Ypu, they are. But if you're careful, you can avoid getting 'stung' by them.
Actually, we used to have an old lionfish, and when it died, my dad put it in the garbage. So my grandpa goes to take out the garbage, and he put his hand right on the lionfish!! He had to go to the emergency room, because he thought it was still poisonous, and his blood pressure went up!
Most Urchins are poisonous too, my dad has been pricked by them a lot, because when he is moving the rocks around he cannot see where they are (some of them blend in with the rock). He has to use a needle to get the spines out before the venom gets in his bloodstream.