Sweet picture, eh? Looks like a sea creature to me, or perhaps some microscopic organism.
Actually it's Victoria crater on Mars, as seen by the Mars Reconnaissance Orbiter. It the one the robot Opportunity has been exploring for the last year or so. If you click on the image you can acually see the rover's tracks off to the left.
The weblike structures at the borrom of the crater are sand dunes.
Thanks to Bad Astonomy for the picture. And to NASA, of course, for actually taking the picture.