Irukandji

• GeneralIt measures 1 cm but causes a syndrome of extreme pain that sets in half an hour later.
• The Australian physician Jack Barnes proved in 1964 that this jellyfish was to blame by deliberately stinging himself, his nine-year-old son and a lifeguard; all three ended up in hospital.
• It is practically invisible in the water and passes straight through conventional stinger nets because of its size.
• It is tiny — the bell measures between 12 and 25 millimetres — but its four tentacles, one at each corner of the cube, stretch to a metre and are all but invisible in the water.
• Its sting is barely felt. Between five and forty minutes later comes Irukandji syndrome: excruciating pain in the back, abdomen and chest, cramps, vomiting, sweating, extreme anxiety, high blood pressure and a racing heart.
• Its identification is one of the great stories of Australian medicine. In 1964 the physician Jack Barnes caught a suspect jellyfish and let it sting him, along with his nine-year-old son and a volunteer lifeguard. All three ended up in hospital, their abdominal muscles rigid as a board, and the cause was proved.
• The species is named after him. Barnes also proposed the use of opioids as treatment and was the man behind the warning measures on the beaches.
• He also popularised a homespun precaution: wearing nylon stockings, which evolved into today's stinger suits.
• At least eight species in northern Queensland are now known to cause the same syndrome.

Skeleton type

Invertebrate - no skeleton (gelatinous cnidarian)

Habitat and environment

Tropical coastal waters

Sources consulted: Wikipedia (es): Carukia barnesi

Best time: Southern summer, above all from November to May

The pins mark the parks and dive sites where its presence is documented.