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The early evolution of eukaryotes has remained a realm of mystery and surprise. The qualitative leap from the prokaryotes to cells, that bear complex and dynamic compartments, is still one of the hardest nuts to be cracked for evolutionary theory. The concept of " symbiogenesis " , postulated by Mereshkowski at the beginning of the last century and much later solidified through molecular evidence by Margulis emerged as central concept to understand, how qualitative and complex traits could be acquired by endosymbiosis. However, Mereshkowski and Margulis left as a burden to evolutionary biology the insight that the conventional model of phylogenetic trees has to be replaced by more reticulate concepts of descendence. This working program is still far from being completed—we have got only glimpses into the complexity of early eukaryotic life. Since the underlying mechanism, endosymbiosis, is cellular, the approach to distangle this complexity must be cell biological in the first place—this remains valid even in the age of molecular genetics. This means that we need ultrastructural research to understand the early evolution of eukaryotes. Three contributions in the current issue perpetuate a long history of this journal on ultra-structural insights on early eukaryotes. Diatoms are curious creatures that seem to lack flagellae. However, they have meanwhile been assigned to the heterokont Chromista, a group that is characterized by two flagella of different length and comprises quite diverse life forms such as Brown Algae or Oomycetes. The work by Idei et al. (2013) in the current issue investigates the ultrastructure of the flagellum for the sperm of the diatoms Thalassiosira lacustris and Melosira moniliformis, based on high-quality serial sections using conventional chemical fixation and contrasting. They show that the sperms are uniflagellate, with no trace of a second basal body (unexpected for heterokonts) and carry an axoneme with a 9+0 microtubule configuration, and a basal body with only a doublet structure. They report further exotic features of the microtubular cytoskeleton in these di-atoms, and also specific differences between the two taxa that complement classical studies on the cytoskeleton in the heterokont Chromista (Hardham 1987, Andersen 1991). Eukaryotic cells arose from endosymbiotic events of bacteria that were later transformed into mitochondria and plas-tids. The Rickettsiales are bacteria that are obligate endo-symbionts and have attracted considerable interest as closest recent relatives of mitochondria, but also as clinically relevant pathogens. The work by Kawafune et al. (2013) in the current issue reports …

You need to see what you want to understand—ultrastructure helps to uncover the mysteries of early life