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According to world literature data 17 species of ixodid ticks have been studied for natural infection with the Lyme disease agent. Analysis of the data on the level of the infection, transovarial and transphase transmission has shown that main biological vectors of Borrelia burgdorferi are the species of the subgenus Ixodes s. str. - I. ricinus, I. persulcatus (Eurasia), I. dammini, I. pacificus (North America). Potential vectors are I. scapularis, I. dentatus, Amblyomma americanum, Dermacentor variabilis. Single isolations were registered for I. neotomae, Haemaphysalis leporispalustris, D. occidentalis. Nonidentified spirocheta was isolated from A. americanum, D. variabilis, D. parumapertum, Rhipicephalus sanguineus. No agent was isolated from I. cookey, D. albipictus, R. reticulatus, H. concinna. On the basis of comparative and ontogenetic data the species from a group of main vectors: I. ricinus, I. persulcatus, I. pacificus had been attributed by me to the phyletic group persulcatus before Lyme disease was discovered and its causative agent isolated. The question whether I. scapularis belongs to the group persulcatus was also discussed at that time but left open due to somewhat aberrant structure of gnathosoma at preimaginal phases (Filippova, 1969, 1971, 1973). 6 palaearctic, 2 indomalayan and 3 nearctic species were referred to the group persulcatus at the time. I. dammini was described later, in 1979. Gnathosoma of its preimaginal phases has an intermediate structure between I. scapularis and other species of the group persulcatus. Sexually mature phase and numph of I. dentatus have much in common with palaearctic members of the group, I. pavlovskyi, I. kazakstani, I. kashmicus. Preimaginal phases of I. scapularis and nymph of I. dentatus were studied by me on the collection material. Thus, it is possible to speak of the belonging of main vectors of B. burgdorferi to a common phyletic group within the subgenus Ixodes s. str. and, therefore, of common origin of ecological medium for the agent. At the same time each species of the vector is an evolutionally developed difference of ecological medium for B. burgdorferi. Roots of the group persulcatus could originate as far as in Paleocene before the land connection between North America and Europe disappeared. Conditions for the existence of recent species, however, appeared considerably later and their flourishing is dated by Pliocene. The main epidemiological role belongs now to I. ricinus, I. persulcatus, I. dammini, I. pacificus. Results of the analysis of taxonomic aspects of the Lyme disease agent transmission and evolutionary characteristics of the vectors resulting from it give an example of coevolution of this agent and species of the group persulcatus with a wide spectrum of coadaptations of spirocheta and species-vectors. Taking into consideration a complex history and rather ambiguous «evolutionary time» of the persulcatus species as an ecological medium for the agent, we cannot ignore that the latter can happen to be a comlex of close species. Considering the peculiarities of the evolution of the family Ixodidae, connections of the spirocheta with species of other genera should be regarded as more late and secondary in respect to the group persulcatus and the leading role in the transmission will likely belong to the species of this group.

Three new species of the genus Mouchetia Gaud, 1961 are described: Mouchetia indochinensis sp. n. from Zosterops japonica (Zosteropidae), M. rumiantzevi sp. n. from Yuhina nigrimenta (Timaliidae), and M. oliferae sp. n. from Leiothrix argentaurus (Timaliidae). The key to all species of the genus Mouchetia known at present is given. The comparison of the original description of M. dolichosikya Gaud, 1961, M. viduata Gaud, 1962, and the data on these species given in «Generic revision of Pteronyssinae» - (Faccini, Atyeo, 1981) has shown that the authors of this revision had made an error in identification of these species and figured the species M. viduata instead of M. dolichosikya. The new species M. indochinensis is closely related to the two species formely described from Zosteropidae, M. dolichosikya and M. viduata. The male of this species differs from M. dolichosikya by the absence of transversal striation on the hysterosomal shield, and differs from M. viduata by trapesoid form of terminal cleft. The female of M. indochinensis differs from these closely related by short hysterosomal shield (190—206 micrometers in length), anterior part of which does not reach the level of anterior margin of trochanter III. The male of M. rumiantzevi differs from three Mouchetia species known from Zosteropidae by the rounded apex of opistosomal lobes and by the lateral setae l1, which are shorter than the distance between external scapular setae sce. The female of M. rumiantzevi differs from these three species by the position of the setae d3 posterior to the level of lateral oil glands gl, and by the close distance between setae d1, which is equal to the distance between setae d2. Both male and female of M. oliferae differ from all other species of the genus Mouchetia by fused propodosomal and scapular shields, by very short setae l1, and by the epimeres I drown close to one another. The male of this species has unique characters: the presence of the U-formed transventral sclerite connecting the epiandrium and anterior tips of epimeres IV, short opistosomal lobes, short leggs III and conical form of tarsus III. The female has some unique characters too: opistosomal lobes are long and drown close to one another, epiginium is low and bowshaped, hysterosomal shield occupies the whole medial part of hysterosoma.

Analysis of literary data and study of the collection material have made in possible to define more precisely the species composition of lice of the genus Eulinognathus, parasitic on jerboas. Adaptation of the lice under study to a definite host has manifested a high degree of specificity. Most parasites are monoxenous and only E. aculeatus was recorded on two species of the genus Jaculus. Differential diagnosis is given for E. biuncatus and E. dipodis which differ in shape of the head, sternal plate of the thorax and male's copulatory organ. Two new species are described on the material collected in Kirghizia. E. tokmaki sp. n., found on Allactaga major, differs from the close species E. allactagae by the separation of abdominal setae into median and lateral groups. Unlike E. gentilis, E. elateri sp. n., found on Allactaga elater, has 6 pairs of tubercles on ventral side of the head. It differs from mostly close species E. allactagae and E. tokmaki sp. n. in smaller size, shepe of sternal plate of the thorax and smaller number of abdominal setae. E. aculeatus and E. hesperius were found to be specific parasites of jerboa in North Africa and do not occur on the territory of the USSR.

Urgency of carrying investigations on this problem is substantiated. Some questions of epizootology, phenology and ecology of warble flies of marals are considered. Data on seasonal and daily dynamics of activity and abundance of warble fly females, developmental periods and passing of larvae to pupation are given.

A description and figures of Hirundinicola stricta sp. n. from the sand martin Riparia riparia of the Ukraine (Vinnitsa District) are given. The species is characterized by a small size of the strobile (length 7.3 to 10.0 mm, width 0.72 to 0.93 mm), limited number of proglottides (50 to 60), zigzag crown consisting of numerous (24 to 32) small (0.010 to 0.012 mm) hooks, small cylindrical cirrus up to 0.025 mm in length and 0.007 to 0.009 mm in diameter, armed with very small spines, relatively short (0.12 to 0.14 mm) bursa of the cirrus, the presence of 16 to 22 testes in the proglottis, dipterous ovary, saccular uterus, the absence of filaments in eggs. The differential diagnosis is given.

The tegument of mature cercariae of Microphallus sp. Podlipajev, 1979, M. claviformis, Levinseniella brachysoma and Maritrema subdolum consists of the outer syncytial layer filled with several types of secretory inclusions. Cytons and subtegumental cell ducts are absent. Covers of Microphallus cercariae have structure typical of larvae of trematodes. The tegument surface of L. brachysoma cercariae carries lamelli, spines are divided into two parts: short massive body sharpened at forend and long thin stalk connected with basal membrane. The tegument surface of M. subdolum larvae forms tongue-like protrusions, modified spines serve as their frame. The development of tegument of the above species during cercaria morphogenesis has been traced. It is shown that at first in embryos syncytial lamina of the tegument is formed. Within itvrudiments of spines have been detected as narrow transversal columns of mediate electron density. Henceforward syncytial layer has thickened, provisory spines have become conic, their matrix has become fibrous. Then the joining of protrusions of subtegumental glandular cells to outer syncytium has begun. These cells have been arranged into three types depending on the character of secret produced. The spines have acquired the species-specific structure. In members of the genus Microphallus they have become massive, and both in L. brachysoma and M. subdolum they have lengthened and subdivided into body and stalk. Spines of M. subdolum have flattened appreciably, their bodies have been found within tegumental tongue-like protrusions.

It was established that host individuals, characterized by a high stability of development, play the main part in the functioning of bream - D. interrupta system. Heterozygous breams turned out to be more stable to the effect of pleurocercoids than homozygous ones. Genetically determined characters of bream infection with pleurocercoids of D. interrupta have been revealed. Mechanism of population-genetic relationships in this parasitic system is discussed.

Narrow specifity of larvae (glochidia) of Margaritifera margaritifera to salmon in the rivers of the Kola Peninsula was proved experimentally. It was found that in the gills of minnow, the other mass fish in the nothern rivers of the USSR, larvae of M. margaritifera cannot develop and perish. Reasons causing the narrow specificity of M. margaritifera to Salmonidae are discussed.

The localization of ectoparasitic isopodes of the family Cymothoidae on the body of fishes is shown to depend on the speed characteristics of fishes and on the location of surface lymphatic system in hosts, which is a source of feeding of bloodsucking isopoodes.

Embryonic development of D. oligochaetophilus in described for the first time. Strong cytoplasmic activity of zigota was observed. The development is characterized by asynchronic cleavage, that proceeds as a forward division of backside blastomere P1. Rombic figure is absent. Bilateral symmetry of embryo is established at the stage of 12 cells. The material of primary ectoderm is dispersed between the AB blastomere and the descendants of С blastomere. Sinking of entoderm is observed at the early stages of cleavage (32 to 36 blastomeres). The "tadpole" embryo appears on the 10-12th day after the cleavage begins. Hatching of the first stage larva takes place on the 30-40th day after egglaying. The description of the first stage larva morphology is given.

A new genus Proteomonas is distinguished in the family Trypanosomatidae. The presence of the endomastigote stage is a peculiarity of the genus as well as the presence of the cells with a long curved intracellular part of the flagellum. Members of the genus form polymorphous colonies of different cell composition on the solid media. The ultrastructure and kinetoplast DNA structure are described.

Being fed on white mice, intoxicated with subtoxic doses of lindane, blocked fleas sharply decreased in number. The inhibition of the vectoral ability of fleas, infected with plague, under the systemic effect of lindane is shown.

Description, original patterns and differential diagnosis of the mature cestode Joyeuxilepis biuncinata (Joyeux et Baer, 1943) are given.

The myxosporidium Thelohanellus nikolskii has been recorded in young of carp in fish-breeding ponds of Moldavia since 1982. Sporogenesis takes place from June to August. Single cysts with mature spores are found in winter and spring. The distribution of cysts in the host's population is of over-dispersed character. Haematological investigation has revealed the threshold level of the invasion when there are observed changes in the blood of infected fishes (8 to 10 cysts per lg of fish weight). The parasite is most pathogenic during the spore formation. Blood of fishes contains increased contents of younger forms of neutrophils, monocytes and thrombocytes.

Summary is absent.