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There is ample evidence that macroscopic animals form geographic clusters termed as zoogeographic realms, whereas distributions of species of microscopic animals are still poorly understood. The common view has been that micrometazoans, thanks to their putatively excellent dispersal abilities, are subject to the "Everything is everywhere but environment selects" hypothesis (EiE). One of such groups, <1 mm in length, are limnoterrestrial water bears (Tardigrada), which can additionally enter cryptobiosis that should further enhance their potential for long distance dispersion (e.g., by wind). However, an increasing number of studies, including the most recent phylogeny of the eutardigrade genus Milnesium, seem to question the general applicability of the EiE hypothesis to tardigrade species. Nevertheless, all Milnesium phylogenies published to date were based on a limited number of populations, which are likely to falsely suggest limited geographic ranges. Thus, in order to test the EiE hypothesis more confidently, we considerably enlarged the Milnesium data set both taxonomically and geographically, and analysed it in tandem with climate type and reproductive mode. Additionally, we time‐calibrated our phylogeny to align it with major geological events. Our results show that, although cases of long distance dispersal are present, they seem to be rare and mostly ancient. Overall, Milnesium species are restricted to single zoogeographic realms, which suggests that these tardigrades have limited dispersal abilities. Finally, our results also suggest that the breakdown of Gondwana may have influenced the evolutionary history of Milnesium. In conclusion, phylogenetic relationships within the genus seem to be determined mainly by paleogeography. [ABSTRACT FROM AUTHOR]

Zoogeographical studies on Tardigrada are limited by the extent of our knowledge on tardigrade taxonomy and faunistics. In this paper we analyse the relationships between the tardigrade fauna of North, Central and South America (Nearctic and Neotropical regions) and provide the first test of whether the tardigrade fauna of the Americas has undergone the great American interchange. Our analyses were based on 384 tardigrade species records obtained for 1702 localities in North, South and Central America. We found that (1) some tardigrade species are distributed, as predicted by the Great American Biotic Interchange (GABI) hypothesis, on both sides of the Panama Isthmus; (2) the Central American tardigrade fauna is specific and different from both the South and the North American faunas, although it is closer to the tropical areas of South America; (3) either the tardigrade fauna of South and North America appear to be more similar to each other than to that of Central America, or there is a Nearctic-Neotropic division of the faunas; and (4) endemism in Central America suggests a more complex biogeographical process than predicted by the connection of two continents. [ABSTRACT FROM AUTHOR]

Given the constantly growing number of described tardigrade species and the scarcity of taxonomically meaningful morphological characters that these microinvertebrates exhibit, in many cases morphometric traits are the primary or even the only means of classic species differentiation, especially between closely related taxa. However, the validity of comparisons is contingent on the assumption that the mounting does not significantly affect the dimensions of morphometric traits, meaning that specimens mounted on different microscope slides may be compared with confidence. Despite the importance of the accuracy of morphometric measurements in tardigrade taxonomy and a long-standing supposition that the pressure exerted by the coverslip on a tardigrade specimen mounted on a microscope slide may deform some of the taxonomically important morphometric traits, the effect of mounting on specimen quality has not yet been addressed conclusively. In this paper we experimentally tested nine mounting methods using a lab-bred clonal strain of Milnesium cf. alpigenum Ehrenberg, 1853. Among all known tardigrades, species of the genus Milnesium Doyère, 1840 exhibit the widest buccal tubes, thus they provide the most sensitive gauge of deformation caused by coverslip pressure. Moreover, using equal-age clonal animals reared under uniform lab conditions allowed us to minimize background noise in the data. Our study showed that among the nine mounting methods tested, thermal inactivation of animals at 60 °C for 30 min followed by briefly pressing the coverslip with an entomological pin produced specimens fixed optimally for morphometry and imaging (i.e. maximally stretched and levelled but not deformed). [ABSTRACT FROM AUTHOR]

A rare species, Doryphoribius zyxiglobus, was found in mosses in New Zealand. So far, it has been cited only three times; from Australia, New Zealand and central China. The original description is very brief and is insufficient by today's taxonomic standards and seems not to be based on the holotype. A photograph of the slide mounted holotype (obtained from The Museum of New Zealand) showed it to be so poorly preserved and oriented that it was deemed probable that little would be gained by its further examination. Consequently, the redescription was based on a few limited measurements from the photograph of the holotype with a complete set of measurements of a paratype and supported by morphometric analysis of a set of topotypes—all borrowed from The Museum of New Zealand. A comparison between sets of specimens from three countries (New Zealand, Australia and China) and a single specimen from South Africa permitted an evaluation of the geographic variation of this species. This paper thus redescribes D. zyxiglobus, reports on populations from widely separated locales and extends its geographical range. [ABSTRACT FROM AUTHOR]

A new eutardigrade species Milnesium krzysztofi sp. nov. is described from Costa Rica. M. krzysztofi sp. nov. differs from the most similar Milnesium katarzynae Kaczmarek et al., 2004 mainly by the presence of spurs on internal claws I-III and on external claw IV. [ABSTRACT FROM AUTHOR]

A new species Macrobiotus magdalenae sp. nov. is described from a liverwort sample collected in Costa Rica (Central America). The new species is most similar to Macrobiotus corgatensis Pilato et al., 2002 but differs from it mainly by the lack of fine granulation on the cuticle. [ABSTRACT FROM AUTHOR]

Four species of the order Eutardigrada were found in material collected in Maramureş (Romania). Of these, three were new for the Romanian fauna: Diphascon (Diphascon) oculatum Murray, 1906, Isohypsibius prosostomus Thulin, 1928, Mesocrista spitsbergense Richters, 1903 and one species, Macrobiotus hufelandi Schultze, 1833, was known from Romania but is new for Maramureş county. [ABSTRACT FROM AUTHOR]