The Blue Lined Octopus (Hapalochlaena fasciata) is one of several species of Blue Ringed Octopus and the most common in Sydney. This small octopus is only about 5cm long and with arms extended may only be 10cm in length.
This type of blue ringed octopus is seen at many sandy dive sites in Sydney but is very well camouflaged and difficult to spot. They are a tiny octopus that can sometimes be confused with being a baby octopus and mistaken as another species on account of its colouring which is usually dull all over, and only shows the blue rings when excited or agitated.
This species of octopus has caused fatalities to humans and divers should be very careful around them. Their venom tetrodotoxin has enough power to kill 10 people. When they bite this venom stops messages being sent to the brain and so the victim becomes paralysed with nearly all motor functions ceasing except the heart.