At first glance, an octopus’s sucker looks like the simple suction cup that tips a toy dart or affixes a GPS to the windshield. In fact, it is a remarkably sophisticated organ that not only can attach to objects with varying degrees of force but also can maneuver them, thanks to specialized muscle groups.
The sucker has two chambers: the outer infundibulum and inner acetabulum. When it attaches to an object—a tasty clam, for instance—the muscles of the infundibulum reshape the sucker rim to conform to the shell surface, forming a seal. The muscles of the acetabulum then contract, producing intense negative pressure inside the water-filled interior of the sucker relative to the external seawater. This pressure differential generates suction. The more the muscles of the acetabulum contract, the higher the negative pressure and the firmer the sucker’s grip. So-called extrinsic muscles, meanwhile, permit the sucker rim to rotate the object in a full circle at a shallow or steep angle to the arm without breaking the seal or reducing the pressure differential.
In addition to their complex musculature, octopus suckers possess elaborate neural circuitry. Specialized neurons called chemoreceptors stud the sucker rim, enabling it to taste surfaces. Along with mechanoreceptors and proprioceptors—which relay information about touch and pressure and about muscle activity, respectively—these chemoreceptors feed into a bundle of neurons called a ganglion that appears to function as the sucker’s own mini “brain,” receiving sensory input and organizing coherent responses. Because the sucker ganglia are connected to one another through a chain of larger brachial ganglia running the length of the arm that control arm movements, neighboring suckers can coordinate their movements without relying on constant direction from the actual brain—to pass an object up or down the length of the arm, for example. Exactly how the brain and the arm and sucker ganglia divvy up neural responsibilities remains to be determined.