Wikipedia

Euglenid

Euglenidsoreuglenoidsare one of the best-known groups ofeukaryoticflagellates:single-celled organisms withflagella,or whip-like tails. They are classified in the phylumEuglenophyta,classEuglenidaorEuglenoidea.Euglenids are commonly found in fresh water, especially when it is rich in organic materials, but they have a few marine andendosymbioticmembers. Many euglenids feed byphagocytosis,or strictly bydiffusion.A monophyletic subgroup known asEuglenophyceaehavechloroplastsand produce their own food throughphotosynthesis.[3][4][5]This group contains the carbohydrateparamylon.

Euglenid
Temporal range:Middle Ordovician–Present[1][2]
Euglena viridis,byEhrenberg
Scientific classificationEdit this classification
Domain: Eukaryota
Clade: Discoba
Superphylum: Discicristata
Phylum: Euglenozoa
Class: Euglenida
Butschli 1884, emend. Simpson 1997
Major groups
Synonyms
  • EuglenoidinaBütschli,1884, Blochmann, 1886
  • EuglenoideaLankester, 1885
  • EuglenoidaCavalier-Smith, 1993

Euglenids split from otherEuglenozoa(a larger group of flagellates) more than a billion years ago. Theplastids(membranous organelles) in all extant photosynthetic species result from secondaryendosymbiosisbetween a euglenid and a green alga.[6]

Structure

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Euglenoids are distinguished mainly by the presence of a type of cell covering called apellicle.Within its taxon, the pellicle is one of the euglenoids' most diverse morphological features.[7]The pellicle is composed of proteinaceous strips underneath the cell membrane, supported by dorsal and ventralmicrotubules.This varies from rigid to flexible, and gives the cell its shape, often giving it distinctive striations. In many euglenids, the strips can slide past one another, causing an inching motion calledmetaboly.Otherwise, they move using their flagella.

Euglenid Body Plan
  1. Dorsalflagellum
  2. Axoneme
  3. Paraflagellar rod
  4. Mastigonemes,"hairs" attached to flagellum
  5. Flagellar pocket vestibulum
  6. Feeding apparatus
  7. Paraxial swelling
  8. Eyespot,photoreceptor used to sense light direction and intensity
  9. Contractile vacuole,regulates the quantity of water inside a cell
  10. Ventral flagellum
  11. Ventral root
  12. Golgi apparatus;modifiesproteinsand sends them out of the cell
  13. Endoplasmic reticulum,the transport network for molecules going to specific parts of the cell
  14. Phagosome
  15. Lysosome,holds enzymes
  16. Nucleus
  17. Nucleolus
  18. Plastidmembranes (3, secondary)
  19. Thylakoids,site of thelight-dependent reactionsofphotosynthesis
  20. Pyrenoid,center ofcarbon fixation
  21. Paramylongranules
  22. Pellicularstrip
  23. Muciferous body
  24. Mitochondrion,createsATP(energy) for the cell (discoidcristae)

Classification

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Examples of euglenid diversity.
1—2.Ascoglenasp. (Euglenales);
3–4.Cryptoglenasp. (idem);
5–9, 14–15, 24–25, 27–29.Trachelomonasspp. (id.);
10.Eutreptiasp. (Eutreptiales);
11, 20.Astasiaspp. (Euglenales);
12.Distigmasp. (Eutreptiales);
13.Menoid[i]umsp. (Rhabdomonadales);
16–18.Colaciumsp. (Euglenales);
19, 26.Petalomonasspp. (Sphenomonadales);
21.Sphenomonassp. (id.);
22–23.Euglenopsissp. (Euglenales);
30.Peranemasp. (Heteronematales)

The first attempt at classifying euglenids was done byEhrenbergin 1830, when he described the genusEuglenaand placed it in the Polygastrica of family Astasiae, containing other creatures of variable body shape and lackingpseudopodsorlorica.Later, various biologists described additional characteristics forEuglenaand established different classification systems for euglenids based on nutrition modes, the presence and number offlagella,and the degree ofmetaboly.The 1942 revision by A. Hollande distinguished three groups, Peranemoidées (flexible phagotrophs), Petalomonadinées (rigid phagotrophs) and Euglenidinées (phototrophs), and was widely accepted as the best reflection of the natural relationships between euglenids, adopted by many other authors.[8]Gordon F. Leedale expanded on Hollande's system, establishing six orders (Eutreptiales,Euglenales,Rhabdomonadales,Sphenomonadales,HeteronematalesandEuglenamorphales) and taking into account new data on their physiology andultrastructure.This scheme endured until 1986, with the sequencing of theSSU rRNAgene fromEuglena gracilis.[8]

Euglenids are currently regarded as a highly diverse clade withinEuglenozoa,in theeukaryotic supergroupDiscoba.[9]They are traditionally organized into three categories based on modes of nutrition: thephototrophs(Euglenophyceae), theosmotrophs(mainly the 'primary osmotrophs' known asAphagea), and thephagotrophs,from which the first two groups have evolved.[10]The phagotrophs, althoughparaphyletic,have historically been classified under the name ofHeteronematina.[9]

In addition, euglenids can be divided into inflexible or rigid euglenids, and flexible or metabolic euglenids which are capable of 'metaboly' or 'euglenid motion'. Only those with more than 18 protein strips in their pellicle gain this flexibility. Phylogenetic studies show that various clades of rigid phagotrophic euglenids compose thebaseof the euglenid tree, namelyPetalomonadidaand the paraphyletic 'Ploeotiida'. In contrast, all flexible euglenids belong to amonophyleticgroup known asSpirocuta,which includes Euglenophyceae, Aphagea and various phagotrophs (Peranemidae,AnisonemidaeandNeometanemidae). The current classification of class Euglenida, as a result of these studies, is as follows:[10][11][12][13][14]

Nutrition

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The classification of euglenids is still variable, as groups are being revised to conform with their molecularphylogeny.Classifications have fallen in line with the traditional groups based on differences in nutrition and number of flagella; these provide a starting point for considering euglenid diversity. Different characteristics of the euglenids' pellicles can provide insight into their modes of movement and nutrition.[18]

As with otherEuglenozoa,the primitive mode of nutrition isphagocytosis.Prey such asbacteriaand smaller flagellates is ingested through acytostome,supported by microtubules. These are often packed together to form two or more rods, which function in ingestion, and inEntosiphonform an extendable siphon. Mostphagotrophiceuglenids have two flagella, one leading and one trailing. The latter is used for gliding along thesubstrate.In some, such asPeranema,the leading flagellum is rigid and beats only at its tip.

Osmotrophic euglenoids

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Osmotrophic euglenids are euglenids which have undergoneosmotrophy.

Due to a lack of characteristics that are useful fortaxonomicalpurposes, the origin of osmotrophic euglenids is unclear, though certain morphological characteristics reveal a small fraction of osmotrophic euglenids are derived from phototrophic and phagotrophic ancestors.[19]

A prolonged absence of light or exposure to harmful chemicals may causeatrophyand absorption of the chloroplasts without otherwise harming the organism. A number of species exists where a chloroplast's absence was formerly marked with separate genera such asAstasia(colourlessEuglena) andHyalophacus(colourlessPhacus). Due to the lack of a developed cytostome, these forms feed exclusively by osmotrophic absorption.

Reproduction

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Although euglenids share several common characteristics with animals, which is why they were originally classified as so, no evidence has been found of euglenids ever usingsexual reproduction.This is one of the reasons they could no longer be classified as animals.[dubious–discuss]

For euglenids to reproduce,asexual reproductiontakes place in the form ofbinary fission,and the cells replicate and divide duringmitosisandcytokinesis.This process occurs in a very distinct order. First, thebasal bodiesand flagella replicate, then thecytostomeand microtubules (the feeding apparatus), and finally the nucleus and remainingcytoskeleton.Once this occurs, the organism begins to cleave at the basal bodies, and this cleavage line moves towards the center of the organism until two separate euglenids are evident.[20]Because of the way that this reproduction takes place and the axis of separation, it is called longitudinalcell divisionor longitudinal binary fission.[21]

Evolution

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The earliest fossil of euglenids is attributed toMoyeria,which is interpreted as possessing a pellicle composed of proteinaceous strips, the defining characteristic of euglenids. It is found inMiddle OrdovicianandSilurianrocks, making it the oldest fossil evidence of euglenids.[1][2]

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References

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  1. ^abGray, Jane; Boucot, A. J. (1989). "IsMoyeriaa euglenoid? ".Lethaia.22(4):447–456.doi:10.1111/j.1502-3931.1989.tb01449.x.
  2. ^abStrother, Paul K.; Taylor, Wilson A.; van de Schootbrugge, Bas; Leander, Brian S.; Wellman, Charles H. (2020)."Pellicle ultrastructure demonstrates thatMoyeriais a fossil euglenid ".Palynology.44(3):461–471.doi:10.1080/01916122.2019.1625457.
  3. ^Karnkowska, Anna; Bennett, Matthew S.; Triemer, Richard E. (2018)."Dynamic evolution of inverted repeats in Euglenophyta plastid genomes".Scientific Reports.8(1): 16071.Bibcode:2018NatSR...816071K.doi:10.1038/s41598-018-34457-w.PMC6207741.PMID30375469.
  4. ^Yoshihisa Hirakawa (2017).Secondary Endosymbioses.Academic Press. p. 323.ISBN9780128026809.
  5. ^"Algaebase:: Subclass: Euglenophycidae".Archived fromthe originalon 2020-07-13.Retrieved2019-10-27.
  6. ^Zakryś, B; Milanowski, R; Karnkowska, A (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.
  7. ^Leander, Brian S.; Farmer, Mark A. (2001-03-01). "Comparative Morphology of the Euglenid Pellicle. II. Diversity of Strip Substructure".Journal of Eukaryotic Microbiology.48(2):202–217.doi:10.1111/j.1550-7408.2001.tb00304.x.ISSN1550-7408.PMID12095109.S2CID2109559.
  8. ^abCarlos E. de M. Bicudo; Mariângela Menezes (16 March 2016)."Phylogeny and Classification of Euglenophyceae: A Brief Review".Frontiers in Ecology and Evolution.4.doi:10.3389/FEVO.2016.00017.ISSN2296-701X.WikidataQ57898656.
  9. ^abSina M. Adl; David Bass; Christopher E. Lane; et al. (1 January 2019)."Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes".Journal of Eukaryotic Microbiology.66(1):4–119.doi:10.1111/JEU.12691.ISSN1066-5234.PMC6492006.PMID30257078.WikidataQ57086550.
  10. ^abGordon Lax; Alastair G. B. Simpson (16 August 2020). "The Molecular Diversity of Phagotrophic Euglenids Examined Using Single-cell Methods".Protist.171(5): 125757.doi:10.1016/J.PROTIS.2020.125757.ISSN1434-4610.PMID33126020.WikidataQ101127864.
  11. ^abG. Lax; M. Kolisko; Y. Eglit; et al. (June 2021). "Multigene phylogenetics of euglenids based on single-cell transcriptomics of diverse phagotrophs".Molecular Phylogenetics and Evolution.159:107088.doi:10.1016/J.YMPEV.2021.107088.ISSN1055-7903.WikidataQ110667805.
  12. ^Alexei Y. Kostygov; Anna Karnkowska; Jan Votýpka; Daria Tashyreva; Kacper Maciszewski; Vyacheslav Yurchenko; Julius Lukeš (10 March 2021)."Euglenozoa: taxonomy, diversity and ecology, symbioses and viruses".Open Biology.11:200407.doi:10.1098/RSOB.200407.ISSN2046-2441.PMC8061765.PMID33715388.WikidataQ125548575.
  13. ^Gordon Lax; Anna Cho;Patrick J. Keeling(30 March 2023). "Phylogenomics of novel ploeotid taxa contribute to the backbone of the euglenid tree".Journal of Eukaryotic Microbiology.70(4).doi:10.1111/JEU.12973.ISSN1066-5234.WikidataQ123348233.
  14. ^Lax G, Keeling PJ (2023)."Molecular phylogenetics of sessileDolium sedentarium,a petalomonad euglenid ".The Journal of Eukaryotic Microbiology.70(e12991): e12991.doi:10.1111/jeu.12991.PMID37424051.
  15. ^Gordon Lax; Won Je Lee; Yana Eglit; Alastair Geoffrey Brinley Simpson (23 March 2019). "Ploeotids Represent Much of the Phylogenetic Diversity of Euglenids".Protist.170(2):233–257.doi:10.1016/J.PROTIS.2019.03.001.ISSN1434-4610.PMID31102975.WikidataQ92132357.
  16. ^Thomas Cavalier-Smith;Ema E Chao; Keith Vickerman (28 August 2016). "New phagotrophic euglenoid species (new genus Decastava; Scytomonas saepesedens; Entosiphon oblongum), Hsp90 introns, and putative euglenoid Hsp90 pre-mRNA insertional editing".European Journal of Protistology.56:147–170.doi:10.1016/J.EJOP.2016.08.002.ISSN0932-4739.PMID27718409.WikidataQ31135651.
  17. ^Thomas Cavalier-Smith(15 September 2016). "Higher classification and phylogeny of Euglenozoa".European Journal of Protistology.56:250–276.doi:10.1016/J.EJOP.2016.09.003.ISSN0932-4739.PMID27889663.WikidataQ39151632.
  18. ^Leander, Brian Scott (May 2001)."Evolutionary morphology of the euglenid pellicle".University of Georgia Theses and Dissertations.
  19. ^Busse, Ingo; Preisfeld, Angelika (14 April 2018)."Systematics of primary osmotrophic euglenids: a molecular approach to the phylogeny of Distigma and Astasia (Euglenozoa)".International Journal of Systematic and Evolutionary Microbiology.53(2):617–624.doi:10.1099/ijs.0.02295-0.PMID12710635.
  20. ^"Euglenida".tolweb.org.Retrieved2017-03-30.
  21. ^"Reproduction".Euglena.Retrieved2017-03-31.

Bibliography

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