Octopuses
Octopuses (or octopi, if you prefer) are cephalopods, invertebrates that also include squid and cuttlefish. They have bulbous heads, large eyes, and eight very useful arms. “Cephalopod” is Greek for “head-foot,” which makes sense, since their limbs are attached directly to their head.
Octopuses are highly intelligent animals, masters of camouflage that have evolved an array of tricks over tens of millions of years to avoid or thwart would-be attackers. They can match the colors and even textures of their surroundings, allowing them to hide in plain sight. If a predator gets too close octopuses can escape quickly, shooting themselves forward by expelling water from a muscular tube called a siphon. Octopuses can also release a cloud of black ink, which obscures them and dulls an encroacher’s sense of smell.
Their soft bodies mean octopuses can fit into impossibly small nooks and crannies, as long as the holes are not smaller than the only hard parts of their bodies: their beaks. If all else fails, octopuses can lose an arm to an attacker and regrow one later.
Super smart
The octopus’s arms are lined with hundreds of suckers, each of which can be moved independently thanks to a complex bundle of neurons that acts as a brain, letting the animal touch, smell, and manipulate objects. Octopuses can open clamshells, maneuver rocks—even dismantle the filtration systems of an aquarium tank. They can also develop opinions about people; one routinely squirted water down the back of a keeper it seemed to dislike. Another shot a jet of water at a light to cause a commotion.
There are around 300 species of octopus and they are found in every ocean. Most live on the seafloor, but some, like the paper nautilus, drift nearer to the surface. Octopuses mostly feed on crabs, shrimp, and mollusks.
Solitary animals, they typically live alone, sometimes in dens they build from rocks, sometimes in shells they pull over on top of themselves. Some even make a door for themselves—a rock pulled into place once they’re safely tucked into their homes.
How Octopuses Work
The octopus belongs to the phylum mollusca, where you will also find its slimy next of kin, the clams, snails and slugs. But octopuses are separated from the mollusks into the class cephalopoda, which includes the most advanced animals of the phylum. Squid, cuttlefish and nautilus belong to this class as well. The octopus has evolved most since the cephalopods originated more than 600 million years ago. While the other cephalopods sport some form of inner or outer shell like their relatives the mollusks, the octopus has none.
The word cephalopod literally means “head-footed” and refers to the fact that these animals’ arms branch directly off of their heads. Some cephalopods have tentacles as well as arms, but the octopus manages just fine with the eight arms it uses for practically everything: eating, moving, hunting, tasting and mating.
Behind the octopus’s head, directly opposite the arms, is its mantle. The mantle is a highly muscled structure that houses all of the animal’s organs. Its gills, hearts, digestive system and reproductive glands are all crammed into this one space. The strong muscles in the mantle protect the organs and help with respiration and contraction. The octopus also has a funnel, sometimes called a siphon, which is a tubular opening that serves as a pathway for water. You’ll find out the purpose for this funnel later in the article.
In place of the protective shell found in many other mollusks, the octopus brandishes a startling array of defense mechanisms. One researcher who calls octopuses “the wizards of camouflage” goes so far as to say that chameleons are humdrum by comparison [source: Stewart]. Masters of disguise, octopuses can alter their skin to take on a diversity of colors and textures to blend in with their surroundings.
On the next page, find out more about the octopus’s magical ability to change colors in less than a second.
Blue Bloods
Not all blood is red like ours; the octopus’s blood is blue. The blue color comes from hemocyanin, the copper-containing protein that binds oxygen in the octopus. Human blood is red because its oxygen-binding protein, hemoglobin, contains iron. In addition to being blue, octopus blood is a poor carrier of oxygen, which helps explain the animal’s sometimes apparent laziness. To cope with the low oxygen levels, the octopus maintains a constant high blood pressure and has three hearts. Two of the hearts pump oxygen-rich blood through the gills, while the third circulates it through the rest of the body.
