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Diagnostic features

Small pennate diatom, asymmetrically boat-shaped in valve view, curved wedge-shaped in girdle view (most commonly seen). Valves differ from each other; although both have raphes, one is much reduced (this is difficult to see, but genus is technically biraphid). Rib-like striae in girdle and valve views. The narrow end of the cell is often attached to larger algae.

Typical habitats

Slow flowing streams and rivers


Kingdom Chromista
Phylum Ochrophyta
Class Bacillariophyceae
Order Cymbellales
Family Rhoicospheniaceae
Common name Diatoms