Epidermal changes during tail regeneration in the Bahamas lancelet, Asymmetron lucayanum (Cephalochordata)

The epidermis of a cephalochordate is described by scanning electron microscopy before tail amputation and at the following intervals thereafter: 1 day, 3 days, 6 days, 10 days and 14 days. Before amputation, the epidermis covering the entire body, including the tail, was a monolayer of non-ciliated cells in a hexagonal array. In one-day amputees, epidermal cells from the wound edge migrated, evidently by means of contractile lobopodia, forming a loosely associated monolayer on the cut surface. In the three-day amputee, cells covering the regenerate had resumed their tight-packed hexagonal array; however, in the six- and ten-day samples, the cells covering the regenerating tail were loosely associated again and smaller than before. Surprisingly, in the same six- and ten-day samples, the epidermal cells covering all body regions anterior to the regenerate had changed conspicuously - their apical cell membranes had shrunk, thereby opening up an intercellular gap, although the cells maintained their hexagonal shape and appeared to have the same neighbours as before. This gapped stage (of unknown significance) lasted about a week, after which the gaps closed up, and all the epidermal cells, including those on the regenerating tail, resumed their close association with their neighbours in a hexagonal grid.