Live cells occur in

  • pairs
  • short chains
  • sometimes clumped together in mucilage masses


  • are circular in valve view
  • are domed and strongly biconvex in girdle view without a distinct girdle region
  • have two yellow-brown chloroplasts that lie closely associated with the inner surface of the valves
    • Valves
      • two valves form a sub-hemispherical shape
      • surfaces are covered with short irregular spines
      • perforated by radiating rows of rounded pores
      • are robust and thick-walled for their size
      • 6 - 10 μm diameter
      • have radiate striae that extend from the edge of the central zone to the valve margin
      • have numerous (1-20) relatively narrow, split, ligulate, non-porous girdle bands, varying in number according to whether or not they span two sibling cells
      • valvocopula (band associated with the valve) seems to lap over the edge of the valve