The narrowing prokaryote-eukaryote divide reveals a complexity spectrum.

Cellular organisms can be divided into two basic types of cells: the prokaryotic cells of Bacteria and Archaea and the eukaryotic cells. The rapidly expanding knowledge of the diversity and ultrastructure of prokaryotic cells has revealed cellular intricacies that warrant a critical reappraisal of the profundity of the prokaryote-eukaryote divide.