Staurosirella pinnata

Valves are ovoid, 3-4 µm wide and 4-10 µm long with rounded ends. Valve face flat, or slightly undulate due to raised costae. In girdle view, frustules are rectangular and form ribbon-like colonies, joined by linking spines. Colonies are attached to the substratum at one end by a frustule with a a mucilage pad, or colonies may be planktonic. Axial area is linear to lanceolate. Striae are distinct, 11-14 in 10 µm. Lineolae are long forming wide striae . Striae vary from parallel in the valve center to radiate toward the valve ends. Striae extend onto the valve mantle. Costae are more slender than the striae. Spines are positioned on costae along the valve margin, except at the apices. Spines are conical at the base and spatulate towards the terminus. A single apical pore field with round poroids is present, displaced toward valve mantle. Girdle bands are open and do not bear perforations.

Samples collected from North America exhibit several morphological variants that are often included under the name Staurosirella pinnata. Since the type of this taxon has not been studied in detail, it is difficult to determine which of these variants corresponds to the “true” S. pinnata. We consider the specimens depicted in this page closely resemble the iconotype specimens presented by Ehrenberg (1843).