Ah! now I don't know what it is. the darters and gobies look just like each other. Well I guess I'll just have to keep doing some research. I tried to take a pic but it is so small and so well camoflaged you can't hardly see it.
I'm not sure where the ghost shrimp originate but I know that they are kept outside at the supplier wich is in california. The most logical reason why it got in there was probably from a bird or something like that.