Fig. 1.

The chambered wall–septa structure of cuttlebone. (A) A cuttlefish with the cuttlebone highlighted in yellow. “N” direction points from the ventral to the dorsal side. “G” denotes the growth direction. Siphuncular zone is the striated area on the posterior-ventral part of the shell. (B) Dorsal and ventral views of the cuttlebone. (C) A transverse view of the cuttlebone (Top) and corresponding chamber height map (Bottom). (D) A scanning electron microscopy (SEM) image of the chambers with walls and septa indicated by white arrows. The top and bottom of the walls are highlighted by green and red dashed lines, respectively. (E) A 3D µ-CT reconstructed wall–septa structure. The walls have wavier top profiles (green) compared to the bottom profiles (red). (F) Representative reconstructed individual walls. The red arrows indicate the triple joints. The contour represents the corresponding mean curvature distribution. (G) Normalized wall length $L/L_0$ plotted against normalized height $h/h_0$ of 11 walls. Eq. 1 is plotted as the solid black line. The labyrinthine pattern of walls near the (H) bottom and (I) top of the chamber. The white boxes in I indicate triple junctions. (J) Overlay of H and I, where the white boxes indicate the splitting locations of the walls. (K) Overlay of the wall bottoms from two adjacent chambers. (L) Side-view and (M) top-view SEM images showing the microstructure of septum. The lower portion of the septum possesses a rotating plywood structure (green), while the crystallites of the upper portion (red) are aligned vertically with the wall.