There are n kinds of jellyfish in the sea.
Some jellyfish are poisonous. Your jellyfish (there are too many types of jellyfish, and it's hard to say the specific type) has been washed ashore. So you stepped on it. ...
It's okay. It won't die. The pain will go away in a few days. There are too many poisonous things in the sea, so be careful in the future.