LINDSAY, S.M.; JACKSON, J.L.; HE, S.Q.; FOREST, D.; University of Maine, Orono: Losing heads & making connections: anterior regeneration in spionid polychaetes

The spionid polychaetes Dipolydora quadrilobata and Pygospio elegans can regenerate lost tails, feeding palps, and anterior segments. Results of anterior ablation experiments indicate the rate of regeneration is slower with increasing amount of tissue lost. We used light microscopy, scanning electron microscopy and confocal laser scanning microscopy to describe the development of external and nervous system structures during regeneration in both species. Following ablation of the anterior through the fifth setiger, we observed the following milestones in anterior regeneration for both species. By day 3 post ablation, a mouth was beginning to form in the regeneration blastema. By day 6, the prostomium was complete, and 1-2 segments were formed, but these lacked setae; short palps were visible, but these lacked any cilia. In 9 days post ablation most worms had regrown 4-5 segments, with these bearing some setae; palps were noticeably longer and the ciliated food groove had begun to form. After 12 days, regenerating worms looked much like intact worms: the new segments had expanded and showed normal setae; nuchal organs and other ciliated sensory organs were well developed; and the ciliated food groove on the palps was further elaborated, though it did not extend to the base of the palp. Light microscopy observations suggest that within each species, worms reach these landmarks at similar times regardless of the amount of anterior tissue removed. Observed regeneration rate differences may simply reflect the need to replace more segments. Initial observations of alpha-tubulin immunoreactivity using CLSM suggest the progress of central nervous system regeneration in spionids is similar to that observed in other polychaetes.