Not a marine biologist, but I am a biology student in my undergrad, and have dissected these recently. That is indeed the butthole. Sea urchins don't have eyes.
The ocean, the sea creatures, it's a whole other world down there. I'm practically an expert, you know. Ask me anything about marine life, and I'll give you a convincing answer. It's like I'm swimming with the dolphins of knowledge, baby!
So regarding this, one day, there I am, waist-deep in the ocean, when I stumble upon a distressed sea urchin. When out of nowhere, I whip out a golf ball ā you heard me, a golf ball! I save the day by removing the obstruction from the butthole of a sea urchin.