Eight arms, no ears, blue blood, rows of suction cups...this is beginning to sound like a science fiction movie, but in fact, we're talking about the octopus! Octopi (the word for more than one octopus) live in oceans all around the world but are generally found in warmer climates. They can range from 3/8 of an inch (the Californian octopus) to 23 feet (the Giant octopus)!
Octopi from different species (types) vary in appearance, but they share the same basic body layout: they have eight arms (each has two rows of suction cups), a head (with two large eyes, a mouth and a very advanced brain), and a mantle, which is the large soft sac attached to their head. Although the mantle hangs off of the head, it can be thought of as the torso of the octopus because it contains so many vital organs like the heart, a digestive system, and gills.
As you may know, an octopus uses the suctions cups (called "suckers") on its arms to grab onto prey, but they also allow the octopus to smell and taste its environment. Imagine if you could taste and smell whatever you held in your hands as soon as you picked it up...an octopus can!
An octopus can also be thought of as an aquatic chameleon because it can change the color of its skin. This is done to express emotion, or for camouflage (pronounced "CAM-o-flaj"), which means blending into its environment so it will be harder for a predator to see it. Octopi can also change the texture of their skin for camouflage purposes.
Scientists continue to discover new and exciting facts about octopi, but this is a difficult task since they tend to be rather shy creatures. In fact, an octopus spends most of its life in crevices, holes, and other hiding places. It does this in part to protect itself from predators.
If the octopus is attacked, it has a few defenses to save itself from being eaten. The mantle of an octopus produces ink (like a squid, which is a relative of the octopus). When threatened, the octopus squirts ink at the predator. This blocks the predator's view of the octopus as it escapes. In some cases, the ink also damages the predator's senses so it can't find the octopus as easily.
Like a squid, an octopus doesn't technically swim away; instead it moves by jet propulsion. It does this by squirting water behind it from an opening in its mantle. The force of the water leaving the mantle pushes the octopus forward. The octopus then takes in more water and repeats this process so that it sprints forward in starts and stops.
Octopi hunt by attaching some of their suckers to their prey (a crab, for example). They then use their beak to make a small hole in the shell of the prey. Afterwards, they inject a poison to kill and partially digest the animal before sucking it out to eat it. There are over 100 species of octopi but only a few are poisonous to humans.
Little Lion Experiment:
When a 3-pound octopus uses its suckers to grab onto its prey, it would take 40 pounds of force to pull the two animals apart! This amazing strength is due to the large number (about 2000) of suckers on an octopus, as well as the properties of suction cups.
When you push down on a suction cup, air is squeezed out, which creates a vacuum. The tiny amount of air left inside can't generate much outward force, but there is plenty of air outside to push inwards (this is called "atmospheric pressure"). This imbalance of the two forces is what makes it hard to pull a suction cup off of an object.
To explore this topic, obtain a small suction cup with a hook on the end (like the ones used to hang up pictures). Attach it to the bottom of a glass table or another very smooth surface [rough surfaces won't work since the texture will allow air to leak in]. Hang weights from the hook until the suction cup finally falls off. The total weight of all the things you hung from the hook equals the amount of force needed to separate that one suction cup. Now imagine having 2000 of those!