This is going to hurt. I'm no goby expert, but I know there's 5000 diferent species, or some similar large number, and your description probably fits about 3000 of them. However only a few are regularly imported. Looked in a baensch atlas or any other books, or tried wetwebmedia.com. Normally you could look on fishbase, but with gobies that will be a hopeless task. Try a google search for knight goby?