Bursellopsis spaniopogon (Ciliophora: Prostomatida): II. Stomatogenesis as Revealed by Light Microscopy and Scanning Electron Microscopy and some Phylogenetic Implications Concerning Prostome Ciliates.

ABSTRACT

In stomatogenesis of Bursellopsis a new circumoral kinety as well as three brush rows have to be formed in the opisthe. The formation of these structures occurs in a stomatogenic field of six to twelve somatic kineties. These stomatogenic kineties can be separated into two groups a left one of three to seven kineties, forming the brush primordia, and a right one of three to five kineties, forming the primordia of the circumoral kinety. Between both groups the presumptive oral opening develops. In the stomatogenic kineties forming the brush primordia, dikinetids develop by kinetosome proliferation. These dikinetids arrange side by side into three horizontal rows. By an excessive kinetosome proliferation in the somatic kineties lying left to these rows the whole organelle gets vertically orientated later on in stomatogenesis. In the right group of stomatogenic kineties short fragments, consisting of dikinetids, develop. These fragments undergo a clockwise circular migration around the presumptive oral opening. By joining head to tail they arrange into the circumoral kinety. The primordia of the brush and of the circumoral kinety originate in front of only a few somatic kineties on the ventral side of the cell ("merotelokinetal stomatogenesis"). The apical ("prostome") position of the oral apparatus is the result of the cell division and has to be considered as secondary. The term "prostome" is therefore not correct in a phylogenetic view. According to the "merotelokinetal" type of stomatogenesis a sister group relationship of the prorodontid and some colpodid ciliates is assumed.