(D + E) early deposited inner parts showing ordered layers with higher contrast in SEM (D, see inset). These layers contain aligned chitin bundles (E, 10–20 nm thick), coated by a dense or fine granular mineral (size granules 99 ± 11 nm, see arrows). Size is presented as mean diameter ± standard deviation. The position of the layer visualized in E is indicated by the D-sign in D.