The present book is a monograph about two groups of hypotrichous ciliates, namely the Amphisiellidae and the Trachelostylidae. It is the third of six volumes which - view the Hypotricha, one of the three major taxa of the spirotrichs. The first volume is about the Oxytrichidae, a rather large group, many species of which have 18 highly characteristically arranged frontal-ventral-transverse cirri and, much more importantly, a comparatively complex dorsal ciliature due to (oxytrichid) fragmen- tion of dorsal kineties during cell division (Berger 1999). The second volume deals with the Urostyloidea, which are characterised by a zigzag-arrangement of the ventral cirri (Berger 2006). Although this pattern is often very impressive, it is a relatively simple feature originating by a more or less distinct increase of the number of frontal-ventral-transverse cirri anlagen. These anlagen produce cirral pairs which are serially arranged in non-dividing specimens. Some - ers are likely astonished that the monograph on urostyloids does not include Urol- tus, a group of tailed species, which also have a distinct zigzagging cirral pattern.
However, morphological and molecular data indicate that the zigzag pattern of U- leptus evolved independently, that is, convergently to that of the urostyloids. Thus, Uroleptus was excluded from the urostyloid review. A zigzag pattern is also known from some oxytrichids, for example, Neokeronopsis, Territricha, Pattersoniella, showing that this pattern evolved several times independently (Berger 1999, 2006, Foissner et al. 2004).