Euglenozoa
| Euglenozoa | |
|---|---|
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| Two Euglena | |
| Scientific classification | |
| Domain: | Eukarya |
| Kingdom: | Excavata |
| Phylum: | Euglenozoa Cavalier-Smith, 1981[1] |
| Classes and unplaced genera | |
| Synonyms | |
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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]
Structure[edit]
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]
Classification[edit]
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]
References[edit]
- ^ 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.
- ^ "Euglenozoa". Retrieved 21 May 2013.
- ^ a b David J. Patterson (1999). "The Diversity of Eukaryotes". American Naturalist 154 (S4): S96–S124. doi:10.1086/303287. PMID 10527921.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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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