Abstract
Sponges (phylum Porifera) are early-branching metazoans demonstrating an outstanding example of whole-body regeneration, cell reaggregation. During the process, single cells form aggregates capable of progressive development and reconstruction of intact sponges. This study provides the first comprehen-sive analysis of cell proliferation and cell death during cell reaggregation in a marine demosponge, Halisarca dujardinii. Relatively high proliferative activ-ity occurs at the early and late stages of the reaggregation. This proliferation seems to be a consequence of intact tissue turnover rather than a prerequisite for aggregate development. The contribution of cell death is limited to a short period during the aggregate epithelization. Cell reaggregation in demosponges appears to be a morphallactic restorative process relying primarily on cell migration, dedifferentiation, and transdifferentiation.