Octopuses move with a simple elegance, but they have no rhythm, according to new research.
Each of an octopus's eight arms is soft, flexible and muscular, and acts as if it has an infinite number of joints, said the study's lead author, Guy Levy, a postdoctoral researcher of neurobiology at the Hebrew University of Jerusalem. But until now, scientists have struggled to understand exactly how these marine animals coordinate their complex crawling movements.
To learn more about these brainy creatures' locomotion, the researchers watched videos of octopuses crawling around water-filled tanks, frame by frame. [8 Crazy Facts About Octopuses]
"The octopus, as usual, surprised us," Levy told LiveScience.
Octopuses use unique strategies to coordinate their arms while crawling, the researchers found. The cephalopods are bilateral symmetric, which means their left and right sides are mirror images of each other. Most bilateral-symmetric animals face forward when they are moving, with a few notable exceptions, such as the crab, which moves sideways.
But octopuses can crawl in any direction relative to their body orientation, the researchers said. In other words, octopuses don't have to turn their bodies to change direction; one of an octopus's arms can simply push off of a surface and propel the animal any which way, Levy said.
The scientists also found that the octopus moves by shortening and elongating its arms, which creates a pushing thrust. The animal does not move by bending or pulling its arms, which simplifies matters for the creature, Levy said.
After watching hours of octopus videos, the researchers determined that the octopus has no detectable rhythm. Most animals have a rhythm when they move, such as people who move their legs in a left-right-left pattern. But an octopus has no such rhythm in its coordination, the researchers said.
"Either there is no pattern, or it's too complicated to identify with the techniques that we used," Levy said.
Octopuses probably developed their unique way of moving because, unlike their clam cousins, they don't have protective outer shells, the researchers said. The octopus is thought to have evolved from a snail-like ancestor whose foot evolved into eight long and slender arms, giving the animals enormous flexibility.
Levy said the locomotive strategy "is simple enough, and it has a small number of parameters, and this is how it succeeds."