Flagellate

"Flagellata" from Ernst Haeckel's Artforms of Nature, 1904
Parasitic excavate (Giardia lamblia)
Green alga (Chlamydomonas)

A flagellate is a cell or organism with one or more whip-like organelles called flagella. The word flagellate also describes a particular construction (or level of organization) characteristic of many protists (eukaryotic organisms) and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagellae. However, the term "flagellate" is included in other terms (such as "dinoflagellate" and "choanoflagellata") which are more formally characterized.[1]

Form and behavior

Eukaryotic flagella 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 often support hairs, called mastigonemes, or contain rods. Their ultrastructure plays an important role in classifying eukaryotes.

Among protoctists and microscopic animals, a flagellate is an organism with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, and some gymnosperms and closely related plants do so. Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do. 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. Among animals, fungi, and Choanozoa, which make up a group called the opisthokonts, there is a single posterior flagellum. They are from the phylum Mastigophora. They can cause diseases and are typically heterotrophic. They reproduce by binary fission.They spend most of their existence moving or feeding. Many parasites that affect human health or economy are flagellates. Flagellates are the major consumers of primary and secondary production in aquatic ecosystems - consuming bacteria and other protists.

"Flagellata" from Encyclopædia Britannica

Flagellates as specialized cells or life cycle stages

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):[2][3][4]

Flagellates as organisms: the Flagellata

In older classifications, flagellated protozoa were grouped in Flagellata (= Mastigophora), sometimes divided in 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 customary grouped in three groups, highly artificial:[7]

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 (A: autotrophic; F: free-living heterotrophic; P: parasitic; S: symbiotic):[8][9]

Although the taxonomic group Flagellata was abandoned, the term "flagellate" is still used as the description of a level of organization and also as a ecological functional group. Another term used is "monadoid", from monad.[11] 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.[12]

References

  1. ↑ Cavalier-Smith T. (1995). "Zooflagellate phylogeny and classification". Tsitologiya. 37 (11): 1010–29. PMID 8868448.
  2. ↑ 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.
  3. ↑ Webster, J & Weber, R (2007). Introduction to Fungi (3rd ed.). Cambridge: Cambridge University Press. pp. 23–24,
  4. ↑ Adl et al. (2012).
  5. ↑ Lahr DJ, Parfrey LW, Mitchell EA, Katz LA, Lara E (July 2011). The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms. Proc. Biol. Sci. 278 (1715): 2083–6.
  6. ↑ Pánek, T., Čepička, I. (2012). Diversity of Heterolobosea. In: Caliskan, M. (ed.) Genetic diversity in microorganisms. InTech: Rijeka, Croatia, pp 3–26, .
  7. ↑ 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, .
  8. ↑ Jeuck, A., & Arndt, H. (2013). A short guide to common heterotrophic flagellates of freshwater habitats based on the morphology of living organisms. Protist, 164 (6): 842-860, .
  9. ↑ Patterson, D.J. (2000). Flagellates: Heterotrophic Protists With Flagella. Tree of Life, .
  10. ↑ Patterson, D.J., Vørs, N., Simpson, A.G.B. & O'Kelly, C., 2000. Residual Free-living and Predatory Heterotrophic Flagellates. In: Lee, J.J., Leedale, G.F. & Bradbury, P. An Illustrated Guide to the Protozoa. Society of Protozoologists/Allen Press: Lawrence, Kansas, U.S.A, 2nd ed., vol. 2, p. 1302-1328, .
  11. ↑ Hoek, C. van den, Mann, D.G. and Jahns, H.M. (1995). Algae An Introduction to Phycology. Cambridge University Press, Cambridge. ISBN 0-521-30419-9.
  12. ↑ Mikryukov, K.A. (2001). Heliozoa as a component of marine microbenthos: a study of Heliozoa of the White Sea. Ophelia 54: 51–73.
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