The blue-ringed octopus is 12 to 20 cm (5 to 8 inches), but its venom is powerful enough to kill humans. There is no blue-ringed octopus antivenom available.
They are currently recognized as one of the world's most venomous marine animals. Despite their small size and relatively docile nature, they can prove fatal to humans.
Spotted this very dangerous tiny Octopus during a night dive in Bali last December. the light is from a flash light. Depth around 18 metres.