Segment regeneration in the vestimentiferan tubeworm, Lamellibrachia satsuma

The ability to regenerate missing body parts varies among species. To elucidate the evolution of regenerative capability, an understanding of the regeneration mechanisms of diverse organisms is required. We focus on vestimentiferan tubeworms, which have a body plan that is unique among annelids. We found that the vestimentiferan Lamellibrachia satsuma is able to regenerate its posterior body parts, but not its anterior body parts. Based on observations of live specimens, we defined five stages in the process of posterior regeneration. The morphogenesis was observed in detail by a series of sections and scanning electron microscopy. The most posterior domain of the opisthosome differentiated from the blastema, while the anterior domain of the opisthosome regenerated from the remaining trunk region. We also examined the expression pattern of the engrailed gene during regeneration, and found that engrailed was expressed in the mesodermal cells of each segment.