Synergy between mechanical injury and toxins triggers the urticating system of marine fireworms

Marine fireworms (Annelida, Amphinomidae) are notorious for their stinging dorsal bristles (notochaetae). In the large-size species Hermodice carunculata, characterized by invasive potential and great predatory ability, notochaetae deter consumers and damage prey. The origin of fireworm defensive and offensive capacities, the mechanism of action of the stinging chaetae, and whether other chemical defenses occur are still uncertain. In the present study, we tested if the urticating system of fireworms is the result of a synergy between mechanical injury, due to notochaetae penetration, and the release of toxins vehiculated. To determine whether and where chemical or structural deterrents were present, different body parts of H. carunculata involved in inter-specific interactions were assayed (i.e. dorsal body wall, gills, dorsal and ventral parapodia). Feeding bioassays were performed to assess palatability against a