Morphogenesis and molecular phylogeny of the soil ciliate Rigidohymena quadrinucleata (Dragesco and Njine, 1971) Berger, 2011 (Ciliophora, Hypotricha, Oxytrichidae)

Morphogenesis in the soil hypotrich ciliate, Rigidohymena quadrinucleata (Dragesco and Njine, 1971) Berger, 2011; was investigated using protargol staining. The main events during binary fission are as follows: (1) the proter retains the parental adoral zone of membranelles entirely, whereas the old undulating membranes dedifferentiate into an anlage that gives rise to the leftmost frontal cirrus and the new undulating membranes of the proter; (2) six streaks of frontoventral-transverse cirral anlagen are segmented in the pattern 1:3:3:3:4:4 from left to right, which form three frontal, four frontoventral, one buccal, five ventral and five transverse cirri, respectively; (3) the postoral ventral cirrus V/3 is not involved in primordia formation demonstrating that this species belongs to the stylonychines; (4) marginal anlagen are formed intrakinetally and the right marginal anlagen develop much earlier than the left ones; (5) the generation of the dorsal kineties is of typical Oxytricha-pattern and three caudal cirri are formed, one at the posterior end of each of dorsal kineties 1, 2 and 4. Phylogenetic analyses based on SSU rDNA sequence data indicate that Rigidohymena is polyphyletic and that R. quadrinucleata clusters with R. candens with full support.