Nitzschia
Nitzschia (NIT-see-uh) is a very large genus of thin, elongated diatoms with pointed ends. Its raphe system, unlike that of many other diatom genera, does not appear as a central solid line but rather wraps around the diatom like train tracks. The short lines within the raphe "tracks" are called fibulae, and their density is often used to identify Nitzschia species apart when striae are not visible. That said, there are many similar species of Nitzschia and it is often difficult to identify specimens to the species level. Many specimens may belong to species which are not described in online resources; some specimens like that are included at the bottom of this page.
The "traintrack" like raphe system is characteristic of Nitzschia species. Here, it can be seen on both the front and back valve faces. It appears here on the face, but may also be positioned along the valve margin.
N. acicularis
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Cells are 30-100 µm in length, 3-4 µm in width.
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Rows of fibulae are 16-21 per 10 µm.
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N. acicularis can be uniquely identified by its very long, thin ends.
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Striae are not visible with a light microscope.
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Cells often appear to have a very faint outline under the microscope.
For more information, visit diatoms.org here.
N. cf. balcanica
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Cells are 23-63 µm in length, 4-5 µm in width.
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Rows of striae are 38-40 per 10 µm. (Striae are faint and may be difficult to view)
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Fibulae may vary in size, and are 12-16 per 10 µm.
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Valves are slightly pinched at the center and pointed at the ends.
For more information, visit diatoms.org here.
Note the difference: The two left-most diatoms are N. cf. palacea, while the right-most diatom is N. dissapata.
N. dissapata
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Cells are 12-72 µm in length, 3-8 µm in width.
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Rows of striae are 32-50 per 10 µm, but are not easily seen under a light microscope.
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Valves are relatively wide and "inflated" looking, in comparison to other Nitzschia species.
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N. dissapata can be easily recognized by its bold, widely, and regularly spaced fibulae with rectangular spaces in between (fibulae are 5-12 per 10 µm).
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Raphe line is eccentrically positioned on the valve face, and does not often follow the valve perimeter.
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Some individuals with very ball-like rounded tips may actually belong to the subspecies N. dissipata var. oligotraphenta (See right-most picture for example).
For more information, visit diatoms.org here.
Note the difference: The left-most diatom is N. cf. palacea, while the right-most diatom is N. dissapata.
N. cf. linearis
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Cells are 60-150 µm in length, 4-6 µm in width.
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Rows of striae are 35-38 per 10 µm.
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In true N. linearis, the valve margin on the side with the raphe has a slight indent at the center. These specimens do not.
For more information, visit diatoms.org here.
Unidentified Nitzschia species present in Lake Mendota
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There are a number of Nitzschia in Lake Mendota which are difficult to define as a specific species because there are many close potential species, but none that fir these specimens closely enough. However, for the sake of presenting a complete portfolio of Nitzschia in Lake Mendota, they are noted here.
For a list of more Nitzschia species, visit diatoms.org here.
The above is a close-up of the below picture of a Nitzschia in girdle view.
