 Encephalitozoan species have evolved to become obligate intracellular parasites, leading to a dramatic reduction in size of their genomes. These genomes are characterized by a high degree of gene density, lack of entrance, and extensive use of repetitive sequences. Additionally, they contain a number of genes related to teloma maintenance, epigenetic regulation, and heterochromate information. This article was authored by and Caroline Moscoranius dos Santos, Alexander Thomas Julian, Ping Dong Liang, and others.