When dealing with this process, stem eukaryotic groups must be differentiated from proper crown eukaryotic groups. Stem eukaryotic groups would have appeared during the long process of acquisition of the eukaryotic traits but went extinct. The problematic then arises for the identification of the first, given that taphonomic loss and inaccuracy of molecular clocks[4] has led to huge phylogenetic gap comprising the intermediate states that would conform the stem eukaryotes.