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

Crawling 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 Research Studies investigators have shown that it is possible to work with intact octopuses to measure attachment forces

The 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 1990 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

What 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

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.

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.