A reinvestigation of spermiogenesis in Amphilina foliacea (Platyhelminthes: Amphilinidea).

Spermiogenesis in the amphilinidean cestode Amphilina foliacea (Rudolphi, 1819) was examined using transmission electron microscopy. The orthogonal development of the two flagella is followed by a flagellar rotation and their proximodistal fusion with the median cytoplasmic process. This process is accompanied by extension of both the mitochondrion and nucleus into the median cytoplasmic process. The two pairs of electron-dense attachment zones mark the lines where the proximodistal fusion of the median cytoplasmic process with the two flagella takes place. The intercentriolar body, previously undetermined in A.foliacea, is composed of three electron-dense and two electron-lucent plates. Also new for this species is the finding of electron-dense material in the apical region of the differentiation zone at the early stage of spermiogenesis, and the fact that two arching membranes appear at the base of the differentiation zone only when the two flagella rotate towards the median cytoplasmic process. The present data add more evidence for a close relationship between the Amphilinidea and the Eucestoda.

Spermatozoon cytoarchitecture of Amphilina foliacea (Platyhelminthes, Amphilinidea).

The mature spermatozoon of Amphilina foliacea Rudolphi, 1819 has been examined using transmission electron microscopy. The male gamete is filiform and tapered at both extremities. Its moderately electron-dense cytoplasm possesses two parallel axonemes of unequal lengths with the 9 + "1" trepaxonematan pattern, a mitochondrion, a nucleus, parallel cortical microtubules, four electron-dense attachment zones, and electron-dense glycogen granules. A crested body is absent. The anterior extremity of the cell exhibits a single axoneme. The anteriormost cortical microtubules have been observed with the appearance of the second axoneme. The number of cortical microtubules reaches a maximum (up to 25) in the nucleated region III of the spermatozoon. A single mitochondrion extends from the middle of region II to the end of region III of the cell. Both axonemes have become disorganized in a similar way: the axonemal doublets disappear first, followed by the central core. The nucleus is surrounded by a few cortical microtubules in the proximal part of region V. In the distal extremity of the mature spermatozoon, there is only the nucleus. Differences of spermatozoon ultrastructure within Amphilinidea and other Neodermata are discussed.

Ultrastructural characteristics of the protonephridial terminal organ and associated ducts of adult specimens of the Aspidogastrea, Digenea and Monogenea, with comments on the relationships between these groups.

Transmission electron microscopical observations were made on the protonephridial terminal organ and associated ducts of three adult trematodes, the aspidogastrean Aspidogaster limacoides Diesing, 1835 and the digeneans Azygia lucii (Müller, 1776) and Phyllodistomum angulatum Linstow, 1907, and the monogenean Ancyrocephalus paradoxus Creplin, 1839. Previously unreported ultrastructural details of the terminal organ of adult trematodes include multiple contact sites (septate junctions and zonulae adherentes) between the membranes of the terminal and adjacent canal cells. Septate junctions traverse the epithelial cytoplasm of the canal wall, and the same type of septate junctions are observed within the cytoplasmic cord at the level of the tip of the flame tuft in both longitudinal and oblique sections of all three trematode species studied. In the monopisthocotylean Ancyrocephalus paradoxus, the absence of any junctions in the cytoplasmic cord and the presence of septate junction within all of the protonephridial ducts are reported. On the basis of the small number of monogenean species in which these features have been studied, in relation to the size of the group, there seems to be a high diversity in some characters of the protonephridial terminal organ. The study confirms that the Aspidogastrea and Digenea possess the same morphology of their protonephridial terminal organ and, although this differs slightly from that of most members of the Monogenea so far studied, it supports previous views on the close relationship of these groups.

Ultrastructure of the ovarian follicles, oviducts and oocytes of Gyrocotyle urna (Neodermata: Gyrocotylidea).

An ultrastructural study of the ovarian follicles and their associated oviducts of the cestode Gyrocotyle urna Grube et Wagener, 1852, a parasite from the spiral valve of the rabbit fish, Chimaera monstrosa L., was undertaken. Each follicle gives rise to follicular oviduct, which opens into one of the five collecting ducts, through which pass mature oocytes. These collecting ducts open into an ovarian receptacle which, in turn, opens via a muscular sphincter (the oocapt) to the main oviduct. The maturation of oocytes surrounded by the syncytial interstitial cells within the ovarian follicles of G. urna follows a pattern similar to that in Eucestoda. The ooplasm of mature oocytes contain lipid droplets (2.0 x 1.8 microm) and cortical granules (0.26 x 0.19 microm). The cytoplasm of primary and secondary oocytes contains centrioles, indicating the presence of the so-called "centriole cycle" during oocyte divisions. A morphological variation between different oviducts was observed. The luminal surface of the follicular and the collecting oviducts is smooth. The zones of the septate junctions are present within the distal portion of the net-like epithelial wall of the collecting ducts close to the ovarian receptacle. The syncytial epithelial lining of the ovarian receptacle, oocapt and main oviduct is covered with lamellae and cilia. Cortical granules secreted from mature oocytes occur freely within the lumen of the main oviduct that functions as a fertilisation canal. A division of the ovary into separated parts with their own collecting ducts as that typical of Gyrocotyle has been observed in neodermates, basal monogenean family Chimaericolidae, and Neoophora (some Proseriata and Fecampiidae). Ultrastructural data thus reveal several unique morphological characteristics of gyrocotylideans, the most basal taxon of tapeworms (Cestoda).

Ultrastructure of the ovary of Amphilina japonica Goto & Ishii, 1936 (Cestoda) and its implications for phylogenetic studies.

The ultrastructure of the ovary of the amphilinidean cestode Amphilina japonica Goto & Ishii, 1936 from the body-cavity of the American sturgeon Acipenser transmontanus Richardson is described using transmission electron microscopy. The characters of the ovary of Amphilina japonica are different from those of all other cestodes. The most important difference is in the nature of the relationship between the germ and accessory cells within the ovary. In A. japonica the oocytes and accessory cells form numerous different intercellular contacts (desmosome-like junctions and zonulae adherentes). Gap junctions are present between the narrow cytoplasmic processes of the accessory cells. Numerous micropinocytotic vesicles and vacuoles from the accessory cells discharge their content into spaces between the oocytes and the accessory cells. The accessory cells are closely associated with the oocytes during the early and middle stages of oogenesis. As the volume of oocytes increases, the accessory cells gradually lose their association with the oocyte surfaces. Peripherally located individual accessory cells of A. japonica give rise to a cellular epithelial layer of irregular shape and thickness which breaks down via numerous invaginations of the basal membrane and underlying basal matrix. The different arrangements of the interconnection of cell components in the Amphilinidea compared with the Gyrocotylidea and Eucestoda (the absence of specialised cell contacts and the syncytial nature of the accessory 'interstitial' cells) are evidence suggesting the presence of unrelated groups within the Cestoda. The nature of the association of the accessory and germ cells in ovary of A. japonica more closely resembles the ovary of non-platyhelminth invertebrates rather than that of other neodermatans.

Ultrastructure of the neodermal sclerites of Gyrocotyle urna Grube and Wagener, 1852 (Gyrocotylidea, Cestoda).

Body sclerites of Gyrocotyle urna Grube and Wagener, 1852, parasites of Chimaera monstrosa L., were studied by transmission electron microscopy. Each sclerite consists of ten to 15 concentric layers varying in electron density and thickness. The sclerites insert in pockets whose epithelia are continuous with the body neodermis but are 14 times thinner. The pocket neodermis bears surface projections with an inner electron-dense cylinder and a small electron-dense cap at their tip. It is surrounded by a well-elaborated basement lamina and bundles of musculature; the perikarya of this part of the neodermis lie underneath the basement membrane. The luminal plasma membrane of the pockets is covered by a coat originating from vesicles and dense bodies most probably discharged from the pocket neodermis, supporting the assumption that the deposition of this material builds up the sclerites. Therefore, sclerites are derivatives of the neodermis. With regard to their ultrastructure, sclerites resemble the calcareous corpuscles of other cestode taxa. They represent a useful phylogenetic character and are an autapomorphy of the Gyrocotylidea.

Slow-moving soil organisms on a water highway: aquatic dispersal and survival potential of Oribatida and Collembola in running water.

BACKGROUND: Oribatida and Collembola are an important part of the soil food web and increase soil fertility by contributing to the recycling of nutrients out of dead organic matter. Active locomotion enables only limited dispersal in these tiny, wingless arthropods, while passive dispersal plays an important role for long-distance dispersal. Previous investigations have focused on passive transport by wind, other animals, or sea currents, whereas studies on transport via running water are missing. However, previous observation of the long survival of submerged terrestrial microarthropods makes passive dispersal with running water very likely. METHODS: By combining field and lab experiments, we studied the potential for passive dispersal of oribatid mites with running water. We investigated terrestrial Oribatida and Collembola: (1) along a stream taking soil and moss samples, (2) in a stream using sticky covers and aquarium nets, and (3) studied their ability to colonise new soil after aquatic transport with the help of floating islands. Furthermore, we investigated the survival of submerged Oribatida species and their floating capabilities in lab experiments to predict dispersal distances with running water. We tested for differences between species using Kruskal-Wallis test for equal medians and Mann-Whitney pairwise-comparison and χ2-test for the influence of body size on aquatic dispersal. RESULTS: Soil and moss samples revealed a pool of 52 oribatid mite species at the stream bank. Within the stream, we caught 180 individuals from 36 oribatid mite species. Only 14 of those species were also found in the soil and moss samples, whereas the remaining 22 were of unknown origin. Based on material caught on sticky covers, an average of 63.9 (± 54.6) oribatid mite individuals fell on one m2 stream water per week. Four species of Collembola (27 individuals) and 21 species of oribatid mites (47 individuals) were collected with aquarium nets. Eight microarthropod species (Oribatida + Collembola) successfully colonised new soil in the floating islands after aquatic dispersal. Lab experiments showed that Oribatida can float for at least 14 hours at the surface of running water and may survive for more than 365 days when submerged. The floating abilities and survival rates were largely species-specific. CONCLUSION: This is the first study to demonstrate successful passive dispersal with running water for two groups of terrestrial soil microarthropods, including subsequent colonisation of new soil. We show that submersion survival, as well as floating abilities, and therefore dispersal capability, are not only high in oribatid mites, but also species-specific. Running waters obviously serve as long-distance dispersal highways for many of these less mobile soil-living animals.

VIRMISCO - The Virtual Microscope Slide Collection.

Digitisation allows scientists rapid access to research objects. For transparent to semi-transparent three-dimensional microscopic objects, such as microinvertebrates or small body parts of organisms, available databases are scarce. Most mounting media used for permanent microscope slides deteriorate after some years or decades, eventually leading to total damage and loss of the object. However, restoration is labour-intensive, and often the composition of the mounting media is not known. A digital preservation of important material, especially types, is important and an urgent need. The Virtual Microscope Slide Collection - VIRMISCO project has developed recommendations for taking microscopic image stacks of three-dimensional objects, depositing and presenting such series of digital image files or z-stacks as an online platform. The core of VIRMISCO is an online viewer, which enables the user to virtually focus through an object online as if using a real microscope. Additionally, VIRMISCO offers features such as search, rotating, zooming, measuring, changing brightness or contrast, taking snapshots, leaving feedback as well as downloading complete z-stacks as jpeg files or video file. The open source system can be installed by any institution and can be linked to common database or images can be sent to the Senckenberg Museum of Natural History Görlitz. The benefits of VIRMISCO are the preservation of important or fragile material, to avoid loan, to act as a digital archive for image files and to allow determination by experts from the distance, as well as providing reference libraries for taxonomic research or education and providing image series as online supplementary material for publications or digital vouchers of specimens of molecular investigations are relevant applications for VIRMISCO.

Respiratory adaptations to a combination of oxygen deprivation and extreme carbon dioxide concentration in nematodes.

To examine physiological adaptations to the two combined stressors O2 deprivation and extreme CO2 concentrations, we compared respiratory responses of two nematode species occurring in natural CO2 springs. The minimum O2 concentration allowing maintenance of respiration in both species was 0.0176µmol O2ml-1 (corresponds to 1.4% O2 in air). After exposure to anoxia, individuals resumed respiration immediately when O2 was added, but on a lower level compared to control and without showing a respiratory overshoot. A species-specific response was found in respiration rate during 20% CO2: the more tolerant species maintained respiration rates, whereas the sensitive species showed a decreased respiration rate as low as after anoxia. The results indicate that during 20% CO2 the sensitive species undergo a survival state. We conclude, that the ability to maintain respiration even under low oxygen and high CO2 concentrations may allow the better adapted species to occupy an ecological niche in the field, where others cannot exist.

Community assembly of terrestrial testate amoebae: how is the very first beginning characterized?

Testate amoebae play an important role at the very first beginning of succession on land. We used litterbags buried into four different soils to study the early colonization (which occurred within less than 55 days) and establishment of testate amoebae. The litterbag cellulose exposed at the youngest mining site poor in nitrogen and phosphorus was colonized firstly in high abundances, whereas the substrate introduced into the reference sites of undisturbed soil was colonized slowly and in low densities. Besides the (expected) small-sized r-strategists (e.g., Euglypha rotunda, Tracheleuglypha dentata, and Trinema lineare), large-sized K-strategists (e.g., Centropyxis spp., Phryganella acropodia) occurred in remarkably high densities on all sites. Species that colonized the cellulose in high densities (e.g., P. acropodia and T. dentata) were found extremely rarely in the adjacent source substrate and vice versa, stressing the importance of the target substrate quality. In the course of the experiment, the influencing environmental factors became more complex, as shown by redundancy analysis (RDA). Concerning the amoebal community, there was a change from variability to stability, as visualized by cluster analysis. Adjacent litterbags within an investigation site revealed amoebal species and abundances with an increasing similarity during exposition time, whereas the litterbags between the four investigation sites were colonized differently. These observations point to a stochastic (variable) beginning of community assembly, changing to a more deterministic (stable) course. No species replacement has been observed, which is an essential part of most successional theories. Thus, the more flexible concept of "community assembly" should be considered instead of "succession" for protozoa. The stochastic beginning of community assembly and the lack of species replacement are explained by a neutral community model.