Euglenozoa are a large group offlagellateDiscoba. 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, andSymbiontida. 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.[4]
Most euglenozoa have two flagella, which are inserted parallel to one another in an apical or subapical pocket. In some these are associated with acytostome or mouth, used to ingestbacteria or other small organisms. This is supported by one of three sets ofmicrotubules that arise from the flagellar bases; the other two support the dorsal and ventral surfaces of the cell.[5]
Some other euglenozoa feed through absorption, and many euglenids possesschloroplasts, the only eukaryotes outsideDiaphoretickes to do so without performingkleptoplasty,[6][7] and so obtain energy throughphotosynthesis. These chloroplasts are surrounded by three membranes and containchlorophyllsA andB, along with other pigments, so are probably derived from agreen alga, captured long ago in anendosymbiosis by a basal euglenozoan. Reproduction occurs exclusively through cell division. Duringmitosis, the nuclear membrane remains intact, and the spindle microtubules form inside of it.[5]
The group is characterized by the ultrastructure of the flagella. In addition to the normal supporting microtubules oraxoneme, each contains a rod (calledparaxonemal), 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: thediplonemids andPostgaardi.[8]
The Euglenozoa are generally accepted as monophyletic. They are related toPercolozoa; the two share mitochondria with disk-shapedcristae, which only occurs in a few other groups.[10]Both probably belong to a larger group of eukaryotes called theExcavata.[11] This grouping, though, has been challenged.[12]
The following classification of Euglenozoa is as described by Cavalier-Smith in 2016,[13] modified to include the new subphylumPlicomonada according to Cavalier-Smithet al (2017).[3]
^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.
