most bristle worms are harmless but there are a few predatory species. i would be concerned for two reasons. one is that the harmless types dont recognise live food as food. they feed on carrion and are attracted to dead food by there smell, so if its a harmless type your clam is not in very good shape. two, bristle worms are rarely active in the light so if its out and about and attracted to your clam with the lights on its probably a predatory species and i would remove it.