Editing Euglena (section)

==Form and function==
When feeding as a heterotroph, ''Euglena'' takes in nutrients by [[osmotrophy]], and can survive without light on a diet of organic matter, such as [[beef extract]], [[peptone]], [[acetate]], [[ethanol]] or [[carbohydrate]]s.<ref>{{Cite book |url=https://books.google.com/books?id=TMpJo2rXAT4C&q=leadbetter+flagellates+unity&pg=PP1 |title=Flagellates: Unity, Diversity and Evolution |last1=Leadbeater |first1=Barry S. C. |last2=Green |first2=John C. |date=2002-09-11 |publisher=CRC Press |isbn=9780203484814 |language=en}}</ref><ref>{{Cite journal |last1=Pringsheim |first1=E. G. |last2=Hovasse |first2=R. |date=1948-06-01 |title=The Loss of Chromatophores in Euglena Gracilis |journal=New Phytologist |language=en |volume=47 |issue=1 |pages=52–87 |doi=10.1111/j.1469-8137.1948.tb05092.x|doi-access=free }}</ref> When there is sufficient sunlight for it to feed by [[phototrophy]], it uses chloroplasts containing the pigments [[chlorophyll a]] and [[chlorophyll b]] to produce sugars by [[photosynthesis]].<ref>{{cite book |last=Nisbet |first=Brenda |title=Nutrition and Feeding Strategies in Protozoa |year=1984 |isbn=978-0-7099-1800-4 |page=[https://archive.org/details/nutritionfeeding0000nisb/page/73 73] |publisher=Croom Helm |url=https://archive.org/details/nutritionfeeding0000nisb/page/73 }}</ref> ''Euglena's'' chloroplasts are surrounded by three membranes, while those of plants and the [[green algae]] (among which earlier taxonomists often placed ''Euglena'') have only two membranes. This fact has been taken as morphological evidence that ''Euglena's'' chloroplasts evolved from a [[eukaryotic]] green alga.<ref>{{cite journal |doi=10.1139/b78-345 |title=The chloroplasts of ''Euglena'' may have evolved from symbiotic green algae |year=1978 |last1=Gibbs |first1=Sarah P. |journal=Canadian Journal of Botany |volume=56 |issue=22 |pages=2883–9}}</ref> Thus, the similarities between ''Euglena'' and plants would have arisen not because of kinship but because of a secondary [[endosymbiosis]]. Molecular phylogenetic analysis has lent support to this hypothesis, and it is now generally accepted.<ref>{{cite journal |bibcode=1995PNAS...92.9122H |jstor=2368422 |title=A Nuclear Gene of Eubacterial Origin in Euglena gracilis Reflects Cryptic Endosymbioses During Protist Evolution |last1=Henze |first1=Katrin |last2=Badr |first2=Abdelfattah |last3=Wettern |first3=Michael |last4=Cerff |first4=Rudiger |last5=Martin |first5=William |volume=92 |year=1995 |pages=9122–6 |journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.92.20.9122 |pmid=7568085 |issue=20 |pmc=40936|doi-access=free }}</ref><ref>{{cite journal |doi=10.1046/j.1529-8817.2003.02075.x |title=Phylogeny of euglenophyceae based on small subunit rDNA sequences: Taxonomic implications |year=2003 |last1=Nudelman |first1=Mara Alejandra |last2=Rossi |first2=Mara Susana |last3=Conforti |first3=Visitacin |last4=Triemer |first4=Richard E. |journal=Journal of Phycology |volume=39 |issue=1 |pages=226–35|s2cid=85275367 }}</ref>

''Euglena'' chloroplasts contain [[pyrenoid]]s, used in the synthesis of [[paramylon]], a form of starch energy storage enabling ''Euglena'' to survive periods of light deprivation. The presence of pyrenoids is used as an identifying feature of the genus, separating it from other euglenoids, such as ''[[Lepocinclis]]'' and ''[[Phacus]]''.<ref name="Marin-2003">{{cite journal |pmid=12812373 |year=2003 |last1=Marin |first1=B |last2=Palm |first2=A |last3=Klingberg |first3=M |last4=Melkonian |first4=M |title=Phylogeny and taxonomic revision of plastid-containing euglenophytes based on SSU rDNA sequence comparisons and synapomorphic signatures in the SSU rRNA secondary structure |volume=154 |issue=1 |pages=99–145 |journal=Protist |doi=10.1078/143446103764928521}}</ref> Pyrenoids may be surrounded by a single paramylon cap (these pyrenoids are called haplopyrenoids), a bilateral paramylon cap (these are called diplopyrenoids), or a cluster of small paramylon grains (called a paramylon center), or may be "naked" and lack associated paramylon bodies.<ref name=Triemer>{{cite book |editor-first1=John D.|editor-last1=Wehr|editor-first2=Robert G.|editor-last2=Sheath|editor-first3=J. Patrick|editor-last3=Kociolek |date= 2014 |edition=2 |title= Freshwater Algae of North America: Ecology and Classification |last1= Triemer|first1=Richard E. |last2= Zakryś |first2=Bożena |chapter= Chapter 10. Photosynthetic Euglenoids |url= |location= |publisher= Elsevier Inc. |page= |isbn=978-0-12-385876-4 }}</ref>

Chloroplast morphology in ''Euglena'' is diverse, and can be broadly divided into four groups. The first group consists of ''[[Euglena archaeoplastidiata|E. archaeoplastidiata]]'', which has a single, parietal chloroplast with two diplopyrenoids. The second group (e.g. ''[[Euglena viridis|E. viridis]]'') has axial, stellate chloroplasts with paramylon center. The third group has parietal, lobed chloroplasts, each with a naked, haplo- or diplopyrenoid; this group is very diverse and identification may be difficult. The fourth group (e.g. ''[[Euglena sanguinea|E. sanguinea]]'') has plate-like, parietal chloroplasts each with a single diplopyrenoid. The chloroplast centers are located deep within the cell, and the chloroplasts are deeply dissected into long bands, which follow the spiral contours of the cell.<ref name=Triemer/>

''Euglena'' have two flagella rooted in [[basal body|basal bodies]] located in a small reservoir at the front of the cell. Typically, one flagellum is very short, and does not protrude from the cell, while the other is long enough to be seen with light microscopy. In some species, such as ''Euglena mutabilis'', both flagella are "non-emergent"—entirely confined to the interior of the cell's reservoir—and consequently cannot be seen in the light microscope.<ref>{{Cite book|last1=Ciugulea|first1=Ionel|title=A Color Atlas of Photosynthetic Euglenoids|last2=Triemer|first2=Richard|publisher=Michigan State University Press|year=2010|isbn=978-0870138799|location=East Lansing|pages=17 & 38}}</ref><ref>{{Cite journal|last1=Häder|first1=Donat-P.|last2=Melkonian|first2=Michael|date=1983-08-01|title=Phototaxis in the gliding flagellate, Euglena mutabilis|journal=Archives of Microbiology|language=en|volume=135|issue=1|pages=25–29|doi=10.1007/BF00419477|s2cid=19307809|issn=1432-072X}}</ref>  In species that possess a long, emergent flagellum, it may be used to help the organism swim.<ref>{{Cite journal|last1=Rossi|first1=Massimiliano|last2=Cicconofri|first2=Giancarlo|last3=Beran|first3=Alfred|last4=Noselli|first4=Giovanni|last5=DeSimone|first5=Antonio|date=2017-12-12|title=Kinematics of flagellar swimming in Euglena gracilis: Helical trajectories and flagellar shapes|journal=Proceedings of the National Academy of Sciences|language=en|volume=114|issue=50|pages=13085–13090|doi=10.1073/pnas.1708064114|issn=0027-8424|pmid=29180429|pmc=5740643|doi-access=free}}</ref> The surface of the flagellum is coated with about 30,000 extremely fine filaments called [[mastigoneme]]s.<ref>{{Cite journal|date=1978-06-01|title=Surface organization and composition of Euglena. II. Flagellar mastigonemes|journal=The Journal of Cell Biology|volume=77|issue=3|pages=805–826|issn=0021-9525|pmc=2110158|pmid=98532|last1=Bouck|first1=G. B.|last2=Rogalski|first2=A.|last3=Valaitis|first3=A.|doi=10.1083/jcb.77.3.805}}</ref>

Like other euglenoids, ''Euglena'' possess a red [[eyespot apparatus|eyespot]], an organelle composed of [[carotenoid]] pigment granules. The red spot itself is not thought to be [[photosensitive]]. Rather, it filters the sunlight that falls on a light-detecting structure at the base of the flagellum (a swelling, known as the paraflagellar body), allowing only certain wavelengths of light to reach it. As the cell rotates with respect to the light source, the eyespot partially blocks the source, permitting the ''Euglena'' to find the light and move toward it (a process known as [[phototaxis]]).<ref name="Schaechter-2011">{{cite book |last=Schaechter |first=Moselio |title=Eukaryotic Microbes |publisher=Elsevier/Academic Press |location=San Diego |year=2011 |isbn=978-0-12-383876-6 |page=315}}</ref>

[[File:Euglena pellicle 2.jpg |thumb|Spiral pellicle strips]]
''Euglena'' lacks a [[cell wall]]. Instead, it has a [[Protozoa#Walls, pellicles, scales, and skeletons|pellicle]] made up of a protein layer supported by a substructure of [[microtubule]]s, arranged in strips spiraling around the cell. The action of these pellicle strips sliding over one another, known as [[metaboly]], gives ''Euglena'' its exceptional flexibility and contractility.<ref name="Schaechter-2011" /> The mechanism of this euglenoid movement is not understood, but its molecular basis may be similar to that of [[amoeboid movement]].<ref>{{cite book |author=O'Neill, Ellis |title=An exploration of phosphorylases for the synthesis of carbohydrate polymers (PhD thesis) |publisher=University of East Anglia |date=2013 |url=http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590735 |pages=170–171 |access-date=2017-10-01 |archive-date=2016-03-21 |archive-url=https://web.archive.org/web/20160321035730/http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590735 |url-status=dead }}</ref> Some species have mucocysts, which are membrane-bound bodies containing mucilaginous threads. Mucocysts are located underneath the pellicle in parallel rows following the arrangement of pellicle strips. Their presence or absence and shape (spherical or spindle-shaped) are an important diagnostic for species-level identification, but are mostly only visible after staining with a dye such as [[neutral red]].<ref name=Triemer/>

In low moisture conditions, or when food is scarce, ''Euglena'' forms a protective wall around itself and lies dormant as a resting cyst until environmental conditions improve.

[[File:2023 Eugenid.svg|center|thumb|upright=2|{{center|'''Euglenid Body Plan'''}}{{ordered list|Dorsal [[flagellum]]|
[[Axoneme]]|
Paraflagellar rod|
[[Mastigoneme|Mastigonemes]], "hairs" attached to flagellum|
Flagellar pocket vestibulum|
Feeding apparatus|
Paraxial swelling|
[[Eyespot apparatus|Eyespot]], photoreceptor used to sense light direction and intensity|
[[Contractile vacuole]], regulates the quantity of water inside a cell|
Ventral flagellum|
Ventral root|
[[Golgi apparatus]]; modifies [[protein]]s and sends them out of the cell|
[[Endoplasmic reticulum]], the transport network for molecules going to specific parts of the cell|
[[Phagosome]]|
[[Lysosome]], holds enzymes|
[[Cell nucleus|Nucleus]]|
[[Nucleolus]]|
[[Plastid]] membranes (3, secondary)|
[[Thylakoid|Thylakoids]], site of the [[light-dependent reactions]] of [[photosynthesis]]|
[[Pyrenoid]], center of [[carbon fixation]]|
[[Paramylon]] [[Granule (cell biology)|granules]]|
[[Protozoa#Walls,_pellicles,_scales,_and_skeletons|Pellicular]] strip|
Muciferous body/Mucocyst|
[[Mitochondria|Mitochondrion]], creates [[Adenosine triphosphate|ATP]] (energy) for the cell (discoid [[crista|cristae]])}}]]