Taxonomy and biogeography of marine Tardigrada

Tardigrada or water bears are a monophyletic taxon whose species are all microscopically small with body sizes ranging from less than 100 µm (0.1 mm) to a few hundred micrometres. Systematically, they represent a subgroup of the Panarthropoda, and are therefore phylogenetically related to the Arthropoda (arthropods) and the Onychophora (velvet worms).

Tardigrades colonize all habitats in which a sufficient film of water is available at least temporarily. The limno-terrestrial species from the taxon Eutardigrada are particularly well known and can be found in a wide variety of limnic habitats, but also live in terrestrial moss cushions, for example. If these biotopes dry out, Eutardigrada can form what is known as “tun state” in which all metabolic processes are virtually “frozen” due to anhydrobiosis. This enables the animals to survive unfavourable and hostile environmental conditions, such as prolonged drought or extreme cold. The taxon Heterotardigrada mainly comprises marine species and these can be found from tidal beaches down to the deep sea. Compared to the more accessible limno-terrestrial tardigrades, the Heterotardigrada are still less well studied. In particular, very little is known about the biodiversity, ecology, bathymetric distribution and biogeography of species from the deep sea, seamounts and the shelf of oceanic islands. In the current project, which is funded by the Deutsche Bundesstiftung Umwelt (DBU) and the German Academic Exchange Service (DAAD), among others, extensive sample material from various expeditions is being analysed in order to expand our knowledge of these little-studied seafloor dwellers.