Light microscope


Distinctively ‘wedge-shape’ in girdle view; form colonies with frustules grouped in rosette formation, a colony form suspected of being common to the genus.

  • Valves broadly arcuate to lunate with slightly tapering poles; 120-160 μm in length, 21-27 μm in breadth at the valve centre
  • Striae, uniseriate, more or less regularly spaced; 9-11 in 10 μm at centre of the valve becoming denser towards the apices 14-15 per 10 μm
  • Puncta 12-14 per 10 μm at centre of valve and 15 per 10 μm at apices
  • Short raphe at both poles, situated within a clear hyaline area; raphe deflected towards the ventral side of the valve, extending from valve face towards mantle edge, turning inwards, terminating in a prominent helictoglossa
  • Single rimoportula at each pole, adjacent to helictoglossa, visible in most specimens
  • Raphe endings extend into clear hyaline area, continuous with sternum
  • Sternum not so well defined and appears slightly diffuse towards the valve centre
  • Small spines covering the valve margin, extending up to poles
  • Occasionally, long bifurcating spines occur

Electron microscope

  • Valves with uniform, uniseriate striae, virgae slightly raised internally, much more even externally; striae pass directly through to the exterior of the valve
  • Small spines situated on both valve margins, irregularly placed, some more developed than others, often broken
  • At the valve centre, two or three larger bifurcating distinctive spines occur
  • Raphe short, occurs at both poles, terminating in a prominent helictoglossa
  • Sternum not so prominent externally, situated towards the ventral margin
  • Single well developed rimoportula at each pole, communicating with the exterior valve surface
  • Ventral valve margin separated from valve face by an area of silica composed of a ridge with an upper crenulated portion, the lower portion smooth, more hyaline, with occasional puncta

At least six open bands (copulae) present, each with a series of irregularly placed puncta, between 3-5. Bands overlap, each becomes progressively smaller away from the valve; each band tapers towards the poles.