FIGURES 16–20 in Three new Craticula species (Bacillariophyta) from the Maritime Antarctic Region

FIGURES 16–20. Craticula obaesa. SEM pictures taken from the holotype population (sample CLW60) from Clearwater Mesa, James Ross Island. 16. Detail view of the central area. Note the difference in shape of the central areolae and the expanded, hooked proximal raphe endings. 17. External detail of a valve apex with the typical longitudinal lines formed by the frets separating the areolae. 18. Internal detail of the central area with focus on the central nodule and the differences in areola structure near the central area. 19. Internal detail of the areolae occlusions. 20. Heribaudii stage. Scale bar represents 10 μm, except for Fig. 19 where scale bar = 1 μm.