Most venomous mollusc
ranked #1
United Kingdom ()

The two closely-related species of blue-ringed octopus, Hapalochlaena maculosa and H. lunulata, found around the coasts of Australia and parts of south-east Asia, carry a neurotoxic venom so potent that their relatively painless bite can kill in a matter of minutes. It has been estimated that each individual carries sufficient venom to cause the paralysis (or even death) of 10 adult people. Fortunately, blue-ringed octopuses are not considered aggressive and normally bite only when they are taken out of the water and provoked. These molluscs have a radial spread of just 100–200 mm (4–8 in).