Light (A, B) and scanning electron (C-I) micrographs of Phryganella hemisphaerica. (A-C) View of many specimens to illustrate variability in shape and size of the shell. (D, E) Apertural view of two specimens showing general shape. (F) Dorsal view. (G) Lateral view. (H) Close up view of aperture to illustrate its thin collar and circular outline. (I) Details of lateral side of the shell to illustrate its rough surface, covered with large pieces of quartz and diatom frustules.