Answer:
The Simplest of Eukaryotic Cells. Microsporidia are intracellular parasites that infect most other eukaryotic cells, although arthropods are the most commonly parasitized. They are the simplest and smallest eukaryotic cells and thus represent a textbook example of reductive evolution [1].
Link: https://designmatrix.wordpress.com/2009/03/10/the-simplest-of-eukaryotic-cells/
