Elektronenmikroskopische Untersuchungen an den Oralcirren und der Haut vonBranchiostoma lanceolatum

Praeoral tentacles and epidermis of the anterior body region ofBranchiostoma lanceolatum Pallas have been investigated by electron microscopy. The epidermis of the praeoral tentacles and the anterior body region are mono-layered and cohere by strong denticulations of the adjoining cell walls. Vertical secretory vesicles at the cell surface give off mucous substances. The secretory vesicles are found only in the body epithelium. Between epithelium cells both epithelia contain two different secondary sensilla types.B. lanceolatum is the lowest chordate in which taste buds of the praeoral tentacles have been found. The taste buds overtop the surface of the epithelium. The praeoral tentacles are stiffened by a skeleton rod, situated asymmetrically and build up in layers. The skeleton rod is surrounded by connective tissue, which includes a coelomic space. Axon bundles of different strength are situated in the connective tissue. Not only the taste buds but also singular sensilla types are innervated by these axon bundles. The relatively strong basement lamina is partially zonated and contains pores. An antagonistically arranged layer of collagen fibres of varying thickness occurs below the basement lamina.