Fig. 5

Semi-thin sections and electron microscopic images of the median organ of adult Sabellaria alveolata. Toluidin-blue staining (a) and electron microscopy (b-e). a An antero-posterior section of the adult median organ (mo) reveals the presence numerous ciliated pits (arrow heads) at the base of the structure. The red dashed squares indicate the position of the images shown in (b) and (e). b A higher magnification of a ciliated pit reveals the presence of numerous ciliated supporting cells (cc) surrounding the epidermal depression, and sending cilia (ci) out of the opening of the pit. A sensory cell (sc) situated near the pit opening sends a distinct cellular process (red arrowheads) towards the epidermal surface. The olfactory chamber (oc) is located in the region where the cellular process reaches the surface. c A close-up supporting cells (cc) present the density of cilia running into the epidermal depression of the pit. d A section showing the inner surface of the pit reveals a dense pattern of cilia (ci) and microvilli. e Close to the pit, but outside the epidermal depression, numerous ciliated supporting cells (cc) cover the epidermal surface. cc, ciliated supporting cell; mo, median organ; sc, sensory cell. Scale bars = 10 μm (b, e), 2 μm (c) and 500 nm (d)