It is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean, and it looks like a jellyfish.
If it does get on your skin, remove it with a towel and wash it off with seawater.
Washing with fresh water makes it easier for poison to enter the body due to the difference in osmotic pressure.
Heat for a while to neutralize protein toxins, cool with ice or cold water to reduce swelling, and seek medical attention.
It can discharge venom in response to irritation from fresh water or vinegar. While vinegar is known to be effective against box jellyfish stings, it has the opposite effect on this species. Never touch anything washed up on the shore or sand. Nematocysts respond to physical stimuli, and they are ejected regardless of whether the hydrozoan is dead or alive.