Can Anyone Tell Me What This Is--->??????

[es355lucille]

Guys & Gals, This is a new tank setup and we are in the curing stage. Well its exciting as we have seen two small crabs moving in and out of the rocks. The other thing we noticed in the LR was this peanut looking thing. The hole in the rock is ~ 3/8" and the inhabitant is just under that size. He has never been fully out, and at first I thought it was just wood or something.......so like all kids do, I poked it (gently and lightly) with a stick.... its definately alive. We have just never seen it come out of the rock.

Anyone have any ideas of what this thing is? And if so is it going to be harmful to fish or soft corals?

Thanks
Brad