Morphogenesis in some freshwater Tintinnids (Ciliophora, Oligotrichida).

The morphogenesis of four freshwater tintinnids was investigated using protargol silver impregnation and scanning electron microscopy. Division is rather similar in Tintinnopsis cylindrata, Tintinnidium pusillum and T. semiciliatum, e.g. the oral primordium develops apokinetally posterior of somatic kinety 10 and the somatic ciliature originates by two rounds of intrakinetal basal body proliferations before cytokinesis. The peculiar ventral organelles form without apparent contact with parental ciliary structures as do the adorai membranelles and the paroral membrane; thus, the ventral organelles might be part of the oral apparatus. The morphogenesis of Codonella cratera differs from that of the other species by the reorganization of some parental ciliary rows and by a second round of somatic basal body proliferation after cytokinesis. Based on morphologic and morphogenetic similarities, Tps. cylindrata is transferred from the Codonellidae to the Tintinnidiidae, and Tps. baltica and Tps. subacuta are newly combined with Codonella: C. baltica nov. comb., C. subacuta nov. comb. We could not discern a unique character defining oligotrichs as a monophyletic group because the enantiotropic cell division is possibly less pronounced in some tintinnids and occurs also in peritrichs and a few prostomatids. We suggest, however, that the enantiotropic cell division evolved convergently in these taxa, and thus adhere to our view that this special mode of cell division is the most reliable apomorphy for the oligotrichs. In addition, the character combination, polar oral apparatus and apokinetal origin of the oral primordium, occurs only in oligotrichs. Morphogenetic similarities suggest a sister group relationship between tintinnids and strobilidiids.