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The main sensory organs (eyes, Haller's organ, and palpal organ) of Dermacentor niveus were examined in scanning and transmitting electron microscopes. The Haller's organ consists of a capsule with five porous SW-WP olfactory sensilla and pleomorphs; anterior pit with porous SW-WP, two grooved DW-WP, two thin NP-SW, and one conical DW-NP sensilla; four posterior DW-WP sensilla; and anterior group of SW-WP and DW-UP sensilla. Duct orifices of two dermal glands are situated near the capsule. Contact chemosensory sensilla of palps are represented by 4 DW-UP and 6 SW-UP sensilla. Eyes possess flattened lenses without the system of radial channels typical of eyes of other ixodid ticks examined. Unipolar photoreceptor cells with microvilli of rhabdomeres running in parallel to longitudinal cells axis contain basal bodies treated as rudiments of the cilia. On the whole, sensory system of D. niveus, dweller of semi-exposed habitats (floodland meadows, tugai forests, and shrub thickets of arid zones) is characterized by combination of features typical of species dwelling in exposed (deserts) and concealed (forests) habitats.

Coevolution of parasites and in particular monogeneans and fishes, was characterized from two related angles — parallel coevolution and host switches, lead to the acquisition of new hosts from taxonomically distant but ecologically similar groups. Modern views on the evolution and taxonomy of gudgeons are discussed. This group is very heterogeneous by morphology and biology, tales unclear taxonomic position in the family Cyprynidae, and can be divided into two tribes or four groups of genera. Analysis of coevolution of dactylogirids, ancyrocephalids, gyrodactylids, and diplozoids with their hosts was carried out. Dactylogyrus spp. and gudgeons show coevolutional connections; in Ancyrocephalus s.l. spp. coevolution and host switches take place; most of Gyrodactylus spp. parasitize fishes of the genus Gobio and are the colonists of gudgeons; and none of the diplozoids parasitize exceptionally gudgeons. From 130 species of 30 genera of the World fauna of gudgeons 31 species 13 genera proved to be infected with monogeneans. We divided the dactylogyrids from gudgeons (49 species) into 13 evolution levels and 30 morphological groups, which were found equal in number with taxonomic groups of hosts. Ancyrocephalids were divided into two evolution levels, which can not be reduced to one initial type, and eight monophyletic groups. Fourteen of 18 species of these monogeneans occurred on the host from the genera Hemibarbus and Squalidus. Different directions of evolution connected with forming of different types of copulatory organ, ventral additional bar, and type of attachment on gills were revealed for Dactylogyrus spp. from different groups of genera of gudgeons (Yang et al., 2006). Monogeneans have lower evolutionary rates, as compared with their hosts, that are expressed in the taxonomic ranks (groups of species in monogeneans and genera or groups of genera in their hosts). Number of species in Dactylogyrus and Ancyrocephalus s.l. usually the same as the number of their host species. However this proportion increases in favor of the parasites owing to the explosion-like speciation of monogeneans parasitizing Hemibarbus and Saurogobio. Distribution of morphological groups of monogeneans on gudgeons in general confirms their grouping into four groups of genera on the base of molecular data. At the same time, in some cases parasitological data agree with the gudgeons' classification based on morphological characters to a greater extent (Banarescu, 1992; Naseca, 1998). The genera Sarcocheilichthys and Gnathopogon take the crucial position in the Sarcocheilichthys group of genera according to the analysis of occurrence of monophyletic groups of Dactylogyrus spp. In the Pseudogobio group of genera, the largest number of the Dactylogyrus spp. groups was found on the genera Saurogobio and Abbottina. The genus Hemibarbus, being the host of some original groups of Dactylogyrus spp. and Ancyrocephalus spp., takes the most isolated position among gudgeons by morphological, molecular, and parasitological data. Relationships of Hemibarbus and Squalidus (both from the Hemibarbus group of genera) are need in further investigations. The Sarcocheilichthys group of genera, which contains the genera Coreius and Paracanthobrama with unclear and ambiguous positions, is situated apart from the Hemibarbus group of genera. High-specialized groups of Dactylogyrus spp. are predominating on the former. The Pseudogobio group of genera is parasitized by numerous primitive groups of Dactylogyrus spp. Groups of Dactylogyrus spp. from the Gobio group of genera are derived undoubtedly from the monogeneans parasitizing the Pseudogobio group of genera, and the Gobio group of genera either derived from the Pseudogobio group of genera or must be included into the latter. Thus, we have one phylum of gudgeons with separate groups of monogeneans (Hemibarbus group of genera) and, contrariwise, other phylum of fish hosts with ancient and specialized monogeneans (Sarcocheilichthys group of genera), which ends in the gudgeons with primitive monogeneans (Pseudogobio group of genera) and evolutionary young monogeneans (Gobio group of genera). The pattern of distribution of the morphological groups of monogeneans by gudgeons is a mirror reflection of modern contradictory views on the taxonomy and evolution of these fishes and may contribute to a more profound understanding of the place of gudgeons in Cyprinidae, their taxonomy and evolution.

Fauna of haemoparasites of batrachians is studied in Kyrgyzstan for the first time. Descriptions of 12 haemoparasites species are given. Eight species have been found in Central Asia for the first time.

The present study aimed to investigate structural changes in communities of fish parasites by the method of "dynamic phase portrait". This method allows revealing equilibrium states of communities and analyzing a response of community near and far from these states. Seasonal succession of the parasite communities in Phoxinus phoxinus of different age from the rivers Ulcheksha and Chovju is considered as an example. The obtained phase portrait were found to reflect the seasonal succession of the parasite communities whether the rate of different parasite species abundance was analyzed by the number or biomass. The process of forming was recorded in the studied parasite communities in May, while in June these communities come to the equilibrium state with maximum species diversity, minimum speed of the diversity's change, and considerable quantity of parasites. However, this equilibrium state is unstable. Interpopulation connections lead to further structural transformations, and at the end of July — the beginning of August, when the above parameters have minimal values, the community comes to a new equilibrium state. Later on, in August—September, when the host fish is invading by a new generation of parasites, the community comes out the equilibrium state. Unlike the parasite communities in the host of age 1+—3+, the community in Phoxinus phoxinus 0+ begins to form in July. Diversity index of such community is lesser.

Fine structure of rostellar glands has been studied in two cestode species different from one another by the level of rostellum development. Secretion of the rostellar glands and rostellar sheath of Dichoanotaenia clavigera are characterized by different morphology, as well as different sites and ways of secretion. In Platyscolex ciliata morphological differences of the secretion of the rostellar sheath gland in the sites of synthesis and excretion were revealed. Possible causes of the morphologically different types of secretion in the rostellar glands of cestodes are discussed.

Helminths collected from 55 Steller's sea lions in the western and central Bering Sea were examined. Helminth species, their localization in the host organism, invasion indices, categories, and host ranges are reported. Helminthofaunas of sea lions from various sea areas are compared. Forming of the recent Steller's sea lion helminthofauna and its links with other host are discussed. It was hypothesized that helminths do nor substantially affect the recent decline of the Steller's sea lion abundance.

Species diversity of helminths in the common shrew from three cut-over lands of different age in Karelia was studied. It was shown, that change of the plant cover in cut-over lands have no a significant effect on the species diversity of helminth communities in Sorex araneus, but the abundance of individual parasite species changes considerably. Changes of the S. araneus infestation with helminths were the greatest in a new cut-over land. Structure of the helminth community comprises four categories of parasites (dominants — 4 species, subdominants — 8, rare species — 13, very rare species — 10) and depends on the time passed since the felling. A redistribution of the species constituting the core of the helminth fauna was to be observed. It was shown, that being an integrated indicator of the status of terrestrial ecosystems, parasites clearly indicate changes not in the structure, but in the abundance and domination of individual species of terrestrial invertebrates and vertebrates in cut-over lands.

Influence of adrenaline, hydrocortisone, and prednisolone on the infestation rate of the carp Cyprinus carpio by Dactylogyrus sp. is investigated, according to the analysis of the abudance index of parasites. Introduction of these hormones into experimental fish resulted in the increase of the abudance index of dactylogyrids. Dependence of changes in the investigated parameters on the nature and character of the hormones' influence on the host immune system and metabolic processes is revealed.