The circular gripping pads lining the arms of an octopus are commonly referred to as suckers. While the everyday term is simple, the internal structure and function of these biological tools are far more complex than a standard rubber suction cup. Scientists often use the Latin term acetabulum when referring to the central, cup-shaped cavity responsible for creating the powerful adhesive force. These hundreds of suckers, arranged in double rows down each arm, allow the octopus to interact with its environment in sophisticated ways.
The Anatomy of a Sucker
Each octopus sucker is a soft, highly muscular organ that lacks any hard skeletal support. The outer portion that contacts a surface is called the infundibulum, which has a flexible rim that creates a watertight seal upon contact. Fine grooves and ridges on the infundibulum help it conform to irregular surfaces, ensuring a leak-proof attachment.
The main body of the sucker is composed of a complex array of muscle fibers that function as a muscular hydrostat. These fibers include radial muscles, circular muscles, and meridional muscles. This intricate structure allows for independent movement and control of each sucker, enabling the octopus to rotate, elongate, and manipulate its grip. The central cavity, the acetabulum, is covered by a roof made up of radial muscle fibers, which generate the suction force.
The Mechanics of Adhesion
The adhesive mechanism of the octopus sucker relies entirely on generating a pressure differential, a process that is actively controlled by the animal’s muscles. When the octopus wants to attach to a surface, the infundibulum is pressed down, creating a tight, watertight seal around the object. This seal isolates the water contained within the central cavity, the acetabulum, from the external water pressure.
To generate the holding force, the radial muscles within the sucker’s roof contract, which actively pulls the roof upwards and increases the volume of the acetabular cavity. Because the volume of the chamber increases while the amount of water inside remains constant, the pressure inside the sucker drops significantly below the ambient water pressure outside. This difference in pressure creates a powerful vacuum effect, where the higher external pressure pushes the sucker firmly onto the surface.
The suckers can generate substantial negative pressures, far below what a simple vacuum could achieve at sea level. The attachment is maintained by the external water pressure and is released when the octopus contracts the circular muscles, which reduces the cavity volume and normalizes the pressure. This muscular control allows the octopus to quickly and precisely attach and detach its suckers, a capability that is essential for its complex movements and foraging behaviors.
Multifunctional Roles of Suckers
The suckers are not merely tools for gripping; they are highly integrated sensorimotor organs that serve multiple roles in the octopus’s life. The strength of the suckers allows for efficient locomotion, enabling the octopus to anchor itself securely to rocks or substrates and crawl across surfaces. By attaching groups of suckers, the animal can manipulate its body, even carrying or moving relatively large objects.
Beyond movement, the suckers play a major part in prey capture and handling. An octopus can use its powerful suckers to securely grasp slippery prey or to pry open the shells of bivalves. The suckers also act as sophisticated sensory organs, equipped with specialized chemoreceptors, which are essentially “taste-by-touch” sensors.
These chemoreceptors allow the octopus to “taste” an object, providing detailed chemical information about its environment and potential food sources. Studies have shown that octopuses can discriminate between different types of prey and non-prey items using contact chemoreception alone. This dual function—providing both a powerful mechanical grip and precise chemical sensory input—makes the octopus sucker one of the most versatile biological structures in the marine world.