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Earth Science

"Argonaut" Octopus Sucks Air Into Shell As Ballast 72

Posted by timothy
from the 8-legs-good dept.
audiovideodisco writes "Even among octopuses, the Argonaut must be one of the coolest. It gets its nickname — 'paper nautilus' — from the fragile shell the female assembles around herself after mating with the tiny male (whose tentacle/penis breaks off and remains in the female). For millennia, people have wondered what the shell was for; Aristotle thought the octopus used it as a boat and its tentacles as oars and sails. Now scientists who managed to study Argonauts in the wild confirm a different hypothesis: that the octopus sucks air into its shell and uses it for ballast as it weaves its way through the ocean like a tiny submarine. The researchers' beautiful video and photographs show just how the Argonaut pulls off this trick. The regular (non-paper) nautilus also uses its shell for ballast, but the distant relationship between it and all octopuses suggests this is a case of convergent evolution."
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"Argonaut" Octopus Sucks Air Into Shell As Ballast

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  • Nah. The Angels just mis-intrepeted the cocktail napkin with God's first specs on it. Then they had to go back and create the same design with hardware instead of software.
  • That's not ballast. (Score:5, Informative)

    by jcr (53032) <jcr@nOSpam.mac.com> on Wednesday May 19, 2010 @04:20PM (#32269508) Journal

    Ballast is weight that counteracts buoyancy. By introducing air into its shell, the animal is adding buoyancy.

    -jcr

    • Unless the air is compressed into a liquid denser than water. Probably not what the octopus is doing... just saying.
      • Re: (Score:3, Insightful)

        by jcr (53032)

        If it had the ability to liquify air, that would be far more interesting.

        -jcr

        • by ceoyoyo (59147)

          Here I read that an octopus was using air in it's shell as ballast. I knew it was a bad sign when I read that shell was "paper thin." And it turns out that yes, there is no such thing as an octopus that can liquify air.

    • by Sir_Lewk (967686)

      By rocking at the surface, the argonaut can also trap a sizeable volume of air, which, in turn, allows it to reach a greater depth before becoming neutrally buoyant. Finn and Norman think that this may allow these unusual octopuses to avoid the surface layers of the ocean, where they would be vulnerable to birds and other top-level hunters.

      I have to say, I am a little puzzled by this.

      • Re: (Score:3, Informative)

        From the comments on TFA: As the Argonaut decends, the volume of air decreases under the increased water pressure. That causes the air to be less buoyant. So with more air, the air pocket maintains its buoyancy force for deeper dives. The Argonaut still has to 'force' its way down to the depth of neutral buoyancy though.

        Also from the comments, the Nautilus traps more air and has a hard shell so they can resist the water pressures more than the Argonauts. This allows the Nautilus to dive to deeper de
    • Ah! So it's not just me.

      Both these passages from the article are exactly backwards:

      By rocking at the surface, the argonaut can also trap a sizeable volume of air, which, in turn, allows it to reach a greater depth before becoming neutrally buoyant.

      The animals created air pockets as they would in the wild but without the ability to dive to the right depth, the air just brought them back to the surface again.
      • Re: (Score:3, Informative)

        by Rene S. Hollan (1943)

        Nope.

        The argonaut traps air, and then forcefully descends to depth. So long as it has not reached the appropriate depth, it has to keep thrusting itself downward with it's jet, but once there, it is neutrally buoyant and no further expenditure of energy is required.

        It if can't get deep enough, then ultimately it will tire and the buoyancy will bring it to the surface again.

        • Damn. Its, not "it's", above.

        • Well to be accurate it does need to continue to expend energy since it's at an unstable equilibrium. (to low and it will keep sinking, to high and it will float to the surface) But the energy required is far less then what it takes to reach that depth in the first place, or to maintain that depth if it didn't have the air bubble.

          • To be equally pedantic, maintaining an unstable equilibrium requires expenditure of energy only if disturbed (and I addressed this in a separate sub-thread), though disturbance is expected to happen. But "at the appropriate depth" as I wrote, it does not need to expend energy. Staying there, of course, is a practical impossibility.

      • by Daniel_Staal (609844) <DStaal@usa.net> on Wednesday May 19, 2010 @04:49PM (#32269906)

        As the pressure increases with depth, the volume of the air will decrease as it is squeezed into a smaller space. Buoyancy is determined by density, which is mass per unit volume. Mass is staying the same, but volume is decreasing.

        Above a certain depth, they will be be positively buoyant, and rise. Below that depth, they will be negatively buoyant, and sink. They gather enough air to be neutral at a certain depth, and stay there. The more air they gather the lower that depth is. If they can't get deep enough, they will tend to rise back to the surface (unless they vent air).

        The article is right.

        • Right, but this is a point of unstable equilibrium: if they rise too high, they will have to expend effort to return to neutral buoyancy depth, and if they dive too deep, they will have to expend effort to rise again. Still, if the alternative is having to prevent one's self from sinking all the time, it's probably less work.

          Also, the deeper they want to hover, the harder they have to struggle to get there.

        • Ok, now I get it. As you said, if it captures less air, the overall volume of the argonaut is reduced -- and density increased -- too quickly, making it neutrally buoyant at a lesser depth. The extra-large air bubble keeps the argonaut from shrinking too much before the desired depth is reached.

          I did a little quick reading to cure my ignorance and learned that divers have a device called a buoyancy compensator that works the same way.
          • Re: (Score:2, Interesting)

            Yes, a buoyancy control device (BCD) - usually an inflatable vest connected to your air cylinder - is standard diving equipment.

            Scuba divers will know that to stay neutrally buoyant, as you dive deeper, you must add extra air to your buoyancy control vest, and vent air when rising.

            Being neutrally buoyant is an unstable equilibrium, so if you are changing depth and do nothing or if you get your correction wrong, you end up rising/sinking even faster.

            If you do maintain your buoyancy well, your energy usage (f

    • Re: (Score:2, Interesting)

      by CoryD (1813510)
      And here I thought in submarine movies the term, "blow the ballast tubes" indicated releasing sea water that is held inside the tubes to allow for bouyancy. Hence, allowing for a sharp decrease in depth. So yes, while "ballast" does indicate a weight keeping a ship or object submerged, it can also be used as a "ballast tube" that causes lift.
      • Re: (Score:3, Interesting)

        by jcr (53032)

        When you "blow the tubes" you're using compressed air to force the water out. The water is the ballast.

        -jcr

        • by CoryD (1813510)

          When you "blow the tubes" you're using compressed air to force the water out. The water is the ballast.

          -jcr

          "indicated releasing sea water that is held inside the tubes"
          "ballast" does indicate a weight keeping a ship or object submerged"
          You don't say, clearly I missed that and didn't articulate that point.

  • by Anonymous Coward

    Gives the term "Break it off inside her" a whole new meaning...

  • "after mating with the tiny male (whose tentacle/penis breaks off and remains in the female)." I have some friends that act like this whenever they get a new girlfriend
  • Neato (: (Score:4, Interesting)

    by DarkKnightRadick (268025) <the_spoon.geo@yahoo.com> on Wednesday May 19, 2010 @04:21PM (#32269528) Homepage Journal

    And for it's next trick, the octopus will change its color!

    Oh wait, some already do that [nationalgeographic.com].

  • I for one (Score:3, Funny)

    by Ka D'Argo (857749) on Wednesday May 19, 2010 @04:23PM (#32269564) Homepage
    hail our new submarine octopus overlords
  • >> whose tentacle/penis breaks off and remains in the female

    - wince -

  • Ubuntu? (Score:5, Funny)

    by Saeed al-Sahaf (665390) on Wednesday May 19, 2010 @04:37PM (#32269762) Homepage
    "Argonaut Octopus" ... That's the new Ubuntu release, right?
    • If Adobe decides to put AIR into their shell, I won't mind. If they tried to do that to me, I would bash them.
    • by bmo (77928)

      No... it goes like this:

      Adjective; Animal with alliteration.

      Arreptitious Argonaut
      Perorating Paper Nautilus
      Oleaginous Octopus.

      See?

      --
      BMO

    • by Chih (1284150)
      Sounds like a Mega Man boss to me
    • by syousef (465911)

      "Argonaut Octopus" ... That's the new Ubuntu release, right?

      after mating with the tiny male (whose tentacle/penis breaks off and remains in the female).

      Yeah that sounds about right.

  • "(whose tentacle/penis breaks off and remains in the female)"

    FAIL!
    • Re: (Score:3, Interesting)

      by Rene S. Hollan (1943)

      It grows back [wikipedia.org]: "Males generally form a new hectocotylus in each new season."

      • Re: (Score:3, Funny)

        by HeckRuler (1369601)
        Argonaut, Part Duex, bad to the bone!
      • by lennier1 (264730)

        Kinda like of Jeebs in Men In Black but he only was a dick whose head could grow back.

      • by harley78 (746436)
        Do these Cephs live that long? Most Octos live only 1 breeding "season". Unless it's just the fems that live that short, IANACE. (ceph expert).
    • If I do a girl so hard that it breaks off, I'll consider that a pretty cool accomplishment.

    • by RockDoctor (15477)

      FAIL!

      It all depends on how you describe it. My palaeontology text book from 1983 describes the hectocotylus and it's intelligent pursuit of and penetration into the female as "Copulation by guided missile".
      HIT!

      What a living organism was doing in a palaeontology text book is another question, best addressed to "Mr Trilobite Eyes." But old Trilobite Eyes knew how to get the attention of a class of undergrads.

  • by pdxp (1213906) on Wednesday May 19, 2010 @05:06PM (#32270088)
    From TFA (emphasis mine):

    Finn and Norman filmed and photographed live animals in the act of trapping their air bubbles, solving a mystery that has been debated for millennia.

    Somehow I am starting to think that exaggeration in the media goes too far sometimes....

  • "Even among octopuses, the Argonaut must be one of the coolest. It gets its nickname -- 'paper nautilus' -- from the fragile shell the female assembles around herself after mating with the tiny male (whose tentacle/penis breaks off and remains in the female)

    I cant have been the only person to notice.

    I have to ask, why does an article on the creatures propulsion system require a detailed and graphic description of the creatures reproduction method? Surely this information could have been buried in the a

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