Killing without a weapon: new morphofunctional and behavioural traits of Hermodice carunculata (Pallas, 1766)

This study offers novel insights into the anatomy and predation strategy of a native invasive species in the Mediterranean Sea: the polychaete Hermodice carunculata, focusing on a population from Pantelleria (Sicily). By integrating direct underwater observations, optical and electron microscopy, and photographic material sourced online, we enhanced understanding of foregut anatomy, identified two feeding modalities, and suggested a relationship between the foregut structure and the species’ behavioural traits. The analysis confirmed that the worm’s pharynx is unarmed and revealed that the pharyngeal epithelium is adorned with bifurcated papillae whose function remains to be clarified. Considering that cnidarians are among the fireworm’s preferred prey, the papillae secretions may play a role in neutralizing nematocyst toxins. During field surveys, the fireworms were detected while feeding on a small assemblage of colonies of Eunicella singularis transplanted during an earlier restoration initiative. Hermodice carunculata could ingest up to 10 cm of a gorgonian branch, corresponding to 20–30 segments of the worm’s body, suggesting that Hermodice carunculata predation may pose a threat for restoration of temperate gorgonian forests. To conclude, this analysis provided valuable insights into the effective feeding strategy of the polychaete, which may inform targeted management approaches for controlling this invasive species.