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The subfamily Trochopodinae consisting of 17 genera including 48 species is considered. A diagnosis of the subfamily is given as well as diagnoses of genera, indicating species, their synonyms, host and localisation.

Microsomacanthus paraparvula sp. n. differs from all other species of the genus by extremely small length of proglottids and genital organs. The size and general shape of the hooks closely resemble those of M. parvula (Kowalewski, 1904). However, the new species performs twice as many proglottids for the same specimen size. The dimensions and topography of the internal organs are also different, the cirrus sac size being one third of that in M. parvula. Finally, the new species represents a distinctly different life cycle using the caddisfly as the intermediate host.

The life cycle of the trematode Mosesia longicirrus was examined in experimental conditions. It is established, that the parasite develops in two intermediate hosts, the first hosts are snails of the genus Juga, the second ones are different species of Ephemeroptera and Plecoptera, the final hosts are birds.

The analysis of specificity of blastocystes was based on the data on hostal association and on experimental data. In experiments we failed to infect the geese (Anser anser) with Blastocystis galli taken from the fowl (Gallus gallus) and also failed to infect the fowl with B. suis taken from the pigs (Sus scrofa domestica). Experimental data and field observations of blastocystes distribution among different groups of hosts point out that the same species of bastocystes can not parasitise in hosts belonging to different classes and orders. The examination of 89 fish specimens belonging to 14 species of Osteichthyes taken from the Neman delta did not discover any blastocystes.

Two new species of endoparasitic copepods Tesonesma reniformes gen. et sp. n. and Cookoides cordatus gen. et sp. n. are described from the chitons of genus Stenosemus: S. albus (L. 1767) (north-western Pacific) and S. exarata (G. O. Sars, 1878) (near South Georgia Islands). Both new species are placed in the family Chitonophilidae. Diagnosis of the genus Tesonesma — Females lacking appendages and segmentation are inside host's body. Famale's body consists of reproductive reniform and digestive tubiform parts. Egg masses lay free in a cavity of host's body. Both sides of the male's body is convex with two thick processes (mandibles). Antenna II have two joints, second one looks like claw. Diagnosis of the genus Cookoides — Females lacking appendages and segmentation are inside host's body. Female's body consists of reproductive heart-shaped and digestive ramifying tubular processes. Both egg sacs attached to surface of genital complex. Male's body is very curved with three tubercles, middle one has small process.

The cellular parenchyma and extracellular matrix of Passerilepis crenata were studied by means of light and transmission electron microscopy. The parenchyma consists of two types of cells. One of them, named parenchymal cells, has nucleated compartment and numerous large and flattened extensions containing lipid droplets and small amount of glycogen. Second type is muscle cells similar to those described for other cestodes studied. It is possible that parenchymal cells represent another type of muscle cells for which relations with myofibriles were not ascetained. The main differencies between these cell types are the structure of granular endoplasmic reteculum, form of glycogen and ability of parenchymal cells to form cell junctions. Extracellular matrix is not abundant. Numerous cavities not found in cestode species studied thus far were observed in cortical parenchyma of P. crenata.

The impact of trematode invasion and extremal environmental factors (drying, acidity of water to pH6, rise of temperature to 28° C, hunting down by copper vitriol and detergents «Lotos» and «Robot» on the heart rate and the heart cycle of unionid mussels have been investigated. In the case of moderate invasion there were established the increasing of heartbeat (to 1.2—1.3 times) and decreasing of duration of heart cycle (on 23—31%). In the case of heavy invasion the heartbeat was progressively decreased (from 8—9 to 3—6 blows per minute to stopping of heart muscle) and the heart cycle was disturbed (heart pause and blow volume of the heart were increased). The consequence of that was the overstrain of the heart muscle. In extremal environmental conditions the heavy trematode invasion is the aggravate factor, which causes in unionid mussels the progressive slowing of heart rate going up to stopping of the heart muscle. In the same conditions the protective and adaptive possibilities of unionid mussels being free of trematode invasion are good enough to maintain the lifability of these animals.

Preliminary data about the distribution of putative catecholamines in a parasitic turbellarian, Graffilla buccinicola (Neorhabdocoela Dalyellioida: Graffillidae), were obtained using glyoxylic-acid-induced fluorescence (GAIF) method. All the main elements of the nervous system, i. е., the brain, cords, single ring commissure, and plexus, were GAIF-positive. Unlike free-living rhabdocoel turbellarians, but similarly to the parasitic platodes (the Neodermata), no GAIF-positive innervation of the small pharynx has been found in G. buccinicola and no GAIF-positive bipolar neurons have been observed in the innervation of the anterior pole of the body. These traits might be related to the parasitic mode of life. On the contrary, the set of GAIF-positive neurons associated with the lateral cords (L-group) is similar to that of the other studied representatives of the Typhloplanoida and Dalyellioida — thus, it was not much affected by a notable increase in the size of the body in comparison to free-living phabdocoels.

Four species of the genus Protomyobia (Acariformes, Myobiidae) are recorded in the fauna of the Russia and nieghbouring countries. Among them Protomyobia caecutiens sp. n. and P. jamesoni sp. n. collected on Sorex caecutiens Laxmann on Kamchatka are described as new species. The taxonomy system of the genus Protomyobia is briefly discussed. The species group "onoi" is included into the species group "claparedei".

The direct correlative dependence between indices of absolute and relative number of two fly species calculated by Peterson's method is shown. The way of calculation of the absolute number of M. domestica and S. calcitrans and the receipt of the selection from subpopulations, which take in account peculiarities of adult fly distribution in different technological regimes of cattle keeping, peculiarities of daily activity and influence of temperature-photo factors on imago, are proposed. The attempt to study the structure and density of subpopulation of two fly species during one generation in North-West Russia is made. The date on mortality on different stage of life cycle are given.

The kinetics of immunocompetent cells in sheep artificially infested with 80, 160, 1000 specimens of Oestrus ovis larvae and immunized with antigen from larvae protein was traced by stableons (E-REC) and antigenfixing (Ag-REC) rosette formation reaction. It was found that E-REC level changes only a little in both infested and reinfested animals. Ag-REC kinetics mates with the rated larvae biomass changes in all age groups. Ag-REC level of infested animals is much higher and then regularly declines in the following cycles of invasion. T-lymphocites level and death level of immunized lambs is much higher than in intact animals at the beginning of parasitism.

In four enzymes among eight ones examined the differences were revealed in the intensity of staining of certain zones (G-6-P, ES) as well as in electrophoretic mobility of some locuses (PGD, RGM) between the capsule forms of trichinellae and Trichinella pseudospiralis. As a result, the validity of isolation of T. pseudospiralis Garkavi, 1972 is confirmed.

Two new species of didimosoat trematodes (Oesophagocystis lydiae sp. n. and Allopseudocolocyntotrema alioshkini sp. n.) are described from mackerel tuna from eastern part of north subtropical zone of Atlantic Ocean.