The greater blue-ringed octopus is, despite its vernacular name, is a small octopus whose size does not exceed 10 centimeters, arms included, for an average weight of 80 grams.
Its common name comes from the relatively large size of its blue rings (7 to 8 millimeters in diameter), which are larger than those of other members of the genus and help to distinguish this type of octopus.
The head is slightly flattened dorsoventrally (front to back) and finished in a tip.
Its eight arms are relatively short.

There is variable ring patterns on the mantle of Hapalochlaena lunulata with varied coloration in correlation to their ambient environment, from yellow ocher to light brown or even white-ish (when inactive).
The blue rings, which number around 60, are spread throughout the entirety of its skin.
The rings are roughly circular in shape and are based on a darker blotch than the background color of the skin.
A black line, with thickness varying to increase contrast and visibility, borders the electric blue circles.
The blue rings are an aposematic adornment to clearly show to all potential predators that the octopus is highly venomous.
The octopus also has characteristic blue lines running through its eyes.
The greater blue-ringed octopus is, despite its vernacular name, is a small octopus whose size does not exceed 10 centimeters, arms included, for an average weight of 80 grams. Its common name comes from the relatively large size of its blue rings (7 to 8 millimeters in diameter), which are larger than those of other members of the genus and help to distinguish this type of octopus. The head is slightly flattened dorsoventrally (front to back) and finished in a tip. Its eight arms are relatively short.
There is variable ring patterns on the mantle of Hapalochlaena lunulata with varied coloration in correlation to their ambient environment, from yellow ocher to light brown or even white-ish (when inactive). The blue rings, which number around 60, are spread throughout the entirety of its skin. The rings are roughly circular in shape and are based on a darker blotch than the background color of the skin. A black line, with thickness varying to increase contrast and visibility, borders the electric blue circles. The blue rings are an aposematic adornment to clearly show to all potential predators that the octopus is highly venomous. The octopus also has characteristic blue lines running through its eyes.
Greater blue-ringed octopus