Octopuses (or octopodes) are mollusks in the Cephelopoda (literally “head-feet”) Class, along with squids, cuttlefish, and nautilus. Unlike their relatives, most octopuses lack an external or internal shell; their squishy bodies can easily squeeze through small spaces. These creatures sport eight muscular arms used for swimming, usually lined with suction cups for walking, climbing, and grasping prey. At the center point of its arms, there’s a hard beak used to crush and eat.
It’s large head or mantle holds two eyes that see with human-like acuity, along with two multi-purpose cavities. Since their gills are internal, octopodes draw water into the mantle cavities to breath. The octopus’s two brachial hearts pump blood through its two gills to be oxygenated, while the third heart distributes blood through the rest of the body. The mantle also contains siphons for expelling waste and water; a frightened octopus can use its siphons for jet propulsion to make a speedy escape.
The mantle cavity also plays a vital reproductive role. To mate, male octopuses load a modified tentacle (the hectocotylus) with sperm, and inject it into a female’s mantle cavity. After the eggs hatch, the female quickly shoos her hatchlings from her lair, leaving them to float amongst surface plankton until they reach adulthood. For the handful that survive, life is still short; octopuses live between six months and two years and die months after mating.
To maximize their short lifespan, octopuses sport a wide array of defense. Many species of octopodes spray ink to make a quick getaway and mask their smell, while some species have been seen walking on two legs while waving the other six about, waltzing away from a fight disguised as a plant. Additionally, all octopodes have chromataphores, allowing them to change color and blend in with their surroundings.
Octopuses are widely considered the smartest invertebrate. In the lab, they’re able to perform elaborate maze and memory tasks, and engage in play activity with balls and bottles. They’ve also been recorded escaping from aquariums to eat unsuspecting inhabitants of nearby tanks. In the wild, octopuses are known to use tools, taking shelter under coconut halves and lining their layers with shells and rocks to create a fortress or “garden.” Mimic octopuses make spectacular use of their smarts by combining their chromataphores and keen observational learning to convincingly imitate other, dangerous species. Despite this astonishing intelligence, octopuses are still probably not psychic.
As a last note, consider the heavily debated plural “octopi.” The word comes from the incorrect assumption that “octopus” is a Latin noun, which would make the plural i-ending correct. Really, octopus comes from the Greek oktapous (“eight-footed”), making this a case of hypercorrection: the over-application of a grammatical rule. Octopuses are pretty darn smart, but it seems humans might be a bit too smart for their own good.