This summer I’ve been taking a Biology class at my community college, and I learned a Thing™.
Halobacteria
PD image by NASA via Wikimedia Commons
Organisms as we typically think of them are classified into two domains: Bacteria and Eukarya. There’s also a third domain–Archaea–but you probably wouldn’t know any of those guys unless you have microscopic vision and hang out in extreme environments like deep-ocean vents, or spend a lot of time looking into your own navel.
Either scenario presents its own special danger.
Domain Bacteria contains microorganisms such as germs and cooties. They are prokaryotes, with cells that lack the nuclei and organelles found in more complex organisms.
Long ago, 
Writer-blogger friend 
Mike Schulenberg 