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Marine tardigrades in the Antarctic and sub-Antarctic regions are poorly understood. During the 59th Japan Antarctic Research Expedition, a sediment sample was collected from Lützow-Holm Bay, East Antarctica. The sediment sample yielded three species of marine tardigrades belonging to the family Styraconyxidae Kristensen & Renaud-Mornant, 1983: Angursa antarctica Villora-Moreno, 1998, Styraconyx cf. qivitoq Kristensen & Higgins, 1984, and S. takeshii sp. nov. The new species resembles S. nanoqsunguak Kristensen & Higgins, 1984 by the overall morphology, but the new species has thick seminal receptacle ducts that do not terminate in typical, swelled vesicles, in contrast to S. nanoqsunguak's narrow seminal receptacle ducts that terminate in small vesicles. The presence of the undivided mouth papilla and the larger body further differentiates the new species from S. nanoqsunguak. We also report a young adult female with a gonopore, but lacking seminal receptacles in the new species. As well as morphological information, we provided the sequences of the new species' nuclear 28S rRNA and mitochondrial cytochrome c oxidase subunit I fragments. Using the former molecular data, phylogenetic analyses of Styraconyxidae were conducted and polyphyly of Styraconyx was suggested. The biogeography of marine tardigrades in the Antarctic and sub-Antarctic regions are also discussed. [ABSTRACT FROM AUTHOR]

Reproductive output is one of the central attributes of life history, and knowledge of age-specific reproduction can enhance the understanding of population performance and dynamics. Tardigrades are microscopic invertebrates that live in marine, freshwater and terrestrial ecosystems. While changes in fertility in relation to age are known to occur in other invertebrate groups, the subject has not been specifically addressed in tardigrades. The current study demonstrates for the first time the effect of lifespan and age on reproductive characteristics of the tardigrade species, Acutuncus antarcticus (Richters 1904), based on the observation of individuals over their entire lifespan under constant environment conditions in the laboratory. Clutch size of A. antarcticus fluctuated conspicuously throughout individual lifespans. Weak effects of age were observed on oviposition interval and hatching success, with the former increasing slightly and the latter decreasing slightly with age. Numbers of oviposition events and eggs produced per individual varied greatly and were correlated with lifespan. No significant relationships between clutch size, hatching time or hatching success with lifespan were detected. The majority of the individuals continued oviposition until shortly before death, with no suggestion of a post-reproductive lifespan. Our observations suggest that any decline in fertility with age in this species of tardigrade is minimal. The study provides new insight into the reproductive biology and ageing of invertebrate species. [ABSTRACT FROM AUTHOR]

Tardigrades are found in most terrestrial and freshwater Antarctic ecosystems and are one of the most diverse and important groups of invertebrates in Antarctica. We developed a new laboratory system for rearing the Antarctic tardigrade Acutuncus antarcticus (Richters 1904), one of the most widespread and common Antarctic tardigrade species. To provide a description of the life history of this tardigrade, survival and reproduction of 68 individuals were observed and recorded daily at a constant temperature of 15 °C. The life-history data obtained are consistent with previous studies of other tardigrades. The exceptionally high hatching success obtained is suggested to be an important life-history characteristic of this species contributing to it often being a common and dominant species in the Antarctic habitats in which it occurs. Furthermore, high hatching success combined with very low variation in development time, under the protocol used in the current study, indicates that A. antarcticus may be a good model species for studies in developmental biology. Integrating data from this and previous studies, the importance of temperature on reproduction and growth in A. antarcticus was inferred. With terrestrial and freshwater ecosystems in some parts of Antarctica experiencing sometimes drastic contemporary climatic and environmental changes, studies of the effect of temperature on generation time and reproductive success in Antarctic tardigrades are urgently required, as these animals are important elements of community structure and function in polar ecosystems. [ABSTRACT FROM AUTHOR]

Tardigrades are important members of the simple terrestrial ecosystems in the extreme environments in Antarctica. This study provides a baseline description of tardigrade species diversity and distribution pattern within the terrestrial and lake environments of the coastal regions around Syowa Station and the neighbouring inland Sør Rondane Mountains, Dronning Maud Land. We combined data obtained from new and previously described collections and updated data available in the existing literature. We recorded five tardigrade species, three of which ( Echiniscus pseudowendti Dastych , Hebesuncus ryani Dastych and Harris , Pseudechiniscus sp.) have not previously been reported from the area, increasing the total recorded tardigrade diversity for this region of continental Antarctica to ten species. The results of our study indicate that tardigrades have been and are major components of the lake environment community in continental Antarctica, with Acutuncus antarcticus (Richters 1904) the most common and dominant species. Our data confirm that the tardigrade species diversity in the vicinity of Syowa Station is very low and suggest potential relationships between individual tardigrade species and terrestrial moss species and depth in freshwater ecosystems. [ABSTRACT FROM AUTHOR]