Fine structure of the posterior midgut in the mite Anystis baccarum (L.).

Homology of the posterior midgut regions (PMG) in different phylogenetic lineages of acariform mites (superorder Acariformes) remains unresolved. In the order Trombidiformes, the ultrastructure of the PMG is known primarily in derived groups; thus this study focuses on species belonging to a relatively basal trombidiform family. PMG of Anystis baccarum consists of the colon and postcolon separated by a small intercolon. The fine structure of the colon and postcolon is close to that of the corresponding organs of sarcoptiform mites with the epithelium showing absorptive and endocytotic activity. The epithelial cells produce a variety of excretory vacuoles and a peritrophic matrix around the feces. Morover, the epithelium of the postcolon is characterized by the highest apical brush border and especially numerous mitochondria suggesting involvement in water and ion absorption. The intercolon functions as a sphincter lined with an epithelium capable of producing excretory granules. A pair of short blind extensions arises assimmetrically from the intercolon into the body cavity. Ultrastructurally, these extensions are similar to the arachnid Malpighian tubules and may be their reduced version. Rare endocrine-like cells have been observed in the colon and postcolon.

Female reproductive system and oogenesis in the mite Bakericheyla chanayi.

The fine structure of the female reproductive system of a cheyletid mite Bakericheyla chanayi (Trombidiformes: Cheyletidae) is investigated for the first time. This system consists of an unpaired ovary, glandular oviduct, receptaculum seminis, long cuticle-lined vagina, and genital atrium terminating in the genital opening. A separate sperm access system has not been found. The receptaculum seminis opens into the distal oviduct region, where fertilization apparently takes place. The ovary contains clusters of oogonia (cystocytes), clustered early meiotic cells, a few growing previtellogenic oocytes, and 3 large nurse cells. The dorsal ovarian region is occupied by the clusters of bacteriocytes which harbor symbiotic bacteria. Oocytes undergo vitellogenesis in individual ovarian pouches, each connected to the corresponding nurse cell by an intercellular bridge. The fine structure of the bridge suggests transport between the interconnected cells in the course of vitellogenesis. The population of cystocytes was shown to be heterogenic. The electron-light cells enter meiosis and develop into the oocytes or nurse cells. The electron-dense cystocytes do not show meiotic transformation and probably give rise to the bacteriocytes. The early development of the nurse cells and oocytes is similar and accompanied by the blebbing of the nuclear envelope, appearance of nuage material and Balbiani bodies.

Fine structure of the silk gland in the mite Ornithocheyletia sp. (Prostigmata, Cheyletidae).

Silk spinning is widely-spread in trombidiform mites, yet scarse information is available on the morphology of their silk glands. Thus this study describes the fine structure of the prosomal silk glands in a small parasitic mite, Ornithocheyletia sp. (Cheyletidae). These are paired acinous glands incorporated into the podocephalic system, as typical of the order. Combined secretion of the coxal and silk glands is released at the tip of the gnathosoma. Data obtained show Ornithocheyletia silk gland belonging to the class 3 arthropod exocrine gland. Each gland is composed of seven pyramidal secretory cells and one ring-folded intercalary cell, rich in microtubules. The fine structure of the secretory cells points to intensive protein synthesis resulted in the presence of abundant uniform secretory granules. Fibrous content of the granules is always subdivided into several zones of two electron densities. The granules periodically discharge into the acinar cavity by means of exocytosis. The intercalary cell extends from the base of the excretory duct and contributes the wall of the acinar cavity encircling the apical margins of the secretory cells. The distal apical surface of the intercalary cell is covered with a thin cuticle resembling that of the corresponding cells in some acarine and myriapod glands. Axon endings form regular synaptic structures on the body of the intercalary cell implying nerve regulation of the gland activity.

Peculiar salivary glands in a silk-producing mite Bakericheyla chanayi (Cheyletidae).

This is the first ultrastructural investigation of salivary glands in the family Cheyletidae. In both sexes of Bakericheyla chanayi, paired acinous salivary glands and tubular coxal glands were shown to be united into the common podocephalic system. The secretory portion of the salivary gland includes medial and lateral lobes composed of the five and two cells, respectively, with clearly distinct ultrastructure. The cytoplasm of the cells is occupied by the secretory granules containing fine fibrous material. The fine structure of both cell types suggest a proteinaceous nature of their secretions. A single central process extending from the apical face of each secretory cell passes through the common acinar cavity to enter the conducting duct. A pair of intercalary cells at the base of the conducting duct links it with the secretory portion of the gland. Extending towards the acinar cavity, protrusions of intercalary cells alternate the apical regions of the secretory cells and form with them highly-specialized contacts characterized by the apical network of microtubules and microfilaments. Two possible ways of secretion are suggested: 1) exocytosis into the acinar cavity and 2) direct passage via the central processes. The detection of axon profiles in the gland body suggests a neural control for the glandular cell function. In tritonymphs, neither secretion nor large lateral lobe cells were observed up to the pharate stage when the lateral lobe undergoes rapid differentiation. The arrangement of the acinous gland is compared to that of other arthropods. Its composition appears to be close to the class three of insect glands. The involvement of the lateral lobe cells in silk production is discussed.

The fine structure of the midgut in the mite Anystis baccarum (L.) (Acari, Actinedida: Anystidae).

The ventriculus and the midgut caeca of the fed females of Anystis baccarum (L.) were investigated by using light and electron microscopy. In addition to the main type of polyfunctional digestive cells, special secretory cells were detected in the anterior region of the ventriculus. The shape and the ultrastructure of the digestive cells vary depending on their physiological state. Intracellular digestion, absorption or excretion processes prevail at different stages of the cell cycle. The secretory cells are characterized by the presence of extensive rough endoplasmic reticulum, filling whole space of the cell. These cells do not contain the apical network of pinocytotic canals, which are typical for the digestive cells. Three types of secretory granules were found in the cytoplasm of the secretory cells that probably correspond to three sequential stages of granulogenesis. The primary secretory granules are formed by the fusion of Golgi vesicles. The primary granules fuse to form complex vesicles with heterogeneous contents. These secondary granules aggregate to form very large inclusions of high electron density (tertiary secretory granules), which probably represent the storage of the secretory product. All types of secretory granules were observed close to the apical plasmalemma.

CF2Cl2 decomposition over nanocrystalline MgO: evidence for long induction periods.

CF(2)Cl(2) has been found to react with nanoscale MgO at 325 degrees C and higher temperatures. In excess of the halocarbon, the reaction results in the formation of MgF(2) as a predominant solid product, with CCl(4), and CO(2) formed as the main gaseous products. The kinetics of the process is characterized by a prolonged induction period, which is as long as 8.5 h at 325 degrees C. The length of the induction period decreases with temperature increase and becomes negligible at 500 degrees C. Complete CF(2)Cl(2) mineralization has been achieved in an excess of MgO at 450 degrees C. Detailed HRTEM and EDX analysis has shown that the induction period involves the formation of small amounts of magnesium halides on the oxide surface and results in its reconstruction leading to initial oriental ordering of the nanocrystals followed by substantial changes in the bulk composition of the nanoparticles. The reaction proved to be structurally sensitive. It has been found that deep fluoridation is possible only for nanoscale MgO samples. The use of samples with lower surface areas results in lengthening of the induction period and decrease of the reaction depth. The MgO transformation to MgF(2) has been found to result in a surface area decrease by more that an order of magnitude as a result of intense sintering of magnesium fluoride under the reaction conditions.

The fine structure of the coxal glands in Myobia murismusculi (Schrank) (Acari: Myobiidae).

The coxal glands of M. murismusculi consist of the proximal tubular portion (tubulus), the distal glandular sac and the terminal excretory duct. The tubulus comprises looped proximal and distal tubes that run in close association with each other. The cells of the proximal tube form numerous short protrusions that project into the neighbouring organs through the pores in their basal lamina. The sac is a distal part of the gland and so it cannot be considered as a homologue of the proximal filter sacculus of other arthropods. A large number of pinocytotic vesicles and lysosome-like bodies in the epithelial lining of the sac imply that the main functions of this organ may be the absorption of substances from the lumen of the gland and their subsequent intracellular transformation. In addition the sac of females was shown to produce dense secretory granules. The ultrastructural features of the glands are discussed and compared to other representatives of Acari.