I just found this online. Could this be what it is? What is this exactly? interoperculum
The interoperculum of these fishes has a cluster of sharp, curved spines, which can be extended outwards, and point in a forward direction. These are probably a defence against being swallowed by predators, and would no doubt be very effective, their forward pointing angle making it impossible for a predator to swallow them, and the Bristlenose's ability to move in any direction enabling it to escape backwards out of the startled predator's mouth. Although they don't look very athletic, Bristlenoses can move with remarkable speed when they want to, scuttling across the rocks with great agility, so they would not be the easiest of targets for a predator anyway.