The Southern Blue-ringed Octopus (Hapalochlaena maculosa) is one of 3 (or perhaps 4) species of blue-ringed octopus

Blue-ringed octopus

The blue-ringed octopuses are three octopus species that live in tide pools in the Pacific Ocean, from Japan to Australia . They are currently recognized as one of the world's most venomous marine animals...

es. It is most commonly found in tidal rock pools along the south coast of Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. As an adult, it can grow up to 20 centimeters long (top of the mantle

Mantle (mollusc)

The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...

 to the tip of the arms

Cephalopod arm

A cephalopod arm is distinct from a tentacle, though the terms are often used interchangeably.Generally, cephalopod arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends. Octopuses have eight arms and no tentacles, while squid and cuttlefish...

) and on average weighs 26 grams. They are normally a docile species, but they are highly venomous, and posses venom capable of killing humans. Their blue rings appear with greater intensity when they undergo an emotional change.