GENERA starting with "o"



  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...


  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...