Light (A, C) and scanning electron (B, D-I) micrographs of Awerintzewia cyclostoma. (A, B) View of many specimens to illustrate variability in shape and size of the shell. (C-E) Broad lateral view of three specimens to show general shape. (F) Narrow lateral view. (G) Apertural view showing oval sross section of the shell and small oval aperture. (H) Close up view of aperture showing its oval outline and bordering rim of organic cement. (I) Portion of shell to show arrangement of flattish particles in the anterior part of the shell.