FIGURES 43–48 in Surirella arctica comb. et stat. nov. (Bacillariophyta)-a rare arctic diatom

FIGURES 43–48. Surirella arctica, external views, SEM. Figs 43–46 represent the same specimen. Fig. 43 External valve view. Fig. 44 Detail of the slightly corrugated valve face showing narrow median area, multiseriate striae, separated by external ridges and partially covered with irregularly arranged siliceous filaments, and tiny papillae on top of the ridges and in the median area. Notice that each fourth or fifth external ridge is sunken below the level of other ridges. Two striae along the sides of these lowered ridges are usually shorter than the rest of the striae. Figs 45, 46 Details of the valve apices with ligulae, narrowing median area and slightly radiating striae towards the valve ends. Fig. 47 Detail of the valve face showing the arrangement of external ridges and striae. Fig. 48 Frustule with a slightly eroded and broken valve face. A craticula-like structure of the lower valve is visible inside. Scale bars = 10 µm (in Figs 43, 48) or 1 µm (in Figs 44–47).