Desmidiales

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Desmids
Micrasterias radiata.jpg
Micrasterias furcata
Scientific classification
(unranked): Archaeplastida
Kingdom: Plantae
Division: Charophyta
Class: Zygnemophyceae
Order: Desmidiales
Families

Closteriaceae
Desmidiaceae
Gonatozygaceae
Peniaceae

Desmids (Gr. desmos, bond or chain)are an order (Desmidiales) in the Charophyta, a division of green algae that forms a sister group to the land plants (Embryophyta).[1] The Desmidiales comprise around 40 genera and 5,000[2] to 6,000[3] species, found mostly but not exclusively in fresh water. Many species may be found in the fissures between patches of sphagnum moss in marshes. With a pH level of approximately 4.0, sphagnum peat provides the ideal environment for this flora. The structure of these algae are unicellular, while the cell is sometimes divided into two symmetrical compartments separated by a narrow bridge or isthmus, wherein the spherical nucleus is located. Each semi-cell houses a large, often folded chloroplast for photosynthesizing. One or more pyrenoids can be found. These form carbohydrates for energy storage. Desmids assume a variety of highly symmetrical and generally attractive shapes, among those elongated, star-shaped and rotund configurations, which provide the basis for their classification.[4] The largest among them may be visible to the unaided eye.[5] Desmidiales lack in flagellae. Desmids commonly reproduce by asexual fission, however, in adverse conditions, Desmidiales may reproduce sexually through a process of conjugation,[6][7] which are also found among the Zygnematales. These two groups are closely related, and comprise the class Zygnematophyceae. The desmids are sometimes treated as members of the Zygnematales,[8] but more often given the separate order Desmidiales. They are also related to the algae genus Spirogyra as some of them are filamentous, such as the species Desmidium swartzii. However, these filaments are arranged in a helix pattern.[4]

Desmids possess characteristic crystals of Barium sulphate at either end of the cell[9] which exhibit a continuous Brownian type motion.

Many desmids also secrete translucent, gelatinous mucilage from pores in the cell wall that acts a protecting agent.

Species[edit]

Benefit to humans[edit]

As photosynthetic algae they benefit by releasing oxygen into the air and manufacturing glucose as food, in turn being predated upon by amoebae and other invertebrates which are then consumed by higher-level predators, thus benefiting the the food chain. They are known to absorb large amounts of strontium and barium from the water, thus recycling these metals.

References[edit]

  1. ^ Gontcharov AA, Marin BA, Melkonian MA (January 2003). "Molecular phylogeny of conjugating green algae (Zygnemophyceae, Streptophyta) inferred from SSU rDNA sequence comparisons". J. Mol. Evol. 56 (1): 89–104. doi:10.1007/s00239-002-2383-4. PMID 12569426. 
  2. ^ Van den Hoek, C., D. G. Mann, & H. M. Jahns, 1995. Algae:An Introduction to Phycology, page 468. (Cambridge: Cambridge University Press). ISBN 0-521-30419-9
  3. ^ Brook, Alan J., 1981. The Biology of Desmids, page 1. (Berkeley: University of California Press). ISBN 0-520-04281-6
  4. ^ a b http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/algdr.html
  5. ^ a b http://www.desmids.com/
  6. ^ name="pmid17272304">Kapraun DF (April 2007). [http://aob.oxfordjournals.org/cg
  7. ^ i/pmidlookup?view=long&pmid=17272304 "Nuclear DNA content estimates in green algal lineages: chlorophyta and streptophyta"]. Ann. Bot. 99 (4): 677–701. doi:10.1093/aob/mcl294. PMC 2802934. PMID 17272304. 
  8. ^ http://onlinelibrary.wiley.com/doi/10.1046/j.1440-1835.2002.00263.x/abstract
  9. ^ Proceedings of the Royal Society -Biological Minerals Formed from Strontium and Barium Sulphates. II. Crystallography and Control of Mineral Morphology in Desmids
  10. ^ http://www.ucmp.berkeley.edu/greenalgae/charophyta/desmidiales.html
  11. ^ http://www.micrographia.com/specbiol/alg/desmi/desm0100.htm

External links[edit]

Further reading[edit]

  • Survey of Clare Island 1990 - 2005, noting the Desmidiales recorded. Ed. Guiry, M.D., John, D.M., Rindi, F. and McCarthy, T.K. 2007. New Survey of Clare Island. Volume 6: The Freshwater and Terrestrial Algae. Royal Irish Academy. ISBN 978-1-904890-31-7