FIGURES 21–26 in Expended range of Gomphonema firmum (Bacillariophyceae), once considered a Lake Baikal endemic, with notes on the identity of G. lanceolatum var. maximum

FIGURES 21–26: Gomphonema firmum from Gyrgyntui, internal views, SEM. Fig. 21. Valve with cingulum consisting of two open valvocopulae. Fig. 22. Detail of central portion of the valve showing hemispherical central nodule, proximal raphe endings (black arrows) and slit-like stigma opening (white arrow), note the pattern of strongly silicified virgae and alveolae containing internal areolar openings. Fig. 23. Headpole showing pseudoseptum (black arrow) and distal raphe ending on helictoglossa (white arrow). Fig. 24. Footpole showing pseudoseptum (black arrow) that masks apical pore field, distal raphe ending on helictoglossa (white arrow), note very small, hardly recognizable paired stubs (small white arrows). Fig. 25. Headpole, valvocopula with septum, which masks helictoglossa (white arrow). Fig. 26. Footpole, valvocopula with septum, note porelli of the bisected pore field (arrows).