Euglenid

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Euglenid
Temporal range: Eocene (53.5Ma) - recent [1]
Ehrenberg euglena viridis.jpg
Euglena viridis , by Ehrenberg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Discoba
Superphylum: Discicristata
Phylum: Euglenozoa
Class: Euglenida
Butschli 1884, emend. Simpson 1997
Major groups
Synonyms
  • Euglenoidina Bütschli, 1884, Blochmann, 1886
  • Euglenoidea Lankester, 1885
  • Euglenoida Cavalier-Smith, 1993

Euglenids or euglenoids are one of the best-known groups of flagellates. They are excavate eukaryotes of the phylum Euglenophyta, classified as class Euglenida or Euglenoidea. Euglenids are commonly found in freshwater, especially when it is rich in organic materials, with a few marine and endosymbiotic members. Many euglenids feed by phagocytosis, or strictly by diffusion. A monophyletic group known as Euglenophyceae have chloroplasts and produce their own food through photosynthesis. [2] [3] [4] This group is known to contain the carbohydrate paramylon.

Euglenids split from other Euglenozoa more than a billion years ago. The plastids in all extant photosynthetic species is the result from secondary endosymbiosis between a phagotrophic eukaryovorous euglenid and a Pyramimonas -related green alga. [5] In January 2024, some fossilized forms of euglenid had been found to be mistakenly classified as Pseudoschizaea shells. [6]

Structure

Euglenid Body Plan (by Patrick Keeling and Yana Eglit) Euglenid body plan.jpg
Euglenid Body Plan (by Patrick Keeling and Yana Eglit)

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. [7] 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.

Classification

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) 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. [8] 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 . [8]

Euglenids are currently regarded as a highly diverse clade within Euglenozoa, in the eukaryotic supergroup Discoba. [9] 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. [10] The phagotrophs, although paraphyletic, have historically been classified under the name of Heteronematina. [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 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: [10] [11] [12] [13] [14]

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. [18]

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. [19]

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.[ dubious – discuss ]

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. [20] Because of the way that this reproduction takes place and the axis of separation, it is called longitudinal cell division or longitudinal binary fission. [21]

Related Research Articles

<span class="mw-page-title-main">Euglenozoa</span> Phylum of protozoans

Euglenozoa are a large group of flagellate Discoba. 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.

<span class="mw-page-title-main">Stramenopile</span> Clade of eukaryotes

The Stramenopiles, also called Heterokonts, are a clade of organisms distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, and in some they have been secondarily lost. Stramenopiles represent one of the three major clades in the SAR supergroup, along with Alveolata and Rhizaria.

<i>Euglena</i> Genus of unicellular flagellate eukaryotes

Euglena is a genus of single cell flagellate eukaryotes. It is the best known and most widely studied member of the class Euglenoidea, a diverse group containing some 54 genera and at least 200 species. Species of Euglena are found in fresh water and salt water. They are often abundant in quiet inland waters where they may bloom in numbers sufficient to color the surface of ponds and ditches green (E. viridis) or red (E. sanguinea).

<span class="mw-page-title-main">Euglenophyceae</span> Unicellular algae

Euglenophyceae (ICBN) or Euglenea (ICZN) is a group of single-celled algae belonging to the phylum Euglenozoa. They have chloroplasts originated from an event of secondary endosymbiosis with a green alga. They are distinguished from other algae by the presence of paramylon as a storage product and three membranes surrounding each chloroplast.

<i>Euglena gracilis</i> Species of single-celled Eukaryote algae

Euglena gracilis is a freshwater species of single-celled alga in the genus Euglena. It has secondary chloroplasts, and is a mixotroph able to feed by photosynthesis or phagocytosis. It has a highly flexible cell surface, allowing it to change shape from a thin cell up to 100 µm long to a sphere of approximately 20 µm. Each cell has two flagella, only one of which emerges from the flagellar pocket (reservoir) in the anterior of the cell, and can move by swimming, or by so-called "euglenoid" movement across surfaces. E. gracilis has been used extensively in the laboratory as a model organism, particularly for studying cell biology and biochemistry.

<span class="mw-page-title-main">Euglenales</span> Order of flagellate eukaryotes

Euglenales is an order of flagellates in the phylum Euglenozoa. The family includes the most well-known euglenoid genus, Euglena, as well as other common genera like Phacus and Lepocinclis.

<span class="mw-page-title-main">Euglenaceae</span> Family of flagellate eukaryotes

Euglenaceae is a family of flagellates in the phylum Euglenozoa. The family includes the most well-known euglenoid genus, Euglena.

<span class="mw-page-title-main">Protozoa</span> Single-celled eukaryotic organisms that feed on organic matter

Protozoa are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically, protozoans were regarded as "one-celled animals".

<i>Phacus</i> Genus of algae

Phacus is a genus of unicellular excavates, of the phylum Euglenozoa, characterized by its flat, leaf-shaped structure, and rigid cytoskeleton known as a pellicle. These eukaryotes are mostly green in colour, and have a single flagellum that extends the length of their body. They are morphologically very flat, rigid, leaf-shaped, and contain many small discoid chloroplasts.

<i>Peranema</i> Genus of protozoans

Peranema is a genus of free-living phagotrophic euglenids. There are more than 20 nominal species, varying in size between 8 and 200 micrometers. Peranema cells are gliding flagellates found in freshwater lakes, ponds and ditches, and are often abundant at the bottom of stagnant pools rich in decaying organic material. Although they belong to the class Euglenoidea, and are morphologically similar to the green Euglena, Peranema have no chloroplasts, and do not conduct autotrophy. Instead, they capture live prey, such as yeast, bacteria and other flagellates, consuming them with the help of a rigid feeding apparatus called a "rod-organ." Unlike the green euglenids, they lack both an eyespot (stigma), and the paraflagellar body (photoreceptor) that is normally coupled with that organelle. However, while Peranema lack a localized photoreceptor, they do possess the light-sensitive protein rhodopsin, and respond to changes in light with a characteristic "curling behaviour."

The Scotokaryotes (Cavalier-Smith) is a proposed basal Neokaryote clade as sister of the Diaphoretickes. Basal Scotokaryote groupings are the Metamonads, the Malawimonas and the Podiata. In this phylogeny the Discoba are sometimes seen as paraphyletic and basal Eukaryotes.

Petalomonas is a genus of phagotrophic, flagellated euglenoids. Phagotrophic euglenoids are one of the most important forms of flagellates in benthic aquatic systems, playing an important role in microbial food webs. The traits that distinguish this particular genus are highly variable, especially at higher taxa. However, general characteristics such as a rigid cell shape and single emergent flagellum can describe the species among this genus.

Heteronema is a genus of phagotrophic, flagellated euglenoids that are most widely distributed in fresh water environments. This genus consists of two very distinguishable morphogroups that are phylogenetically closely related. These morphogroups are deciphered based on shape, locomotion and other ultrastructural traits. However, this genus does impose taxonomic problems due to the varying historical descriptions of Heteronema species and its similarity to the genus Paranema. The species H. exaratum, was the first heteronemid with a skidding motion to be sequenced, which led to the discovery that it was not closely related to H. scaphrum, contrary to what was previously assumed, but instead to a sister group of primary osmotrophs. This suggests that skidding heteronemids can also be distinguished phylogenetically, being more closely related to Anisoma, Dinema and Aphageae, than to other species within Heteronema.

Cryptoglena(/ˌkɹɪptoʊˈgliːnə/) is a genus of photosynthetic euglenids that was first described in 1831 by Christian Gottfried Ehrenberg. Today, its circumscription is controversial: Bicudo and Menezes consider twenty-one species as Cryptoglena, of which, nine are uncertain. Cryptoglena species are water-based, living in both freshwater and marine environments. They are biflagellated, with one internal flagellum and one external flagellum, which allows movement through environments as demonstrated by Kim and Shin in the species C. pigra. The cells of Cryptoglena resemble a coffee bean, as they have a groove that runs the length of the cell on one side and makes them U-shaped in cross section. They are ovoid in shape and are small, with the larger cells being on average 25 x 15 μm. After being first described in 1831, little work was done on the genus until the late 1970s and early 1980s, after the scanning electron microscope completed development and was implemented into laboratories. Work then proceeded with the developments of molecular biology, which allows for classifications based on DNA sequences. For Cryptoglena the main DNA used for classification are small subunit (SSU) and large subunit (LSU) rDNA.

Postgaardia is a proposed basal clade of flagellate Euglenozoa, following Thomas Cavalier-Smith. As of April 2023, the Interim Register of Marine and Nonmarine Genera treats the group as a subphylum. A 2021 review of Euglenozoa places Cavalier-Smith's proposed members of Postgaardia in the class Symbiontida. As Euglenozoans may be basal eukaryotes, the Postgaardia may be key to studying the evolution of Eukaryotes, including the incorporation of eukaryotic traits such as the incorporation of alphaproteobacterial mitochondrial endosymbionts.

<i>Urceolus</i> Genus of flagellates

Urceolus is a genus of heterotrophic flagellates belonging to the Euglenozoa, a phylum of single-celled eukaryotes or protists. Described by Russian biologist Konstantin Mereschkowsky in 1877, its type species is Urceolus alenizini. Species of this genus are characterized by deformable flask-shaped cells that exhibit at least one flagellum that is active at the tip, arising from a neck-like structure that also hosts the feeding apparatus. They are found in a variety of water body sediments across the globe. According to evolutionary studies, Urceolus belongs to a group of Euglenozoa known as peranemids, closely related to the euglenophyte algae.

<i>Ploeotia</i> Genus of flagellates

Ploeotia is a genus of heterotrophic flagellates belonging to the Euglenida, a diverse group of flagellated protists in the phylum Euglenozoa. Species of Ploeotia are composed of rigid cells exhibiting two flagella. The genus was described by Félix Dujardin in 1841.

<span class="mw-page-title-main">Peranemid</span> Group of flagellates

The peranemids are a group of phagotrophic flagellates, single-celled eukaryotes or protists. They belong to the Euglenida, a diverse lineage of flagellates that contains the closely related euglenophyte algae. Like these algae, peranemids have flexible cells capable of deformation or metaboly, and have one or two flagella in the anterior region of the cell. They are classified as family Peranemidae (ICZN) or Peranemataceae (ICBN) within the monotypic order Peranemida (ICZN) or Peranematales (ICBN).

<span class="mw-page-title-main">Spirocuta</span> Group of flagellates with flexible cells

Spirocuta is a clade of euglenids, single-celled eukaryotes or protists belonging to the phylum Euglenozoa. They are distinguished from other euglenids by active deformation of their cell shape, a process called euglenid motion or metaboly. This is made possible by a high number of spirally arranged protein strips that run below their cell membrane and confer the cell with flexibility. These strips compose the helicoidal pellicle, a trait referenced by the alternative name Helicales.

<span class="mw-page-title-main">Anisonemia</span> Group of flagellates

Anisonemia is a clade of single-celled protists belonging to the phylum Euglenozoa, relatives of the Euglenophyceae algae. They are flagellates, with two flagella for locomotion. Anisonemia includes various phagotrophic species and a group of primary osmotrophic protists known as Aphagea.

References

  1. ↑ Lee, R.E. (2008). Phycology, 4th edition . Cambridge University Press. ISBN   978-0-521-63883-8.
  2. ↑ 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. PMC   6207741 . PMID   30375469.
  3. ↑ Yoshihisa Hirakawa (2017). Secondary Endosymbioses. Academic Press. p. 323. ISBN   9780128026809.
  4. ↑ "Algaebase :: Subclass: Euglenophycidae". Archived from the original on 2020-07-13. Retrieved 2019-10-27.
  5. ↑ 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. ISBN   978-3-319-54908-8. PMID   28429314.
  6. ↑ Cassella, Carly (21 January 2024). "Bizarre Fossils Are Neither Plant Nor Animal, But a 'Weird Fusion' of Life". ScienceAlert . Archived from the original on 22 January 2024. Retrieved 22 January 2024.
  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. ISSN   1550-7408. PMID   12095109. S2CID   2109559.
  8. 1 2 Carlos 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. ISSN   2296-701X. Wikidata   Q57898656.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  9. 1 2 Sina 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. ISSN   1066-5234. PMC   6492006 . PMID   30257078. Wikidata   Q57086550.
  10. 1 2 Gordon 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. ISSN   1434-4610. PMID   33126020. Wikidata   Q101127864.
  11. 1 2 G. 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. ISSN   1055-7903. Wikidata   Q110667805.
  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. ISSN   2046-2441. PMC   8061765 . PMID   33715388. Wikidata   Q125548575.
  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. ISSN   1066-5234. Wikidata   Q123348233.
  14. ↑ Lax G, Keeling PJ (2023). "Molecular phylogenetics of sessile Dolium sedentarium, a petalomonad euglenid". The Journal of Eukaryotic Microbiology. 70 (e12991): e12991. doi: 10.1111/jeu.12991 . PMID   37424051.
  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. ISSN   1434-4610. PMID   31102975. Wikidata   Q92132357.
  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. ISSN   0932-4739. PMID   27718409. Wikidata   Q31135651.
  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. ISSN   0932-4739. PMID   27889663. Wikidata   Q39151632.
  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 . PMID   12710635.
  20. ↑ "Euglenida". tolweb.org. Retrieved 2017-03-30.
  21. ↑ "Reproduction". Euglena. Retrieved 2017-03-31.

Bibliography

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