To the ocean-dwelling life forms known as octopuses, humans are the interlopers on this planet. Octopuses have been around almost 300 million years and during that time have evolved some truly amazing survival tools. One of the most notable is their array of eight arms – which has earned them their name – covered with suction cups. They use their powerful arms to grip rocks, capture prey and move around. You might expect scientists to have a long Latin word word for the round, concave suction cups that are such an important survival tool, but they don't. They just call them suckers.
TL;DR (Too Long; Didn't Read)
The suction cups on an octopus' arms are called suckers. The internal wall is the infundibulum, and the cavity in the center is the acetabulum.
Anatomy of a Sucker
"Sucker" may not be the most sophisticated word possible, but biologists make up for the lack of scientific verbiage when discussing the anatomy of one. The soft, squishy part of the sucker that is most visible is the infundibulum. This is surrounded on the extreme edge by a rim of mucous-like epithelium. In the center of the infundibulum is a roundish cavity known as the acetabulum.
Each sucker is attached to the arm by a muscular base that can rotate the sucker in any direction and can elongate it to twice its normal length. This muscle connects to the musculature in the walls of the acetabulum and infundibulum, giving the animals such touch sensitivity that they can "walk" an item along an arm simply by moving the suckers.
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Why Are Suckers So Strong?
Suckers are able to maintain a powerful grip because of their suction cup-like shape, but there's even more to it. When scientists examined a sample of suckers under a microscope, they discovered tiny concentric grooves in the infundibulum. These grooves, along with the squishiness of the material from which the suckers, are probably most responsible for the strength of the seal the animals are able to achieve on irregular submarine surfaces. The muscle fibers, which extend radially from the center to the rim of each sucker, also contribute to strength.
A True Blue Blood
Octopuses display so many characteristics to distinguish them from mammals, such as humans, that it's hard to enumerate all of them. Consider the facts that they have three hearts, for example, or that they can change their color at will, not only to escape predators but to communicate with each other. One such defining characteristic is the color of their blood: It's blue. Whereas the red color in human blood comes from iron-rich hemoglobin, the blood coursing through the veins of an octopus contains hemocyanin, which is copper-based. Copper is more efficient for transporting oxygen in low temperatures, but it makes the animals highly sensitive to changes in pH. For this reason, octopuses may be more vulnerable to ocean acidification that other marine animals.