Octopuses are famous for their astounding versatility in maneuvering their environment. They employ the incredible dexterity of their arms, twisting, bending, and curling with almost infinite freedom of movement.
A new study from the University of Chicago has revealed a critical mechanism of the octopus’s nervous system that accounts for this exceptional movement on control over its eight arms and the hundreds of suckers with remarkable precision. This pioneering work may explain why an octopus can nimbly explore its environment, manipulate objects, and capture prey.
The study describes for the first time the complex neural circuitry of the octopus arm. Led by Cassady Olson, a graduate student in Computational Neuroscience, and co-authored by Grace Schulz, a graduate student in Development, Regeneration, and Stem Cell Biology, the study takes advantage of the biology of the California two-spot octopus (Octopus bimaculoides).
The nervous system that drives the movement of octopus arms is much more complicated than that found in any other animal. Each arm has a highly dense network of more neurons than the octopus within its brain.
Central to this system is a large axial nerve cord (ANC), which runs along the length of each arm. The ANC is not a simple, unbroken conduit for nerve signals; rather, it is segmented, with each segment forming an enlargement over each sucker, allowing for fine control over both arm movement and sucker functionality.
Credit: Cassady Olson
Clifton Ragsdale, PhD, Professor of Neurobiology at UChicago and senior author of the study, explains, “If you’re going to have a nervous system controlling such dynamic movement, that’s a good way to set it up. We think it’s a feature that specifically evolved in soft-bodied cephalopods with suckers to carry out these worm-like movements.”
The ANC’s segmented nature means that the nerves controlling movement are organized into distinct units, each corresponding to a segment of the arm. These segments are separated by gaps, or septa, where nerves and blood vessels exit to control nearby muscles.
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The study’s findings suggest that these segments work together to enable the precise coordination needed for complex movements. This arrangement also allows the arms to perform independent movements while maintaining fluidity and coherence.
One of the most fascinating aspects of octopus arms is the ability of each sucker to move and change shape independently. This is made possible by the topographical map created by the nervous system, with nerves from the ANC connecting to each sucker through the septa. This setup enables the suckers not only to perform mechanical tasks like grasping but also to engage in sensory functions.
Octopus suckers are equipped with a dense array of sensory receptors that allow the animal to “taste” and “smell” objects they touch. This unique sensory ability turns each sucker into a multi-functional tool, combining the properties of a hand, tongue, and nose.
Olson and her team have dubbed this sensory-motor mapping “suckeroptopy,” a term highlighting the sophisticated control system that allows octopuses to navigate and manipulate their environments precisely.
While octopuses are the primary focus of the study, Olson’s research also explored the nervous system of longfin inshore squid (Doryteuthis pealeii), another soft-bodied cephalopod. Like octopuses, squid possess arms and suckers, but they also have specialized tentacles.
The study found that squid tentacles follow a different neural pattern—though the tentacle clubs, which are equipped with suckers, have segmented ANC structures similar to those of octopus arms, the tentacle stalks, which lack suckers, do not.
This discovery suggests that the segmented ANC structure is specifically adapted for controlling dexterous, sucker-equipped appendages requiring more complex movement and sensory feedback. Squid, which relies more on vision to hunt, do not use their suckers for the same sensory tasks as octopuses, who use their arms to explore the ocean floor. This distinction underscores how evolution tailors neural structures to the specific demands of an animal’s environment and behavior.
The study’s findings also provide insight into the broader evolutionary trends within cephalopods. Though octopuses and squid diverged from each other more than 270 million years ago, both species have evolved similar neural strategies to control their appendages in ways that maximize their effectiveness in different environments.
The segmented structure of the ANC is one example of how cephalopods have adapted over millions of years to meet the specific needs of their lifestyles—whether that involves foraging on the ocean floor, evading predators, or capturing prey.
As Ragsdale notes, “Organisms with these sucker-laden appendages that have worm-like movements need the right kind of nervous system. Different cephalopods have come up with a segmental structure, the details of which vary according to the demands of their environments and the pressures of hundreds of millions of years of evolution.”
Journal Reference:
- Olson, C.S., Schulz, N.G. & Ragsdale, C.W. Neuronal segmentation in cephalopod arms. Nat Commun 16, 443 (2025). DOI: 10.1038/s41467-024-55475-5
Source: Tech Explorist
