Secondary‐tail formation during stolonization in the Japanese green syllid, Megasyllis nipponica

Abstract

AbstractBenthic annelids belonging to the family Syllidae show a distinctive sexual reproduction mode called “stolonization,” in which posterior segments are transformed into a reproductive individual‐like unit called a “stolon.” Megasyllis nipponica forms a stolon head and a secondary tail in the middle of the trunk before a stolon detaches, while, in the case of posterior amputation, posterior regeneration initiates at the wound after amputation. To understand the difference between posterior regeneration and secondary‐tail formation during stolonization, detailed comparisons between the developmental processes of these two tail‐formation types were performed in this study. Morphological and inner structural observations (i.e., cell proliferation and muscular/nervous development) showed that some processes of posterior regeneration, such as blastema formation and muscular/nervous regeneration at the amputation site, are missing during secondary‐tail formation. In contrast, the secondary tail showed some unique features, such as the formation of ventrolateral half‐tail buds that later fused in the middle and muscle/nerve branches formed before the detachment of the stolon. These novel features in the process of stolonization are suggested to be adaptive since the animals need to recover a posterior end quickly to stolonize again.