Regeneration, the ability to restore body parts after amputation, is a widespread yet highly variable phenomenon across animal species. While some species exhibit extensive regenerative abilities, others, like humans, show limited potential. The reasons for these differences remain an open question. Among animal phyla, annelids are known for their remarkable regenerative capabilities, though the molecular and cellular mechanisms underlying this process are not well understood. Platynereis dumerilii, an annelid, is particularly notable for exhibiting both successful and aborted regeneration events.To better understand the origin, plasticity, and fate of the cells involved in blastema formation during successful regeneration, we developed specific tools to track different cell populations. Using these tools, we discovered that posterior regeneration is partly driven by a population of plastic, proliferative gut cells whose regenerative potential varies along the antero-posterior axis of the worm. Our findings support a hybrid, flexible model of successful posterior regeneration in Platynereis, which relies on different degrees of cell plasticity. We plan to compare this model with the aborted regeneration process. Platynereis provides a powerful system to unravel both the common and divergent molecular and cellular processes behind successful regeneration in animals.