Figure 1.

Rock-boring sea urchin Paracentrotus lividus (A) has hundreds of oral tube feet specialized for locomotion and adhesion (B). Tube feet have a proximal cylindrical motile stem and a distal flattened disc with a duo-glandular adhesive epidermis with adhesive and de-adhesive secretory cells (C,E). After detachment, circles of adhesive secretion remain attached to the substrate and can be visualized after staining with an aqueous solution of Crystal Violet (D,F). Abbreviations: AC, adhesive secretory cell; AE, adhesive epidermis; CT, connective tissue; Cu, cuticle; D, disc; DC, de-adhesive secretory cell; L, lumen; M, myomesothelium; NE, non-adhesive epidermis; NP, nerve plexus; NR, nerve ring; S, stem; Sk, skeleton; TF, tube feet.