1st Coral stings can be deceiving!

That's what happened with me. When I built my first inwall 75 gallon (hence my username), I didn't have front-access. That meant to do anything in my tank, I had to go into my fishroom and reach over a number of Euphylliads. Over time it went from being scratchy to what you showed in your picture.

 

It's the same reason why when you go snorkling, they will tell you do your best to not make any contact with the coral reefs. Coral poisoning can be bad, even deadly if it gets in the blood stream.
Latex gloves are great. I also have a set of Coralife's full arm gloves as well.

 

i got stung by my hydnophora, felt like a mosquito sting, now i cant feel it at all.

frogspawn has no affect on me either...

 

Right on man. When I tell my snorkelers not to touch the reef in anyway shape or form, well their safety is the least of my worries. It seems like the national past time in China and Italy is snorkeling in way to far where the reef is super shallow, standing up and stomping corals to death.