Euglena Ehrenberg, 1830

Lectotype species: Euglena viridis (O.F.Müller) Ehrenberg

Original publication: Ehrenberg, C.G. (1830). Neue Beobachtungen über blutartige Erscheinungen in Aegypten, Arabien und Sibirien, nebst einer Uebersicht und Kritik der früher bekannten. Annalen der Physik und Chemie, Ser. 2 8: 477-514.

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Type designated in: Dujardin, F. (1841). Histoire naturelle des Zoophytes, Infusoires, comprenant la physiologie et la clasification de ces animaux et la manière de les étudier à l'aide du microscope. pp. i-xii, 1-684. Paris: Librarie Encyclopédique de Roret.

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Description: Green flagellates with elongate, ovoid or fusiform cells, varying in length from 20 to 500 _m, and with 2 flagella originating within an anterior invagination of the cell. The highly mobile long flagellum emerges from the subapical canal opening as the organelle of locomotion, the other is so short that it ends within the reservoir (basal region of the invagination). The locomotory flagellum is doubled in thickness by a paraflagellar rod and bears a complex array of fibrous material, including a unilateral row of long fine hairs (visible only in the electron microscope). Locomotion involves helical rotation of the cell; most species exhibit euglenoid movement (rapid changes of body shape) when swimming stops, a few are almost rigid. Chloroplasts vary in shape (discs, plates or ribbons), size, number per cell (from 2 to several hundred) and pyrenoid type (naked, sheathed, projecting, immersed or absent); chloroplast lamellae have 3 or more thylakoids except in the pyrenoid matrix where there are only 2; the chloroplasts are grass-green and contain chlorophylls a and b, _-carotene, astaxanthin, antheraxanthin, diadinoxanthin and neoxanthin. All species are photoauxotrophic, some facultatively heterotrophic, none phagotrophic. The reserve carbohydrate is paramylon, solid grains or links of a _-1,3-linked glucan with helical organization. Aging cells fill with brown droplets of lipid (lipofuscin) and cyclic metaphosphates. All species have an extraplastidial, _-carotene-containing, orange-red eyespot that curves partway around the canal-reservoir junction in the anterior cytoplasmic matrix, opposite a crystalline swelling (presumed photoreceptor) on the base of the long flagellum. All species are strongly phototactic. Cells have helical symmetry, usually with an imposed bilateral symmetry, with or without slight cell flattening. Pellicle consists of flexible, elastic, interlocking, proteinaceous strips that spiral along the cell and intussuscept at both ends. Pellicle lies within the cell membrane and cells are naked except for a thin layer of mucilage secreted from subpellicular muciferous bodies. Some species form mucilaginous cysts or palmellae. Mitosis in Euglena is completely intranuclear, with a persisting and dividing nucleolus, high chromosome numbers (ca. 45 in E. gracilis, ca. 86 in E. spirogyra), staggered and untidy chromatid segregation, nucleoplasmic microtubules only (no cytoplasmic ones) and tiny kinetochores (only 4 microtubules) per chromatid in E. gracilis). Reproduction is by longitudinal fission. Records of sexual reproduction are rare and unsubstantiated. Ultrastructural details of Golgi bodies, mitochondria, flagellar roots, endoplasmic reticulum and contractile vacuole are well documented and diagnostic for the class. Euglena gracilis (and less easily E. anabaena, deses, pisciformis, stellata and viridis) can be grown axenically in undefined media such as 0.2% beef extract; E. gracilis grows phototrophically or heterotrophically on acetates, organic acids, alcohols, or sugars, with an absolute requirement for cobalamin (vitamin B12). It is therefore used in hospitals to assay blood for B12, lack of which causes pernicious anemia in humans. E. gracilis, though relatively rare in nature, is the dominant research organism in euglenology and many areas of physiology and biochemistry. Cells grown in the dark reduce their chloroplasts to proplastids that can divide and survive for years but, given light, will expand, synthesize chlorophyll and resume photosynthesis within 24 hours, thus providing ideal material for research on chloroplast physiology and development. Permanently colorless races without chloroplasts can be produced in culture using heat, ultraviolet irradiation, streptomycin and other antibiotics, antihistamines and other chemicals; some of the bleached races are identical to naturally occurring species of Astasia, especially A. longa. Strains of E. gracilis are also used in research on DNA, RNA, photoinduction of enzyme synthesis, lipid metabolism, heterotrophic nutrition, respiratory pathways, flagellar movement and photoreception. This wide use of Euglena in research is summarized in Buetow (1968a, 1968b, 1982, 1989). Euglena spp. are predominantly freshwater organisms of worldwide distribution, occurring in farmyards, greenhouse tanks, agricultural drainage channels, muddy ponds, peaty pools and acidic lakes (down to pH 2.5). Waters contaminated by animals often produce blooms, especially of E. viridis. Brackish species can color estuarine mudflats green in dull light, the color vanishing in full sunshine as the cells creep away from the mud surface. A few species have been recorded from the open sea. Emend. Marin & Melkonian (in Marin et al. 2003: 101).

Information contributed by: G.F. Leedale. The most recent alteration to this page was made on 2017-12-30 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Most recent taxonomic treatment adopted: Cavalier-Smith, T. (2016). Higher classification and phylogeny of Euglenozoa. European Journal of Protistology 56: 250–276, 2 figs.

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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 30 December 2017. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 23 May 2024

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