They are creepy looking but kinda fun to watch. I use to throw food in for mine to see him come out. Mine looked exactly like the OP's pics. I'd say he was only about 12" maybe a bit longer, I had to remove him when I decided to make it a reef tank, ended up ripping him into three pieces trying to get him out, felt kinda bad but I didn't have anywhere to keep it besides. Mine burrowed several holes in one rock and would block up the holes with bits of crushed coral and sand, your best bet is find the rock and remove it.