The southern member of the blue-ringed group. Its rings are smaller and less distinct than the northern species and only flash when the animal is disturbed.
To about 12 cm overall and usually much less, mottled yellow-brown with rings that are faint and hard to see until the animal is disturbed, when they flash an intense iridescent blue. That is the difference between this and the northern blue-ringed octopus: the southern species has smaller, more numerous and much less distinct rings, so a calm animal may look like an ordinary small brown octopus. Do not rely on seeing rings to identify one.
It lives in shallow water in southern Australia — rock pools, rubble, seagrass, and inside bottles, cans and empty shells — which is exactly the ground a person picks things up on. The saliva contains tetrodotoxin, produced by bacteria the animal carries rather than by the animal itself. The bite is small, often painless and can go unnoticed; the toxin blocks nerve signals, so the effect is progressive paralysis with the person conscious throughout. There is no antivenom. The treatment is assisted breathing until the toxin clears, which means getting to a hospital, and people have survived several hours of rescue breathing. In the water the rule is simple and absolute: do not handle one, and do not pick up a shell, a bottle or a can on southern Australian rubble without looking inside it first.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
