Introduction to the Basal Eukaryotes

A number of eukaryote lineages that branched very early in eukaryote evolution are still extant today. Most of them have no fossil record at all. However, studying these protists is important for what it can tell us about the earliest steps in eukaryote evolution. These primitive eukaryotes are also important in medicine and veterinary science: some cause human and animal diseases such as giardia (hikers' diarrhea) and trypanosomiasis (African sleeping sickness). Yet others live in symbiotic relationships with other organisms: the flagellate Streblomastix shown above lives in the intestines of termites, and it and several other protists assist in the digestion of wood.

The relationships among these protists were not clear until the advent of techniques such as electron microscopy and DNA sequencing. A picture of the "family tree" of the early eukaryote lineages is just beginning to arise. For now, we will simply list some of the important groups of basal protists, and provide sources of additional information on the Internet.

For more information:
Visit the Tree of Life for more information about the relationships among the basal eukaryotes.

Or visit Cells Alive! for information about parasitic microbes.

Source: Margulis, L., Corliss, J.O., Melkonian, M. and Chapman, D.J. (eds.) 1991. Handbook of Protictista. Jones and Bartlett, Boston.

This photograph of Streblomastix was provided by Erol Kepkep.