Well that's just plain icky. Thanks for the ID. I was hoping otherwise, of course, because the tips were kinda bubbly rather than straight, but oh well. Guess the newbie gets yet another learning experience.
If you can fish the rock out, you might even be able to slide it off. Believe it or not, that's what I did with a couple I found in my last aquarium. Mind you, they were smaller than this.
Cover it with very thick kalk paste slowly squeezed through a syringe (turn off your pumps for a bit to let it set into a crust completely covering the pest).
You can also bury the rock with sand and sometimes they pop off and poke up through the sand, then you can scoop and toss.
If you can easily remove the rock, you can also torch it with a lighter.