Not all free-living microorganisms have cosmopolitan distributions -: the case of Nebela (Apodera) vas Certes (Protozoa: Amoebozoa: Arcellinida)

Aim To review and critically assess the evidence that the testate amoeba species Nebela vas does not have a cosmopolitan distribution, in contradiction to the paradigm of microbial distribution that 'everything is everywhere'. Location Terrestrial and wetland habitats world-wide. Methods Relevant data were assembled on the morphology, ecology and global geographical distribution of N. vas from a comprehensive literature review of published original records. The data were collated, analysed and summarized. The roles of long-term and short-term agents of dispersal are discussed. Results A clear and repeated pattern has been elucidated of a microbial species, with a distinctive and unmistakeable morphology, that inhabits acid, damp terrestrial and wetland habitats in the southern cool-temperate and sub-Antarctic zones - including similar high-altitude habitats in the Tropics. It is almost entirely confined to the Gondwanaland continents and Southern Hemisphere islands. It is definitively absent from Holarctic regions. It is proposed that the continental distribution of N. vas is a consequence of continental drift following its original speciation in the Mesozoic or earlier, whereas its distribution on sub-Antarctic islands (glaciated in the Pleistocene) has been effected by dispersal from South America by wind around the Southern Ocean. Main conclusion Nebela vas is a proven instance of a microbial species that does not have a cosmopolitan distribution.