Electron micrographs of T. regenti gland ducts and openings. A, TEM of postacetabular and circumacetabular ducts reinforced by microtubules (arrows) and surrounded by common muscular layer; scale bar = 500 nm. B, TEM of the section through the apical part of cercarial head organ; yellow arrows show postacetabular ducts, red arrows show circumacetabular ducts and white arrows point to putative ducts of the head gland; note a sensory papilla adjoining with the gland duct opening covered by tegumental folds; scale bar = 5 μm; (also see Additional File 2). C, detail of four gland openings on the head organ of cercaria viewed by SEM; arrows point to sensory papillae in the proximity of the openings; scale bar = 5 μm. D, detail of a postacetabular gland duct in TEM leading to surface opening covered by tegumental folds (wide arrow) on the apex of cercaria, sensory papilla in the proximity of gland duct opening is pointed by thin arrow; scale bar = 2 μm. M, muscular layer; dCA and dPA, ducts of circumacetabular and postacetabular glands, respectively; SP, sensory papilla; HG, head gland; N, nucleus of the head gland.