ABSTRACT
The overall mobility (protraction, retraction, lateral tilting) of the Aristotle’s lantern of the cidarid echinoid Stylocidaris affinis is very restricted and much lower than that displayed by the camarodont lantern of Paracentrotus lividus. To examine the reason for this remarkable difference the dental apparatus of Stylocidaris affinis has been analyzed by means of a mathematical model that takes into account both structural and physiological (active forces and passive stretch resistances) data concerning protractor and retractor muscles and their interaction with the ligamental structures (peristomial membrane and compass depressor ligaments). The main result of the present analysis shows how the physiological factors related to the muscular component play a major role, in comparison with structural factors, in explaining the observed differences in mobility between the two lanterns.
