Climacosphenia elongata, GU44BM-7, except as noted A valve with valvocopula in LM, showing consistently narrow craticular bars, some double (arrowheads) (GU44X-2) B apical part of a valve with valvocopula in SEM, showing the progressive narrowing of the annular ring (series of small arrows) and the wider space between craticular bars where the nucleus resides (thick arrow) C narrow portion of valve with valvocopula showing the fibmbriae D basal pole of valve with valvocopula, showing the scattered pattern of areolae inside the annulus gradually becoming regular striae, development of costae (arrow), and complex unions in the craticular bars E external view of apical pole showing annulus (double-headed arrow) and spines F frustule in girdle view showing the two girdle bands G, H valvocopula near basal pole and in tapering part at top of “stem,” respectively, showing complex versus simple unions in the craticular bars (TK4). Scale bars: 100 µm (A); 50 µm (B); 10 µm (C–H).