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Diatoms of the United States is now known as Diatoms of North America.
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GENERA starting with "o"


Odontidium 2

  1. Sternum distinct
  2. Transapical ribs heavily silicified
  3. Spines simple
  4. Girdle structure complex
  5. Rimoportula present

Araphid - Frustules of Odontidium have heavily silicified transapical ribs that extend internally from the valve face. The sternum is distinct, and may be relatively broad, or may be narrow. Spines are simple and located at the valve face/mantle boundary. Spines are considered non-functional. Girdle band structure is complex, with many alternating open copulae and a pleural band. The copulae possess porose ligulae. One rimoportula...


  1. Marginal ridge present
  2. Areolae slit-like
  3. Areolae with dentate projections

Asymmetrical biraphid - SPECIES OF ORICYMBA ARE NOT KNOWN TO OCCUR IN NORTH AMERICA This genus has slightly dorsiventral, or nearly symmetric, valves. The valve face is flat and is separated from the valve mantle by a marginal ridge. A distinct, isolated stigma is present, located between the central nodule and the ventral striae. The raphe is slightly lateral. Proximal raphe ends are widened slightly and deflected to the primary side. Distal...

Orthoseira 1

  1. Carinoportulae one to several, near midvalve
  2. Spines marginal, variable in length
  3. Frustules linked by spines to form short chains

Centric - The frustules of Orthoseira are cylindrical and form filamentous colonies linked by marginal spines. The valve surface is flat and possesses one or more unique process, the carinoportula. Internally, the valves may (or may not) have internal ‘caverns’, positioned at the valve mantle interface. The marginal spines, if present, are variable in length. Orthoseira typically grows in subaerial habitats, often with...

Oxyneis 2

  1. Valve margin elliptic or panduriform
  2. Septae present
  3. Cells form short chains or zigzag colonies

Araphid - Valves are relatively small in size and elliptic or panduriform in valve outline. Septae are present on the copulae (girdle bands). Oxyneis is considered a close relative of Tabellaria. The two genera share the presence of septae, which may be detached in some preparations. Species within the genus are characteristic of acidic lakes and peatland waters.