ABSTRACT
The first transmission and scanning electron microscopical studies in combination with freeze-fracture technology have disclosed some important morphological and ultrastructural features in the freshwater oligotrichid Limnostrombidium viride. (I) The dikinetids (paired basal bodies) of the girdle kinety have a club-shaped cilium associated only with each left basal body. The electron-dense (paraflagellar) body on one side of its "9×2+2"-axoneme and the regular array of intramembranous particles indicate a sensory, perhaps photoreceptor function of these club-shaped cilia. (II) The stichomonad endoral membrane is proximally covered by a cytoplasmic fold and distally by multiple membranous layers. Thus entirely covered, the endoral is probably no longer involved in food capture; nonetheless, its associated microtubules might stabilise the cytopharynx. (III) Instead of a contractile vacuole, a horizontal ring-canal with supposed osmoregulatory function occurs. (IV) The extrusive nature of the trichites is not only observed in electron micrographs, but the attachment sites of these organelles also display a rosette of "8+1"-particles in the P-face of freeze-fracture replicas typical for ciliate extrusomes. (V) The neoformation organelle, the subsurface tube in which stomatogenesis takes place, shows short basal bodies and normal axonemes about 1 µm long. It is accompanied by numerous membrane vesicles, which might provide membrane material for the outgrowing cilia.
