Wierd Organism and a crab ID please

A couple weeks ago, I noticed this hitch hiker crab on a couple of sponges I got. I dumped him into one of my tanks which had no coral and left him there. Today I decided to put some LR w/polyps in the tank so I was just wondering what type of crab he is and is it reef safe? It has a little green patch on the back of it. It looks like some kind of coral to me.






Also, I noticed this other hitch hiker in a tank with some LR that I recently got. I have no idea what it is. It looks and moves like a worm.

 

I've thought about that actually the rust thing but they've been in the tank for years. About 6 years actually and no problem as yet. I am gonna be changing the substrate soon to aragonite reef sand because I'm thinking about making this tank a full reef.

Thanks for the ID on the crab. Is it reef safe though? and what about that weird worm? I checked out the worm pages on the ID stickies but still don't know what it is.

 

Here's another pic of the crab this shot is kinda showing the green patch on his back more clearly.

 

I'm with mission on the crab but I'm not sure what that worm is

 

And here's a short video of the worm

 

I know that I've seen this type of creature many times before mainly in the reef tank at my work. No one there seemed to know what it was. Only now that I have one in my tank, I'm interested in finding out what it is.

 

I just looked through some images on google and I think it's a spaghetti worm. What do you think?

 

Yes.