Starfish and Our Mystery Goby

Last night Amy and I went out on what I think will be our final (for now at least) salt-water fish buying run. We took Marlin I back to the store and much to our happiness they returned him for store credit (not their usual policy, but the people there were very nice about it). We'll probably hold onto the store credit for a while.  We then went over to the East side pet store (the last of 4 places in Madison that sell salt-water fish) and picked up a small purple fish (not pictured), a starfish, a nano frag with some polyps on it and some grape-plants.

The starfish has been busy moving  around the thank, I think it'll do pretty good in there. Also pictured is our mystery goby. We got him the same day we got Nemo, he was labled as an "engineer goby" but we found out later that he might be something else as all the other "engineer gobys" we saw were larger, eel-like, with horizontal black stripes, not vertical.  He's made himself a nice home under that rock, poking out from time to time. I wonder what he is. Any ideas?