Pathfinder poisonous barbs were a defensive weapon unique to the Pathfinders. Flaps on the sides of their heads hid the sharp weapons which could launch to hit a close opponent and fatally poison them.
They were at least partially metallic in nature based on the fact that when Jool screamed in proximity to them the sharpened tips melted, suggesting they may be an artificial implant.
When Rygel found Shreena's body, apparently bitten by a serpent, he took a sample of her barbs for Aeryn Sun. ("Self-Inflicted Wounds - Wait for the Wheel")