The Forces Exerted by the Tube Feet of the Starfish During Locomotion

Abstract

1. Doubt has existed as to whether the tube feet of a starfish in locomotion act as a system of levers or whether they form a traction system, attaching to the substratum and contracting so as to pull the animal along. 2. This problem has been investigated by recording the forces exerted by a single tube foot. The recording apparatus is described. 3. It is shown that both lever and traction methods can be used according to circumstances. (a) When the starfish is walking on a horizontal surface it is shown that the tube feet certainly act as struts and that they probably also act as levers. (b) When the starfish is climbing upon a vertical surface (or meeting with resistance upon a horizontal surface) the tube feet attach themselves to the substratum and form a traction system.