Mid Blue-Ringed Octopus is another one of the smaller, but more deadly marine animals that inhabit shallow coastal. They normally found at reefs and rubble areas.
Mid Blue-Ringed Octopus is small, and rarely is larger than about 20 centimeters from the tip of one tentacle across to the tip of the opposite tentacle. The blue-ringed octopus is normally light in color, with dark brown bands over its eight arms and body, with blue circles superimposed on these dark brown bands. When the octopus is disturbed or taken out of the water, the colors darken and the rings turn a brilliant electric-blue color, and it is this color change that gives the animal its name.
The octopus secretes a very deadly venom, either by biting with its parrot-like beak, or by squirting the poison into the water surrounding its prey (usually small crustaceans like crabs). The poison is so strong that it causes immediate respiratory paralysis and death can occur within an hour and a half. The direct bite from the blue-ringed octopus is usually painless, and may not be noticed immediately by the victim, who may have mistakenly picked up an interesting looking octopus while searching through a tide pool. However, the deadly effects of the poison will be noticed immediately. The poison apparently interferes with the body's nervous system. The victim will immediately experience numbness of the mouth and tongue, blurring of vision, loss of touch, difficulty with speech and swallowing, and paralysis of the legs and nausea. If the victim does not receive medical treatment immmediately, full paralysis may occur within minutes, followed by unconsciousness and death due to heart failure and lack of oxygen. There is no antivenom for the poison from a blue-ringed octopus. It is usually necessary to perform continuous CPR on a victim until the effects of the venom have subsided. This may take several hours, but it may mean the difference between life or death for the victim. ( these paragraph are taken from http://longwood.cs.ucf.edu/~MidLink/seawasps.html)
Hope u all be careful when u are diving. Underwater world is beautiful and can be dangerous as well.