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Diatoms of the United States is now known as Diatoms of North America.
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Agardh 1830      Category: Asymmetrical biraphid
TYPE SPECIES: Cymbella cymbiformis Agardh




CLASS: Bacillariophyceae
  ORDER: Cymbellales
    FAMILY: Cymbellaceae

  1. Valves slightly to strongly asymmetric to the apical axis
  2. Valves symmetric to the transapical axis
  3. Distal raphe ends deflected dorsally
  4. Stigmata, if present, located on the ventral side

The valves of Cymbella are slightly to strongly dorsiventral, or asymmetric to the apical axis. Valves are symmetric to the transapical axis. The terminal raphe fissures are deflected to the dorsal side, an important diagnostic feature. Apical pore fields are present at both poles. Striae are uniseriate. One or more stigmata may be present. If a stigma or stigmata are present, they are located on the ventral side of the central area. Internally, the stigmata are convoluted internal occlusions. Also internally, the proximal raphe may be continuous across central area. Cymbella cells grow predominately in benthic habitats, and often produce mucilaginous stalks that are secreted through the apical porefield.

Historically, Cymbella has been a large, heterogenous group and is not considered to be a natural, or monophyletic group of species. Recently, a number of genera have been split from Cymbella, including Cymbopleura, Delicata and Encyonopsis.

Cite This Page:
Spaulding, S., and Edlund, M. (2008). Cymbella. In Diatoms of the United States. Retrieved May 23, 2018, from

Contributor: Sarah Spaulding | Mark Edlund - December 2008
Reviewer: Marina Potapova - May 2010