OCTOPUSES ’WALK’ ON 2 ARMS

[Anonymous]

Octopuses ‘walk’ on 2 arms to get by predators
Animals use other 6 arms to mimic coconuts,
algae

While pigs are not
yet flying, coconuts are walking and clumps of algae are tiptoeing — sort of.
The coconuts and clumps of algae are really octopuses walking on two arms and
using their six non-walking arms to camouflage themselves as plant material in
order to hide from lurking predators.

These octopuses are
the first animals without a hard skeleton known to walk on two limbs. Octopuses
normally travel along the ocean floor using all or many of their eight arms in a
sort of crawl. Their muscles are supported by fluid and not bone. Using
underwater video, the scientists analyzed the strides of Octopus marginatus and
Octopus aculeatus. For both species, each walking arm stayed in contact with the
sandy ocean floor for more than half of the stride, qualifying the pitter patter
of two octopus arms as official walking.

These findings
appear in the 25 March, 2005 issue of the journal Science published by AAAS, the
nonprofit science society.

“It wouldn’t
surprise me if other octopus species also walk,” said Science author Christine
Huffard, from the University of California, Berkeley.

Huffard observed
octopuses seemingly impersonating coconuts in Indonesia and octopuses walking
like floating algae in Australia. She explained that many octopus species around
the world have strong, muscular back legs that could be used for walking on two
limbs.

‘Impersonating’
plants
By walking on only two arms, the other six arms can be used to
transform their bodies into clumps of algae or rolling coconut shells that may
not interest predators. Clumps of algae and coconut shells are commonly found in
the shallow, coastal seawaters that these octopuses call home.

Octopus predators
such as sharks, sting rays, predatory reef fish and flounder scan the sea floor
for creatures doing the traditional “octopus crawl” which involves the octopus
pushing and pulling its body along the ocean floor using many of its eight
arms.

By shifting to a
camouflaged walk, the octopus may slip past their predators’ octopus-detection
schemes without having to stand still. Camouflaged walking — always in the
backward direction and on the back pair of legs — is probably hardwired into
their brains as well as their arms.

When threatened by
a predator, something kicks in and the octopuses start walking without
consciously thinking, “I need to move the right arm and the left arm,” Huffard
explained.

From octopus to
soft robot
A walking octopus whose legs require limited guidance from the
brain excites Science coauthor Robert Full from the University of California,
Berkeley.

This discovery adds
to our growing understanding of how soft-limbed creatures perform complex
behaviors without too much communication between limb and brain. A better
understanding of how walking octopus arms work could help scientists design
better artificial materials and improved soft robots, Full said.

“This discovery
provides true inspiration for the beginning of a new age of soft robotics. The
videos are almost unbelievable,” Full said.

A walking octopus
also provides another chance for scientists to study the interactions animals
with soft limbs have with their environment, explained Full, who is also
intrigued by how elephants use their soft trunks.

Algae and
coconuts
The “algae octopus” is no stranger to life in the algae
impersonation business. When they are not moving, their long arms and
walnut-size bodies look like algae. This is the first time, however, scientists
have seen an octopus take this algae impersonation show on the road.

Not surprisingly,
Octopus marginatus has prior coconut experience. This species is known to crawl
inside empty coconut shells for shelter, pulling the two sides of the shell
together with the suckers on their arms.

According to local
diving lore from Indonesia, octopuses inside real coconut shells will stick
their arms out of the shells and walk around, Huffard said. While this may be
just a story, the scientists caught plenty of curious octopus muscle activity on
video.

A muscle beach
without ego
The most amazing muscles at the beach are not flexed by the
people playing sand volleyball.

Bands of muscle in
the octopus arms are oriented in three directions. The muscle contractions start
near the top of the walking arms and move down to the tips of the arms. These
waves of muscle contractions give the arms the flexibility they need for
walking, the authors suggest. The fluid filling the muscles provides
stability.

When the “coconut
octopus” rolls along the sand on its back two arms, these fluid-filled muscular
limbs serve as conveyor belts. At least one of these conveyor belts is on the
ground at all times, which qualifies the movement as walking.

The arms of the
“algae octopus” move in a somewhat similar fashion but they hold the other six
arms in a different manner. Imagine a ragged head of broccoli running along the
bottom of the ocean.

Huffard hopes to
return to Indonesia and Australia in the near future to continue studying these
walking octopus species.

[Author]

April 24, 2005 at 10:07 AM