Euglenozoa are a large group of flagellateDiscoba. 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 15–40 μm (0.00059–0.00157 in) in size, although some euglenids get up to 500 μm (0.020 in) long.[3]
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.[4]
Some other euglenozoa feed through absorption, and many euglenids possess chloroplasts, the only eukaryotes outside Diaphoretickes to do so without performing kleptoplasty,[5][failed verification] and so obtain energy through photosynthesis. These chloroplasts are surrounded by three membranes and contain chlorophyllsA 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.[4]
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.[6]
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.[8]
Both probably belong to a larger group of eukaryotes called the Excavata.[9] This grouping, though, has been challenged.[10]
Phylogeny
The phylogeny based on the work of Cavalier-Smith (2016):[11]
The following classification of Euglenozoa is as described by Cavalier-Smith in 2016,[11] modified to include the new subphylum Plicomonada according to Cavalier-Smith et al (2017).[12]
Class Symbiontida Yubuki, Edgcomb, Bernhard and Leander, 2009
References
^Zakryś, B; Milanowski, R; Karnkowska, Anna (2017). "Evolutionary Origin of Euglena". Euglena: Biochemistry, Cell and Molecular Biology. Advances in Experimental Medicine and Biology. Vol. 979. pp. 3–17. doi:10.1007/978-3-319-54910-1_1. ISBN978-3-319-54908-8. PMID28429314.
