Severe Sting by Unknown Jelly

I was stung by an unknown jelly in August 2011, while swimming at a depth of 5-6 feet. Attached is a picture of the wound on day 6. The only part of the jelly I saw was the piece of tentacle still attached to my arm afterwords (in the image you can see a line across my forearm where I pinched the poor creature between my fore-arm and bicep, my bicep sustained the brunt of the damage)
The tentacle/tendril was very slender and translucent, with a florescent dot in a repeating pattern down its length.
In the following months the area around the sting would repeatedly break out into hives, and it has left an immense scar.
Not sure what type of jelly it was, but I am labeling this "Box Jelly" simply based upon the amount of tissue damage caused.
It is worth note that there was a jellyfish warning issued shortly after I was stung.