PZ Myers. 2004 Oct 27. How do octopus suckers work?. <http://pharyngula.org/index/weblog/how_do_octopus_suckers_work/>. Accessed 2008 May 17.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Wednesday, October 27, 2004

How do octopus suckers work?

Whoa, it's been a while since I've said anything about my infatuation with cephalopods. Let's correct that with a nifty paper I found on octopus suckers.

Here's a typical view of a tangle of octopus arms, all covered with circular suckers. The octopus can cling to things, grasp prey and other objects with those nifty little discs, and just generally populate people's nightmares with the idea of all those grappling, clutching, leech-like appendages.

Octopus suckers are actually beautiful little tools, though, with a fair amount of sophistication in their organization. Don't compare them to the simple rubber suction cups on kids' toy dart guns; these have their own elaborate muscular regulatory mechanisms. This diagram illustrates the internal structure of a single octopus sucker.

Schematic cutaway diagram of an octopus sucker. A, acetabulum; AR, acetabular roof; AW, acetabular wall; C, circular muscle; CC, crossed connective tissue fibers; D, dermis; E, extrinsic muscle; EC, extrinsic circular muscle; EP, epithelium; IN, infundibulum; IC, inner connective tissue layer; M, meridional muscle; OC, outer connective tissue layer; R, radial muscle; S1, primary sphincter muscle; S2, secondary sphincter muscle.

There are two main regions, an infundibulum (IN) on the attachment face of the sucker, and a deeper chamber called the acetabulum (A) (if you don't recall any Latin, "infundibulum" just means "funnel", while "acetabulum" is "vinegar cup"—anatomy is littered with funnels and cup-shaped structures, so these are actually very generic names). Both regions are muscular, covered with a dense sheet of radial muscles (R) and rings of circular and meridional muscles (C and M).The whole thing is surrounded by supple sheets of connective tissue and epithelia.

The way it works is that the sucker is pressed against a surface, and the flexible outer margin of skin conforms to it, forming a seal. Then the radial muscles contract. Now muscle is a relatively incompressible tissue; when it contracts, it changes its length, but it cannot change its volume. When you make a muscle in your arm to show off to the girls, you are reducing the length of the bicep, so it has to bulge outwards to maintain a constant volume. This principle is also how your tongue works: when muscles contract to flatten it, the volume has to stay the same so it protrudes.

When the radial muscles in the sucker contract, the walls of the acetabulum and infundibulum get thinner. The muscle volume has to go somewhere, so the circumference of the cup-shaped acetabulum has to increase, increasing the volume of the acetabular chamber. Since the infundibulum is sealed against a surface, water can't get in; so we have the same quantity of water in a larger chamber, which means the pressure is reduced, generating suction. They can release their grip by relaxing the radial muscles, or contracting the circular muscles, which would reduce the volume of the acetabulum.

An octopus can generate a respectable amount of force with this mechanism. At sea level, they can create a pressure differential of 100-200 kPa (kilopascals; 100 kilopascals is approximately equal to one atmosphere), and at greater depths, where the water pressure is greater, they can generate correspondingly greater amounts of force.

A closeup view of the sucker reveals other details.

Scanning electron micrograph of sucker of Octopus bimaculoides/bimaculatus. The radial grooves and ridges are visible on the infundibulum (I) and the orifice that opens into the acetabulum (A) is visible. The infundibulum is encircled by a rim of loose epithelium (E) that is separated from the infundibulum by a narrow groove. The scale bar equals 1.0 mm.

The infundibulum is grooved. This allows the pressure differential to be distributed to the entire surface of the sucker as it is flattened against an object. Further, the surface of the infundibulum is covered with chitinous denticles that provide a fine network of channels that similarly transmit the force everywhere, and also provide a raspy surface that restricts lateral movement (remember how when you shot your rubber-tipped dart gun at a window it would stick, but you could easily slide the dart around? Octopus suckers wouldn't do that—they'd be locked firmly in one place.)

The authors mention that squid have an additional refinement that makes their suckers even more effective. They contain a piston-like structure inside an interior chamber, coupled so that when something tries to pull away from the sucker, it lifts the piston, further decreasing pressure inside and strengthening its grip—like a Chinese finger-trap, the more you struggle, the harder it is to get away.

Kier WM, Smith AM (2002) The structure and adhesive mechanism of octopus suckers. Integr. Comp. Biol. 42:1146–1153.

1. Ooh, neat! Now I have another excuse to go the Seattle aquarium again, to observe these items in action.
   #: Posted by  on  10/27  at  10:03 AM
2. This post sucks! [/rimshot]
   #: Posted by  on  10/27  at  10:39 AM
3. Hey Professor Meyers. While this is a completely different topic from the fascinating discussion of the octopus, I was wondering what your take is on the recent discovery of "Flores Man" in Indonesia. From the short article I read about it, it is a momentous find and there is some debate over how to classify this potentially "new" human species. I am nowhere near a scientist, which is why I turn to you for some insight.
   
   I really enjoy your blog and look forward to your comments.
   #: Posted by  on  10/27  at  12:28 PM
4. Carl Zimmer has an article on Flores. I haven't read the paper yet, but soon...
   #: Posted by PZ Myers  on  10/27  at  12:46 PM
5. I adore cephalopods myself...thanks for this lovely and clear explanation of one of their more fascinating features.
   
   I second the question on Flores Man. I actually rushed here after seeing an article on it, as I was curious as to your comments (including your opinion on how accurate the mainstream reporting has been.)
   #: Posted by  on  10/27  at  01:09 PM
6. I love cephalopods, too. Unfortunately, my infatuation is culinary as well as academic. I keep trying to give up octopus as food. Two nights ago, I blew a whole year of octopus-eating abstinence. I'm still feeling a little guilty. But, man, raw octopus cured in wasabi is tasty.
   
   Whenever I backslide into my old octophagic ways, my partner shames me by whispering "Remember Gregori!" All octopus fans should read Gravity's Rainbow. Octopus Gregori is far and away the most compelling character in the book, IMO.
   #: Posted by Lindsay Beyerstein  on  10/28  at  04:54 PM
7. But I don't think there is any contradiction between thinking the octopus is brilliant and beautiful and admirable, and thinking it is also delicious!
   #: Posted by PZ Myers  on  10/28  at  05:01 PM
8. Yeah, this article just made me hungry.
   
   They're a little chewy though.
   #: Posted by Matt McIrvin  on  10/29  at  03:17 PM
9. Genetic Engineering could improve Octopuses, giving then Iron-based haemoglobine instead of their actual Copper based one. That way, via transgenics, both their respiration and circulation will become more eficient and they could evolve to bigger sizes, bigger & quicker brains, speedy reflexes.
   #: Posted by  on  11/01  at  07:49 PM
10. LIARS, your all stupid to believe this CraP!
    #: Posted by fredd  on  11/09  at  12:55 PM
11. You don't believe in the octopus? Wow.
    #: Posted by PZ Myers  on  11/09  at  01:51 PM
12. I most definitely DO believe in the Octopus! I guess Fredd does nOt suck and chooses to remain that way.
    Sucking is great, Mr Meyers, thank you for your work!
    #: Posted by  on  12/02  at  08:43 AM