On the geographic distribution, of Loxodes rex (Protozoa, Ciliophora) and other alleged endemic species of ciliates

There is no consensus on the question of whether or not free-living protist species have biogeographies, with the strongest disagreement coming from a dvocates of the hypothesis that the extraordinary abundance of protists dri ves their ubiquitous dispersal. If the probability of a species being ubiqu itous is a function of its absolute global abundance, then the species that are least likely to be ubiquitous are those with relatively small global p opulations, i.e. the largest species. Among the free-living ciliated protoz oa, a prime candidate for such an organism must be the large (similar to 12 00 mum long), unmistakable, fragile, non-encysting karyorelictid Loxodes re x. This ciliate was known only from fresh waters in tropical Africa and it was long considered to be a rare example of an endemic ciliate. Here it is reported that Loxodes rex is thriving in a pond in Thailand. The status of other alleged endemic ciliate species is discussed.