Morphogenesis of Kiitricha marina Nozawa, 1941 (Ciliophora, Spirotrichea), a possible model for the ancestor of hypotrichs s. l.

Recent studies suggested that the marine ciliate Kiitricha Nozawa, 1941 represents a basal branch in the spirotrichs. The present study reflects the morphogenetical investigation of Kiitricha marina Nozawa, 1941. The results listed below show an extremely unusual developmental pattern compared with all other known forms in the class Spirotrichea or hypotrichs s. l.(i)The differentiation of the ciliary structures from the primordia occurs after cell division. This makes Kiitricha marina Nozawa, 1941 unique among hypotrichs s. l.(ii)Since the anlage of the undulating membranes in the opisthe derives from the division of the dedifferentiated parental structure and thus is not formed independently, Kiitricha marina Nozawa, 1941 is also unique among spirotrichs.(iii)Most somatic cirral structures appear in a post-anlage pattern, i.e. all cirri exhibit a primary arrangement in the sense that they are distributed as though they had just been segregated from the anlagen.(iv)Unlike most other known hypotrichs s. l., the undulating membrane-anlage does not contribute a frontal cirrus.(v)The dorsal kineties are formed in two ways: (a) from the posterior portion of the cirral anlagen which later generate the new dorsal kinety segments; and (b) by the irregular proliferation of dikinetids in the long dorsal kineties.(vi)All cirral anlagen are formed intrakinetally from the dedifferentiated parental cirri and develop in a primary mode. Taken collectively, these findings suggest that Kiitricha is a basal branching hypotrich and therefore a possible model for the ancestor of the hypotrichs s. l.