Figure 1.

(a) Photograph of the frontal view of an octopus sucker. Infundibulum (I); orifice (O); and rim (R). (b) Schematic structure (transversal section) of an octopus sucker. The upper part in grey (light and dark grey) is the acetabulum (A). The lower disk-like black-coloured portion is the infundibulum (I). The light grey-coloured portion is the protuberance of the acetabular roof (AR); and O is the orifice. (c–f) Scanning electron microscopy images of an octopus sucker. (c) Infundibulum (please, refer to black box 1 in (b)). Radial (RG) and circumferential (CG) grooves. (d) Rim (please, refer to black box 2 in (b) and label R in (a)). (e) Surface of acetabular protuberance (please, refer to black box 3 in (b)). (f) Enlargement of white box in (e). (g) Sucker configuration during adhesion process [5]. The restoring elastic force (white arrow) is balanced by the cohesive forces of the water (grey arrow). (h) Enlargement of (g) considering the contribution of hairs. The restoring elastic force (white arrow) is counterbalanced by the cohesive forces of the water (grey arrows) and the adhesion force exerted by hairs (black arrows).