Portuguese man-of-war found recently on the Cornish beaches. They can give you a nasty sting if you stand on the purple-blue tentacles. I think these are what we used to call blue bottles or blou blasie in South Africa. According to South African advice urine is good for pain relief if you do get stung, and always use salt water not fresh to wash the affected area. Conflicting advice in the use of vinegar. UK and Australians say yes, South Africans say no.
My daughter stood on a blue bottle when she was very small whilst with a friend on the beach whilst I returned home for something. Fortunately my friend rushed her into the pharmacy across the road where she was treated. I felt very guilty though when I saw her tear-streaked face and the red welts on her foot.
Cornwall in Colours 
It’s hard to imagine something so pretty can cause so much hurt! I don’t think I would have realised what it was if I chanced upon it on the beach.
The ‘sail’ is harmless, it’s those buried tentacles that do the harm and unfortunately sometimes they stretch out quite far so you can accidentally step on one.
Goodness! I’ve heard that other varieties of jellyfish do this as well, although I have been fortunate not to have fallen victim to this!
Wow, I never saw something like this, what creatures!
I especially like the different degrees of shadow cast by the translucent surfaces.
They are weird things.We never forget events like your daughter’s sting do we?
She doesn’t remember that incident, but she does remember getting her finger trapped in the front door when she wasn’t much older!
I can never resist a puzzle, so I decided to look into this one and it turns out the research has only just been done! A vinegar rinse came up as the best treatment, but it’s not known why. It doesn’t seem to be because it’s acidic as other similar acids don’t work. However, it works by stopping the tentacles discharging more poison. A hot compress or bath is good, too, because it reduces the effect of the venom. All the other suggested treatments (bicarb, urine etc.) appear to make things worse. Similarly ice. Details here: http://www.mdpi.com/2072-6651/9/5/149/htm
Haha… you sound a lot like me! Only I gave up on this one. Thanks for doing the research Ros. I shall bear this in mind if I ever have the misfortune to run into one of these creatures.