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According to the traditional views mites of the family Pterygosomatidae belong to the cohort Anystina (Krantz, 1978; Kethley, 1982). Kethley (1982), however, noted similarities between these mites and representatives of the cohort Eleutherengona. In the tree diagram suggesting relationships among higher taxa Prostigmata proposed by Kethley (in Norton et al., 1993) this family derives from the eleutherengone clade. However, the characters and ranges of taxa upon which Kethley's hypothesis was based were not stated. In this paper, the external morphology of pterygosomatid mites is analyzed. The data provide strong evidence supporting a close relationship between Pterygosomatidae and the "higher" eleutherengone mites (Raphignathae and Heterostigmata). The setation of Pterygosomatidae is similar that of Raphignathae by the absence of trichobothria, adanal setae, and by the strongly reduced leg setation. In these mites, as in the "higher" eleutherengones (Raphignathae) an aedeagus is present, in females, the genital and anal openings are situated close to each other and are covered by a pair of common folds, in males these openings are fused, the leg femora are not separated onto basi- and telofemur, the naso, sejugal furrow, genital papillae, and the larval Claparede's organs are absent. Some similarities in the structure of the gnathosoma and the chelicerae with Anystina (including Parasitengona) are, probably, symplesiomorphies or convergently developed. Moreover, in pterygosomatids, the gnathosomal setation is represented by a single pair of gnathobasal setae, and the cheliceral and adoral setae, present in anystoid mites and early derivative eleutherengones, are absent. We believe, therefore, that Pterygosomatidae is a separate branch within the cohort Eleutherengona. Its exact position is, however, still unclear. Among pterygosomatid genera, mites of the genus Pimeliaphilus, which possess the maximal setation, are closest to the "freelivings" habitus. These mites are known from different parts of the world parasitizing mostly secretively living arthropods. We suggest that ancestors of the family were initially associated with arthropods and parasitism of pterygosomatids on lizards is the result of host switching from arthropods to these hosts.

The results of experiments held in 1982—1983 in Tuva plague natural focus with flea Amphipsylla primaris primaris (Jordan et Rothschild, 1915) from natural populations, whish were inflected and fed on specific host — flat-headed vole (Alticola strelzovi), are analyzed. The initial infectivity of the insects in autumn was higher than in spring: 90 and 50% respectively. Accumulation of the agent in aggregated form in the organism of A. p. primaris, estimated by the quantity of fleas with "lumps" and partial blocks, was more active in imago of both sexes in autumn than in spring, while sucking flea were observed in spring more often than in autumn. Irrespective of season, the part of males with visible accumulations of Y. pestis was more, and their alimentary activity was higher than that of females. Fleas died much more quickly in spring. Part of the males with proventriculus block exceeded that of females in spring experiment. Females with alimentary canal obstruction prevailed in autumn. Thus, sex of the insect and season of the experiment conducting influenced on all studied indices. Besides that, Y. pestis ability for the proventriculus block formation in fleas during different seasons can change by the opposite way depending on sex of the ectoparasites.

he occurrence of tumors, their influence upon the organism of Phoxinus phoxinus (L.), its parasite fauna, and parasite component community were investigated in the upstream of the Pechora River. According to the data obtained, tumors could occur in the fishes of every age group, but one-year (0+) or two-year (1+) old minnow is affected by tumors more frequently. The tumors lesion extensiveness ranges from 0.02 to 3%. From 1 to 3 tumors were recorded on one fish specimen. The investigated tumors were in progressive stage (Georgiev, 2000), since the vascular ingrowth and dissemination (in few cases) of the tumors were observed. Tumors are colored in intensive-black and taupe. The taupe tumors usually have a compact capsule at its peripheries, which isolates affected tissue from muscle fibers. In the intensive-black tumors the invasion of tumor cells to the adjacent transversal striated musculature is observed. Distinct symptoms of necrosis are revealed in all slides of the new growths. Blood vessels are formed in most tumors, and the blood flow is recorded before the completion of the vessels forming, that apparently supplies the tumors feeding. Metastases in different organs revealed in several minnow specimens. Tumor affected individuals of the minnow has parasite species complex practically identical (by species list and quantity) with the same of the even-aged unaffected fishes. However, the parasite component communities of the affected individuals are characterized by 4 groups of species, while the parasite component communities of the intact individuals — by 3 groups. The parasite communities of affected and unaffected one-year fishes are similar by the number of the groups of species, but differ in the number of species.

A checklist of protozoa parasitizing fishes in the Volga basin is given. The checklist includes host species names for the each parasite and data on the occurrence of parasites in different parts of the Volga basin. The data on parasitic protozoa from 52 fish species are presented. The list containes 224 species and 10 subspecies names of the parasites. 9 species (Trypanosoma gracilis, Eimeria cheni, E. sinensis, Zschokkella striata, Chloromyxum cyprini, Myxobolus amurensis, M. drjagini, M. pavlovskii, and Balantidium ctenopharyngodoni) were introduced into the Volga basin from the Amur basin along with acclimatizated fishes.

The fauna of fish parasites in Lake Baikal is represented by 5 faunistic complexes, namely the boreal plain, boreal submountain, arctic freshwater, Baikal, and Sino-Indian ones. The parasites of the boreal plain complex are dominant by the number of species (43%). Hypotheses on the origin of the recent fish and parasite faunas of Lake Baikal were advanced on the base of the data on the parasite species composition and their distribution among hosts, as well as on the base of paleontological data. It is shown that invasion of new fish species and their parasites to Baikal led to the change of the composition of natural faunistic fish complexes and parasite systems. Invading fishes play the roles of intermediate and definitive hosts in parasite systems of Baikal, that led to the change of the initial structure of these systems.

The results of a parasitological study of the burbot Lota lota L. inhabiting the Kola region are presented. 51 species of parasite were found on burbot in 16 waterbodies belonging to the White Sea and Barents Sea basins (Muxosporea — 7, Suctoria — 1, Peritricha — 6, Monogenea — 1, Cestoda — 6, Trematoda — 13, Nematoda — 6, Acanthocephala — 5, Hirudinea — 3, Bivalvia — 1 and Crustacea — 2 species). Data on the infestation of burbot by different parasite species and their prevalence in investigated waterbodies were obtained.

The cestode species Mathevolepis larbicus Karpenko, 1982 parasitizing shrews in Russian Far East is restored. As the holotype was lost, the neotype is selected. The redescription and differential diagnosis of the species are given.

Optimal photoperiod and temperature conditions for rearing of the mosquito Culex pipiens pipiens f. molestus without blood feeding (through autogenous eggs) were experimentally substantiated. This method may be used in order to obtain relatively small quantities of mosquitoes or for preservation of a laboratory colony. Optimal conditions of rearing are the short-day photoperiod (12 h of light per day) at 20°C, when 87% of the females produce autogenous eggs rafts consisting of 52 eggs on the average. It should be emphasized that larval food must be adequate and abundant, because the quality and quantity of it has a pronounced effect on the autogeny rate.