Euglenozoa

The Euglenozoa are a large group of flagellate protozoa. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. There are two main subgroups, the euglenids and kinetoplastids. Euglenozoa are unicellular, mostly around 15-40 µm in size, although some euglenids get up to 500 µm long.

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Most euglenozoa have two flagella, which are inserted parallel to one another in an apical or subapical pocket. In some these are associated with a cytostome or mouth, used to ingest bacteria or other small organisms. This is supported by one of three sets of microtubules that arise from the flagellar bases; the other two support the dorsal and ventral surfaces of the cell.^[2]

Some other euglenozoa feed through the absorption, and many euglenids possess chloroplasts and so obtain energy through photosynthesis. These chloroplasts are surrounded by three membranes and contain chlorophylls a and b, along with other pigments^[1], so are probably derived from a captured green alga. Reproduction occurs exclusively through cell division. During mitosis, the nuclear membrane remains intact, and the spindle microtubules form inside of it.^[2]

The group is characterized by the ultrastructure of the flagella. In addition to the normal supporting microtubules or axoneme, each contains a rod (called paraxonemal), which has a tubular structure in one flagellum and a latticed structure in the other. Based on this, two smaller groups have been included here: the diplonemids and Postgaardi.^[3]

The euglenozoa are generally accepted as monophyletic. They are related to Percolozoa; the two share mitochondria with disc-shaped cristae, which only occurs in a few other groups.^[4] Both probably belong to a larger group of eukaryotes called the excavates.^[5]

References

1. ^ ^{a b} T. Cavalier-Smith (1981). "Eukaryote Kingdoms: Seven or Nine?". BioSystems 14: 461-481.
2. ^ ^{a b} David J. Patterson (1999). "The Diversity of Eukaryotes". American Naturalist 145: S96-S124.
3. ^ Alastair G.B. Simpson (1997). "The Identity and Composition of Euglenozoa". Archiv für Protistenkunde 148: 318-328.
4. ^ Baldauf et al. (2000). "A Kingdom-Level Phylogeny of Eukaryotes Based On Combined Protein Data". Science 290: 972-977.
5. ^ Alastair G. Simpson (2003). "Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)". International Journal of Systematic and Evolutionary Microbiology 53: 1759-1777.