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 user 2005-04-24 at 10:05:00 am Views: 82
  • #9078

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

    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

    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

    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

    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,

    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
    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

    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

    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