My divemaster said that it’s a starfish. I have to take his word. I wasn’t willing to pull it out from under the rock. The spikes are pretty impressive. Anyway a quick look-up on the internet says that starfish don’t have spikes. So these are spines. I didn’t have any other comparable pictures. From where I was this was a creature that said, “Leave me alone.” And I did. And…. well, I’ve just returned from night dive. My divemaster showed me a sea urchin at night. And in about a month or so I’ll post some dramatic night images. But the one on top is probably a sea urchin. They come out at night. Then again, maybe the starfish come out at night also. So far I didn’t find anything comparable on the ‘net. By the time this post finally is published maybe the answer will be a little more clear. There is another contender – nudibranch – a kind of ocean slug. There’s quite a lot of variation and some suggestion that urchin and starfish are the wrong answer….