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.