Of all the six eukaryote supergroups, four are exclusively composed of unicellular organisms. Unicellular organisms vary in size, with the smallest bacteria measuring only a third of a micron (300 nanometers) across, ranging up to the titanic plasmodial slime molds, which can grow to 20 cm (8 in) across. The largest unicellular organisms may have millions of nuclei scattered throughout the cellular envelope. To observe some of the smallest unicellular organisms requires an electron microscope, while the very largest can be seen with a microscope or anything that enhances images.