Simplified diagrams of the anatomical organization of the holothurian nervous system. A. Lateral view of an adult sea cucumber, oral end to the right. The dashed line corresponds to the cross section at the mid-body level shown in (B). C. Higher magnification of the boxed area in (B) showing the relationship between the radial nerve cords and other radial organs. ce, coelomic epithelial lining of the body cavity; ctl, connective tissue layer of the body wall; en, ectoneural part of the radial nerve cord; hn, hyponeural part of the radial nerve cord; lm, longitudinal muscle band; nr, nerve ring; rc, radial canal of the water-vascular system; rnc, radial nerve cord; tn, tentacular nerve. Not to scale.