Light (A, B) and scanning electron (C-I) micrographs of Arcella arenaria. (A-C) View of many specimens showing variability in shape and size of the shell. (D) Apertural view to show smooth apertural surface. (E-F) Aboral view showing depressed segments of surface. (G) Lateral view. (H) Close up view of aperture to show distinct apertural lip and surrounding large pores. (I) Portion of shell surface showing small organic alveoli on the aboral surface.