SCHMIDT-RHAESA, A.; ROTHE, B.H.; University Bielefeld, Germany; University Bielefeld, Germany: Postembryonic development of the musculature in kinorhynchs

Labelling of f-actin with phalloidin and investigation using confocal laser scanning microscopy is an ideal tool to reveal the architecture of the muscle system in wholemounts of microscopically small animals. The invesitgation of postembryonic stages of the kinorhynch species Pycnophyes kielensis and P. dentatus shows the development of longitudinal and dorsoventral muscles. During postembryonic development, the number of externally visible “segments” is raised from 10 to 13. We demonstrate the successive extension of dorsal and ventral longitudinal as well as dorsoventral muscles. Longitudinal muscles appear as more or less continuous strands until the last juvenile stage, but as clearly separated “segmental” portions in adults. This corresponds to a thickening of cuticular attachment sites for the musculature, the pachycycli. Ultrastructural invesitgations show that in juvenile stages the muscle cells are closely interdigitating over these pachycycli. Finally, investigation of several specimens shows that muscular development is not strictly linked to the molting cycle.