FIGURES 58–65. SEM. Planothidium marganaiensis G.G in Planothidium marganaiensis sp. nov. (Bacillariophyta), a new cavum-bearing species from a karst spring in south-western Sardinia (Italy)

FIGURES 58–65. SEM. Planothidium marganaiensis G.G.Lai, Ector & C.E.Wetzel sp. nov. Type population from the San Giovanni spring, Sardinia (Italy). Figs 58–62: Rapheless valve (SV). Figs 58–60: External view showing depressions along the apical axis and multiseriate striae. Note the striae continuing shortly onto the valve mantle, without interruption (Figs 58–59). Figs 61–62: Internal view showing the round cavum with a narrow aperture towards the valve mantle. Figs 63–65: Raphe valve (RV). Fig. 63: External view showing multiseriate striae not extended on the valve mantle and distal raphe ends bent unilaterally. Figs 64–65: Internal view showing striae sunken between raised virgae and composed of areolae covered by individual hymenes. Note the proximal external raphe ends slightly deflected into opposite sides and distal raphe terminating on poorly developed helictoglossae, continuing shortly onto the valve mantle.