Rostellar gross anatomy and the ultrastructural and histochemical characterization of the rostellar tegument-related structures in Hymenolepis nana

Abstract

The gross anatomy of the protrusible rostellum in the scolex of adult Hymenolepis nana is described and the rostellar tegument and tegumentary cytons are characterized by electron microscopic and histochemical observations. The rostellum is divided by a shell of muscle-basal lamina complex into the ‘outer’ and the ‘inner’ regions. The rostellar tegumentary cytons (RTCs), located in the ‘outer’ region, produce paraldehyde fuchsin (PAF)-reactive, electron-dense granules. These granules are transferred to the rostellar tegument and release their content to form a thick covering on the rostellar surface. Also present in the tegument are moderately dense, ellipsoidal granules which occupy only a limited region of the tegument in the protruded rostellum, and seem to have roles when the rostellum is retracted. The ‘outer’ region of the rostellum is refractory to staining for carbohydrates, weakly positive for proteins, and strongly reactive to methyl green-pyronin and Luxol fast blue. The scolex structural homologies between H. diminuta and H. nana, and the significance of the presence of different types of tegumentary granules in H. nana, are discussed.