Locomotion
 

Locomotion of octopuses and relatives involves creeping about on the sea bottom using suckers and arm muscles, jetting, and combination of the two. 

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  Crawling
  The topic of locomotion is divided into sections of crawling, considered here, and JET PROPULSION and NAVIGATION & LEARNING considered elsewhere.
 
Research study 1
 

graph comparing theoretical versus actual suction forces in suckers of octopuses Octopus bimaculatusphotograph of Octopus bimaculatus courtesy Birch Aquarium, La Jolla, CaliforniaCrawling in octopuses involves attachment and release of suckers, accompanied by large and powerful muscle contractions in the arms to pull the body along.  In an early study at La Jolla, California the force of adhesion of suckers of octopuses Octopus bimaculatus is measured.  Freshly excised suckers are suspended by a thread to a spring balance, and allowed to touch and fasten to smooth wood.  Attachment is stimulated by applying a small electrical shock.  The piece of wood is then pulled away until the attachment is broken.  The accompanying graph shows that measured forces are always about 45-70% less than the theoretical maximum based on the area of a sucker at 1atm pressure (=1.033kg . cm-2).  Parker 1921 J Exp Zool 33: 391. Photograph courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, California.

NOTE  it’s not surprising that sucker strengths are less than theoretical maxima, what with the suckers being cut from the animal and stimulated by electrical shock.  In later studies presented here investigators have shown that it is possible to work with intact octopuses to measure attachment forces

 
Research study 1.1
 

dissection of squid Loligo to show main parts of heart and circulatory systemStudy of blood circulation and heart function in octopuses Enteroctopus dolfleini at the University of Washington, Seattle shows that vascular pressure and heart rate increases by several-fold during locomotion.  Thus, resting rates of about 12 systemic heart beats . min-1 (at 8oC) may increase to 21 beats . min-1 during slow crawling/swimming exercise.  During this time, systolic pressures increase by about 50%.  Recovery following even such mild exercise takes a relatively long time, around 10-15min.  Ventilatory frequency is more or less independent of contraction frequency in the circulatory system, although the respiratory movements are always at the slower rate.  When swimming, of course, ventilation of the mantle cavity will be directly related to the frequency of jet propulsion. There is a noticeable lack of synchrony between beat frequencies of the branchial heart and beat frequency of the systemic heart.  Also of interest is that  hemolymph flows from the branchial hearts to the main systemic heart are augmented by rhythmic contractions of the ctenidia themselves (see diagram), although the relative importance of this to overall circulatory performance is not known.  The authors remark that arm and diagram of hemolymph circulatory system in an octopus Enteroctopus dofleinigeneral body musculature play a greater relative role in maintaining peripheral circulatory pressure in comparison with, say, their comparable role in vertebrates.  Johansen & Martin 1962 Comp Biochem Physiol 5: 161.

NOTE  the paper provides an excellent review of older literature relating to circulatory-system physiology in cephalopods; in fact, a quick scanning of the references-cited section reveals that about 60% of the articles referred were written prior to 1930

Features of circulatory system as discussed in text. De-oxygenated
hemolymph returns via the vena cava, is filtered through the kidneys, then
pumped via the branchial hearts to the ctenidia. Oxygenated hemolymph
is pumped from the systemic heart via the aorta to the rest of the body

 
Research study 2
 

cross-sectional drawin of octopus sucker showing the different partsThe soft part of the sucker in an octopus is called the infundibulum. It is flexible and dextrous.  Contraction of numerous radial muscles in the infundibulum flattens it, and enables it to mold to the shape and texture of the substratum.  The sucker can even fold in on itself like a mittened hand to grip fine objects like fishing line. Complete flattening of the sucker is prevented by simultaneous contraction of meridional and circumferential muscles embedded within the radial musculature of both he infundibulum and acetabulum (these first 2 muscle types are not shown in the drawing). Once the sucker matches the contours of the substratum, the mucus and loose skin on its rim completes the seal. The radial muscles of the acetabulum contract, lowering the pressure within the acetabulum, and hydrostatic pressure presses the sucker to the substratum. Relaxation of the radial musculature, perhaps in conjunction with contraction of circular muscles, releases the pressure and the sucker detaches.  Kier & Smith photograph of suckers of a dead octopus showing morphology1990 Biol Bull 178: 126.

NOTE  lit. “funnel” L.

NOTE  lit. “cup to hold vinegar” L.


Suckers of a dead octopus. The white area is the infundibulum, while the area on "top" of the white glistening centre is the acetabulum 1X

 
 
photograph of octopus Enteroctopus dolfleini showing suckers taken from a video

CLICK HERE to see a video of sucker use in an octopus Enteroctopus dolfleini.

NOTE the video replays automatically

 
Research study 3
 

photograph of an octopus in its denWhat level of pressure can an octopus generate in its suckers?  Prior to 1990 scientists believed that the suckers could not generate pressures below a vacuum, that is, below 0 MPa.  Measurements, however, of sucker pressures in Octopus spp. show that pressures below a vacuum can be generated (-0.17 MPa, or 2.7 times below ambient air pressure).  The lower limit on pressure is apparently set, not by failure of the sucker muscles, but by cavitation.  At cavitation pressure, the pressure is sufficiently low to rupture the cohesiveness of the water molecules and cavities, or bubbles, are explosively formed.  At this point the sucker releases its attachment.  Smith 1991 J Exp Biol 157: 257.

NOTE  a unit of pressure named after Pascal, the French mathematician, physicist, and philosopher whose experiments with barometers in the mid-1600’s laid the foundation for study of atmospheric pressures.  One Pascal is equivalent to 10 one-millionth of an atmosphere of pressure at sea level.  One MegaPa is therefore equivalent to 10 atm of pressure, and 0.1 MPa is equivalent to 1atm or 14.5lbs . inch-2.

NOTE  the studies include Octopus bimaculoides/bimaculatus from California and O. vulgaris from the Atlantic

An octopus' sucker works like a toilet-bowl plunger. Stick the plunger into the toilet, seat
the rubbery part, then pull back on the handle to decrease the pressure inside the bulb

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Knowing all this, would deep-dwelling octopuses require relatively larger- or relatively smaller-diameter suckers to hold on to the substratum? Think about this then CLICK HERE for an explanation.

 
 
photograph of an octopus Enteroctopus dolfleini from above taken from a video

CLICK HERE to see a video of an Enteroctopus dolfleini crawling about in an open aquarium tank.

NOTE the video replays automatically

   
 
Research study 4
 

An octopus arm does double duty for crawling and catching prey.  The absence of a skeleton and a variety of different kinds of musculature enable movements of the arm in 3 dimensions.  It can extend and contract, be held rigid, twist, or bend in any direction at any location along its length.  Control of twisting is by oblique muscles arranged along the length of the arm in both right- and left-handed helices, so twisting is possible in either direction.  Large axial nerves extending down the length of each arm control the movements of both arms and suckers.  The axial-nerve cord is actually a series of interlinked ganglia, each gangion located above one of the suckers.   Mather 1998 J Comp Psychol 112: 306.

NOTE each sucker contains musculature in 3-dimensional array, and is capable of a wide range of movements.  The basal musculature, on which the sucker sits, is extensible to almost twice its resting length. 

 
 
photograph of an octopus Enteroctopus dolfleini taken through aquarium glass from the start of a video

CLICK HERE to see a video of the agility of a crawling Enteroctopus dolfleini.

NOTE the video replays automatically

 
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