Some tardigrades have great migratory capacities, and eu-tardigrade species such as Macrobiotus hufelandi and Milnesium tardigradum may be true cosmopolitan species. The eggs of Macrobiotus species have been found in air-plankton collected by airplanes at several thousand feet. In Greenland, hetero-tardigrades have been found in rainwater samples after the powerful foehn storms. It is known that Echiniscus testudo is capable of migrating with the winds from one continent to another in its anhydrobiotic stage. However, the species has never been found in Australia, so it is not a true cosmopolitan. Dispersal in marine tardigrades is lesser known, but the tidal tardigrade, Echiniscoides sigismundi, may spread with the empty exuvia of the barnacles inside of which it lives. More than a hundred eggs of this tardigrade were found on one ex-uvium from the barnacle, Semibalanus balanoides. Ships may also help to disperse marine tardigrades. One example is the subspecies of Echiniscoides sigismundi in Australia. Along the coast of eastern Australia and in the Coral Sea, the subspecies Echiniscoides sigismundi polynesiensis is found, but in Nielsen Park in Sidney Harbor, the nominate form (Echiniscoides sigis-mundi sigismundi) was found on barnacles. The nominate form was described from Northern Europe and the subspecies, E. sigismundi polynesiensis, from the island of Tiahura in the Pacific Ocean. The only explanation for the presence of the nominate form in Sidney Harbor must be that ships from Europe have carried it from Europe to Australia.
Many species of tardigrades are not cosmopolitan. Species found in hot or warm springs may be endemic. The meso-tardigrade, Thermozodium esakii, discovered in a hot sulfur spring in Nagasaki, was only found on one occasion, and may be extinct now. The very aberrant eutardigrade, Eohypsibius nadjae, was described from a cold mud volcano from west Greenland. Later, it was found in cold springs in the Faroe Islands and in the northern part of Italy. This unique species may be an Arctic relict that survived in cold springs. Several genera of Heterotardigrada show the old Gondwana (South America, Southern Africa, India, Antarctica, Australia, and New Zealand) distribution.
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