Most prokaryotic organisms are composed of a single cell, although some form simple filaments or live in colonies. A few types of bacterium, notably some cyanobacteria, differentiate to form several distinct cell types. No bacteria, however, develop macroscopic bodies with functionally differentiated tissues. Only eukaryotes have evolved those. Simple multicellular organisms, composed of multiple similar cells, occur widely within the eukaryotic tree of life, and a few of these evolved into complex multi-