Excavate protists include free-living and parasitic species, from both aerobic and anaerobic habitats. The parasites include Naegleria fowleri (Heterolobosea), causative agent of a rare but deadly form of human amebic encephalitis, Giardia species (Diplomonadida), responsible for the gastrointestinal complaint giardiasis, and several metamonad species that cause, or are associated with, various illnesses in animals.

The excavates may be among the most ancient of living eukaryotes. The jakobids, especially Reclinomonas americana, have the most eubacterial-like mitochondrial genomes of any eukaryotes that have been studied, while metamonads such as Giardia lack many of the cell structures ("organelles"), including mitochondria, that are considered typical for eukaryotic cells. The species (or species complex) variously known as Giardia lamblia, G. intestinalis, and G. duodenalis, is commonly used as a model system for primitive eukaryotic cell structure and function, and it is the subject of a nuclear genome sequencing project. 

The taxonomy and diversity of this group is still imperfectly understood. For example, the jakobids were first recognized as a group in 1993 (O'Kelly 1993), the malawimonads in 1999 (O'Kelly and Nerad 1999). Species from anaerobic habitats, and those endocommensal or parasitic in organisms other than humans, their pets, and their livestock, are poorly known. Even for known species, the diagnostic features may be obscure, or may be found only in out-of-the-way books and journals, or may be difficult to interpret.

This site attempts to provide up-to-date information on the excavates, with a focus on ongoing research on excavate diversity in the author's laboratory. As an online monograph, it is intended to show what the most recent research has discovered on the morphology, taxonomy, habitat, distribution and evolutionary history of these potentially most ancient of the living eukaryotes, and present this information as a resource for persons interested in, or working on members of, this assemblage.

Excavates Online copyright © 2000 by Charles J. O'Kelly. Distribution for noncommercial purposes permitted so long as this copyright notice is included and acknowledgement is made. Modifications, and commercial use of the site or any part thereof, not permitted without the written consent of the author.

Excavates Online is part of the Molecular Evolution and Organelle Genomics program at the University of Montreal, and is funded in part by a grant (9904444) from the US National Science Foundation.