Penium margaritaceum Brébisson 1848

    Cells large, cylindrical with rounded apices, slightly constricted at the middle; 4-10 times longer than broad. Cells measure 75-160 µm in length, 13-21 µm in breadth. Cell wall brown in colour with some girdle bands and a sculpture of minute granules that may be scattered or more or less regularly arranged in longitudinal rows. Chloroplasts axial, longitudinal plates, two per semi cells with a central pyrenoid each.