Someone's excavating

A couple of weeks ago i noticed a small hole in one of my rocks that is looking new wnd white as opposed to all the rest of the aged greenish brown rock. I watched as this hole has continued to grow. its about the shape of say a roll of life savers and maybe an inch and a half deep. there is fresh sand being deposited along the ledge of the rock, you can see it has been pushed over the edge and has spilled down the side. along the edge of the bottom inside the hole being dug are 2 roundish slghtly oval holes about the size of a pencil eraser. I have been watching day and night but have yet to see what the heck is doing the excavating. got any ideas?

 

What do you have in the tank? a pistol shrimp? Haha

 

Could be a peanut worm. That was what I was seeing before I saw my first one come out of the hole I'd been watching.

 

I guess I'm wondering if this is yet another bad hitch hiker or really nothing to worry about. I dont know how you can say since i still havenlt seen the darn thing!

 

Well, no one can say since we haven't seen it either LOL.