Sponges Various type of sponges can produce irritations and pain for long periods. There are many species of tropical sea worms found under rocks and in coral. These can produce painful and itchy rashes lasting for hours. Antihistamine or steroid application might help. Considered to be the most venomous marine creature.
Death can occur with minimal contacts.
Chironex are found in the warm waters of Pacific and Indian oceans. When death does not occur, the pain is excruciating and often stings leave significant scars. Fatalities have been reported, but usually victims survive after suffering from excruciating pain. Other Jellyfish Many other jellyfish species are found. Contact with those may vary from a mild local itch to severe burning with throbbing pain.