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Two Euglena.jpg
Two Euglena
Scientific classification
Domain: Eukarya
Kingdom: Excavata
Phylum: Euglenozoa
Cavalier-Smith, 1981[1]
Classes and unplaced genera


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.[2]


The two main sub-groups of micro-organisms classified to be Excavata-Euglenozoa as listed above are incorrect. The two correct sub-groups as should be are: euglenoids and kinetoplasmids. Take note that euglenoids and euglenids are different. 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.[3]

Some other euglenozoa feed through 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, 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.[3]

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.[4]


The euglenozoa are generally accepted as monophyletic. They are related to Percolozoa; the two share mitochondria with disk-shaped cristae, which only occurs in a few other groups.[5] Both probably belong to a larger group of eukaryotes called the excavates.[6] This grouping, though, has been challenged.[7]


  1. ^ T. Cavalier-Smith (1981). "Eukaryote Kingdoms: Seven or Nine?". BioSystems 14 (3–4): 461–481. doi:10.1016/0303-2647(81)90050-2. PMID 7337818. 
  2. ^ "Euglenozoa". Retrieved 21 May 2013. 
  3. ^ a b David J. Patterson (1999). "The Diversity of Eukaryotes". American Naturalist 154 (S4): S96–S124. doi:10.1086/303287. PMID 10527921. 
  4. ^ Alastair G.B. Simpson (1997). "The Identity and Composition of Euglenozoa". Archiv für Protistenkunde 148: 318–328. doi:10.1016/s0003-9365(97)80012-7. 
  5. ^ Baldauf, S. L.; Roger, A. J.; Wenk-Siefert, I.; Doolittle, W. Ford (2000). "A Kingdom-Level Phylogeny of Eukaryotes Based on Combined Protein Data". Science 290 (5493): 972–977. doi:10.1126/science.290.5493.972. PMID 11062127.  edit
  6. ^ Alastair G. Simpson (2003). "Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)". International Journal of Systematic and Evolutionary Microbiology 53 (Pt 6): 1759–1777. doi:10.1099/ijs.0.02578-0. PMID 14657103. 
  7. ^ Cavalier-Smith T (December 2009). "Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree". Biol Lett 6 (3): 342–5. doi:10.1098/rsbl.2009.0948. PMC 2880060. PMID 20031978. 

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