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Annelids provide suitable models for studying regeneration. By now, comprehensive informa- tion is restricted to only a few taxa. For many other annelids, comparative data are scarce or even missing. Here, we describe the regeneration of a member of the Cirratulus cirratus species complex. Using phalloidin- labeling and antibody-stainings combined with subse- quent confocal laser scanning microscopy, we provide data about the organization of body wall musculature and nervous system of intact specimens, as well as about anteriorly regenerating specimens. Our analyses show that C.c f.cirratus exhibits a prominent longitu- dinal muscle layer forming a dorsal muscle plate, two ventral muscle strands and a ventral-median muscle fiber. The circular musculature forms closed rings which are interrupted in the area of parapodia. The nervous system of C.c f.cirratus shows a typical rope- ladder like arrangement and the circumesophageal con- nectives exhibit two separate roots leading to the brain. During regeneration, the nervous system redevelops remarkably earlier than the musculature, first consti- tuting a tripartite loop-like structure which later become the circumesophageal connectives. Regenera- tion of longitudinal musculature starts with diffuse ingrowth and subsequent structuring into the blas- tema. In contrast, circular musculature develops inde- pendently inside the blastema. Our findings constitute the first analysis of regeneration for a member of the Cirratuliformia on a structural level. Summarizing the regeneration process in C.c f.cirratus ,fi ve main phases can be subdivided: 1) wound closure, 2) blastema for- mation, 3) blastema differentiation, 4) resegmentation, and 5) growth, respectively elongation. Additionally, the described tripartite loop-like structure of the regen- erating nervous system has not been reported for any other annelid taxon. In contrast, the regeneration of circular and longitudinal musculature originating from different groups of cells seems to be a general pattern in annelid regeneration. J. Morphol. 000:000-000 |
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