A comparison of some of the different ring patterns that can occur in the Greater Blue-ringed Octopus.
The deadly Hapalochlaena lunulata, or Greater Blue-ringed Octopus.
It injects its prey (typically small crustaceans and) with a powerful, paralyzing neurotoxin called “tetrodotoxin”. Although their bodies are less than 7 cm (~3 inches) long, their toxin is powerful enough to severely injure, or even kill an adult human.
The cells responsible for vibrant colouration of the blue-ringed octopus are called iridocytes. They work by differentially reflecting light off tiny iridescent crystals of guanine.
Hapalochlaena maculosa, one of the few species known collectively as blue-ringed octopodes. They are arguably the most venomous of all marine animals, and are certainly very dangerous relative to their small size (this particular species typically not exceeding 20 cm in length). Their rings become most dramatically blue when they are agitated or frightened - otherwise they appear a dull brown colour.