Regeneration of posterior segments and terminal structures in the bearded fireworm, Hermodice carunculata (Annelida: Amphinomidae)

Like many other annelids, bearded fire- worms, Hermodice carunculata, are capable of regener- ating posterior body segments and terminal structures lost to amputation. Although previous research has examined anterior regeneration in other fireworm spe- cies, posterior regenerative ability in fireworms remains poorly studied. As the morphology of the anal lobe (a small, fleshy terminal structure of unknown function) has been used to distinguish East and West Atlantic H. carunculata populations, there is a more imminent need to understand the morphology and organization of tissues in specimens undergoing poste- rior regeneration, and the timeframe in which signifi- cant developmental changes occur. To further investigate this phenomenon, we amputated the poste- rior segments of living H. carunculata specimens col- lected from the Gulf of Mexico and monitored posterior regeneration over a 6-month study period. Although many aspects of posterior regeneration in H. caruncu- lata are consistent with the findings of other annelid regeneration studies, histological analysis revealed that once formed, anal lobe morphology remains rela- tively unchanged at all stages of posterior regenera- tion; East Atlantic morphotypes were not observed in the West Atlantic specimens studied here. Additionally, we found that the ventral nerve chord, which is par- tially responsible for the regeneration of lost body parts in polychaete annelids, terminates within the anal lobe, suggesting that this structure may play a role in the formation of new segments. J. Morphol. 000:000- 000, 2014. V C 2014 Wiley Periodicals, Inc.