Diving with Octopus

Imagine a creature from another world that has 9 brains, 3 hearts, and blue blood. It sounds like an alien from another world, but they actually live here on this planet. Their collective name is octopuses and fossil records have shown that they have been around for at least 300 million years which is a long time before the dinosaurs arrived. All species of octopus are venomous but only one (The Blue-ringed octopus) is dangerous to humans.