Jellyfish stings

[PussyCat]

Jellyfish belong to a group known as Cnidaria. Other Cnidaria include

Sea anemones
Corals
Hydroids (such as the Portuguese man-of-war)

(See also Introduction to Bites and Stings.)
Cnidaria cause more poisonings than any other marine animal.
Cnidaria have stinging units (nematocysts) on their tentacles. A single tentacle may contain thousands of them. The severity of the sting depends on the type of animal. The sting of most species results in a painful, itchy rash, which may develop into blisters that fill with pus and then rupture. Other symptoms may include weakness, nausea, headache, muscle pain and spasms, runny eyes and nose, excessive sweating, and chest pain that worsens with breathing. Stings from the Portuguese man-of-war (in North America) and the box jellyfish (in Australia in the Indian and South Pacific oceans) have caused death.