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Rhynchotalona falcata (G.O. Sars, 1861) was found in the plankton of a gravel pit located in the lowlands of Slovakia. This is the first record of this taxon for Slovakia, although it is widely distributed in Western Europe. We do not know to date, whether it is a rare, native species of Slovakian fauna, or accidentally introduced one from north-west regions of Europe. Some notes on its biology and distribution in Europe are provided. [ABSTRACT FROM AUTHOR]

We recovered subfossil chydorid cladoceran remains, which morphologically resemble the remains of Unapertura latens, from the surface sediments of two small lakes (TK-32, TK-18) located in the Central Arctic Treeline region, Northwest Territories, Canada. This species had previously been described only from lakes in Europe, primarily in southern Finland. We compared head shields and postabdomens from Canadian and Finnish sites and found them to be morphologically identical. The occurrence of Unapertura remains in North America suggests that this group of chydorids may be much more widely distributed than previously reported. [ABSTRACT FROM AUTHOR]

The highly enlarged proboscis in adult thorny-headed worms of the genus Apororhynchus suggests that its inner organization might be specialized as well. However, what kind of changes occurred in the stem line of monogeneric Apororhynchida is widely unknown and there are different conceptions regarding the presence/absence of several muscles. To expand our knowledge on this topic, I examined ethanol-fixed specimens, whole mounts, and semi-thin sections of three Apororhynchus species using the light microscope. Incorporation of previously published data increased the overall sample to five out of six Apororhynchus species known to date. Combined data suggest that Apororhynchida kept the full set of muscles which already evolved in the stem line of Acanthocephala: proboscis receptacle, a receptacle surrounding muscle (receptacle protrusor), retinacula, neck retractor, proboscis and receptacle retractors, circular and longitudinal musculature under the metasomal tegument, and a single muscular layer beneath the proboscis wall. However, especially proboscis receptacle and receptacle protrusor underwent considerable re-organization in the apororhynchid stem line: both muscles are subdivided into sail-like strands extending from the cerebral ganglion to the proboscis wall. This reorganization reflects that the two muscles still suspend the cerebral ganglion but are not implicated in the eversion of the proboscis. Spatially separated subtegumental longitudinal muscle cords and a sphincter at the posterior proboscis margin could be additional apomorphies of Apororhynchida. Finally, lack of a muscle plate, a midventral longitudinal muscle, and of lateral receptacle flexors and the absence of an apical sensory organ indicate a basally branching position of Apororhynchida relative to other Archiacanthocephala. [ABSTRACT FROM AUTHOR]

This study is concerned with structural and mineralogic transformations and changes in the physical and mechanical properties of volcanogenic sedimentary rocks in the North Paramushir hydrothermal magmatic system as a result of the interaction with thermal waters of various compositions and origins. We identified the following hydrothermal metasomatic facies that developed in tuffites and tuffs: opalites (monoopalite, opal-clay, and opal-alunite), as well as low- and moderate-temperature propylites. We show the position of each new facies in the structure of the hydrothermal magmatic system. We obtained correlative relationships of the physical and mechanical properties of the rock to the intensity and character of secondary alteration. It is pointed out that all of these rocks obey a common trend in the interrelationships between their properties, which may provide evidence of a common origin and progressive direction of hydrothermal processes in the interior of the North Paramushir system. [ABSTRACT FROM AUTHOR]

The results of study of crichtonite group minerals in pyropes from the Internatsionalnaya kimberlite pipe are reported. Most of the studied samples are characterized by high concentrations of Sr, Ca, Na, and LREEs in comparison with minerals of the LIMA series from kimberlites of South Africa, whereas the average concentrations of Ba and K are significantly lower. Crichtonite group minerals in pyropes are characterized by predomination of Na over K in most samples and by a high concentration of AlO (up to 4.5 wt %). Findings of inclusions of crichtonite group minerals with high concentrations of incompatible elements provide evidence for the metasomatic origin of host chromium-rich pyropes. [ABSTRACT FROM AUTHOR]

We analyzed a lacustrine sediment core covering the Holocene from Lake Einstaken, Nordaustlandet, for its fossil Cladocera (Crustacea) with an aim to reconstruct past aquatic communities in this environmentally extreme and unexplored region. In the analysis, we encountered remains (carapaces, ephippia, headshields, and postabdomens) of an unknown chydorid (Chydoridae, Aloninae) species during two separate periods in the early Holocene. The remains had some comparable morphological characters with the European Alona guttata s.str. Sars, 1862 and with the glacial relict Alona werestschagini Sinev, , but they differed clearly from the previous species; the headshield had broadly rounded rostrum and narrow fornices, the ephippium was heavily pigmented and reticulated, and the postabdomen had convex dorsal and ventral margins. The postabdomen had evidently similar morphology with Alona bergi Røen, , which has been described, although inadequately, from arctic Canada and northern Greenland. We conclude, based on the morphology of the postabdomen, that the unknown remains belong to species closely resembling A. bergi, named here Alona cf. bergi, and assume that the species, whether the true A. bergi or some other cryptic species of the A. guttata group, is a postglacial relict of the high arctic adapted to cold climate. Herewith, we emphasize the need for extensive biogeographical investigations into both fossil and intact specimens of chydorids in the arctic. [ABSTRACT FROM AUTHOR]

Comparative study on morphological variability of the polymorphic species Daphnia galeata Sars from the lakes of the Todzha Depression was carried out. The purpose of this study was to estimate the population variability and adaptive opportunities of this species. It was revealed, that almost all samples from the populations were reliably differed from each other based on body size. We did not find any significant differences based on the number of paired spines on postabdomen and fecundity between most of the populations. All individuals were characterized by pointed helmet, and helmet length varied markedly among the populations across the lakes. Moreover, it was found a high morphological variability of helmet length and shape and some traits of head for D. galeata. In spite of the fact that helmet length of D. galeata was extremely variable, the samples from the different lakes organized an overlapping cloud in the space of the second and third principal component axes. We assume that the morphological variation of D. galeata from the lakes of the Todzha Depression belongs to populational and depends on the environmental conditions. [ABSTRACT FROM AUTHOR]