitudinal muscles, so the uterus doesn't come out of the middle field of the proglottid.

Three fish trematode species are found from the new hosts: Pseudobacciger harengulae in Sardina pilchardus and ; Diphterostomum brusinae in Parapristipoma octolineata, Pagellus acarne and Umbrina canadensis; 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.

Amphimermis polaris sp. n. is described from IV instar larvae of tundra leatherjackets Tipula (Pterelachisus) carinifrons carinifrons Holm, and T. (Savtshenkia) glaucocinerea Lundstr. According to the last revision of Amphimermis taxonomy by Baker and Poinar (1994), this new species belongs to the group "elegans" of the genus and can be distinguished from other species of the group by the male body length, spicula length, distribution of precloacal papillae and amphid size. The validity of A. artyukhovskii Baker et Poinar, 1994 is discussed.

An influence of joint affect of the trematode infection (rediae and cercariae of Echinostomatidae), environment temperature (8, 18-19, 28°), and different concentrations of nitrate lead (15, 50, 85 mg/l) on the lung and skin transpirations in the pond snails was studied.

In check-list of feather mites recorded from 90 species of the passerines living in the North-West of Russia is given. It includes 118 mite species belonging to 21 genera, 9 families, 2 superfamilies. The data for each mite species contain a list of passerine hosts recorded in the North-West of Russia, regions of recording, type host, main host-parasite associations and geographical distribution in general lines. A taxonomic composition of the feather mite fauna discovered and some its peculiarities are discussed. The brief review of recent papers on feather mites associated with the passerines in Europe and the European part of Russia is given.

Copepods are similarly distributed on right and left sides of the crucian. Copepods are usually located near pectoral and abdominal fins. Their distribution is slightly different on males and females of the host.

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