Although I have never stepped on one, I know people to have so I always watch where I'm walking along the shore for dead jellyfish which can be found quite often. They look nothing like the majestic creatures they appear to be when alive and in water. Dead and onshore they are just piles of smelly slime that stink up your shoes.
I don't know what plant this leaf is from but it reminded me of my desire to someday give scuba diving a try. I would like to see all these creatures in their native habitat rather than how they look after washed ashore.