The ultrastructure and possible functions of nephrocytes in the trombiculid mite Hirsutiella zachvatkini (Acariformes: Trombiculidae)

The ultrastructure of nephrocytes during the post-larval development of the trombiculid mite Hirsutiella zachvatkini (Schluger) was investigated by means of transmission electron microscopy. Nephrocytes are situated either individually or in groups inside the haemocoelic space and are always ensheathed by a basal membrane. They contain numerous tubular elements, electron-dense inclusions and sometimes electron-lucent vacuoles. Invaginations of the plasma membrane, often in the form of labyrinthine channels, with coated pits of plasma membrane and characteristic slit diaphragms linking adjacent pedicels, typically occupy the peripheral parts of the cells. However, no distinct zonation of organelles in the nephrocytes of trombiculids was observed. The number of nephrocytes in the haemocoel and the intensity of development of their tubular elements and in particular of labyrinthine channels vary significantly during the ontogenesis of mites. The possible functions of nephrocytes and their structure and differentiation in comparison with other arachnids are discussed.     

Ultrastructure of testes and spermatogenesis in the trombiculid mite,Hirsutiella zachvatkini (Schluger)

Summary

Spermatogenesis and sperm ultrastructure of the trombiculid mite Hirsutiella zachvatkini (Schluger 1948) have been investigated using transmission electron microscopy and compared with other arachnids studied. Sperm differentiation takes place in groups of synchronously developed germ cells of the two large sac-like paired testes. Each testis is composed of a secretory epithelium, which occupies their medio-ventral regions, and of a germinative epithelium situated in the latero-dorsal parts of testes together with large somatic cells. The germ cells are represented on sections by spermatogonia, spermatocytes, early, middle and late spermatids, and mature spermatozoa. Spermatocytes and spermatids contain two centrioles, which disappear afterwards, and a small Golgi-like structure forming an acrosomal cistema. Mature spermatozoa, which lie both within the meshes of somatic cells and also free in the lumen of testes, are compact oval aflagellate cells provided with peripheral channels. They also contain an acrosome, flattened between the cell membrane and the round electron-dense chromatin body, an oval body of lesser density lying in close proximity to the chromatin body, and a group of 5–7 mitochondria with spherically arranged cristae situated immediately behind the nuclear bodies. An acrosomal filament may be sometimes seen beneath the acrosome in the middle spermatids and disappears in the mature spermatozoa. These findings show that the mode of differentiation and pattern of organization of the male sex cells in trombiculid mites are of rather primitive type compared with other acarine spermatozoa.     

Resting nymphal stages and the nature of individual development in trombiculid mites (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.     

Ultrastructure of organelles during microsporogenesis inTillandsia pallidoflavens (Bromeliaceae)

InTillandsia pallidoflavens none of the organelles undergoes fundamental de- and redifferentiation during microsporogenesis. The plastids are amoeboid, exhibit complex internal structures and gradually start accumulating polysaccharides from meiotic prophase I onwards. These observations contradict reports for other taxa. The ultrastructure of mitochondria and dictyosomes, respectively, is more or less orthodox. The extensive ER, which is only poorly stained by standard methods was identified by image intensifiying techniques. The ribosomes are not only associated with the ER or occur as polyribosomes free in the cytoplasm, but can also form more or less dense clusters.     

Intraspecific variability and sympatry in closely related chigger mite species of the genus Hirsutiella (Acari: Trombiculidae)

Intraspecific variability in three closely related chigger mite species of the genus Hirsutiella Schluger et Vysotzkaya, 1970, H. steineri (Kepka, 1966), H. llogorensis (Daniel, 1960), and H. alpina Stekolnikov, 2001 has been studied based on materials collected in Caucasus and Turkey. It is established that both H. steineri and H. llogorensis include Western Caucasian and Asian forms, the first one being larger than the second one. Western Caucasian samples of H. steineri are also split into large and small forms. The large form inhabits screes with larvae occurring mainly on snow voles, and the small form inhabits meadows and forests with larvae parasitizing snow voles as well as mice of the genus Apodemus and pine voles. Asian population of H. steineri include small low-mountain form which is hard to distinguish from H. llogorensis. In the light of the new data on variability, morphological border between these two species are specified. Correlations between some characters and altitude above sea level are shown within the Western Caucasian and Asian forms of both species, and also in H. alpina. All the three species can occur together on the same individual hosts, but they have different sets of main hosts and different distribution among biotopes in the area of sympatria. The border between H. steineri and H. llogorensis in the places of sympatria can be indistinct owing to the presence of small ecological forms of H. steineri. Our results give a basis for the construction of alternative hypotheses concerning the processes of speciation in trombiculids. Chiggers species could be formed in allopatric way, on the base of such geographical forms, as Western and Asian forms of the Caucasian Hirsutiella species, but they could also be formed in sympatric way, distributing among neighbouring biotopes (e.g., screes and meadows, or screes and forests), as large and small forms of Western Caucasian H. steineri do.     

Ultrastructure of the rotifer integument: peculiarities of Sinantherina socialis (Monogononta: Gnesiotrocha)

The rotifer integument is a well‐described syncytium that contains an apical intracytoplasmic lamina (ICL) that functions for both skeletal support and muscle insertion. To date, there is limited information on the structure of the integument in species of Gnesiotrocha, a diverse subclade of Monogononta that consists of solitary, colonial, sessile, and planktonic species. In this study, we examined the ultrastructure of the integument in the colonial rotifer Sinantherina socialis to determine how it corresponds to that of other monogononts. The integument of S. socialis was broadly similar to that of other rotifers, consisting of a thickened glycocalyx, multilaminate ICL, and syncytial epidermis. However, it was different in several regards. The ICL consisted of three distinct layers from apical to basal: layer 1 consisted of at least two electron‐dense laminae; layer 2 was a thickened matrix of amorphous, electron‐dense material or was fibrous; and layer 3 was an electron‐dense lamina of varying thickness that covered the underlying syncytium. Significantly, layers 1 and 2 formed a ridge‐and‐groove like system of finger‐like projections across the trunk surface that has not been observed in other rotifers. A voluminous syncytial cytoplasm (up to 3 μm thick) was present beneath the ICL and was mostly electron lucent and with few organelles. Bundles of potential microtubules were scattered throughout the syncytium. We hypothesize that the voluminous cytoplasm with microtubules serves as skeletal support for the rotifer's sessile lifestyle, while the external ridges may function as a texture‐based deterrent to predators, or serves to trap secretions from the species' defensive glands. Basally, the epidermis was highly folded and bordered by a thin basal lamina that separated the plasmalemma from the blastocoel. Membrane‐bound vesicles were present throughout the integument's cytoplasm and are hypothesized to function in the secretion of extracellular matrix and in the maintenance of the ICL.     

Origin of the quiescent center in the root of Capsella bursa-pastoris (L.) Medik

The origin of the quiescent center in the embryonic radicle of Capsella bursa-pastoris was investigated by in-situ hybridization to cellular polyadenylic-acid-containing RNA using [³H]polyuridylic acid as a probe. In the globular embryo, autoradiographic silver grains were localized in all cells of the presumptive root apex except in the hypophysis. As the inner cell formed by a transverse division of the hypophysis cut off new cells toward the central procambial cylinder of the embryo, these cells remained characteristically unlabeled, in contrast to the labeled cells of the rest of the embryo. In the embryonic radicles of mature seeds and of seedlings, cells derived from the hypophysis appeared as a nonmeristematic, unlabeled, hemispherical group, bounded by the procambium to the inside and the root epidermis to the outside. When root tips excised from 2-d-old seedlings were incubated in [methyl-³H]thymidine, sectioned, and autoradiographed, cells derived from the inner cell of the hypophysis were found to be unlabeled, thus showing that they constitute the specific cells of the quiescent center. These results present evidence for the single-cell origin of the quiescent center in an angiosperm root and a role for the hypophysis in it.Abbreviations poly(A)⁺RNA polyadenylicacid-containing RNA - [³H]poly(U) [³H]polyuridylic acid - QC quiescent center This work was supported in part by National Science Foundation grants PCM-7902898 and DCB-8709092.     

Ultrastructure of the eye of Urastoma cyprinae (Turbellaria,Alloeocoela)

Summary Urastoma cyprinae (Graff) is a microturbellarian which has been recorded both as a free-living organism by Westblad (1955) and Marcus (1951) and as a commensal in various lamellibranch molluscs (see Burt & Drinnan 1968). The material used in this study came from oysters, Crassostroea virginica, collected off the coast of Prince Edward Island, in which hosts it occurs in large numbers especially during the summer months when the oysters are spawning (Fleming et al. 1981). When U. cyprinae is exposed to light as happens, for example, when an oyster is opened, it shows a marked negative phototactic response.Preliminary work on the fine structure of the photoreceptors in U. cyprinae shows that the two eyes each consists of: (1) a single cup cell full of relatively large, electron-dense pigment granules; (2) a tripartite conical lens system; and (3) what appear to be two photosensitive rhabdomes. The pigment cup cell has a single, well defined nucleus situated basally and close to the membrane of the pigment cell furthest away from the rhabdomeres. The lens system consists of a cone made up of three, separate but equal, parts. Each part has two, flat inner surfaces which join at an angle of 120°, an outer rounded surface, and a rounded upper surface. When these three parts fit together, the cone-shaped lens is formed with the apex of the lens within the cup of the pigment cell and the rounded, convex, broad end of the cone lying more or less at the same level as the top of the pigment cup and below the epidermis layer. The rhabdomeres lie between the electron dense lenses and the inside of the pigment cup. They show connections to the visual cells which are bipolar: one extension joining the rhabdomeres; the other constituting the axon which extends into the centrally situated brain or into the longitudinal, lateral nerves. The axons that enter the brain, form connections with other axons from the other eye. The axons that extend posteriorly in a lateral position, presumably play a role in facilitating the avoidance reaction.The chemical nature of the unusual lens has not yet been determined. This is presently under investigation and will be reported later at which time our work will be discussed in relation to other types of rhabdomeric eyes in the Turbellaria.     

The potential role of phoresy in the evolution of parasitism: radiolabelling (tritium) evidence from an astigmatid mite

Using tritium as a radiolabel marker of interspecific fluid transfer, we present experimental evidence that the heteromorphic deutonymph of an astigmatid mite (Hemisarcoptes cooremani) acquires materials (at least water) directly from the haemolymph of its beetle host (Chilocorus cacti). This acquisition is above that obtained from atmospheric vapour. The material acquired from the host is necessary for the completion of the ontogeny of H. cooremani and is likely procured through the action of the caudal ventral suckers of the heteromorphic deutonymph (hypopus). On gross morphological criteria, this mite-beetle relationship was previously defined as phoretic (for dispersal). Scanning electron photomicrographs of the physical relationship between the hypopodes and the heetles shed light on the parasitic nature of the hypopus of H. cooremani. Our findings are discussed in terms of the evolution of parasitism from a free-living astigmatid form. This transition into parasitism is facilitated by the heteromorphic hypopus and represents a classic wolf-insheep's-clothing strategy. The heteromorph retains the characteristic phoretic morphology while exploiting the host in transit.     

桉小卷蛾触角感器的超微结构

[目的] 桉小卷蛾是桉树、番石榴等林木和果树的一种重要害虫。为确定桉小卷蛾成虫触角上的感器对寻找生存环境及对外界环境的各种刺激所起的作用,研究了桉小卷蛾触角感器的种类、形态和分布。[方法] 利用扫描电镜对桉小卷蛾成虫触角感器进行了详细观察和研究。[结果] 桉小卷蛾雌、雄蛾触角由柄节、梗节和鞭节组成,触角的外侧面覆盖有鳞片;雄性触角略短于雌虫,且鞭节近1/4处有一凹陷。共发现7种感器,即鳞形感器、毛形感器、锥形感器、腔锥形感器、耳形感器、刺形感器和Böhm氏鬃毛,其中以毛形感器数量最多。[结论] 桉小卷蛾雌雄成虫触角的感器种类、分布、数量有一定的规律但又有差异。建议应用气相-触角电位联用技术GC-EAD和触角电位EGA等技术进一步解析触角感器的功能。     

Functional morphology and ultrastructure of mouthparts in unfed water mite larvae Piona carnea (Koch, 1836) (Acariformes: Pionidae)

Mouthparts of unfed larvae Piona carnea (Koch, 1836) (Acariformes: Pionidae) were studied on whole-mount preparations, semi-thin sections and with TEM and SEM methods. The mouth apparatus is incorporated within the pseudotagma, gnathosoma, composed of the infracapitulum and of the chelicerae resting on the roof of the latter. The gnathosoma inclines to the long axis of the body and is inserted at its base into the idiosoma by the circumcapitular fold. The basal cheliceral segments are long and fused. An anterior projection, the proposed fused fixed digits, protrudes from the distal end of the basal cheliceral segment forward between the movable digits. The movable digits are always found in protruded position, strongly curved upward and show a groove on their inner sides. The ventral wall of the infracapitulum is made of the mentum posterior and the malapophyses anterior to the palp articulation. The malapophyses are squeezed between the large palps and envelope the distal portion of the chelicerae from the sides. The ventral portion of the fused malapophyses are provided with a characteristic ventral cuticular fork of unknown function. Each malapophysis terminates by a flexible lateral lip provided by several rigid jags looking posterad. The palps face downward and backward, and bear on the tibia the large curved palpal claws turned laterad. The palp femur bears on the ventral aspect a characteristic wide spade-like projection provided with its own muscles originating on the dorsal wall of the femur. The labrum is a thick cuticular arrow-like structure protruding forward into the preoral cavity, whereas the cervix is a thin weakly sclerotized plate. The particular labral valve projects forward from the dorsal basis of the labrum into the preoral cavity. The labrum and the cervix are provided by their own small labral and cervical muscles originating on the cervical apodemes. The pharynx is totally separated from the ventral wall of the infracapitulum and is devoid of ventral dilators. The dorsal pharyngeal dilators originate on the thick and sclerotized capitular apodeme and, posteriorly, on the paired cuticular branches, capitular apodemes, which end freely in the body cavity and are combined with the common salivary duct. The short sigmoid pieces serve for origin of the levator muscles of the chelicerae. Retraction of the gnathosoma and the chelicerae is mediated by several sets of muscles originating on the dorsal plate.     

The effect of salinity on respiratory metabolism,survival and moulting in the first zoea of Macrobrachium amazonicum (Heller) (Crustacea,Palaemonidae)

Survival, duration of intermoult cycle and respiratory metabolism were evaluated as a function of salinity (0–35‰; 25° C) in early zoeae of the cinnamon shrimp, Macrobrachium amazonicum. Zoeae are extremely resistant to salinity, mortality occurring only in fresh and sea-water after several days. Moulting occurs in all salinities, longer cycles being recorded in 0 and 35‰ S. The metabolism-salinity curve is broadly U-shaped between 0 and 28‰ S but declines sharply in sea-water. Such physiological responses characterise the early zoeae as strongly euryhaline and typically estuarine. Data are discussed in relation to the degree of adaptation of the organism to the freshwater biotope and the position of the species within the generic pattern of adaptive radiation.     

Ultrastructure and phylogeny of the spermatozoid ofChara vulgaris (Charophyceae)

At maturity, spermatozoids of the green algaChara vulgaris are biflagellated, contain little cytoplasm, and coil for approximately 2 1/2 gyres within the mother cell wall. The anterior of the cell contains an ovoid headpiece anchoring two slightly staggered basal bodies that are positioned above and directly in front of approximately 30 linearly arranged mitochondria. An elongated stellate pattern occupies the transition zone between the BBs and axonemes. Flagella emerge from the cell just in front of the nucleus and encircle the full length of the spermatozoid. The spline comprises a maximum of 38 microtubules surrounding the anterior mitochondria and gradually decreases posteriorly to a minimum of 11. The dense nucleus is narrow, cylindrical, and occupies the central revolution of the cell. Six starch-laden plastids and associated mitochondria are linearly arranged at the cell posterior. Phylogenetic analyses of charalean taxa and archegoniates based on spermatogenesis strongly support the orderCharales, withNitella as the sister group toChara. Diagnostic features ofChara spermatozoids include absence of a lamellar strip and axonemes embedded in the cell for almost the entire length of the anterior mitochondria. Potential relationships amongCharales, Coleochaetales and archegoniates are evaluated in regards to the probable course of evolution of streamlined biflagellated gametes.     

Ultrastructure of nuclear inclusions and the separation ofVerbenaceae andOleaceae (incl.Nyctanthes)

TEM observations were carried out on 40 taxa of the familyVerbenaceae and 35 taxa of the familyOleaceae, in order to ascertain distribution, ultrastructure and morphology of the intranuclear proteinic inclusions in the mesophyll parenchymatic cells. The investigated genera amount to some 25% and 60% respectively of the genera of the two families. Inside theVerbenaceae, lamellar inclusions (L-type) occur in 6 out of 23 investigated genera: they are mostly present inside the tribesCitharexyleae andVerbeneae (both belonging toVerbenoideae), while they are absent in other subfamilies. All of the investigatedOleaceae genera show intranuclear crystalline inclusions (C 1-type) of three different shapes. Among theAsteridae this is a character peculiar toOleaceae. They appear to be a well defined natural group, including the controversial genusNyctanthes.     

Ultrastructure of the stylar canal cells ofCitrus limon (Rutaceae)

The ultrastructure of the canal cells and the canal filling substance ofCitrus limon have been studied. At maturity the canal cells are very rich in cytoplasm. Their inner tangential walls lining the canal are much thickened and formed by two layers: the outer corresponds to the original wall, the inner is formed by subsequent deposition of abundant materials of different origin. This thickening occurs at the same time as the filling of the stylar canal. Both events are paralleled by considerable dictyosomic activity, the formation of a large amount of rough endoplasmic reticulum, and the incorporation of small cytoplasmic masses into the cell wall, due to plasmalemma evaginations. — The material in the stylar canal has a heterogeneous ultrastructure aspect and consists of polysaccharides, proteins and lipids; it presumably provides nutrients for the growing pollen tubes.Research performed under CNR program Biology of Reproduction.     

The ultrastructure of the so-called olfactory setae on the antennula ofDaphnia magna Straus (Crustacea,Cladocera)

A group of nine sensory setae is found on the tip of the antennula ofDaphnia magna in both sexes. Inside a seta four dendrites are situated, each with one receptor cilium. The receptor cilia extend through a liquor space into the exterior part of the seta. The exterior part of the liquor space is divided from the interior part by a knob-like thickening of the innermost layer of the epicuticle, the basal bead. The basal bead narrows the liquor space and the receptor cilia. The interior part of the liquor space is surrounded by five sheath cells, the exterior part by a thin cuticle. In the exterior part the receptor cilia branch partly and reach a terminal pellet on the tip of the seta. The terminal pellet is a thickened part of the epicuticle. It is permeable to several dissolved substances. It is the exterior part of the receptor that projects over the tip of the antennula and seems to be the entire seta. During the premoult the fifth sheath cell builds up the articulation of the seta, the fourth the basal bead, and the third the shaft of the seta. The first sheath cell forms the cuticular sheath. The organ seems to be a chemoreceptor, but the adequate stimulus is as yet unknown.     

Ultrastructure of germination and mucilage production inHalosphaeria appendiculata (Halosphaeriaceae)

The germination of ascospores of the marine fungusHalosphaeria appendiculata was investigated with transmission electron microscopy. Prior to germination, settled ascospores became surrounded by a fibro-granular layer. Small, membrane-bounded vesicles and larger electron-dense membrane-bounded vesicles aggregated at the site of germ tube formation where the plasmalemma adjacent to the aggregation was convoluted. The vesicles appeared to fuse with the plasmalemma, releasing their contents. Enzymatic digestion of the spore wall probably occurred at the time of germ tube emergence. After the nucleus had migrated into the newly formed germ tube, a septum was formed to delimit the germ tube from the ascospore. The growing germ tube can be divided into 3 morphological regions, namely the apical, sub-apical and vacuolated regions, and is typical of other fungi. A mucilaginous sheath was associated with the older mycelium. The germ tube displaced the polar appendage, and the ascospore, germ tube and appendage were enclosed in a mucilaginous sheath. In ascospores which subtended old germ tubes, the nucleus and lipid body became irregular in shape and the cytoplasm was more vacuolated. Microbody-like structures remained associated with the lipid throughout development, and were present in old ascospores.     

Ultrastructure of the epidermis of adult and embryonic Paravortex species (Turbellaria,Eulecithophora)

The epidermis and associated structures of adult and embryonic Paravortex cardii and Paravortex karlingi, internal parasites of Cerastoderma edule, have been examined using scanning and transmission electron microscopy. The cellular epidermis of adult Paravortex bears cilia and microvilli which differ in number and distribution between P. karlingi and P. cardii. Cellular organelles include mitochondria, lipid bodies, Golgi bodies, and ultrarhabdites. Epidermal nuclei are located in the proximal portion of the cells. The development of the tegument of embryo Paravortex has been described and a possible origin for the embryo capsule is suggested. These findings are discussed in relation to the phylogenetic status of the Turbellaria in relation to other Platyhelminthes and in the functional adaptation of the epidermis for a parasitic mode of life.Abbreviations bb- basal bodies - bl- basal lamella - c- cilia - cp- capsule - dc- dark cells - e- embryos - ep- epidermis - g- Golgi bodies - int- interdigitation (of cells) - l- lipid - lf- lamellar fold - mc- migrating cell - mf- membranous folds - mt- mitochondria - mv- microvilli - n- nucleus - nb- neoblasts - p- projections of epidermis - par- parenchyma of mother - pr- primary rootlet - rc- rhabditogen cells - sr- secondary rootlet - ur- ultrarhabdites - vt- vitelline material     

The role of glycogen during the ontogenesis of Chironomus anthracinus (Chironomidae, Diptera)

Large fluctuations in glycogen content were found in larvae, pupae and adults of Chironomus anthracinus (Zetterstedt) from the profundal zone of Lake Esrom, Denmark. In 2nd, 3rd and 4th instar larvae the glycogen concentration (expressed as percentage of dry weight) increased during periods of aerobic conditions to a maximum of 25%, but decreased in periods of hypoxia longer than two months to 10–12% in young larvae. A further decrease to about 5% took place, when moulting from 2nd to 3rd or from 3rd to 4th instar occurred after overturn. Prior to pupation the glycogen concentration was restored to 26–28%. The glycogen concentration approximated 22% in young pupae, but decreased during the pupal stage and newly hatched adults contained 12–15%. Finally, the glycogen store of both males and females was further reduced during the swarming period. Thus, glycogen seems to be an important energy source (1) during periods with hypoxic conditions, (2) during periods with high internal energy requirement such as ecdyses and metamorphosis, and (3) during the non-feeding adult life stage.