Fig. 6
Semithin sections and electron microscopic images of the median organ of adult Idanthyrsus australiensis. Toluidin-blue staining (a), HES staining (b-d) and electron microscopy (e-j). a An antero-posterior section of the adult median organ (mo) reveals the presence of numerous ciliated pits bearing ciliary tufts (arrow heads) at the base of the structure. The red dashed squares indicate the position of the images shown in (f) and (e). b An anterior-posterior section at the base of the median organ (mo) exhibits the distinct neurite bundles (nm) innervating the (mo). The red arrow marks the position of ocelli. c The tip of the median organ (mo) possess a dense ciliation (ci) and a prominent nervous system innervation (ns). d Under higher magnification the proximity of photo-sensitive ocelli (red arrows) and the neurite bundles (nm) innervating the (mo) becomes obvious. e An electron microscopic image of the ciliated pit shows presence of numerous ciliated supporting cells (cc) at the base of the epidermal depression and an olfactory chamber (oc) in close proximity. f The area surrounding the ciliary pits is covered with cilia originating from numerous ciliated supporting cells (cc). g A cross section of the inner surface of the ciliated pit reveals a dense mixture of cilia (ci) and microvilli (mv) covering the surface of the supporting cells. h, i An electron microscopic image of the ocelli reveals presence of a pigment cell (pc) and a sensory cell (sc) sending the sensory membrane (sm) towards the pigment cell cup. Note that the pigment granules are not visible due to fixation artefacts. j The rhabdomeric-like sensory membrane can be described as microvillar, but with a whorled appearance. br, brain; cc, ciliated supporting cell; ci, cilia; cu, cuticle; mo, median organ; mv, microvilli; nm, neurite bundle innervating the median organ; ns, nervous system; oc, olfactory chamber; pc, pigment cell forming the pigment cup; sc, sensory cell; sm, sensory membrane. Scale bars = 1 μm (e, g), 5 μm (f, h), 2 μm (i) and 200 nm (j)