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Flagellate

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File:Haeckel Flagellata.jpg
"Flagellata" from Ernst Haeckel's Artforms of Nature, 1904
File:Giardia lamblia.jpg
Parasitic Excavata (Giardia lamblia)
File:Chlamydomonas (10000x).jpg
Green algae (Chlamydomonas)

A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word flagellate also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagella. However, several derivations of the term "flagellate" (such as "dinoflagellate" and "choanoflagellate") are more formally characterized.<ref name="pmid8868448">Template:Cite journal</ref>

Form and behaviorEdit

Flagella in eukaryotes are supported by microtubules in a characteristic arrangement, with nine fused pairs surrounding two central singlets. These arise from a basal body. In some flagellates, flagella direct food into a cytostome or mouth, where food is ingested. Flagella role in classifying eukaryotes.

Among protoctists and microscopic animals, a flagellate is an organism with one or more flagella. Some cells in other animals may be flagellate, for instance the spermatozoa of most animal phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, and some gymnosperms and closely related plants do so.<ref>Philip E. Pack, Ph.D., Cliff's Notes: AP Biology 4th edition.</ref> Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do.<ref name="Hibbett2007">Template:Cite journal</ref> Many protists take the form of single-celled flagellates.

Flagella are generally used for propulsion. They may also be used to create a current that brings in food. In most such organisms, one or more flagella are located at or near the anterior of the cell (e.g., Euglena). Often there is one directed forwards and one trailing behind. Many parasites that affect human health or economy are flagellates in at least one stage of life cycle, such as Naegleria, Trichomonas and Plasmodium.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Flagellates are the major consumers of primary and secondary production in aquatic ecosystems - consuming bacteria and other protists.Template:Citation needed

File:Flagellata 1.png
"Flagellata" from Encyclopædia Britannica

Flagellates as specialized cells or life cycle stagesEdit

An overview of the occurrence of flagellated cells in eukaryote groups, as specialized cells of multicellular organisms or as life cycle stages, is given below (see also the article flagellum):<ref>Raven, J.A. 2000. The flagellate condition. In: (B.S.C. Leadbeater and J.C. Green, eds) The flagellates. Unity, diversity and evolution. The Systematics Association Special Volume 59. Taylor and Francis, London. pp. 269–287.</ref><ref>Webster, J & Weber, R (2007). Introduction to Fungi (3rd ed.). Cambridge: Cambridge University Press. pp. 23–24, [1]</ref><ref name="Adl et al. 2012">Adl et al. (2012).</ref>

Flagellates as organisms: the FlagellataEdit

In older classifications, flagellated protozoa were grouped in Flagellata (= Mastigophora), sometimes divided into Phytoflagellata (= Phytomastigina, mostly autotrophic) and Zooflagellata (= Zoomastigina, heterotrophic). They were sometimes grouped with Sarcodina (ameboids) in the group Sarcomastigophora.

The autotrophic flagellates were grouped similarly to the botanical schemes used for the corresponding algae groups. The colourless flagellates were customarily grouped in three groups, highly artificial:<ref>Fritsch, F.E. The Structure and Reproduction of the Algae. Vol. I. Introduction, Chlorophyceae. Xanthophyceae, Chrysophyceae, Bacillariophyceae, Cryptophyceae, Dinophyceae, Chloromonadineae, Euglenineae, Colourless Flagellata. 1935. Cambridge, England: Cambridge University Press, [2].</ref>

  • Protomastigineae, in which absorption of food-particles in holozoic nutrition occurs at a localised point of the cell surface, often at a cytostome, although many groups were merely saprophytes; it included the majority of colourless flagellates, and even many "apochlorotic" algae;
  • Pantostomatineae (or Rhizomastigineae), in which the absorption takes place at any point on the cell surface; roughly corresponds to "amoeboflagellates";
  • Distomatineae, a group of binucleate "double individuals" with symmetrically distributed flagella and, in many species, two symmetrical mouths; roughly corresponds to current Diplomonadida.

Presently, these groups are known to be highly polyphyletic. In modern classifications of the protists, the principal flagellated taxa are placed in the following eukaryote groups, which include also non-flagellated forms (where "A", "F", "P" and "S" stands for autotrophic, free-living heterotrophic, parasitic and symbiotic, respectively):<ref>Template:Cite journal</ref><ref>Patterson, D.J. (2000). Flagellates: Heterotrophic Protists With Flagella. Tree of Life, [3].</ref>

Although the taxonomic group Flagellata was abandoned, the term "flagellate" is still used as the description of a level of organization and also as an ecological functional group. Another term used is "monadoid", from monad.<ref>Hoek, C. van den, Mann, D.G. and Jahns, H.M. (1995). Algae An Introduction to Phycology. Cambridge University Press, Cambridge. Template:ISBN. </ref> as in Monas, and Cryptomonas and in the groups as listed above.

The amoeboflagellates (e.g., the rhizarian genus Cercomonas, some amoebozoan Archamoebae, some excavate Heterolobosea) have a peculiar type of flagellate/amoeboid organization, in which cells may present flagella and pseudopods, simultaneously or sequentially, while the helioflagellates (e.g., the cercozoan heliomonads/dimorphids, the stramenopile pedinellids and ciliophryids) have a flagellate/heliozoan organization.<ref>Mikryukov, K.A. (2001). Heliozoa as a component of marine microbenthos: a study of Heliozoa of the White Sea. Ophelia 54: 51–73.</ref>

ReferencesEdit

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External linksEdit

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