New research reveals how tube feet coordinate locomotion through local feedback rather than central control.
The oral surface of Asterias rubens is covered with hundreds of tube feet. (Credit: Amandine Deridoux / CC BY-NC 4.0, shared via Google Drive)
Sea stars may appear to glide slowly across the seabed, but their movement is the result of a remarkably sophisticated system. Unlike animals with a centralised brain, sea stars rely on hundreds of flexible tube feet working together to crawl, climb and even move upside down. New research now sheds light on how this coordination happens—and how sea stars adapt their movement to changing physical demands.
Tube feet are small, extendable structures operated by the water vascular system. Each functions as a muscular hydrostat, capable of attaching to surfaces, pulling, and releasing in sequence. Traditionally, scientists assumed that some form of overall coordination must exist to synchronise these actions. However, recent experimental work suggests a very different picture.
Using advanced optical imaging techniques, researchers were able to visualise and measure the adhesive contact of individual tube feet in real time. The results show that sea stars regulate their speed not by synchronising all feet at once, but by adjusting how long each tube foot remains attached to the surface. When the animal moves faster, individual tube feet release more quickly. When mechanical demands increase, they stay attached for longer.
To test this idea, researchers increased the effective body weight of sea stars by adding small external loads. Under these conditions, the animals slowed down, and the tube feet automatically increased their adhesion time. Similar adjustments occurred when sea stars were observed crawling upside down, where gravity places different stresses on the body. In both cases, no central coordination was required. Each tube foot responded locally to mechanical feedback.
The study concludes that sea star locomotion emerges from decentralised control, where each tube foot adjusts its behaviour based on load and resistance. The overall movement pattern is an emergent property of these local interactions rather than a centrally planned sequence.
Beyond marine biology, these findings have broader implications. Understanding how complex, adaptive movement arises in a brainless organism offers valuable insights for the design of soft robots and multi-contact systems, where robustness and adaptability are critical. Sea stars, it turns out, may hold important lessons for both biology and engineering.
