Analysis code and data for the morphometrics and kinematics of tube feet

Hydrostatic skeletons, such as an elephant trunk or a squid tentacle,
permit the transmission of mechanical work through a soft body. Despite
the ubiquity of these structures among animals, we generally do not
understand how differences in their morphology affect their mechanical
properties. Therefore, the present study used mathematical modeling,
morphometrics, and kinematics to understand the transmission of force and
displacement in the tube feet of the juvenile six-rayed star Leptasterias
sp. An inverse-dynamic analysis revealed that the forces generated by the
feet during crawling primarily serve to overcome the submerged weight of
the body. This load was disproportionately generated by the feet at more
proximal positions along each ray, which were used more frequently for
crawling. Due to a combination of mechanical advantage and muscle mass,
these proximal feet exhibited a greater capacity for force generation than
the distal feet. However, the higher displacement advantage of the more
elongated distal feet offer a superior ability to extend the feet into the
environment. Therefore, the morphology of tube feet demonstrates a
gradient in gearing along each ray that matches their role in behavior.