Looks like a curlycue to me. Regardless, it's a pest. Where it's at I'd be tempted to mash a glob of JB waterweld (or reef epoxy if you want to spend more for the same product) over the top of it. Leave the epoxy on for a few weeks and then you can just pry it off if it bothers you there.
I would super glue that sucker. Big dot of glue right over it while holding the scoly out of the water. Keep it out of the water until the glue dries (less than 1 minute) should take care of the issue