The mechanisms of coordination of the starfish tube feet

Kerkut, G.A.

Behaviour 6(3): 206-232


ISSN/ISBN: 0005-7959
DOI: 10.2307/4532796
Accession: 023910965

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There are 2 concepts of the way in which the tube feet of a starfish can be coordinated to point in a given direction. One suggests that the pointing is effected through the central nervous system, the other suggests that it is achieved by mechanical tensions acting directly on the tube feet. Two types of pointing are described, positive pointing-where the feet point towards a given direction, and negative pointing-where the feet point away from a given direction. A quantitative method is described by which it is possible to determine the degree of coordination that occurs in the positively and negatively pointing animal. The experiments show that the excitation is conducted in a decremental manner (due to the many intermediate synapses) in both directions around the nerve ring and also along the radial nerve cords. Certain modifications are suggested in the plan of the starfish nervous system presented by J. E. Smith. Smith's view was that there were separate tracts running down the nerve cord carrying specific messages to the feet indicating in which direction they should point. Evidnece presented in this paper indicates that though this view is substantially correct it does not explain other phenomena such as the mixing up of messages after certain operations have been made on the radial nerve cord. Additional evidence is presented showing that the circum-oesophageal nerve ring has 5 centers that can control the starfish's reactions and that this ring plays a role similar to that of the brain in the other invertebrates. During normal locomotion the starfish uses both its central nervous system and the tensions acting on the tube feet to control the direction to which the feet step. The balance between the 2 systems is varied by the specific environmental conditions in which the animal finds itself.