Here are 20 examples of unicellular organisms:

1. Amoeba: A type of protozoan that moves by extending its pseudopodia 
2. Euglena: A type of flagellated protozoan that is photosynthetic and can also feed heterotrophically .
3. Paramecium: A type of ciliate protozoan that is covered in cilia and feeds on bacteria and other small organisms.
4. Plasmodium: A type of parasitic protozoan that causes malaria in humans .
5. Salmonella: A type of bacteria that can cause food poisoning in humans.
6. Protozoans: A diverse group of unicellular eukaryotic organisms that include amoebas, ciliates, and flagellates.
7. Fungi: Some fungi, such as yeasts, are unicellular.
8. Algae: Some types of algae, such as diatoms and dinoflagellates, are unicellular.
9. Bacteria: Most bacteria are unicellular and are classified into two main groups: gram-positive and gram-negative bacteria.
10. Archaea: Archaea are unicellular prokaryotic organisms that are found in extreme environments such as hot springs and deep-sea hydrothermal vents.
11. Cyanobacteria: Cyanobacteria are photosynthetic bacteria that can be unicellular or form colonies 
12. Heliozoa: Heliozoa are a type of protozoan that have radiating pseudopodia and are found in freshwater and marine environments 
13. Radiolarians: Radiolarians are a type of protozoan that have intricate mineral skeletons and are found in marine environments 
14. Diatoms: Diatoms are a type of unicellular algae that have intricate silica shells and are found in freshwater and marine environments 
15. Foraminifera: Foraminifera are a type of protozoan that have intricate calcium carbonate shells and are found in marine environments 
16. Dinoflagellates: Dinoflagellates are a type of unicellular algae that have two flagella and can be photosynthetic or heterotrophic 
17. Ciliates: Ciliates are a type of protozoan that have hair-like cilia for movement and feeding 
18. Yeast: Yeast is a type of fungus that is used in baking, brewing, and winemaking 
19. Mycoplasma: Mycoplasma is a type of bacteria that lacks a cell wall and can cause respiratory infections in humans .
20. Chlamydia trachomatis: Chlamydia trachomatis is a type of bacteria that can cause sexually transmitted infections in humans .