Light (A, C) and scanning electron (B, D-I) micrographs of Trigonopyxis arcula. (A, B) View of many specimens to illustrate variability in shape and size of the shell. (C, D) Apertural view of two specimens showing smooth apertural surface and characteristic triangular aperture. (E) Dorsal view. (F) Lateral view. (G, H) Close up views of aperture to illustrate its variability in shape. (I) Detail of apertural side to illustrate its smooth surface and numerous pores in the organic cement.