Washing out remaining venom and pieces of spine will help minimize damage, speed healing and prevent infection. Leave an inaccessible spine alone only if it hasn't penetrated a joint, nerve or blood vessel. Seek appropriate medical care. Some wounds will require surgical cleansing and repair, antibiotics for infection control, as well as antivenins and life support for severe stings. Hydroids such as fire coral produce an immediate burning sensation followed within 30 minutes by an itchy rash that takes several days to heal.
Jellyfish stings cause burning and leave a trail of bumps and welts.
Serious jelly encounters can result in a severe burning sensation, muscle spasms, vomiting, shock, even collapse. Deactivate remaining nematocysts with a 5 percent vinegar solution until the stinging stops. Use isopropyl alcohol if you don't have vinegar. Apply shaving cream and scrape skin with a razor to remove nematocysts. A paste of mud, flour or talc scraped with a dive knife or credit card also works.