Euglenid: Difference between revisions

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{{Short description|Class of protozoans}}
{{Short description|Class of protozoans}}
{{Automatic taxobox  
{{Automatic taxobox
| image = Ehrenberg euglena viridis.jpg
| image = Ehrenberg euglena viridis.jpg
| image_upright = 1.1
| image_upright = 1.1
| image_caption = ''[[Euglena|Euglena viridis]]'', by [[Christian Gottfried Ehrenberg|Ehrenberg]]
| image_caption = ''[[Euglena|Euglena viridis]]'', by [[Christian Gottfried Ehrenberg|Ehrenberg]]
| display_parents = 3
| taxon = Euglenida
| taxon = Euglenida
| authority = Butschli 1884, emend. Simpson 1997
| authority = Butschli 1884, [[Emendation (zoology)|emend]]. Simpson 1997
| subdivision_ranks = Major groups
| subdivision_ranks = Major groups
| subdivision =
| subdivision = * [[Petalomonadida]]
* [[Petalomonadida]]
* [[Alistosa]]
* [[Alistosa]]
* [[Karavia]]
* [[Karavia]]
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* Euglenoidea <small>Lankester, 1885</small>
* Euglenoidea <small>Lankester, 1885</small>
* Euglenoida <small>Cavalier-Smith, 1993</small>
* Euglenoida <small>Cavalier-Smith, 1993</small>
| fossil_range={{fossil range|Middle Ordovician|Present|ref=<ref name="Gray 1989">{{cite journal|last1=Gray|first1=Jane|last2=Boucot|first2=A. J.|title=Is ''Moyeria'' a euglenoid?|journal=Lethaia|volume=22|issue=4|pages=447–456|doi=10.1111/j.1502-3931.1989.tb01449.x|date=1989}}</ref><ref name="Strother 2020">{{cite journal|last1=Strother|first1=Paul K.|last2=Taylor|first2=Wilson A.|last3=van de Schootbrugge|first3=Bas|last4=Leander|first4=Brian S.|last5=Wellman|first5=Charles H.|title=Pellicle ultrastructure demonstrates that ''Moyeria'' is a fossil euglenid|journal=Palynology|date=2020|volume=44|issue=3|pages=461–471|doi=10.1080/01916122.2019.1625457|doi-access=free}}</ref>}}
| fossil_range = {{fossil range|Middle Ordovician|Present|ref=<ref name="Gray 1989">{{cite journal|last1=Gray|first1=Jane|last2=Boucot|first2=A. J.|title=Is ''Moyeria'' a euglenoid?|journal=Lethaia|volume=22|issue=4|pages=447–456|doi=10.1111/j.1502-3931.1989.tb01449.x|date=1989 |bibcode=1989Letha..22..447G }}</ref><ref name="Strother 2020">{{cite journal|last1=Strother|first1=Paul K.|last2=Taylor|first2=Wilson A.|last3=van de Schootbrugge|first3=Bas|last4=Leander|first4=Brian S.|last5=Wellman|first5=Charles H.|title=Pellicle ultrastructure demonstrates that ''Moyeria'' is a fossil euglenid|journal=Palynology|date=2020|volume=44|issue=3|pages=461–471|doi=10.1080/01916122.2019.1625457|bibcode=2020Paly...44..461S |doi-access=free}}</ref>}}
}}
}}


'''Euglenids''' or '''euglenoids''' are one of the best-known groups of [[Eukaryote|eukaryotic]] [[flagellate]]s: single-celled organisms with [[flagella]], or whip-like tails. They are classified in the phylum [[Euglenozoa|Euglenophyta]], [[class (biology)|class]] '''Euglenida''' or '''Euglenoidea'''. Euglenids are commonly found in fresh water, especially when it is rich in organic materials, but they have a few marine and [[Endosymbiont|endosymbiotic]] members. Many euglenids feed by [[phagocytosis]], or strictly by [[diffusion]]. A monophyletic subgroup known as [[Euglenophyceae]] have [[chloroplast]]s and produce their own food through [[photosynthesis]].<ref>{{cite journal|title=Dynamic evolution of inverted repeats in Euglenophyta plastid genomes|journal=Scientific Reports|year=2018|first1=Anna|last1=Karnkowska|first2=Matthew S.|last2=Bennett|first3=Richard E.|last3=Triemer|volume=8 |issue=1 |page=16071 |doi=10.1038/s41598-018-34457-w |pmid=30375469 |bibcode=2018NatSR...816071K |pmc=6207741}}</ref><ref>{{cite book|url=https://books.google.com/books?id=c93WDgAAQBAJ&dq=Rapaza+viridis+two+genera+Eutreptiales+and+Euglenales&pg=PA323|title=Secondary Endosymbioses|page=323|author=Yoshihisa Hirakawa|publisher=Academic Press|year=2017|isbn=9780128026809}}</ref><ref>{{Cite web |url=https://www.algaebase.org/pub_taxonomy/?id=163213 |title=Algaebase :: Subclass: Euglenophycidae |access-date=2019-10-27 |archive-date=2020-07-13 |archive-url=https://web.archive.org/web/20200713195620/https://www.algaebase.org/pub_taxonomy/?id=163213 |url-status=dead }}</ref> This group contains the carbohydrate [[paramylon]].
'''Euglenids''' or '''euglenoids''' are one of the best-known groups of [[Eukaryote|eukaryotic]] [[flagellate]]s: single-celled organisms with [[flagella]], or whip-like tails. They are classified in the phylum [[Euglenozoa]], [[class (biology)|class]] '''Euglenida''' or '''Euglenoidea'''. Euglenids are commonly found in fresh water, especially when it is rich in organic materials, but they have a few marine and [[Endosymbiont|endosymbiotic]] members. Many euglenids feed by [[phagocytosis]], or strictly by [[diffusion]]. A monophyletic subgroup known as [[Euglenophyceae]] have [[chloroplast]]s and produce their own food through [[photosynthesis]].<ref>{{cite journal|title=Dynamic evolution of inverted repeats in Euglenophyta plastid genomes|journal=Scientific Reports|year=2018|first1=Anna|last1=Karnkowska|first2=Matthew S.|last2=Bennett|first3=Richard E.|last3=Triemer|volume=8 |issue=1 |page=16071 |doi=10.1038/s41598-018-34457-w |pmid=30375469 |bibcode=2018NatSR...816071K |pmc=6207741}}</ref><ref>{{cite book|url=https://books.google.com/books?id=c93WDgAAQBAJ&dq=Rapaza+viridis+two+genera+Eutreptiales+and+Euglenales&pg=PA323|title=Secondary Endosymbioses|page=323|author=Yoshihisa Hirakawa|publisher=Academic Press|year=2017|isbn=978-0-12-802680-9}}</ref><ref>{{Cite web |url=https://www.algaebase.org/pub_taxonomy/?id=163213 |title=Algaebase :: Subclass: Euglenophycidae |access-date=2019-10-27 |archive-date=2020-07-13 |archive-url=https://web.archive.org/web/20200713195620/https://www.algaebase.org/pub_taxonomy/?id=163213 }}</ref> This group contains the carbohydrate [[paramylon]].
 
Euglenids split from other [[Euglenozoa]] (a larger group of flagellates) more than a billion years ago. The [[plastid]]s (membranous organelles) in all extant photosynthetic species result from secondary [[endosymbiosis]] between a euglenid and a green alga.<ref>{{cite book|pmid=28429314|doi=10.1007/978-3-319-54910-1_1|volume=979|year=2017|pages=3–17|last1=Zakryś|first1=B|last2=Milanowski|first2=R|last3=Karnkowska|first3=A|title=Euglena: Biochemistry, Cell and Molecular Biology |chapter=Evolutionary Origin of Euglena |series=Advances in Experimental Medicine and Biology|isbn=978-3-319-54908-8}}</ref>


Euglenids split from other [[Euglenozoa]] (a larger group of flagellates) more than a billion years ago. The [[plastid]]s (membranous organelles) in all extant photosynthetic species result from secondary [[endosymbiosis]] between a euglenid and a green alga.<ref>{{cite book|pmid=28429314|doi=10.1007/978-3-319-54910-1_1|volume=979|year=2017|pages=3–17|last1=Zakryś|first1=B|last2=Milanowski|first2=R|last3=Karnkowska|first3=A|title=Euglena: Biochemistry, Cell and Molecular Biology |chapter=Evolutionary Origin of Euglena |series=Advances in Experimental Medicine and Biology|isbn=978-3-319-54908-8}}</ref>
== Structure ==
== Structure ==
Euglenoids are distinguished mainly by the presence of a type of cell covering called a [[Pellicle (biology)|pellicle]]. Within its taxon, the pellicle is one of the euglenoids' most diverse morphological features.<ref>{{Cite journal|last1=Leander|first1=Brian S.|last2=Farmer|first2=Mark A.|date=2001-03-01|title=Comparative Morphology of the Euglenid Pellicle. II. Diversity of Strip Substructure|journal=Journal of Eukaryotic Microbiology|language=en|volume=48|issue=2|pages=202–217|doi=10.1111/j.1550-7408.2001.tb00304.x|pmid=12095109|s2cid=2109559 |issn=1550-7408}}</ref> The pellicle is composed of proteinaceous strips underneath the cell membrane, supported by dorsal and ventral [[microtubule]]s. 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 called [[metaboly]]. Otherwise, they move using their flagella.
Euglenoids are distinguished mainly by the presence of a type of cell covering called a [[Pellicle (biology)|pellicle]]. Within its taxon, the pellicle is one of the euglenoids' most diverse morphological features.<ref>{{Cite journal|last1=Leander|first1=Brian S.|last2=Farmer|first2=Mark A.|date=2001-03-01|title=Comparative Morphology of the Euglenid Pellicle. II. Diversity of Strip Substructure|journal=Journal of Eukaryotic Microbiology|language=en|volume=48|issue=2|pages=202–217|doi=10.1111/j.1550-7408.2001.tb00304.x|pmid=12095109|s2cid=2109559 |issn=1550-7408}}</ref> The pellicle is composed of proteinaceous strips underneath the cell membrane, supported by dorsal and ventral [[microtubule]]s. 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 called [[metaboly]]. Otherwise, they move using their flagella.
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[[Axoneme]]|
[[Axoneme]]|
Paraflagellar rod|
Paraflagellar rod|
[[Mastigoneme|Mastigonemes]], "hairs" attached to flagellum|
[[Mastigoneme]]s, "hairs" attached to flagellum|
Flagellar pocket vestibulum|
Flagellar pocket vestibulum|
Feeding apparatus|
Feeding apparatus|
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[[Nucleolus]]|
[[Nucleolus]]|
[[Plastid]] membranes (3, secondary)|
[[Plastid]] membranes (3, secondary)|
[[Thylakoid|Thylakoids]], site of the [[light-dependent reactions]] of [[photosynthesis]]|
[[Thylakoid]]s, site of the [[light-dependent reactions]] of [[photosynthesis]]|
[[Pyrenoid]], center of [[carbon fixation]]|
[[Pyrenoid]], center of [[carbon fixation]]|
[[Paramylon]] [[Granule (cell biology)|granules]]|
[[Paramylon]] [[Granule (cell biology)|granules]]|
[[Protozoa#Walls,_pellicles,_scales,_and_skeletons|Pellicular]] strip|
[[Protozoa#Walls, pellicles, scales, and skeletons|Pellicular]] strip|
Muciferous body|
Muciferous body|
[[Mitochondria|Mitochondrion]], creates [[Adenosine triphosphate|ATP]] (energy) for the cell (discoid [[crista|cristae]])}}]]
[[Mitochondria|Mitochondrion]], creates [[Adenosine triphosphate|ATP]] (energy) for the cell (discoid [[crista]]e)}}]]


== Classification ==
== Classification ==
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The first attempt at classifying euglenids was done by [[Christian Gottfried Ehrenberg|Ehrenberg]] in 1830, when he described the genus ''[[Euglena]]'' and placed it in the Polygastrica of family Astasiae, containing other creatures of variable body shape and lacking [[pseudopod]]s or [[lorica (biology)|lorica]]. Later, various biologists described additional characteristics for ''Euglena'' and established different classification systems for euglenids based on nutrition modes, the presence and number of [[flagella]], and the degree of [[metaboly]]. 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.<ref name="Bicudo 2016">{{cite Q|Q57898656|doi-access=free }}</ref> Gordon F. Leedale expanded on Hollande's system, establishing six orders ([[Eutreptiales]], [[Euglenales]], [[Rhabdomonadales]], [[Sphenomonadales]], [[Heteronematales]] and [[Euglenamorphales]]) and taking into account new data on their physiology and [[ultrastructure]]. This scheme endured until 1986, with the sequencing of the [[SSU rRNA]] gene from ''[[Euglena gracilis]]''.<ref name="Bicudo 2016"/>
The first attempt at classifying euglenids was done by [[Christian Gottfried Ehrenberg|Ehrenberg]] in 1830, when he described the genus ''[[Euglena]]'' and placed it in the Polygastrica of family Astasiae, containing other creatures of variable body shape and lacking [[pseudopod]]s or [[lorica (biology)|lorica]]. Later, various biologists described additional characteristics for ''Euglena'' and established different classification systems for euglenids based on nutrition modes, the presence and number of [[flagella]], and the degree of [[metaboly]]. 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.<ref name="Bicudo 2016">{{cite Q|Q57898656|doi-access=free }}</ref> Gordon F. Leedale expanded on Hollande's system, establishing six orders ([[Eutreptiales]], [[Euglenales]], [[Rhabdomonadales]], [[Sphenomonadales]], [[Heteronematales]] and [[Euglenamorphales]]) and taking into account new data on their physiology and [[ultrastructure]]. This scheme endured until 1986, with the sequencing of the [[SSU rRNA]] gene from ''[[Euglena gracilis]]''.<ref name="Bicudo 2016"/>


Euglenids are currently regarded as a highly diverse clade within [[Euglenozoa]], in the [[eukaryotic supergroup]] [[Discoba]].<ref name="Adl 2019">{{cite Q|Q57086550}}</ref> They are traditionally organized into three categories based on modes of nutrition: the [[phototroph]]s ([[Euglenophyceae]]), the [[osmotroph]]s (mainly the 'primary osmotrophs' known as [[Aphagea]]), and the [[phagotroph]]s, from which the first two groups have evolved.<ref name="Lax 2020">{{cite Q|Q101127864}}</ref> The phagotrophs, although [[paraphyletic]], have historically been classified under the name of [[Heteronematina]].<ref name="Adl 2019"/>  
Euglenids are currently regarded as a highly diverse clade within [[Euglenozoa]], in the [[eukaryotic supergroup]] [[Discoba]].<ref name="Adl 2019">{{cite Q|Q57086550}}</ref> They are traditionally organized into three categories based on modes of nutrition: the [[phototroph]]s ([[Euglenophyceae]]), the [[osmotroph]]s (mainly the 'primary osmotrophs' known as [[Aphagea]]), and the [[phagotroph]]s, from which the first two groups have evolved.<ref name="Lax 2020">{{cite Q|Q101127864}}</ref> The phagotrophs, although [[paraphyletic]], have historically been classified under the name of [[Heteronematina]].<ref name="Adl 2019"/>


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 the [[basal (phylogenetics)|base]] of the euglenid tree, namely [[Petalomonadida]] and the paraphyletic '[[Ploeotiida]]'. In contrast, all flexible euglenids belong to a [[monophyletic]] group known as [[Spirocuta]], which includes Euglenophyceae, Aphagea and various phagotrophs ([[Peranemidae]], [[Anisonemidae]] and [[Neometanemidae]]). The current classification of class Euglenida, as a result of these studies, is as follows:<ref name="Lax 2020"/><ref name="Lax 2021">{{cite Q|Q110667805}}</ref><ref name="Kostygov 2021">{{cite Q|Q125548575}}</ref><ref name="Lax 2023">{{cite Q|Q123348233}}</ref><ref name="Lax Keeling 2023">{{cite journal|vauthors=Lax G, Keeling PJ|title=Molecular phylogenetics of sessile ''Dolium sedentarium'', a petalomonad euglenid|journal=The Journal of Eukaryotic Microbiology|volume=70|number=e12991|date=2023|pages=e12991 |doi=10.1111/jeu.12991|doi-access=free|pmid=37424051}}</ref>
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 the [[basal (phylogenetics)|base]] of the euglenid tree, namely [[Petalomonadida]] and the paraphyletic '[[Ploeotiida]]'. In contrast, all flexible euglenids belong to a [[monophyletic]] group known as [[Spirocuta]], which includes Euglenophyceae, Aphagea and various phagotrophs ([[Peranemidae]], [[Anisonemidae]] and [[Neometanemidae]]). The current classification of class Euglenida, as a result of these studies, is as follows:<ref name="Lax 2020"/><ref name="Lax 2021">{{cite Q|Q110667805}}</ref><ref name="Kostygov 2021">{{cite Q|Q125548575}}</ref><ref name="Lax 2023">{{cite Q|Q123348233}}</ref><ref name="Lax Keeling 2023">{{cite journal|vauthors=Lax G, Keeling PJ|title=Molecular phylogenetics of sessile ''Dolium sedentarium'', a petalomonad euglenid|journal=The Journal of Eukaryotic Microbiology|volume=70|number=e12991|date=2023|article-number=e12991 |doi=10.1111/jeu.12991|doi-access=free|pmid=37424051}}</ref>
* Euglenida ''incertae sedis'': ''[[Atraktomonas]]'', ''[[Calycimonas]]'', ''[[Dolium]]'', ''[[Dylakosoma]]'', ''[[Tropidoscyphus]]'', ''[[Michajlowastasia]]'', ''[[Parastasiella]]'', ''[[Dinemula]]'', ''[[Paradinemula]]'', ''[[Mononema]]'', ''[[Ovicola]]'', ''[[Naupliicola]]'', ''[[Embryocola]]'', ''[[Copromonas]]''.
* Euglenida ''incertae sedis'': ''[[Atraktomonas]]'', ''[[Calycimonas]]'', ''[[Dolium]]'', ''[[Dylakosoma]]'', ''[[Tropidoscyphus]]'', ''[[Michajlowastasia]]'', ''[[Parastasiella]]'', ''[[Dinemula]]'', ''[[Paradinemula]]'', ''[[Mononema]]'', ''[[Ovicola]]'', ''[[Naupliicola]]'', ''[[Embryocola]]'', ''[[Copromonas]]''.
* Order [[Petalomonadida]] {{au|Cavalier-Smith 1993}}
* Order [[Petalomonadida]] {{au|Cavalier-Smith 1993}}
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** Clade [[Anisonemia]] {{au|Cavalier-Smith 2016}}
** Clade [[Anisonemia]] {{au|Cavalier-Smith 2016}}
*** Order [[Anisonemida]] {{au|Cavalier-Smith 2016}}
*** Order [[Anisonemida]] {{au|Cavalier-Smith 2016}}
**** Family [[Anisonemidae]] {{au|Kent 1880 emend. Cavalier-Smith 2016}}
**** Family [[Anisonemidae]] {{au|Kent 1880 [[Emendation (zoology)|emend]]. Cavalier-Smith 2016}}
*** Order [[Natomonadida]] {{au|Cavalier-Smith 2016}}
*** Order [[Natomonadida]] {{au|Cavalier-Smith 2016}}
**** Suborder [[Metanemina]] {{au|Cavalier-Smith 2016}}
**** Suborder [[Metanemina]] {{au|Cavalier-Smith 2016}}
***** Family [[Neometanemidae]] {{au|Cavalier-Smith 2016}}
***** Family [[Neometanemidae]] {{au|Cavalier-Smith 2016}}
**** Suborder [[Aphagea]] {{au|Cavalier-Smith 1993 emend. Busse & Preisfeld 2003}} [Rhabdomonadina {{au|Leedale 1967 emend. Cavalier-Smith 1993}}]<ref name="Higher Euglenozoa">{{cite Q|Q39151632}}</ref>
**** Suborder [[Aphagea]] {{au|Cavalier-Smith 1993 [[Emendation (zoology)|emend]]. Busse & Preisfeld 2003}} [Rhabdomonadina {{au|Leedale 1967 [[Emendation (zoology)|emend]]. Cavalier-Smith 1993}}]<ref name="Higher Euglenozoa">{{cite Q|Q39151632}}</ref>
***** Family [[Astasiidae]] {{au|Kent 1884}}
***** Family [[Astasiidae]] {{au|Kent 1884}}
***** Family [[Distigmidae]] {{au|Hollande 1942}}
***** Family [[Distigmidae]] {{au|Hollande 1942}}
** Order  [[Peranemida]] {{au|Bütschli 1884}}
** Order  [[Peranemida]] {{au|Bütschli 1884}}
*** Family [[Peranemidae]] {{au|Bütschli 1884}}
*** Family [[Peranemidae]] {{au|Bütschli 1884}}
** Clade [[Euglenophyceae]] {{au|Schoenichen 1925, emend. Marin & Melkonian 2003}} [Euglenea {{au|Butschli 1884, emend. Busse & Preisfeld 2002}}]
** Clade [[Euglenophyceae]] {{au|Schoenichen 1925, [[Emendation (zoology)|emend]]. Marin & Melkonian 2003}} [Euglenea {{au|Butschli 1884, [[Emendation (zoology)|emend]]. Busse & Preisfeld 2002}}]
*** Euglenophyceae ''incertae sedis'': ''[[Ascoglena]]'', ''[[Euglenamorpha]]'', ''[[Euglenopsis]]'', ''[[Glenoclosteroium]]'', ''[[Hegneria]]'', ''[[Klebsina]]'', ''[[Euglenocapsa]]''.
*** Euglenophyceae ''incertae sedis'': ''[[Ascoglena]]'', ''[[Euglenamorpha]]'', ''[[Euglenopsis]]'', ''[[Glenoclosteroium]]'', ''[[Hegneria]]'', ''[[Klebsina]]'', ''[[Euglenocapsa]]''.
*** Order [[Rapazida]] {{au|Cavalier-Smith 2016}}
*** Order [[Rapazida]] {{au|Cavalier-Smith 2016}}
**** Family [[Rapazidae]] {{au|Cavalier-Smith 2016}}
**** Family [[Rapazidae]] {{au|Cavalier-Smith 2016}}
*** Order [[Eutreptiales]] {{au|Leedale 1967, emend. Marin & Melkonian 2003}}
*** Order [[Eutreptiales]] {{au|Leedale 1967, [[Emendation (zoology)|emend]]. Marin & Melkonian 2003}}
**** Family [[Eutreptiaceae]] {{au|Hollande 1942}}
**** Family [[Eutreptiaceae]] {{au|Hollande 1942}}
*** Order [[Euglenales]] {{au|Leedale 1967, emend. Marin & Melkonian 2003}}
*** Order [[Euglenales]] {{au|Leedale 1967, [[Emendation (zoology)|emend]]. Marin & Melkonian 2003}}
**** Family [[Phacaceae]] {{au|Kim et al. 2010}}
**** Family [[Phacaceae]] {{au|Kim et al. 2010}}
**** Family [[Euglenaceae]] {{au|Dujardin 1841, emend. Kim et al. 2010}}
**** Family [[Euglenaceae]] {{au|Dujardin 1841, [[Emendation (zoology)|emend]]. Kim et al. 2010}}


==Nutrition==
==Nutrition==
The classification of euglenids is still variable, as groups are being revised to conform with their molecular [[phylogeny]].  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.<ref>{{Cite journal|last=Leander|first=Brian Scott|date=May 2001|title=Evolutionary morphology of the euglenid pellicle|url=http://athenaeum.libs.uga.edu/handle/10724/20165|journal=University of Georgia Theses and Dissertations}}</ref>
The classification of euglenids is still variable, as groups are being revised to conform with their molecular [[phylogeny]].  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.<ref>{{Cite journal|last=Leander|first=Brian Scott|date=May 2001|title=Evolutionary morphology of the euglenid pellicle|url=https://athenaeum.libs.uga.edu/handle/10724/20165|journal=University of Georgia Theses and Dissertations}}</ref>


As with other [[Euglenozoa]], the primitive mode of nutrition is [[phagocytosis]].  Prey such as [[bacteria]] and smaller flagellates is ingested through a [[cytostome]], supported by microtubules.  These are often packed together to form two or more rods, which function in ingestion, and in ''Entosiphon'' form an extendable siphon.  Most [[Phagocytosis|phagotrophic]] euglenids have two flagella, one leading and one trailing.  The latter is used for gliding along the [[Substrate (biology)|substrate]].  In some, such as ''[[Peranema]]'', the leading flagellum is rigid and beats only at its tip.
As with other [[Euglenozoa]], the primitive mode of nutrition is [[phagocytosis]].  Prey such as [[bacteria]] and smaller flagellates is ingested through a [[cytostome]], supported by microtubules.  These are often packed together to form two or more rods, which function in ingestion, and in ''Entosiphon'' form an extendable siphon.  Most [[Phagocytosis|phagotrophic]] euglenids have two flagella, one leading and one trailing.  The latter is used for gliding along the [[Substrate (biology)|substrate]].  In some, such as ''[[Peranema]]'', the leading flagellum is rigid and beats only at its tip.
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For euglenids to reproduce, [[asexual reproduction]] takes place in the form of [[binary fission]], and the cells replicate and divide during [[mitosis]] and [[cytokinesis]]. This process occurs in a very distinct order. First, the [[basal bodies]] and flagella replicate, then the [[cytostome]] and microtubules (the feeding apparatus), and finally the nucleus and remaining [[cytoskeleton]]. 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.<ref>{{Cite web|url=http://tolweb.org/Euglenida/97461|title=Euglenida|website=tolweb.org|access-date=2017-03-30}}</ref> Because of the way that this reproduction takes place and the axis of separation, it is called longitudinal [[cell division]] or longitudinal binary fission.<ref>{{Cite web|url=http://euglenabiology.weebly.com/reproduction.html|title=Reproduction|website=Euglena|access-date=2017-03-31}}</ref>
For euglenids to reproduce, [[asexual reproduction]] takes place in the form of [[binary fission]], and the cells replicate and divide during [[mitosis]] and [[cytokinesis]]. This process occurs in a very distinct order. First, the [[basal bodies]] and flagella replicate, then the [[cytostome]] and microtubules (the feeding apparatus), and finally the nucleus and remaining [[cytoskeleton]]. 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.<ref>{{Cite web|url=http://tolweb.org/Euglenida/97461|title=Euglenida|website=tolweb.org|access-date=2017-03-30}}</ref> Because of the way that this reproduction takes place and the axis of separation, it is called longitudinal [[cell division]] or longitudinal binary fission.<ref>{{Cite web|url=http://euglenabiology.weebly.com/reproduction.html|title=Reproduction|website=Euglena|access-date=2017-03-31}}</ref>
== Evolution ==
== Evolution ==
The earliest fossil of euglenids is attributed to ''[[Moyeria]]'', which is interpreted as possessing a pellicle composed of proteinaceous strips, the defining characteristic of euglenids. It is found in [[Middle Ordovician]] and [[Silurian]] rocks, making it the oldest fossil evidence of euglenids.<ref name="Gray 1989"/><ref name="Strother 2020"/>
The earliest fossil of euglenids is attributed to ''[[Moyeria]]'', which is interpreted as possessing a pellicle composed of proteinaceous strips, the defining characteristic of euglenids. It is found in [[Middle Ordovician]] and [[Silurian]] rocks, making it the oldest fossil evidence of euglenids.<ref name="Gray 1989"/><ref name="Strother 2020"/>
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==Bibliography==
==Bibliography==
* {{cite book|last1=Ciugulea|first1=I.|last2=Triemer|first2=R. E.|year=2010|title=A Color Atlas of Photosynthetic Euglenoids|publisher=Michigan State University Press|location=East Lansing, MI|isbn=9780870138799 |url=https://books.google.com/books?id=0FVFAQAAIAAJ}}
* {{cite book|last1=Ciugulea|first1=I.|last2=Triemer|first2=R. E.|year=2010|title=A Color Atlas of Photosynthetic Euglenoids|publisher=Michigan State University Press|location=East Lansing, MI|isbn=978-0-87013-879-9 |url=https://books.google.com/books?id=0FVFAQAAIAAJ}}
* {{cite journal|last1=Leander|first1=B. S.|last2=Triemer|first2=R. E.|last3=Farmer|first3=M. A.|year=2001|title=Character evolution in heterotrophic euglenids|journal=European Journal of Protistology|volume=37|issue=3|pages=337–356|doi=10.1078/0932-4739-00842 |s2cid=4181281 }}
* {{cite journal|last1=Leander|first1=B. S.|last2=Triemer|first2=R. E.|last3=Farmer|first3=M. A.|year=2001|title=Character evolution in heterotrophic euglenids|journal=European Journal of Protistology|volume=37|issue=3|pages=337–356|doi=10.1078/0932-4739-00842 |s2cid=4181281 }}
* {{cite book|author1=Leander, B.S.|author2=Lax, G.|author3=Karnkowska, A.|author4=Simpson, A.G.B.|year=2017|chapter=Euglenida|editor1=Archibald, J.M.|editor2=Simpson, A.G.B.|editor3=Slamovits, C.|title=Handbook of the Protists|publisher=Springer|pages=1–42|doi=10.1007/978-3-319-32669-6_13-1|isbn=978-3-319-32669-6 }}
* {{cite book|author1=Leander, B.S.|author2=Lax, G.|author3=Karnkowska, A.|author4=Simpson, A.G.B.|year=2017|chapter=Euglenida|editor1=Archibald, J.M.|editor2=Simpson, A.G.B.|editor3=Slamovits, C.|title=Handbook of the Protists|publisher=Springer|pages=1–42|doi=10.1007/978-3-319-32669-6_13-1|isbn=978-3-319-32669-6 }}
* {{cite journal|last=Leedale|first=G. F.|year=1978|title=Phylogenetic criteria in euglenoid flagellates|journal=BioSystems|volume=10|issue=1–2 |pages=183–187|doi=10.1016/0303-2647(78)90040-0 |pmid=656566 |bibcode=1978BiSys..10..183L |url=https://dx.doi.org/10.1016/0303-2647%2878%2990040-0|url-access=subscription}}
* {{cite journal|last=Leedale|first=G. F.|year=1978|title=Phylogenetic criteria in euglenoid flagellates|journal=BioSystems|volume=10|issue=1–2 |pages=183–187|doi=10.1016/0303-2647(78)90040-0 |pmid=656566 |bibcode=1978BiSys..10..183L }}
* {{cite book|last1=Wołowski|first1=K|last2=Hindák|first2=F|year=2005|title=Atlas of Euglenophytes|location=Krakow|publisher=VEDA Publishing House of the Slovak Academy of Sciences|isbn=9788022408363|url=https://books.google.com/books?id=4lVFAQAAIAAJ}}
* {{cite book|last1=Wołowski|first1=K|last2=Hindák|first2=F|year=2005|title=Atlas of Euglenophytes|location=Krakow|publisher=VEDA Publishing House of the Slovak Academy of Sciences|isbn=978-80-224-0836-3|url=https://books.google.com/books?id=4lVFAQAAIAAJ}}


== External links ==
== External links ==

Latest revision as of 18:17, 15 October 2025

Template:Short description Template:Automatic taxobox

Euglenids or euglenoids are one of the best-known groups of eukaryotic flagellates: single-celled organisms with flagella, or whip-like tails. They are classified in the phylum Euglenozoa, class Euglenida or Euglenoidea. Euglenids are commonly found in fresh water, especially when it is rich in organic materials, but they have a few marine and endosymbiotic members. Many euglenids feed by phagocytosis, or strictly by diffusion. A monophyletic subgroup known as Euglenophyceae have chloroplasts and produce their own food through photosynthesis.[1][2][3] This group contains the carbohydrate paramylon.

Euglenids split from other Euglenozoa (a larger group of flagellates) more than a billion years ago. The plastids (membranous organelles) in all extant photosynthetic species result from secondary endosymbiosis between a euglenid and a green alga.[4]

Structure

Euglenoids are distinguished mainly by the presence of a type of cell covering called a pellicle. Within its taxon, the pellicle is one of the euglenoids' most diverse morphological features.[5] The pellicle is composed of proteinaceous strips underneath the cell membrane, supported by dorsal and ventral microtubules. 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 called metaboly. Otherwise, they move using their flagella.

File:2023 Eugenid.svg
Euglenid Body Plan
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Classification

File:Algen I. (Schizophyceen, Flagellaten, Peridineen) (1910) (17950163265).jpg
Examples of euglenid diversity.
1—2. Ascoglena sp. (Euglenales);
3–4. Cryptoglena sp. (idem);
5–9, 14–15, 24–25, 27–29. Trachelomonas spp. (id.);
10. Eutreptia sp. (Eutreptiales);
11, 20. Astasia spp. (Euglenales);
12. Distigma sp. (Eutreptiales);
13. Menoid[i]um sp. (Rhabdomonadales);
16–18. Colacium sp. (Euglenales);
19, 26. Petalomonas spp. (Sphenomonadales);
21. Sphenomonas sp. (id.);
22–23. Euglenopsis sp. (Euglenales);
30. Peranema sp. (Heteronematales)

The first attempt at classifying euglenids was done by Ehrenberg in 1830, when he described the genus Euglena and placed it in the Polygastrica of family Astasiae, containing other creatures of variable body shape and lacking pseudopods or lorica. Later, various biologists described additional characteristics for Euglena and established different classification systems for euglenids based on nutrition modes, the presence and number of flagella, and the degree of metaboly. 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.[6] Gordon F. Leedale expanded on Hollande's system, establishing six orders (Eutreptiales, Euglenales, Rhabdomonadales, Sphenomonadales, Heteronematales and Euglenamorphales) and taking into account new data on their physiology and ultrastructure. This scheme endured until 1986, with the sequencing of the SSU rRNA gene from Euglena gracilis.[6]

Euglenids are currently regarded as a highly diverse clade within Euglenozoa, in the eukaryotic supergroup Discoba.[7] They are traditionally organized into three categories based on modes of nutrition: the phototrophs (Euglenophyceae), the osmotrophs (mainly the 'primary osmotrophs' known as Aphagea), and the phagotrophs, from which the first two groups have evolved.[8] The phagotrophs, although paraphyletic, have historically been classified under the name of Heteronematina.[7]

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 the base of the euglenid tree, namely Petalomonadida and the paraphyletic 'Ploeotiida'. In contrast, all flexible euglenids belong to a monophyletic group known as Spirocuta, which includes Euglenophyceae, Aphagea and various phagotrophs (Peranemidae, Anisonemidae and Neometanemidae). The current classification of class Euglenida, as a result of these studies, is as follows:[8][9][10][11][12]

Nutrition

The classification of euglenids is still variable, as groups are being revised to conform with their molecular phylogeny. 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.[16]

As with other Euglenozoa, the primitive mode of nutrition is phagocytosis. Prey such as bacteria and smaller flagellates is ingested through a cytostome, supported by microtubules. These are often packed together to form two or more rods, which function in ingestion, and in Entosiphon form an extendable siphon. Most phagotrophic euglenids have two flagella, one leading and one trailing. The latter is used for gliding along the substrate. In some, such as Peranema, the leading flagellum is rigid and beats only at its tip.

Osmotrophic euglenoids

Osmotrophic euglenids are euglenids which have undergone osmotrophy.

Due to a lack of characteristics that are useful for taxonomical purposes, 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.[17]

A prolonged absence of light or exposure to harmful chemicals may cause atrophy and 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 as Astasia (colourless Euglena) and Hyalophacus (colourless Phacus). Due to the lack of a developed cytostome, these forms feed exclusively by osmotrophic absorption.

Reproduction

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 using sexual reproduction. This is one of the reasons they could no longer be classified as animals.Script error: No such module "Unsubst".

For euglenids to reproduce, asexual reproduction takes place in the form of binary fission, and the cells replicate and divide during mitosis and cytokinesis. This process occurs in a very distinct order. First, the basal bodies and flagella replicate, then the cytostome and microtubules (the feeding apparatus), and finally the nucleus and remaining cytoskeleton. 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.[18] Because of the way that this reproduction takes place and the axis of separation, it is called longitudinal cell division or longitudinal binary fission.[19]

Evolution

The earliest fossil of euglenids is attributed to Moyeria, which is interpreted as possessing a pellicle composed of proteinaceous strips, the defining characteristic of euglenids. It is found in Middle Ordovician and Silurian rocks, making it the oldest fossil evidence of euglenids.[20][21]

Gallery

References

Template:Reflist

Bibliography

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External links

Template:Discoba Template:Taxonbar Template:Authority control

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  21. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Strother 2020
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