Octopuses have three hearts.
– Octopus blood contains the copper-rich protein hemocyanin for transporting oxygen. Although less efficient under normal conditions than the iron-rich hemoglobin of vertebrates, in cold conditions with low oxygen pressure, hemocyanin oxygen transportation is more efficient than hemoglobin oxygen transportation.
– Octopuses are highly intelligent, possibly more so than any other order of invertebrates. Maze and problem-solving experiments have shown evidence of a memory system that can store both short- and long-term memory.
– The octopus has been shown to use tools. At least four specimens of the veined octopus have been witnessed retrieving discarded coconut shells, manipulating them, and then reassembling them to use as shelter.
– Due to their intelligence, octopuses in some countries are on the list of experimental animals on which surgery may not be performed without anesthesia, a protection usually extended only to vertebrates.
– An octopus has a highly complex nervous system, only part of which is localized in its brain. Two-thirds of an octopus’s neurons are found in the nerve cords of its arms, which have limited functional autonomy. Octopus arms show a variety of complex reflex actions that persist even when they have no input from the brain.
– All octopuses are venomous, but only one group, the blue-ringed octopus, is known to be deadly to humans.
– Most octopuses can eject a thick, blackish ink in a large cloud to aid in escaping from predators. The main coloring agent of the ink is melanin, which is the same chemical that gives humans their hair and skin color. This ink cloud is thought to reduce the efficiency of olfactory organs, which would aid an octopus’s evasion from predators that employ smell for hunting, such as sharks. Ink clouds of some species might serve as pseudomorphs, or decoys that the predator attacks instead.
– An octopus’s camouflage is aided by certain specialized skin cells which can change the apparent color, opacity, and reflectivity of the epidermis. Chromatophores contain yellow, orange, red, brown, or black pigments; most species have three of these colors.
– Octopuses can use muscles in the skin to change the texture of their mantle to achieve a greater camouflage. In some species, the mantle can take on the spiky appearance of seaweed, or the scraggly, bumpy texture of a rock, among other disguises.
– When under attack, some octopuses can perform arm autotomy, in a manner similar to the way skinks and other lizards detach their tails. The crawling arm serves as a distraction to would-be predators. Such severed arms remain sensitive to stimuli and move away from unpleasant sensations.