Octopus Suckers
...the arms of the octopus by a short muscular base that is capable of rotating the entire sucker in any direction. The muscular base also aids in orienting suckers for adhesion to an object enabling the sucker to extend forward, rotate backwards, and bending (Kier and Smith 2002). The sucker of an octopus is made up of a tightly packed array of muscle. There are no skeletal elements or fluid-filled spaces within the sucker. Radial muscle fibers cover the inner and outer surface walls of the acetabulum that extend down to the connective tissue that is present at the border of the acetabulum and the infudibulum. The suckers are attached to the arms of the octopus by a series of muscle bundles that originate from the connective tissue layer that surrounds the arm muscles and extends to converge on the sucker. The sucker musculature is enclosed on its inner and outer surface by sheets of connective tissue fibers forming an inner and outer connective tissue capsule, similar to collagen (Kier and Smith 2002). The mechanics of the sucker is fairly obvious. The sucker forms a seal at the rim and reduces pressure in the acetabular cavity. The attachment force of the sucker is the product of the area of attachment and the pressure differential between the environmental pressure and the pressure inside the sucker (Smith 1991). Smith (1991), who tested the negative pressure generated by octopus suckers and the tensile strength of sea water, discovered that water is also able to sustain negative pressures in suckers. Water under negative pressures can cause several factors that affect the tenacity of animal suction. Water’s tensile strength varies which causes one issue for the octopus’ sucker’s pressure that water can withstand is unpredictable; therefore, the negative pressure that a single sucker needs to apply varies under certain degrees. Sucker size affects the ability to maintain grip (Kier and Smith 2002). Depth is also a factor. A small sucker in deep water could potentially generate as much if not more force than that of a large sucker in shallow water. This may be why shallow water octopuses generally have larger suckers than deep water octopuses (Smith 1991). There is no limit on a sucker’s tenacity is non existent. This is determined by the cavitation threshold of water; or the failure of water tension, which may limit the attachment force of the sucker. As depth increases, cavitation will cease to be limiting because ambient pressure increases with the depth while the cavitation threshold is unchanged (Kier and Smith 2002). The suction cup of the sucker has the ability to avoid leaks which causes the musculature of the sucker to have maximum stress and strength. The sucker of an octopus has a lot of force. A sucker must not only resist perpendicular forces that tend to lift the sucker from the surface of an object but it must also resist the forces that slide the sucker parallel to the surface. During attachment, suckers use force that must also overcome water resistance that reduces the pressure of the sucker. Water in a sucker is like placing a cup upside down and trying to force it to go down under water with air pressure in it. Water is solid tension against the sucker. Water in a sucker can cause negative pressures, if the sucker is able to generate enough strength to overcome negative pressures, then the potential force of a sucker is greater than we realize. Suckers can be much stronger underwater, and they can work without significant shape changes. In deep water with greater pressure changes can cause higher attachment forces. The constant wear from the friction caused by these forces is part of the reason why the sucker linings are shed every once and a while. Suckers begin to develop in the embryo of an octopus. Nixon and Mangold (1996) studied the development of Octopus vulgaris and discovered that there are three primary suckers present on each arm at hatching. Each sucker has muscles and the infundibulum has its cuticle covering. In young, the sucker is still developing into a deep sphincter. From the three primary suckers on each arm, the number increases to an average of five on each arm in about 4-6 days to 6-12 suckers in 10 days, 16-22 suckers at 20 days, 23-27 suckers at 30 days bringing O. vulgaris to at least 110+ suckers on each arm at adulthood (Nixon and Mangold 1996). There are many different sizes shapes and kinds of suckers. The most intriguing are light-emitting suckers. These suckers are rare to find in octopuses. Balser et. al. (1999) who studied light emitting suckers said that light-emitting organs are only found in breeding females. Stauroteuthis syrtensis, a sea finned octopus, has been found to have blue-green lights emitted from their suckers. Light-emitting suckers have characteristics of simple photophores i.e. light emitting organs common among deep sea marine fishes and insects, such as fireflies; and suckers and are believed to have evolved from suckers. When stimulated, light-emitting suckers give off moderately bright light which can last up to five minutes. Some light emitting organs, such as sucker, can glow continuously or blink on and off every few seconds. The light emitting sucker is unable to attach to surfaces; they lack adhesive function unlike a typical octopus sucker. The overall morphology of a light-emitting sucker is typical of a normal octopus sucker. But the development of the musculature of the infundibulum and the acetabulum is greatly reduced. The light-emitting suckers on S. syrtensis are arranged in a single row along the oral surface of each arm. The location of these light organs on S. syrtensis indicates that they may act as lures (Balser et. al. 1999). The reason for light-emitting suckers is not known, but it’s been hypothesized that they enable and octopus to lure prey by shallow water octopuses, or used in communication, and can also be used for sexual signaling. Communication and to lure prey are thought to be the two main possible functions of a light emitting sucker. Visual communication is universal for octopuses. An octopus that sees the light emitting sucker could take it as a warning or as a welcome. Light can be seen ...