New live rock critters

[Endy]

New to the hobby and I'm setting up my first salt water tank. I have just purchased my live rock and I was taking a look after I got it into the tank.
There are a couple of things going on but a couple I need some advice on.

1st there is a crab of some sort about the size of a thumb nail living in one of the holes in the rock. Should I just leave him be or is he not good for my tank at this critical stage of stabilization?

2nd there is few little flutey feathery things living on a couple of rocks. What are these things and will they survive? The Rock is partially cured from the aquarium store and it shouldn't take the month to 6 weeks to stabilized.

http://i249.photobucket.com/albums/gg205/ENDYMI0N/aqrock.jpg

Lastly... What the heck is this thing??? It looks like a large almond in the shell. I don't think its alive. Any thoughts???

http://i249.photobucket.com/albums/gg205/ENDYMI0N/nut.jpg

[reef bound]

I would banish the crab to the sump if you have one......We missed a box crab when we went through our rock when we set up our tank and I'm pretty sure he ate a good bunch of my zoas, he definitely ate alot of snails as we found the shells in his house.
The feathery things are feather dusters and should be ok. If not, more will show up in time. The almond shaped thing looks like a little clam or mussel of some sort to me. We've got a couple of those as well, and they made it through our cycling.

[Endy]

**Update**

2nd Pic
I caught this thing opened a little and then shut itself up real quick when I flashed a light to get a better look. It must be a clam of some sort. Should he be ok to leave alone??

[Oxymoron]

The small clam should be ok and survive the cycling process. It will open up to filter feed from time to time. I have one that hitchhiked on my LR and it's still alive. I'll add that both the clam and feather duster's are both harmless filter feeders and are beneficial to your tank. Get the crab out while you have the chance lol.