The new ACR is formed by alignment of the two rightmost cirral anlagen, proving that Lamtostyla belongs to the Amphisiellidae. Based on these data, improved definitions are given for all amphisiellid genera. Onychodromopsis flexilis is redescribed emphasizing somatic variation and the fine structure of the oral apparatus. It has cortical granules and an oxytrichid FVT-cirral pattern but two to three right and one to two left marginal rows. The morphogenetic processes are very similar to those of Oxytricha granulifera .
Physiological regeneration resembles development in the proter.
The data show that O. flexilis belongs to the Oxytrichidae and is closely related to Oxytricha .