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Name derivation: |
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Greek stephanos meaning "Crown" and diskos meaning "disk." |
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Classification: |
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Stephanodiscus Ehrenberg, 1845. There are 166 species of which 44 have been taxonomically accepted.Order Thalassiosirales; Family Stephanodiscaceae |
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Morphology: |
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The frustules are generally discoid (girdle length < valve diameter), but can be cylindrical (girdle length > valve diameter). They occur as single free-floating cells. The valves have a circular outline with punctae (puncture marks) that radiate outward from the middle to the end to the cell. The punctae are in multi-seriate (more than one) rows and alternate with smooth spaces. At the end of each row aof multi punctae, single punctae radiate in a single line towards the center of the cell. In the center of the cell the punctae have no standard order. This can sometimes make the ornamentation of the cell appear to have two distinct sections or not. On the outer edge of the smooth space is a short, stout spine. The cells are more rectangular in girdle view and have no intercalary bands. The chromatophores can range from small, round and numerous to one or two irregularly shaped ones. Single auxospores are formed within a single frustule and are either spherical or elliptical. |
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Similar genera: |
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Coscinodiscus lacks spines, and differs in its ornamentation in valve view. They do not have alternating multi-seriate rows that alternate with a smooth row. Cyclotella lacks the crown of spines, and also differs in its ornamentation in valve view. It has two distinct regions (and inner region and an outer region) of ornamentation.
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Habitat: |
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Found in both fresh water and marine systems. It is widely distributed in lakes across the United States. |
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References: |
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Ehrenberg, C.G. 1845. Neue Untersuchungen über das kleinste Leben als geologisches Moment. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königlich-Preussischen Akademie der Wissenschaften zu Berlin, 1845: 53-87. Guiry, M.D. and G.M. Guiry 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 19 September 2013. Whitford, L. A. and Schumacher G. J. 1973. A Manual Of Fresh-Water Algae. Sparks Press. |
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