Octopuses have blue blood. Not from royal genes, but from copper. Unlike a lot of other marine invertebrates, octopuses have a high metabolic rate, and therefore a high demand for oxygen. Copper-based hemocyanin is more efficient for transporting oxygen.
Octopuses also have three hearts: two just to pump blood through the gills and one more to circulate it to the organs.
Many octopuses are able to escape danger by releasing a squirt of obscuring ink as they zoom away on a jet of water. The ink also contains tyrosinase, a compound that burns predators’ eyes and temporarily paralyzes their senses of smell and taste.
All octopuses (plus all cuttlefishes and some squids) are venomous, although only the blue-ringed octopus of Australia is dangerous to humans.
Octopuses are masters of camouflage, literally changing color, brightness, pattern and even texture in a flash to hide in plain sight or advertise for a mate.
Octopus’s eight arms can perform separate tasks simultaneously thanks to a large nerve cluster, like a minibrain, at the base of each controlling its movement.
Octopuses are standouts for their large brains. They can navigate mazes, solve problems, remember, predict, use tools and take apart just about anything from a crab to a lock.
Octopuses can come ashore. During short nocturnal forays at low tides, a few coast-dwelling species appear to hunt for easy pickings such as crabs and shellfish.