Sea slug identification

[Sea la vie]

I need help identifying what I believe was a sea slug. I was waist deep in the water at Hilton Head Beach, South Carolina (eastern Atlantic). A wave came and I suddenly felt a horrible stinging/biting sensation on the top of my knee. This beach is notorious for sea nettle jelly fish stings and I had been stung twice already during the trip. This sensation felt entirely different and was much more painful. The pain was so intense I was screaming and flailing around. I tried swiping whatever it was off, but it was almost like it had latched on. My friend came over and I was screaming that whatever it was, was stuck on me. I looked at my knee and I saw a tiny almost transparent creature that looked much like a sea slug. He aggressively pushed it off with his thumb and the pain continued for hours after. There was a red ring where it had either suctioned on or bit me that lasted hours as well. To this day, I have no idea what it was. It was such a bizarre encounter. Any clue what this could have been? 

[seabass]

Hi, welcome to Nano-Reef.com.

 

It's possible that it was just a tentacle fragment of a jelly that was broken off by the surf.

[billygoat]

You almost certainly ran into a jelly or part of a jelly. Some sea slugs can appropriate nematocysts from the animals that they eat and use them to sting in self defense, but in a temperate beach environment such as the one you describe, the only possible culprit for your sting is a jelly.