Sulfolobus acidocaldarius, Escherichia coli, Methanococcus jannaschii, Pyrolobus fumarii and Euglena haematodes are some names of unicellular organisms. The names represent the genus and species. The domains are at the top of biological taxonomy. Single-celled creatures fall into all three domains: Eukaryota, Eubacteria and Archaea.
The Archaea were discovered in the early 1970s. They are single-celled prokaryotes, as are bacteria. DNA testing shows the two groups are unique, but share a common ancestor. Scientists believe the Archaea are more closely related to Eukaryota, to which humans belong, than they are to bacteria. Archaea exist in the most severe environments on earth. They thrive near volcanoes, in hot springs, in salty seas, in sewage and in the extreme cold of the ocean floor.
Another interesting group of unicellular organisms is Euglena. They produce chlorophyll from sunlight like other algae. However, if the sunlight is too bright, they move to more appropriate lower light areas. They can shift their food source from chlorophyll to obtaining nutrients from the water if they do not have enough light for photosynthesis. Amoeba can chase food down by the use of pseudopods, artificial feet that form in their cellular membrane.
The diversity and sheer numbers of unicellular organisms ensure their place in scientific research.