ABSTRACT
Phylogenetic inferences based on hundreds of genes and taxa have helped in defining the main eukaryotic groups and their respective evolutionary paths. Much debated is the position of the root of the tree of eukaryotic life, essentially because it points to the last common ancestor and to the origin and evolution of the eukaryotic cell. The study of soil protists largely depended on cultivation-based techniques, with their known limitations and biases. The advent of molecular environmental sampling opened a new era for soil protists, but their study lags far behind their marine and freshwater counterparts. Identification of soil protists is more difficult than that of their marine counterparts, principally because the reference molecular databases are biased towards marine species. The diversity of protists in the environment seems to exceed that of multicellular organisms. The complex interactions of the soil food web, with or without the structuring effect of plant roots, offer an exciting field of almost untapped investigations.
