Irukandji – Carukia Barnesi – Thumbnail sized, causes potentially fatal Irukandji Syndrome.
Box Jellyfish – Chironex Fleckeri – Up to 20 cm on each side of bell, tentacles up to 3 m long. “You have virtually no chance of surviving the venomous sting, unless treated immediately. The pain is so excruciating and overwhelming that you would most likely go into shock and drown before reaching the shore. So don't go swimming alone! Be sure to know the first aid procedures.”
Blue Ringed Octopus – Hapalochlaena Maculosa – A mere ounce, and the size of a golf ball. It is found in the shallow coral and rock pools of Australia. The animal is usually brownish yellow, but electric blue rings light up when disturbed – if you’re picking it up, by the time you see the blue rings it’s too late. Its venom is highly toxic (maculotoxin, a poison more violent than anything found on land creatures). The bite is painless, but there is no known antivenin… and the bite can kill within minutes. The only treatment is hours of heart massage and artificial respiration. Fortunately, it is not aggressive, and bites only happen when it is picked up out of its pool, or stepped on.
P.S. I am fascinated by ultra-venemous animals such as these 3. All are found near Queensland Australia. YOU HAVE BEEN WARNED.