Poison Ocellate Octopus is a type of blue-ringed octopus. They are highly venomous, with yellowish skin and a distinctive blue ring under each eye that can be displayed rapidly when the octopus feels threatened.
Despite their small size, each octopus has enough venom to kill approximately 26 adult humans. Victims are often unaware of being bitten, because the bite is nearly painless, and the neurotoxin instantly numbs the skin on contact.
Most bites result in death within minutes from respiratory failure. There have been documented cases of victims surviving when immediately put on artificial respiration, typically for a minimum of 10 hours, which is how long it takes to metabolize the venom. No antivenom is currently available.
These octopuses are not aggressive, and very few human fatalities have ever been recorded.
I was photographing what I believed to be a common juvenile octopus, about the size of my thumbnail, during a dive in Anilao, Philippines, when it flashed the blue ring seen in this photo as a warning. The octopus then swam into a small vacant clam shell and closed the two halves to hide.
When Poison ocellate octopuses feel seriously threatened their color changes to a high contrast striped pattern. Read more in our post, Biodiversity from the Muck to the Reef: Scuba Diving Anilao, Philippines.