Thanks, everyone! You guys are wonderful. Cooper (aren't you the artist?) I think you're right:it is the stuff they call 'fire coral' which isn't a real coral at all, just like you said. Looked it up and I think it's a hydroid. ANYWAY, it hurt. But is was a brownish rust color, and soft like a moss or plant.
So I'm trying really hard to come back to CC for a vacation -- it's been a long time. But if I do accidently sit on that fire coral again,I certainly will:
Expose my butt, spray on windex, ammonia, vinegar and WD40 while doing cartwheels, pee into a wetsuit and drink strawberry smoothies loaded with rum punch, topping it off with Belikins. By that time I won't care about a few stings!
Seriously though, you did give good advice, and I thank you for it! Cynth