blue-ringed octopus

noun

-ˈriŋd-ˈäk-tə-pəs, -ˌpu̇s 

: any of several venomous octopuses (genus Hapalochlaena) of the Indo-Pacific region that display brilliant blue rings on the skin when alarmed or agitated and are capable of inflicting a fatal bite due to the injection of tetrodotoxin