Future directions
Future research on Milnesium should concentrate on the Nearctic realm to verify whether taxa from this region are mixed with the species currently known only from the Palaearctic, within clades A and B, or whether they constitute their own, separate clade(s). Given that the Nearctic and the Palaearctic have only limited connection through the Bering strait, but they share the same climate types, mixed clades would support the EiE hypothesis. If, however, Nearctic and Palaearctic species form separate clades, then this would further strengthen the evidence that Milnesium species generally exhibit limited natural dispersal abilities. Furthermore, in order to uncover the early evolution of the genus Milnesium , sampling ought to focus in Antarctica, Australia and New Zealand, as the areas in the Southern Hemisphere seem to encompass the most basal lineages and are likely to help us understand the effect of the Gondwana breakdown on the early diversification of Milnesium .
Crucially, the remaining milnesiid genera need to be included in a phylogenetic framework to date the diversification events within this group more reliably. Moreover, as the basal part of the tree is characterised by shallow branching, which does not allow for resolving the phylogenetic relationships between the major clades, new molecular markers or entire genomes should be analysed. Furthermore, the verification of the mutation rates for other groups of tardigrades could provide important enhancement to the molecular clock analysis, and help us better understand the evolution of this phylum. Last but not least, a greater taxonomic effort should be made to describe the apparently overwhelming number of putative new species in the genusMilnesium , without neglecting the need to integratively redescribe the number of classically delineated species.