Micrometazoans are animals smaller than 2 mm. Their biogeography is poorly understood, and tardigrades provide a tractable phylum for exploring distribution patterns at a variety of scales. Polylepis forest habitat offers considerable advantages for making tardigrade comparisons across a wide range of scales in the Andes. This thesis aims to improve identifications of tardigrades with a character matrix approach, to assess the relative importance of habitat and bryophyte host on tardigrades, to describe the fine-scale spatial structure of tardigrade assemblages, and to estimate the sampling effort required for a reliable estimate of tardigrade diversity within Polylepis forest. Samples of bryophytes and lichens were collected from Polylepis forest and neighbouring habitats, and the tardigrades extracted and identified, mostly to operational taxonomic units. Some new species were discovered during the course of this work; one is described here. Abundance, diversity and composition of tardigrade samples were compared quantitatively. The thesis presents the first example of a character matrix for a tardigrade genus, bringing together information for the genus Isohypsibius from many different sources and describing suites of characters for each species. It will facilitate identification within the genus in future. Tardigrade assemblage data were highly variable within the samples, with empty samples dominating one study. Analysis of one forest site indicated that at least 50 samples would be needed to characterise the tardigrade diversity there. Although both were important, habitat-scale effects were more influential on tardigrade abundance, diversity and composition than host-scale effects. In both cases, microenvironmental and resource filters are the likely mechanisms driving these differences. Based on the results, recommendations are made for expanding such research into broader geographical scales: standardising sample volume, replicate sampling across hosts on the forest floor, recognising the importance of habitat-scale effects when selecting study sites, and the development of character matrices for tardigrade genera.

Tardigrades are microscopic aquatic invertebrates that are known for their ability to survive extreme conditions. Different species of tardigrades tolerate extreme conditions to a varying degree. It has been suggested that limnic tardigrades would have a lower tolerance to desiccation compared to limno-terrestrial tardigrades. In this study limno-terrestrial species Ramazzottius oberhaeuseri and the limnic species Hypsibius dujardini is compared in regard to their tolerance to desiccation and freezing. The results show that there indeed is a difference in the tolerance and that Ramazzottius oberhaeuseri show better tolerance.

A seasonal survey of the distribution of terrestrial tardigrades on Dugger Mountain, Alabama, was conducted during the time period from April 1997 through April 1998. Cryptogams from five trees (Quercus alba), three on north-facing slopes and two on south-facing slopes, were sampled seasonally at three stations (645 m, 410 m, 183 m) along an unnamed tributary of the South Fork of Terrapin Creek. Trees were chosen based on their location outside the riparian zone. Tardigrades were extracted from the samples, mounted individually in Hoyer's medium, and identified to species with phase microscopy. Seasonal and altitudinal variations in the distribution of the populations on the north- and south-facing slopes were determined. Present on Dugger Mountain were tardigrades belonging to 12 species (Macrobiotus cf. areolatus/tonollii, Macrobiotus cf. echinogenitus, Macrobiotus islandicus, Macrobiotus richtersi, Minibiotus intermedius, Milnesium tardigradum, Diphascon pingue, Hypsibius pallidus, Echiniscus cf. arctomys. Echiniscus virginicus, Pseudechiniscus ramazzottii, and Pseudechiniscus suillus). Due to the small numbers of individuals of each species, the total numbers of tardigrades of all species were pooled. There were no significant differences in the mean number of species or the mean number of all tardigrades per sample at each station (altitude). However, seasonal differences in both abundance and number of species were detected in pooled samples due to the high numbers collected in spring 1997.

At Huntington Beach, SC meiofauna distribution was investigated. The purpose of the study was to determine tardigrade species present and any significant differences in the distribution pattern. Meiofauna were analyzed to determine if there were significant differences in their distribution patterns in relation to abiotic variables. Cores were taken in the intertidal zone along three elevations. Each core was divided into depth samples and was processed to remove meiofauna. Each taxon (>1500 specimens) and tardigrades was statistically analyzed using three-way ANOVA to compare distribution patterns. There were eighteen taxa identified and an estimated 330,338 specimens. The seven dominant taxa were Nematoda, Copepoda, Oligochaeta, Mystacocarida, Sarcomastigophora, Halacaroidea, and Turbellaria. The community and each taxon demonstrated one or more significant differences in their distribution pattern. Tardigrada had 326 specimens collected and 300 identified to species in five genera. Elevation was a source of significant variation for tardigrades.

Although many estimates of species numbers have been attempted using various techniques, many smaller phyla remain poorly known without such estimates. For most of these it is unclear if they are species-poor or just poorly studied. The phylum Tardigrada is one of these phyla. Specialists have created a regularly updated checklist for the known tardigrade species, which as of 15 July 2013 listed 1190 taxa (species and subspecies). Of these, 1008 are limnoterrestrial and 182 are marine. These were the most up-to-date data at the time of our analysis. As species accumulation curves show little sign of levelling out, they do not provide a useful tool for estimating global tardigrade diversity from existing species numbers. A new technique has recently been developed that uses the more complete knowledge of higher taxonomic levels to estimate the asymptotic number of species. We applied this technique to limnoterrestrial and marine tardigrades. We estimate that the global total for limnoterrestrial tardigrades is 1145 (upper 95% CI = 2101), and the global total for marine tardigrades is 936 (upper 95% CI = 1803). This yields 87% completeness for our knowledge of limnoterrestrial tardigrades, and only 19% completeness for our knowledge of marine tardigrades. Thus, although many more marine species remain to be discovered, it appears that tardigrades are both poorly studied and relatively species poor.

Samples of moss, lichens, liverworts and leaf litter collected in the Lower and Upper Peninsulas of the state of Michigan, USA, contained 28 species of water bears (phylum Tardigrada). Eighteen species were considered cosmopolitan, widely distributed in several biogeographical regions. One species, Minibiotus jonesorum sp. n., is described and illustrated. This new species is characterized by having ten transverse bands of polygonal pores that increase in size from anterior to posterior, three macroplacoids that increase in size from anterior to posterior and by lacking a microplacoid or leg granulation. The medial and posterior pores of M. jonesorum sp. n. are polygonal and much larger than the trefoil pores of M. furcatus, the most similar species in the genus.

STORAGE CELLS AND THEIR ROLE IN TARDIGRADE PHYSIOLOGY Abstract Tardigrades possess remarkable tolerance to numerous stress conditions (e.g. almost complete desiccation, exposure to very low sub-zero temperature, heat stress and even exposure to space in low Earth orbit). Indeed, they are among the most radiation-resistant multi-cellular organisms. The body cavity of tardigrades is filled with the storage cells (SC). Their role in anhydrobiosis has been discussed. The main objectives of this work were to analyse (i) the occurrence of mitosis in SC, (ii) the factors constraining anhydrobiotic survival, and (iii) the general ultrastructure of SC and their ultrastructure concerning the stress conditions. Our model species, R. cf. coronifer is one of the most extensively studied tardigrades concerning anhydrobiosis. Comprehensive histochemical techniques were used in combination with SEM, TEM, and confocal microscopy. First, mitotic divisions of tardigrade SC occur with a higher frequency in juveniles than in adults and correlate with animal growth. Mitosis is more frequent in moulting tardigrades, but the overall mitotic index is low. Furthermore, tardigrades of R. cf. coronifer can survive the maximum of 6 repeated desiccation cycles with significantly declining survival rate with repeated desiccations and...