I think I should share this experience, as well as the laughter involved, because getting terribly inappropriate cover art isn't the end of the world.
My first reaction was "It's Flipper! On my damn book!" and then about ten minutes of walking around the house and laughing helplessly. You need to do this, because it keeps you from calling the editor, which is not advisable at this moment. Trust me on this.
The next thing you do is tell your best friend and show it to her. Mine said, "Oh, god" and then prompted me to go directly to step #3, do not pass go, do not collect $200. She also reminded me that she has had two covers that are worse. This is why I love her.
Step #3: You call your agent, and have the agent handle it. That's why you pay them the 15%.
I'll probably know today if there is anything I can do about it. 95% chance is, probably not. Then my fairly serious SF adventure novel will forever be bound in a dust jacket with Flipper in drag on it, and I'll have to live with it. And you live with it, boys and girls, because that's the publishing industry.
There is no great loss without some small gain. I can stop pointing to the Down's Syndrome, Nickelodeon-slimed girl on another cover of mine, the one I refer to as "The Stupidest-Looking Cover of All Time." For sheer idiocy, I think this actually surpasses it, something I had not thought possible.