Meeting Abstract

61.5  Tuesday, Jan. 6  Neoblasts in Nemertodermatida SMITH III, Julian P.S.*; EGGER, Bernhard ; TYLER, Seth; LADURNER, Peter; ACHATZ, Johannes; MERLIE, Sara; Winthrop University; University of Innsbruck; University of Maine; University of Innsbruck; University of Maine; Winthrop University

Our current understanding of the stem-cell (neoblast) system in Platyhelminthes comes primarily from a wealth of experiments on regeneration in the Tricladida, supplemented by recent studies of, e.g., the macrostomorph Macrostomum lignano and the acoel Isodiametra pulchra. To date, there are no comprehensive studies of the neoblast system in the potentially more primitive Nemertodermatida. Accordingly, we have carried out preliminary S-phase (BrdU and EdU) and M-phase (anti-phosphoH3) labeling experiments in Flagellophora cf apelti, Sterreria cf psammicola, and Nemertinoides elongatus, supplementing these light-microscopic histochemical studies with electron microscopy. We have found neoblast populations in all three species, and interestingly, both Sterreria and Nemertinoides appear to have neoblasts in the epidermis, a feature unknown in triclads, macrostomorphs, polyclads, or acoels, but long known to be true of the catenulid flatworms. Comparison of our results with similar studies from other lophotrochozoans shows that annelids and nemertines possess epidermal stem cells and suggests that the presence of epidermal neoblasts may constitute the plesiomorphic state in the Platyhelminthes, whereas Acoela and Rhabditophora both generate new epidermis instead through inwandering of neoblasts from the parenchyma.