Euglenozoa Explained

Euglenozoa are a large group of flagellate Discoba. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. Euglenozoa are represented by four major groups, i.e., Kinetoplastea, Diplonemea, Euglenida, and Symbiontida. Euglenozoa are unicellular, mostly around NaNμm in size, although some euglenids get up to 500μm long.[1]

Structure

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 absorption, and many euglenids possess chloroplasts, the only eukaryotes outside Diaphoretickes to do so without performing kleptoplasty,[3] 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 green alga, captured long ago in an endosymbiosis by a basal euglenozoan. 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.[4]

Classification

Historically, euglenozoans have been treated as either plants or animals, depending on whether they belong to largely photosynthetic groups or not. Hence they have names based on either the International Code of Nomenclature for algae, fungi, and plants (ICNafp) or the International Code of Zoological Nomenclature (ICZN). For example, one family has the name Euglenaceae under the ICNafp and the name Euglenidae under the ICZN. As another example, the genus name Dinema is acceptable under the ICZN, but illegitimate under the ICNafp, as it is a later homonym of an orchid genus, so that the synonym Dinematomonas must be used instead.

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 Excavata.[6] This grouping, though, has been challenged.[7]

Phylogeny

The phylogeny based on the work of Cavalier-Smith (2016):[8]

A consensus phylogeny following the review by Kostygov et al. (2021):[9]

Taxonomy

Cavalier-Smith (2016/2017)

The following classification of Euglenozoa is as described by Cavalier-Smith in 2016, modified to include the new subphylum Plicomonada according to Cavalier-Smith et al (2017).[10]

Phylum Euglenozoa Cavalier-Smith 1981 emend. Simpson 1997 [Euglenobionta]

Kostygov et al. (2021)

Phylum Euglenozoa Cavalier-Smith 1981 emend. Simpson 1997[9]

External links

Notes and References

  1. Web site: Euglenozoa . Encyclopedia of Life . National Museum of Natural History - Smithsonian Institution . 16 January 2020.
  2. Patterson DJ . The Diversity of Eukaryotes . The American Naturalist . 154 . S4 . S96–S124 . October 1999 . 10527921 . 10.1086/303287 . 4367158 .
  3. Dorrell RG, Smith AG . Do red and green make brown?: perspectives on plastid acquisitions within chromalveolates . Eukaryotic Cell . 10 . 7 . 856–868 . July 2011 . 21622904 . 3147421 . 10.1128/EC.00326-10 .
  4. Simpson AG . The Identity and Composition of Euglenozoa . Archiv für Protistenkunde . 1997 . 148 . 3 . 318–328 . 10.1016/s0003-9365(97)80012-7.
  5. Baldauf SL, Roger AJ, Wenk-Siefert I, Doolittle WF . A kingdom-level phylogeny of eukaryotes based on combined protein data . Science . 290 . 5493 . 972–977 . November 2000 . 11062127 . 10.1126/science.290.5493.972 . 2000Sci...290..972B . Ford Doolittle .
  6. Simpson AG . Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota) . International Journal of Systematic and Evolutionary Microbiology . 53 . Pt 6 . 1759–1777 . November 2003 . 14657103 . 10.1099/ijs.0.02578-0 . free .
  7. Cavalier-Smith T . Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree . Biology Letters . 6 . 3 . 342–345 . June 2010 . 20031978 . 2880060 . 10.1098/rsbl.2009.0948 .
  8. Cavalier-Smith T . Higher classification and phylogeny of Euglenozoa . European Journal of Protistology . 56 . 250–276 . October 2016 . 27889663 . 10.1016/j.ejop.2016.09.003 . free .
  9. Kostygov AY, Karnkowska A, Votýpka J, Tashyreva D, Maciszewski K, Yurchenko V, Lukeš J . Euglenozoa: taxonomy, diversity and ecology, symbioses and viruses . Open Biology . 11 . 3 . 200407 . March 2021 . 33715388 . 8061765 . 10.1098/rsob.200407 .
  10. Cavalier-Smith T . Euglenoid pellicle morphogenesis and evolution in light of comparative ultrastructure and trypanosomatid biology: Semi-conservative microtubule/strip duplication, strip shaping and transformation . European Journal of Protistology . 61 . Pt A . 137–179 . October 2017 . 29073503 . 10.1016/j.ejop.2017.09.002 . free .

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