Kinematic data and mathematical modeling of sea star locomotion

It is unclear how animals with radial symmetry control locomotion without
a brain. Using a combination of experiments, mathematical modeling, and
robotics, we tested the extent to which this control emerges in sea stars
from the local control of their hundreds of feet and their mechanical
interactions with the body. We discovered that these animals (Protoreaster
nodosus) compensate for an experimental increase in their submerged weight
by recruiting more feet that synchronize in the power stroke of the
locomotor cycle. Mathematical modeling replicated this response to loading
in the absence of nervous communication and demonstrated how the body
weight serves as a regulator of recruitment. We built a robotic sea star
with an array of independently-controlled actuators that were also
recruited in greater numbers under higher loads due to their collective
mechanics. These findings demonstrate that an array of actuators in
biological and robotic systems are capable of cooperative transport with
dynamic adjustments to loading. This form of distributed control contrasts
the conventional view of animal locomotion as governed by the central
nervous system and offers inspiration for the design of engineered devices
with arrays of actuators.