[Dermal glands of water mites (Acariformes: Parasitengona: Hydrachnidia) and their possible eco-physiological significance].

Functional and comparative morphology is the basis for investigation of animal kingdom, its diversity and possible evolution. Moreover, it is extremely valuable in understanding of functioning of the living systems in unity of their organ and tissue structures. In the present paper, the organization of dermal glands and their possible eco-physiological role in the life of adult water mites are analyzed on the basis of the available data and original investigations from the point of view of fundamental functional-morphological approaches in the study of various groups of arthropods developed by Prof. Yu.S. Balashov.

[Possible evolutionary scenarios in the parasitengona mites (Acariformes: Parasitengona) based on anatomical peculiarities of their digestive system].

Five possible evolutionary scenarios of the higher acariform mites from the cohort Parasitengona are proposed on the basis of the detailed examination of anatomy of the excretory organ and midgut in the representatives of terrestrial mite families Trombiculidae and Microtrombidiidae, and in freshwater mite families Teutoniidae and Pionidae, on different developmental stages including parasitic larva. These scenarios explain possible ways of evolutionary transformation within the Parasitengona from one or several ancestor with the open digestive tract.

[Morphology of Parasitengona mites (Acariformes: Parasitengona) and their possible evolutionary scenario].

On the basis of the analysis of morphology and biology of representatives of the Parasitengona, mostly trombiculids, trombidiids and water mites, a new attempt is made to clarify probable evolutionary scenario in this group of the higher trombidiform mites (Actinedida). It is supposed that the very old ancestral group of terrestrial arachnids, having bite-sucking mouth-parts, poorly differentiated sac-like midgut and capability to extra-oral digestion, fed predatory on different small soil arthropods at all phases of the life cycle. They were small segmented orthotrichous homeomorphic arachnids at the rank of genus or family. The favorable feeding conditions of the adult phase have led to the small eggs rich in yolk and the small larva. The latter have led in turn to the necessity of intensive feeding at the larval stage to complete the ontogenesis. Further in evolution, this group gave rise at once to two or even more large paraphyletic branches. Most of them retained feeding on arthropods with transition of larvae to much more effective parasitic feeding provided with the additional specialization of the larval stage. This branch comprise divergently radiated paraphyletic terrestrial and secondary-water water mites each having long course of evolution resulted in the recent groups of Calyptostomatoidea, Erythraeoidea, Trombidioidea and several superfamilies of water mites. Another branch of the ancestral Parasitengona has followed the way of adaptation of larvae to feeding on vertebrates, which were being attacked by the larvae in the environment of pasture. The parasitism on vertebrates has lead to several radical specializations of these mites and their significant evolutionary progress. At the same time, the similar ontogenetic dynamics, as well as synchronous reduction of particular developmental stages in all parasitengones, inevitably indicate the monophyletic origin of the whole branch of Parasitengona with Pterygosomatidae as the most probable sister group.

[Extra-oral digestion and the problem of parasitism in Parasitengona mites (Acariformes)].

An analysis of the extra-oral digestion in Parasitengona being a highly specialized group of Acariform mites is carried out from the viewpoint of functional morphology and ecology. The significance of the extra-oral digestion in the life strategy of these mites and their larval parasitism is also evaluated. The morphological pre-adaptations of this mode of feeding as well as its probable evolutionary consequences are demonstrated by an example of trombiculid mites (Trombiculidae). It is shown, in particular, that parasitism in general may be considered as a particular life scenario implying that the feeding preferences of the organism are evolutionary formed in a close association with other organisms, which provide a parasite with a feeding substrate mainly already prepared for utilization. Based on this assumption, all Parasitengona, including both larval and post-larval instars, irrespectively of the size of their potential victim, preferably should not be considered as parasites, but as micro-predators.

[Thirty years of the electron microscope investigation in zoology and parasitology in the Zoological Institute of the Russian Academy of Sciences]. / Tridtsat' let élektronno-mikroskopicheskikh issledovanii v zoologii i parazitologii v Zoologicheskom institute RAN.

The history of the electron microscope investigations in zoology and parasitology in the Zoological Institute of the Russian Academy of Sciences and progress in scanning and transmission electron microscope investigations in this field of biology to the moment are briefly accounted.

[Structure of eyes in trombidioid mites (Acariformes: Trombidioidea)]. / Stroenie glaz krasnotelkovykh kleshchei (Acariformes: Trombidioidea).

The eyes or ocelli of trombidioid mite larvae of Euschoengastia rotundata, Hirszutiella zachvatkini and Camerotrombidium pexatum, and larvae and adults of Platytrombidium fasciatum were studied by means of transmission electron microscopy. These species together with larvae of Odontacarus efferus, Ericotrombidium hasgelum, Walchia chinensis and adult E. rotundata and H. zachvatkini were also studied under scanning electron microscope. The eyes of larvae are not inverted and characterized by an epicuticular lamellar lens. The group of phoreceptor cells with rhabdomeres arranged typically of Chelicerata is underlaid by a pigment cup. The eyes of adult mites are inverted, perikarions of photoreceptor cells are situated between the lens and rhabdomeres; tapetum occupies the space between the pigment cup and rhabdomeres. Sensitivity of eyes to light is similar to that of primary eyes of spiders dwelling on soil surface.

Ultrastructure of the integument during moulting of the quiescent tritonymphal instar of trombiculid mite Hirsutiella zachvatkini (Acariformes: Trombiculidae).

The ultrastructure of the integument of the quiescent reduced tritonymph of the trombiculid mite Hirsutiella zachvatkini (Schluger) was investigated by means of transmission electron microscopy. Mites were investigated daily during the 14-16 day tritonymphal period (imagochrysalis). This period includes the deutonymphal moult (1-3 days), the quiescent tritonymph period (2-4 days), and the tritonymphal moult into the adult mite (6-10 days). A distinct recognizable feature of the tritonymphal moulting cycle is a sequence of events independent of precise time intervals. This process involves partial destruction and reorganization of the hypodermis of the previous instar, and formation of a new hypodermis of the subsequent instar from islands of rudimentary hypodermal cells. The integument of the reduced tritonymph differs greatly from that of both larva and active deutonymph and adult. It consists of a simply organized hypodermal layer of varying thickness and a thick clear poorly lamellate cuticle with curved pore canals, and lacking setae. The epicuticle is very thin and without a clear protein layer. The tritonymphal instar as such with its own cuticle situated near the hypodermis is encased within the detached covering of the previous active deutonymph, and may be considered a calyptostasic and entirely pharate instar. There is a tendency for reduced tritonymphal stage to be eliminated from ontogenesis and this stage is not homologous to the pupa of insects.

[Resting nymphal stages and the nature of individual development in trombiculid mites (Acariformes: Trombiculidae)]. / Pokoiashchiesia nimfal'nye stadii i kharakter individual'nogo razvitiia krasnotelkovykh kleshchei (Acariformes: Trombiculidae).

A morphological expression of quiescent nymphal instars (calyptostases) in trombiculid mites (Trombiculidae) is analysed. The analysis takes into consideration ontogenetic functions of different instars during the individual development of these mites, which includes an alternation of active and regressive quiescent instars. Cyclic start and blocking of different integumental differentiation programs in Trombiculidae is caused by the cyclic reduction and renewal of particular functions of respective instars, whereas internal organs of these mites do not transform significantly during the life cycle. The reduction of some functions, particularly the locomotion and feeding, in the quiescent nymphal instars with changed integumental function has an inevitable result in a complication and prolongation of the moulting process. The moulting of these instars begins at once after finishing the previous moulting cycle, i.e. it is realized in "automatic pattern" without the intermoult phase. In general, the organization of both quiescent proto- and tritonymph is the same, because it expresses concordant morphological correlations and synchronous reductions of certain functions and structures in these instars during the evolutionary process. At the same time, the trombiculid mites and, perhaps, other representatives of Parasitengona reveal the most generalized type of ontogenesis in Acariformes within the "alternating calyptostasy" phenomenon.

[Ultrastructural organization of hypodermis and formation of cuticle in pharate larva of Leptotrombidium orientale (Acariformes: Trombiculidae)]. / Ul'trastrukturnaia organizatsiia pokrovov i formirovanie kutikuly u faratnykh lichinok Leptotrombidium orientale (Acariformes: Trombiculidae).

The ultrastructural organization of hypodermis and the process of cuticle deposition is described for the pharate larvae of a trombiculid mite, Leptotrombidium orientale, being under the egg-shell and prelarval covering. The thin single-layered hypodermis consists of flattened epithelial cells containing oval or stretched nuclei and smooth basal plasma membrane. The apical membrane forms short scarce microvilli participating in the cuticle deposition. First of all, upper layers of the epicuticle, such as cuticulin lamella, wax and cement layers, are formed above the microvilli with plasma membrane plaques. Cuticulin layer is seen smooth at the early steps of this process. Very soon, however, epicuticle starts to be curved and forms particular high and tightly packed ridges, whereas the surface of hypodermal cells remains flat. Then a thick layer of the protein epicuticle is deposited due to secretory activity of hypodermal cells. Nearly simultaneously the thick lamellar procuticle starts to form through the deposition of their microfibrils at the tips of microvilli of the apical plasma membrane. Procuticle, as such, remains flat, is situated beneath the epicuticular ridges and contains curved pore canals. Cup-like pores in the epicuticle provide augmentation of the protein epicuticle mass due to secretion of particular substances by cells and to their transportation through the pore canals towards these epicuticular pores. The very beginning of the larval cuticle formation apparently indicates the starting point of the larval stage in ontogenesis, even though it remains for some time enveloped by the prelarval covering or sometimes by the egg-shell. When all the processes of formation are over, hungry larvae with a fully formed cuticle are actively hatched from two splitted halves of prelarval covering.

[The origin of parasitism in trombiculid mites (Acariformes: Trombiculidae)]. / O proiskhozhdeniia parazitizma u krasnotelkovykh kleshchei (Acariformes: Trombiculidae).

On the basis of literary data and original investigations some phylogenetic, ecological and morphological aspects of the origin of parasitism in trombiculid mites are carefully considered for the first time. It is shown that parasitism in this group of trombidiform mites is a relatively young historical phenomenon and was formed after their ontogenesis had differentiated into active and quiescent stages. Therefore, in the life pattern of trombiculid mites the character of individual development, that defines their biotopical restriction, is much more important than the phase parasitism. Primitive organization of the digestive system and extraintestinal digestion, so characteristic of this group, are one of the main reasons of the origin of their parasitism. Under pasture conditions trombiculid mites, that initially were predators-entomophages with bite-sucking mouth parts, pass easily to parasitism on vertebrate animals and become primary lymphophages. They use the vertebrate host's organism exclusively as a source of food and by the extent of polyphagia are very close to free-living blood-sucking insects. Stylostome, that develops during feeding of trombiculid larvae and some other closely related groups of trombidiform mites, is a universal structure for achieving a large amount of food on a wide range of animals during a relatively short period of time and reflects wide host-parasite specificity of these parasitic mites. From the historical view the larvae of trombiculid mites did not pass from one group of hosts to the others, but owing to morphological preadaptation to parasitism passed in a definite historical period, not earlier than Paleogene, to parasitism on all classes of terrestrial vertebrates, especially on mammals, their primary hosts.

[The alveolar salivary glands of hungry larvae of the chigger Hirsutiella zachvatkini]. / Al'veoliarnye sliunnye zhelezy golodnykh lichinok krasnotelkovogo kleshcha Hirsutiella zachvatkini.

Heteromorphic parasitic larvae of Hirsutiella zachvatkini have four pairs of simple alveolar salivary glands possessing characteristic peculiarities of electron microscopic organisation. Each of paired granulosecreting salivary glands has its own dynamics of secretory activity, which is stimulated by a specific functional role connected with feeding on the host.

[External structure of cuticle injuries and larval mouth parts of the chiggers Euschoengastia rotundata and Neotrombicula vulgaris (Trombiculidae)]. / Vneshnee stroenie porazhenii kozhi i rotovogo apparata lichinok krasnotelkovykh kleshchei Euschoengastia rotundata i Neotrombicula vulgaris (Trombiculidae).

When E. rotundata larvae parasitize the abdominal part of the body of their host (Clethrionomys glareolus), capsules with round terminal opening are formed from which hind part of the mite's body projects forwards. Organization of the capsules shows that their walls are formed by a substance (probably by larval saliva) which differs from host's tissues. At the bottom of the capsules there are larval adhesive sites with openings in the proximal parts of stylostomes which resemble in their structure these of N. vulgaris larvae. The latter do not form capsules when feeding on their natural hosts, Microtus arvalis. Proximal part of stylostome is formed in both cases by amorphous glutinous substance bearing imprints of mite's mobile digits of chelicerae and hypostome. Mouth parts of hungry mites and satiated larvae of both species differ only in relative sizes of constituent parts. Soft apical part of hypostome turns backwards during the feeding and forms a sucker. The feeding of larvae of trombiculids in capsules, which is formally regarded as ectoparasitism, can apparently be considered as a special type of parasitism.

[Morphofunctional characteristics of the larval mouth apparatus of the chigger, Neotrombicula pomeranzevi (Trombiculidae)]. / Morfofunktsional'nye osobennosti rotovogo apparata lichinok krasnotelkovogo kleshcha Neotrombicula pomeranzevi (Trombiculidae).

Gnathostoma of larvae of the chigger mite N. pomeranzevi is situated terminally on the trunk. The base of the gnathostoma is gnathocoxa represented by conglutinated coxae of pedipalps. Gnathocoxa narrows apically and passes into hypostome protruding up to the cheliceral blades. Lateral borders of the hypostome are bent dorsally thus forming a groove in which cheliceral blades are located. The cheliceral blades have a small groove in their internal surface. Larval chelicerea are free because their tactum is missing. Cheliceral apodemes which serve for the insertion of muscles, elevators of chelicerae, are jointed to the base of inner walls of basal cheliceral joints. Lateral gnathostoma bears five-jointed palps which have strong three-apical claws on tibia. Palps do not take part in the attachment of larvae to the host. The dorsal wall of gnathostoma is formed by the epistoma and caudal subcheliceral plate which further is branched into two cheliceral apodemes. Subcheliceral plate and apodemes serve as an attachment place of muscles, dilatators of the pharynx. The mouth opening is situated not far from the apical end of hypostome and goes into a large pharynx passing along the bottom of gnathosoma. On the whole, the mouth parts of larvae are adapted well for sucking liquid food.

[Pathologichohistological skin changes in red-backed mice parasitized by larvae of the trombiculid mite, Neotromibcula pomeranzevi (Trombiculidae)]. / Patologogistologicheskie izmeneniia kozhi krasno-serykh polevok pri parazitirovanii lichinok krasnotelkovogo kleshcha Neotrombicula pomeranzevi (Trombiculidae).

During the feeding of N. pomeranzevi larvae on their natural hosgs, large-toothed redbacked voles (Clethronomys rufocanues Sandev.), in the skin of the latter are formed tubular structures or stylosomes characteristic of all trombiculids. During the formation of the stylosome the saliva of the mites and the interstitial fluid of the host are supposed to interact. The walls of the stylosome consist of two layers, are homogenous and do not include cellular elements. Around the stylosomes are formed the foci of necrosis and destruction of tissues. Behind the distal ends of the stylosomes are observed light interstitial cavities, which of then contain a great number of cellula relements of lymphoid and epithelioid nature. These cavities serve apparently as a reservoir of nutritive substratum for larvae. The feeding of trombiculids is accompanied by a reactive response of the connective tissue, the hyperemy of the superficial capillaries and the cellular infiltration of the affected area. The mass parasitism of larvae causes the ulceration of the host's skin and on its surface appear crusts from necrotic tissues.

[Histopathological changes in the skin of the rabbit fed on by preimaginal phases of the tick, Alveonasus lahorensis (Argasidae)]. / Patologicheskie izmeneniia kozhi krolika pri pitanii preimaginal'nykh faz kleshcha Alveonasus lahorensis (Argasidae).

During the feeding of larvae and nymphs of A. lahorensis haemorrhagic inflammation develops in the rabbit's skin. Lymphocytes and macrophages are the dominant cell elements in the reaction while during the feeding of nymphs eosinophilous leucocytes are observed in great number in the infiltrate. Around the oral parts of the tick an infiltration of collagenous fibres of the connective tissue is formed, which serves for a more firm attachment of the parasite, while beneath the proboscis a light band is formed from which the tick sucks the food substratum. By the end of the feeding of nymphs III in the place of skin affection a crust can be formed on account of the host's atrophied tissues, and in the integuments there are formed necrotic foci due to the hystolitic and toxic effect of the saliva.