Evolutionary terrestrialization scenarios for soil invertebrates

DNA-based phylogenetic reconstructions provide insight into the terrestrialization of soil invertebrate lineages and a test of Ghilarov's hypothesis. Some metazoan lineages have conquered the land through a single terrestrialization event, other have made the transitions between marine, freshwater and soil habitats many times. Major terrestrializations happened early in the Paleozic and came with new body plans and new classes of animals; minor terrestrializations happened later and did not change the body plan much. Freshwater, intertidal and cavernicolous stages in between the marine environment and the soil are proposed for different lineages of soil invertebrates. Nematodes, amphipods and potworms show marine regressions but in tardigrade, hexapod, chelicerate and myriapod lineages hardly ever a species returned to the marine environment after terrestrialization.