Over 250 years ago Johann August Ephraim Goeze, a Protestant pastor from Quedlinburg, Germany, discovered the first tardigrade. The German physiologist and anatomist Carl August Sigismund Schultze (1795–1877) later named the first species Macrobiotus hufelandi C.A.S. Schultze, 1834, a designation that remains valid today. By the first third of the twentieth century numerous new species had been discovered in Germany and were comprehensively compiled for the first time by the German zoologist Ernst Marcus in 1936. Since then additional faunistic studies have been conducted. This new checklist of tardigrades in Germany provides an overview of all known species found in the country to date. It includes 91 limno-terrestrial or limnic species and eight marine species, with 21 belonging to Heterotardigrada and 78 to Eutardigrada. Germany is the type locality (terra typica) for 24 tardigrade species. The number of identified tardigrade species varies significantly depending on the extent of studies conducted in different federal states. Baden-Württemberg has the highest number of species identified, with 80 species recorded across eleven studies. In this state the Black Forest, with its remarkable diversity of 72 identified tardigrade species is one of the most intensively studied regions worldwide. In Hesse 30 species have been recorded from five studies, while Berlin has documented 23 species from two studies. Fewer species have been reported from other federal states. The 99 tardigrade species identified in Germany represent about 7

The species of the genus Ramazzottius (Ramazzottiidae, Eutardigrada) are among the most common and widespread tardigrade species in the world. Most of the 28 Ramazzottius species have been described only with morphological characters which were most of the time represented only with drawings. The discovery of a new species of this genus in the Black Forest (Germany) provided the opportunity to compare this species with the type specimens of ten Ramazzottius species, to propose the status of species dubia for Ramazzottius edmondabouti, and through new photographs to elucidate the anatomy of animals and eggs (in particular of the head sensory regions, eye spots, buccal tube, ornamentations of the dorsal posterior cuticle, and morphology of egg processes). These thorough observations led to a better understanding of the diversity and evolution, not only of this cosmopolitan genus, but also of other eutardigrade genera. The new species Ramazzottius kretschmanni is described with an integrative approach integrating morphological (light and electron microscopy observations and morphometric data) and molecular (cox1 and ITS2 genes) data. The PTP and ASAP analyses confirmed the validity of the new species from a molecular point of view. The new species is morphologically similar to Ramazzottius oberhaeuseri, but is distinguishable by the smooth cuticle, the presence of a “cheek-like” area on the head, and the size of egg processes as well as different sequences of the molecular markers.

Tardigrades can survive harsh environmental conditions, such as drought and low temperature. To withstand freezing, they enter cryobiosis, a state of biological organization in which metabolic activity slows down or comes reversibly to a standstill. Thus, cryobiosis resembles anhydrobiosis, where tardigrades (and a few other invertebrate groups) undergo extreme desiccation and appear not to age in the dry state. The lack of ageing in the anhydrobiotic state, the so-called 'Sleeping Beauty' hypothesis, is assumed also to pertain to cryobiosis, but this has not been investigated. To test this, a group of tardigrades was subjected to sub-zero temperature treatment by alternating weekly periods of freezing at -30 degrees C and feeding at 20 degrees C. The temporarily frozen tardigrades lived twice as long as the control group, but both control and temporarily frozen groups had similar lifespans if the time spent frozen was excluded. This represents the first demonstration that the 'Sleeping Beauty' hypothesis applies to cryobiosis, meaning that tardigrades do not age while frozen.

The integration of morphological data and data from molecular genetic markers is important for examining the taxonomy of meiofaunal animals, especially for eutardigrades, which have a reduced number of morphological characters. This integrative approach has been used more frequently, but several tardigrade taxa lack molecular confirmation. Here, we describe Crenubiotus ruhesteini sp. nov. from the Black Forest (Germany) integratively, with light and electron microscopy and with sequences of four molecular markers (18S, 28S, ITS2, cox1 genes). Molecular genetic markers were also used to confirm the recently described Crenubiotus genus and to establish its phylogenetic position within the Macrobiotoidea (Eutardigrada). The erection of Crenubiotus and its place in the family Richtersiidae are confirmed. Richtersiidae is redescribed as Richtersiusidae fam. nov. because its former name was a junior homonym of a nematode family.

Comparative analyses of life-history theory studies are based on the characteristics of the life cycles of different species. For tardigrades, life-history traits are available only from laboratory cultures, most of which have involved parthenogenetic species. The discovery of a new gonochoristic bisexual Mesobiotus species in a moss collected on the island of Elba (Italy) provides us with the opportunity to describe Mesobiotus joenssoni sp. nov. and to collect data on the life-history traits of cultured specimens to increase our knowledge of the life-history strategies present in tardigrades. This new species is differentiated from all other species of the genus by the presence of granules (~1 µm in diameter) on the dorsal cuticle of the last two body segments, two large bulges (gibbosities) on the hindlegs and long, conical egg processes. The species exhibits sexual dimorphism in body length, with females being longer than males of the same age. The mean lifespan of specimens was 86 days, with a maximum of 150 days. The mean age at first oviposition was 19.8 days and the mean egg hatching time 15.4 days. The life-cycle traits correspond to those collected for the only other two macrobiotid species with gonochoric amphimictic reproduction examined so far.

Mit der Entdeckung des kleinen Wasserbaren durch Johann August Ephraim Goeze 1773 und der ersten taxonomischen Beschreibung von Macrobiotus hufelandi C.A.S. Schultze, 1834 aus der Umgebung von Freiburg im Breisgau beginnt die Wissenschaft von den Tardigraden. Sie sind in ihrer Umwelt haufigen Veranderungen des Mikroklimas ausgesetzt, die ihr Uberleben direkt beeinflussen. So konnen sie lange Zeitraume im Zustand der Kryptobiose uberdauern. Die zugrundeliegenden Mechanismen dafur sind noch weitgehend unklar. Weltweit sind inzwischen etwa 1.200 terrestrische, limnische und marine Arten bekannt; in Deutschland sind es etwa 110 Arten. Fur Baden-Wurttemberg wurde jetzt erstmals eine Artenliste zusammengestellt, die 76 Tardigradenarten in 29 Gattungen umfasst.

Tardigrades may be divided into the following feeding groups: herbivores, carnivores and omnivores. However, little is known about their specific feeding preferences. Here, we used a number of laboratory experiments with 18 potential food sources, representing a wide variety of organisms, to test feeding preferences, survival and fecundity of three tardigrade species, representing different feeding modes. We also tested for differences in preferences between juveniles and adults, and differences in survival between two age groups: one that started the experiment as juveniles and the other as adults. In our experiments, Milnesium inceptum is confirmed to be a carnivore, being able to reproduce only on animal prey. We also show that Hypsibius exemplaris is a herbivore, feeding on cyanobacteria, algae and fungi. Paramacrobiotus fairbanksi, on the other hand, is demonstrated to be an omnivore, feeding on cyanobacteria, algae, fungi and animals. In some cases, juveniles preferred different types of food than adults. Reproduction was strongly affected by food type. Finally, we demonstrate that tardigrades may ingest food types that they are not able to digest. Thus, gut content analysis may be misleading as a method of studying tardigrade feeding habits.

Intra- and interspecific variability, being at the very core of alpha taxonomy, has been a long-standing topic of debate among tardigrade taxonomists. Early studies tended to assume that tardigrades exhibit wide intraspecific variation. However, with more careful morphological studies, especially those incorporating molecular tools that allow for an independent verification of species identifications based on phenotypic traits, we now recognise that ranges of tardigrade intraspecific variability are narrower, and that differences between species may be more subtle than previously assumed. The taxonomic history of the genus Milnesium, and more specifically that of the nominal species, M. tardigradum described by Doyère in 1840, is a good illustration of the evolution of views on intraspecific variability in tardigrades. The assumption of wide intraspecific variability in claw morphology led Marcus (1928) to synonymise two species with different claw configurations, M. alpigenum and M. quadrifidum, with M. tardigradum. Currently claw configuration is recognised as one of the key diagnostic traits in the genus Milnesium, and the two species suppressed by Marcus have recently been suggested to be valid. In this study, we clarify the taxonomic status of M. alpigenum, a species that for nearly a century was considered invalid. We redescribe M. alpigenum, using a population collected from the locus typicus, by the means of integrative taxonomy, i.e. including light microscopy, scanning electron microscopy, ontogenetic observations, and genetic barcoding. Moreover, the redescription of M. alpigenum allowed us to verify the uncertain taxonomic status of two popular laboratory models that were originally considered to be M. tardigradum; though one was recently reidentified as M. cf. alpigenum. Our analysis showed that both laboratory strains, despite being morphologically and morphometrically nearly identical to M. alpigenum, in fact represent a new species, M. inceptum sp. nov.  The two species, being disnguishable only by statistical morphometry and/or DNA sequences, are the first example of pseudocryptic species in tardigrades.

Tardigrades are well known to withstand very low temperatures in the anhydrobiotic state. However, they even tolerate such low temperatures like −196 °C in the fully hydrated state which is then described with the term cryobiosis. Although this extreme subzero temperature tolerance got quite a lot of attention, there is little knowledge regarding their physiological and biochemical adaptations connected to ecological representative subzero temperatures. General studies on cold tolerance have highlighted some strategies including freeze avoidance, rapid cold hardening and freeze tolerance. Although studies on survival rates, cooling rates and ice formation in tardigrades show high interspecific variations in subzero temperature survival, the water bears seem to tolerate ice formation within their bodies and therefore belong to freeze-tolerant organisms. Calorimetric studies also provide evidence for homogenous ice nucleation, indicating that ice formation is not largely affected by ice-nucleating agents. Ability to tolerate low temperatures and freezing even in embryonic developmental stages further increases the adaptive benefit of tardigrades to cope with low-temperature events.

Survival in microhabitats that experience extreme fluctuations in water availability and temperature requires extreme adaptations. Antonie van Leeuwenhoek was the first who describe the phenomenon of the resurrection of a desiccated rotifer in 1702. As with some rotifers and other small organisms, tardigrades enter a desiccated state known as anhydrobiosis to withstand such environmental conditions. This allows them to cope with the temporal variation of available water and to extend their lifespan in an anhydrobiotic state by up to 20 years without biological aging, according to the Sleeping Beauty hypothesis. Heat shock proteins serve as molecular chaperones to preserve or restore protein integrity, and tardigrade-specific intrinsically disordered proteins (TDPs) as well as metabolite help prevent the formation of damaging cellular compartments aggregates during water stress.

A survey is presented about the early history of tardigrade research spanning the time from 1773, when the first description of a tardigrade was published by Goeze, until 1929, when the most comprehensive monographic approach by E. Marcus, unsurpassed today, was published. Almost from the beginning, two topics dominated “tardigradology”, i.e. phylogeny and systematics as well as cryptobiosis, especially anhydrobiosis, but also other issues (e.g. morphology, development and life history) have followed successfully with ongoing technical and preparatory improvements.

Tardigrades are among the most stress tolerant animals and survived even unassisted exposure to space in low earth orbit. Still, the adaptations leading to these unusual physiological features remain unclear. Even the phylogenetic position of this phylum within the Ecdysozoa is unclear. Complete genome sequences might help to address these questions as genomic adaptations can be revealed and phylogenetic reconstructions can be based on new markers. Here, we present a first draft genome of a species from the family Milnesiidae, namely Milnesium tardigradum . We consistently place M. tardigradum and the two previously sequenced Hypsibiidae species, Hypsibius dujardini and Ramazzottius varieornatus , as sister group of the nematodes with the arthropods as outgroup. Based on this placement, we identify a massive gene loss thus far attributed to the nematodes which predates their split from the tardigrades. We provide a comprehensive catalog of protein domain expansions linked to stress response and show that previously identified tardigrade-unique proteins are erratically distributed across the genome of M. tardigradum . We further suggest alternative pathways to cope with high stress levels that are yet unexplored in tardigrades and further promote the phylum Tardigrada as a rich source of stress protection genes and mechanisms.

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 Doyere, 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 degrees C for 30min 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).

In September 2007 tardigrades became the first animal in history to survive the combined effect of exposure to space vacuum, cosmic radiation and ultraviolet radiation in low Earth orbit. The main results from this experiment were reported in 2008, but some of the results have remained unpublished. Here we report that descendant generations of space-exposed tardigrades of the species Milnesium tardigradum did not show reduced performance. This indicates that individual tardigrades that survived the exposure to environmental extremes in space, and were able to reproduce, did not transfer any damage to later generations. Repair of environmentally induced damage may therefore follow a make or break' rule, such that a damaged animal either fails to repair all damage and dies, or repairs damage successfully and leaves no mutations to descendants. We also report that two additional tardigrade species, Echiniscus testudo and Ramazzottius oberhaeuseri, showed high survival after exposure to space vacuum and cosmic radiation within the TARDIS experiment.

In the present study we provide new insights into the mating behaviour of a bisexual tardigrade, Isohypsibius dastychi, revealing a process much more complex than expected. Mating included mutual stimulation that preceded semen ejaculation and egg deposition. If no mating occurred, egg absorption was observed. In addition, the life history and the influence of temperature on development were studied at two temperatures (12 and 20 °C). At both temperatures I. dastychi underwent three moults until adulthood with increasing inter-moult phases from the first to the third moult. As animals maintained at 12 °C became adults significantly later and also were significantly larger than animals at 20 °C, it is unlikely that either age or size determines the transition to adulthood. Generation time of females was significantly shorter than that of males, and both males and females were iteroparous. The consequences of our findings are discussed.

A new species of Tardigrada Doyere, 1840, Echiniscus pardalis n. sp., is described from two moss samples collected in the Parco Naturale delle Alpi Marittime (NW Italy). It belongs to the Echiniscus arctomys species-group, but differs from other 49 known members of the group mainly by the irregularly and distantly scattered deep pores on the plates and by a unique subsurface cuticular pattern on the plates, resembling that of a leopard's fur. The new species is most similar to eight species from the arctomys group: E. barbarae Kaczmarek & Michalczyk, 2002, E. crebraclava Sun, Li & Feng, 2014, E. dearmatus Bartos, 1935, E. mosaicus Grigarick, Schuster & Nelson, 1983, E. nigripustulus Horning, Schuster & Grigarick, 1978, E. nobilis Mihelcic, 1967, E. tardus Mihelcic, 1951 and E. vinculus Horning, Schuster & Grigarick, 1978. The differences between the new species and these eight species are thoroughly discussed. They mainly concern the presence/absence and relative size of shallow dimples surrounding individual tubercles, the relative length of cirrus A, the presence/absence of a spine on the first pair of legs, the presence/absence of a spur on the internal/external claws and the number of teeth on the collar of the hind legs. This paper is the first result published on Tardigrada collected during the European Distributed Institute of Taxonomy's in All Taxa Biodiversity Inventories+Monitoring programme.

A simple method for an underwater pose determination of scuba divers can provide a deeper insight in the biomechanics of scuba diving and thereby improve education and training systems. In this work, we present an inertial sensor-based approach for the pose determination of the upper body and the shank orientation during fin kicks. Accelerometer measurements of gravity and a gyroscope-based method are used to determine absolute body angles in reference to the ground and the angular change of the shanks during fin kicks. The proposed algorithms were evaluated with data acquired from ten divers and a camera-based gold standard. The results were analyzed to a mean error of 0° with a standard deviation of 10° for the upper body pose determination. The absolute angle of the shanks at the turning points between fin kicks was determined with an error of 0° ± 11°, the relative shank angle with an error of 0° ± 8°.

Symsagittifera roscoffensis is a plathelminth living in symbiosis with the green algae Tetraselmis convolutae. Host and symbiont are a model system for the study of endosymbiosis, so far mainly focused on their biochemical interactions. S. roscoffensis is well known for its positive phototaxis that is hypothesized to optimize the symbiont's light perception for photosynthesis. In this study, we conducted a detailed analysis of phototaxis using light sources of different wavelength and brightness by videotracking. Furthermore, we compared the behavioral data with the electron transfer rate of the photosystem from cultured symbiotic cells. The symbiotic algae is adapted to low light conditions showing a positive electron transfer rate (ETR) already at a photosynthetically active radiation (PAR) of 0.112 µmol m−2 s−1 (mol photons per square meter and second), and S. roscoffensis showed a positive phototactic behaviour for light intensities up to 459.17 µmol m−2 s−1 which are not optimal regarding the needs of the symbiotic cells and even may harm host and symbiont. Red light can not be detected by the animals and therefore their eyes seem to be not suitable for measuring the exact photosynthetically active radiation to the benefit of the photosymbionts.