THE ULTRASTRUCTURE OF THE SOMATIC AND ORAL CORTEX OF THE KARYORELICTEAN CILIATE LOXODES STRIATUS

The ultrastructure of the somatic and oral cortex of the karyorelictea n ciliate Loxodes striatus was reinvestigated with the Fernandez-Galia no silver carbonate impregnation technique, scanning electron microsco py and ultrathin sections. The laterally compressed ciliate has a dens ely ciliated right lateral side with 11 somatic kineties. The right do rsolateral kinety surrounds the posterior end of the cell. The left la teral side of the cell is sparsely ciliated showing only two separate longitudinal kineties, their two anterior ends meet near the anterior end of the cell and their posterior ends meet near the posterior end o f the cell. These two kineties thus do not form a single circumcellula r kinety as stated in the literature. The somatic dikinetids are shown to be slightly different compared to earlier data. The kinetodesmal f iber, T-shaped in cross-section, is one broad shovel-like structure wi th a keel. The buccal cavity is located at the anterior left end of th e cell and has a tube-like vestibular extension of unknown function. T he 4 longitudinal oral kineties are all composed of dikinetids with di fferent kinetosome-associated fiber systems. From right to left there is a loxodid paroral of closely spaced dikinetids with the anterior ki netosome ciliated; an intravestibular kinety in which the posterior ki netosome is ciliated (this kinety extends into the vestibular extensio n); 3-5 widely spaced anterior left buccal dikinetids in which the ant erior kinetosome is ciliated. On the left margin of the buccal cavity lies a closely spaced file of dikinetids which owing to the orientatio n of the kinetosome-associated fiber systems, quite surprisingly, is a n inverted somatic kinety. The kinetids of this kinety have the anteri or kinetosome ciliated and the posterior kinetosome has a kinetodesmal fiber each. Because of the kinetodesmal fibers in this kinety it is n o true buccal kinety, instead the term left pseudobuccal kinety is sug gested. It is assumed that this inverted kinety, probably originating from the somatic kinety Ki, has secondarily taken over the function of an adoral ciliature, because the primary adoral ciliature, the intrav estibular kinety, during evolution, has sunken down into the oral cavi ty. Detailed schematic drawings of the somatic dikinetid and the 4 ora l dikinetids with their kinetosome-associated fiber systems are presen ted. This study is a prerequisite to a light and scanning electron mic roscopical investigation on stomatogenesis in the genus Loxodes (see a ccompanying paper), undertaken with the authors' aim to reconstruct ci liate evolution via ciliate morphogenesis.