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
 

photograph of suckers of a dead octopus showing morphologyThe soft part of the sucker in an octopus is called the infundibulum1. It is flexible and dextrous.  Contraction of numerous radial muscles in the infundibulum flattens it, and cross-sectional drawin of octopus sucker showing the different partsenables 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 acetabulum2(these first 2 muscle types are not shown in the drawing). Once the sucker3 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. photograph of texture of cuticle of the rim of an octopus' suckerRelaxation of the radial musculature, perhaps in conjunction with contraction of circular muscles, releases the pressure and the sucker detaches.  Kier & Smith 1990 Biol Bull 178: 126.

NOTE1  lit. “funnel” L.

NOTE2  lit. “cup to hold vinegar” L.

NOTE3 in a later paper the same authors review the adhesive  mechanism in suckers in several species, including southern California Octopus bimaculoides (or O. bimaculatus as the authors do not specify).  New information includes a description of the short muscular base on each sucker that is both rotatable and extensible, enabling food and other objects to be passed along an arm to the mouth and to “walk” the arm along the substratum.  The authors also provide an electronmicrograph (see photo on Right) of the fine structure of the cuticle covering the epithelial surface of the infundibulum part of the sucker.  The fine denticles (4um diameter) and grooving aid in adhesion of the sucker to the substratum.  Kier & Smith 2002 Integr Comp Biol 42: 1146.

 
 
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

 
Research study 5
 

diagram of video set-up for viewing octopus behaviourOctopus arms are thicker at the base and taper evenly towards the tip, with correspondingly smaller sized suckers along the way. The extent of size reduction depends upon species, but for a full-sized Octopus bimaculoides the reduction in sucker diameter may be >90% (down to <1mm at the arm tips). The question arises as to whether the different-sized suckers are used for different jobs, for example, the larger basal ones perhaps for anchoring, medium ones for crawling, and smaller ones for catching and manipulating prey. This is investigated for California Octopus bimaculoides by researchers at Brooklyn College, New York who videotape individual octopuses engaged in various behaviours in aquarium tanks. Activities exhibited during videotaping include crawling, feeding, capturing live crabs, and lifting objects. One such object is a transparent dome within which is placed a live crab. The dome is fastened to the aquarium bottom by electromagnets whose attachment force can be varied experimentally. Video records are analysed for arm(s) used, and sucker location, numbers used and their sizes, extent of distorsion, and so on. Sometimes only a single arm is monitored; other times, multiple arms. Now, anyone who has watched octopuses in motion, whether in the lab or in the field, will appreciate the almost insurmountable difficulty there would be in quantifying arm and sucker behaviour. The present study is no exception. Actually, the author makes reference to an undocumented viewpoint that suckers are just “passive agents reflexively reacting to surface contact”, but no one even the slightest bit familiar with octopus behaviour would hold that view. Some findings in the study are that certain arms tend to do certain things in combination with different functional groups of suckers. When constrained to the use of a single arm, an octopus prefers to use suckers in mid-arm location. Crawling is done by extending an arm, attaching distal suckers, then pulling the body towards the attached suckers by shortening the arm. An attack on a crab within the dome involves an octopus spreading itself more or less evenly over the dome, and attaching basal arm suckers to the dome and some but not all distal arm suckers to the aquarium floor. Force to lift the dome appears to be generated by lengthening the arms between the suckers fixed on the dome and those fixed on the tank floor. Even when the octopus is constrained to use of a single arm, the same pattern is observed, but with mid-arm suckers attaching to the dome and suckers both proximal and distal attaching to the aquarium floor. On single-arm dome trials with weak electromagnetic force, an octopus anchors to the dome with a mean of 10 mid-arm suckers, with 16 being used for strong electromagnetic force. Grasso 2008 Am Malac Bull 24: 13. Photograph courtesy Roger Hanlon, Marine Biological Laboratory, Woods Hole, Massachusetts.

photograph of octopus Octopus bimaculoides showing suckersNOTE sucker numbers are highly variable in octopuses, not only between closely related species, but also within similar sizes of the same species. For example, an early study comparing sucker number in octopuses Octopus bimaculoides with a few dozen other species shows a range of 160-190 (mean 175) for 4 O. bimaculoides individuals with 30cm arm length. The closely related O. bimaculatus, also in California, has 230-290 suckers (mean 250) for 3 individuals of 30cm arm length. These species as well as Enteroctopus dolfleini all have double rows of suckers, but species with only single rows will have proportionately fewer suckers. Voight 1993 Malacologia 35 (2): 351.

NOTE based upon sucker numbers, their location, and degree of activity/distorsion (free, light contact, partly attached, and attached), the author estimates the number of possible combinations to be in the range of 1024 


This photo of Octopus bimaculoides provides a good view of
comparative sucker sizes along an arm. In the 6 o'clock
position at the bottom of the photo, small suckers at a
curled arm tip are juxtaposed with large suckers at an arm base

 
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