- Rotational symmetry of cell face outline is 360 degrees with one end broader than other
In this section
Valves identical, both possessing a raphe (i.e. the genus is biraphid). Large cells shaped like an Egyptian sarcophagus in valve view, with large brown chloroplast (often having a "fold" at one edge). Wedge shaped in girdle view. A cluster of 3 pores occurs on the valve face near the central raphe ends (although these may be difficult to see). Often attached to the bed by long mucilaginous stalks, which may be more abundant than the cells themselves. Forms thick blooms commonly referred to as "didymo" or "rock snot".