Light (A, B) and scanning electron (C-I) micrographs of Trinema complanatum. (A) View of many specimens to illustrate variability in shape and size of the shell. (B) View of live specimen showing numerous bright granules filling the cytoplasm. (C) Apertural view to show general shape and regular arrangement of shell-plates. (D) Lateral view to illustrate apertural invagination and compression of the shell in the apertural region. (E, F) Dorsal view showing structure of the shell and its compression in apertural region. (G, H) Close up view of aperture to illustrate its circular shape, arrangement of numerous denticulate apertural-plates in two or three rows, and three to four rows of small shell-plates, surrounding aperture. (I) Detail of shell surface to show large, circular shell-plates and small, oval shell-plates, which haphazardly fill the interstices between them.