line, sinus, cavity, nerve, complex, oviduct, sinuses, simple, groove, nerves, organs, chamber, impression, entire, muscles, region, commissure, areas, wall, epithelium, area, regions, artery, gonoduct, lobes, marks, lobe, vein, trunks, scar, markings, tentacles, gland, eyes, margin, aperture, gills, fibres, arteries, myostracum, impressions, glands, duct, tentacle, grooves, roof, layer, muscle, thickening, structures, cortex, substance, walls, border, shell, veins, membrane, commissures, fold, shallow, fields, indistinct, zone, ridge, present, edge, organ, gonoducts, origin, fluid, oviducts, deferens, siphon, eminence, paths, opening, vessel, membranes, sac, mechanism, vessels, canals, cords, apex, hemispheres, anlage, fig, primordia, derivatives