It is in fact... the rough surface of a starfish, snapped by zoologist Alexander Semenov. He explains:
When I first began to experiment with sea life photography I tried shooting small invertebrates for fun with my own old DSLR camera and without any professional lights or lenses. I collected the invertebrates under water and then I've shot them in the lab. After two or three months of failure after failure I ended up with a few good pictures, which I've showed to the crew. It has inspired us to buy a semi-professional camera complete with underwater housing and strobes. Thus I've spent the following field season trying to shoot the same creatures, but this time in their environment. It was much more difficult, and I spent another two months without any significant results. But when you're working at something every day, you inevitably get a lot of experience. Eventually I began to get interesting photos - one or two from each dive. Now after four years of practice I get a few good shots almost every time I dive but I still have a lot of things that need to be mastered in underwater photography.