Electron microscopical observations on the ciliate Furgasonia blochmanni Fauré-Fremiet, 1967: Part I: An update on morphology.

Light- and electron microscopical observations on the morphology of the nassulid ciliate Furgasonia blochmanni show that it has somatic kinetids which reveal the nassulid pattern of somatic mono- and dikinetids with a 'B-cartwheel' in the lumen of the kinetosome and paired alveolocysts as regular components of the kinetids. The buccal ciliature consists of a paroral membrane and three adorai membranelles. In contrast to the majority of the nassulid ciliates F. blochmanni has a paroral membrane of the stichodyad type in the adult stage. In adult cells the kinetosomes of the stichodyad show a unique hitherto undescribed arrangement, with the posterior kinetosome of each dyad rotated 90° compared to the anterior one which is orientated like a somatic kinetosome with triplet 9 pointing posteriorwards. The adorai membranelles are very similar to the corresponding structures of other nassulid ciliates and are not 'peniculi'. The cytopharyngeal basket of F. blochmanni consists of the same elements as in the genus Nassula. This type of a cytopharynx is described and compared with the corresponding structures of other nassulid, cyrtophorid and chonotrichid ciliates revealing that both the order Nassulida itself and the suborders Nassulina and Microthoracina can be characterized by the unique morphological features of their cytopharyngeal baskets. This update on morphology, a prerequisite for the examination of morphogenesis, leads to phylogenetic conclusions on the systematic position of F. blochmanni which differ from the view held by Grain et al. [23] who transferred the genus Furgasonia to the hymenostomes. These conclusions are more in accord with the recent classification of nassulid ciliates presented by de Puytorac, Grain and Mignot [51].