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Diatoms of the United States is now known as Diatoms of North America.
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Mann et Stickle in Round, Crawford and Mann 1990      Category: Symmetrical biraphid
TYPE SPECIES: Cosmioneis pusilla Mann and Stickle in Round, Crawford and Mann




Smallest to largest - 3 taxa sorted by maximum length

Image Credit: Rex Lowe

CLASS: Bacillariophyceae
  ORDER: Naviculales
    FAMILY: Cosmionidaeae

  1. Striae uniseriate and radial
  2. Valve face flat, with broad valve mantle
  3. Central area elliptical
  4. Internal proximal raphe ends anchor-shaped
  5. External proximal raphe ends expanded

Valves of species in the genus Cosmioneis are lanceolate to elliptical in outline, with capitate to rostrate ends. The valve face is flat, and the valve mantles are relatively broad. Striae are uniseriate and radial, and are composed of round to oval areolae. Striae become irregular near the central area. The axial area is narrow and linear, except at the central area, where the central area is expanded and ellipitical. Externally, the proximal raphe ends are expanded. Internally, the proximal raphe ends are anchor-shaped. Internally, the areolae are covered by hymenes. Living cells possess two H-shaped plastids.

Cosmioneis is a small genus found in alkaline, aerophilic habitats of North America. Some species are common in coastal waters. The genus includes the species C. pusilla (W. Smith) Mann and Stickle and its allies.

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

Contributor: Sarah Spaulding | Mark Edlund - December 2008
Reviewer: Sam Rushforth - April 2010