Scientists at the Hebrew University
of Jerusalem studied nine common octopuses (Octopus vulgaris) that
fishers had scooped out of the ocean for them. Once the animals got
comfortable in the lab, the scientists put them one at a time into a tank
with a transparent floor. They used cameras underneath and next to the
tank to meticulously track how the invertebrates crawled.
The footage revealed three ways that
octopuses are weird.
They can go in any direction at any
time.
Let’s talk about octopus bodies for
a moment. Like you or I, an octopus has “bilateral symmetry.” This means it has
a left and a right side that are mirror images of each other. If you could fold
an octopus (or a human) in half on a line running between the eyes, the halves
would line up.
But unlike a human, an octopus also
has “radial symmetry.” Think of a jellyfish or a sea anemone, whose parts
radiate outward from a center point. The octopus arranges its eight arms this
way.
It’s not always easy to tell which
way an octopus is facing. “The soft and very flexible body of the animal
can be misleading and conceal the accurate body direction,” the authors write.
So they coded their videos according to where the octopus’s midline,
running through its four left and four right legs, was pointing.
Octopuses do seem to prefer moving
at 45-degree angles, rather than directly forward or backward. The authors
think this is because an octopus’s eyes are on the sides of its head. It
may have the worst vantage point at the border between its two fields of
vision. Despite this preference, though, octopuses are liable to go anywhere at
any time.
They have two orientation systems.
A neck is not among the octopus’s
many assets. This means it can’t swivel its head around on its body. To turn
its face, it has to rotate its whole self.
But the scientists found that
octopuses control their body orientation and their movement independently. In
other words, which way they’re facing is irrelevant to which way they’re going,
and vice versa. They can turn their bodies around while crawling in one
direction. Or they can change directions while keeping their bodies facing the
same way.
They have no rhythm.
Octopuses crawl by pushing.
They scrunch up an arm, anchor it to the ground, and then
stretch it out again to propel themselves forward. The scientists tracked these
“steps” to see in what order the study animals used their arms.
They saw that octopuses step
without any pattern or rhythm at all. Not left-right, left-right. Not
one-two-three-four. This absence of a pattern is different from how most
other animals move. Actually, scratch that: it’s the opposite of every
known animal.
Perhaps the octopus’s soft body
would be impossible to control with the strategies that other animals use, says
author Guy Levy. So the animals have had to evolve their own way of getting
around. When octopuses swim, their locomotion is much simpler: the arms
move together. But the “rhythm-less stepping,” Levy says, “is different
than all types of known locomotion patterns in nature.”
On the one hand, this is startling
and new. “On the other hand, everything in the octopus is different and
surprising,” Levy says. “We expected surprises.”
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