Rotational symmetry of cell face outline is 360 degrees with one end broader than other, though may be only slightly; may be ~violin shaped
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Raphes absent, club-shaped in valve view, wedge-shaped in girdle view; prominent ribs (costae) cross the valve face (also visible in girdle view).
Meridion cf circulare -
Club or violin-shaped in valve view, wedge shaped in girdle view, much smaller than Didymosphenia; may be single stigmata at the edge of the central area; stalks commonly attach cells to the substrate.
Gomphonema -
Club-shaped in valve view, never with swelling at wide end, wedge shaped in girdle view; central area commonly offset from widest part of the valve; commonly attached to substrates with stalks, but less abundantly than Didymosphenia.
Gomphoneis -
Club-shaped in valve view, with swellings at both the narrow and wide ends, wedge shaped in girdle view; large; one or more (commonly 3) pores (stigmata) at the edge of the central area; gelatinous stalks often very abundant (sometimes more common than the cells).
Didymosphenia