Figure 6

Schematic of muscle function during introvert retraction in Echinoderes . Transition from full eversion (A) to full retraction (C) of the introvert. Anterior is to the top. Only the muscle groups considered to be directly involved with introvert retraction are represented. Arrows indicate the directional movements of the introvert and scalids. (A) Introvert and mouth cone are everted. Introvert retractors, introvert circular muscle, and introvert circular muscle retractors are stretched. (B) Introvert is half-retracted, and the mouth cone is retracted. Introvert distal retractors are contracted, introvert proximal retractors are stretched, introvert circular muscle is contracted to a smaller diameter than the neck, and introvert circular muscle retractors are stretched. (C) Introvert and the mouth cone are fully retracted. Introvert retractors, introvert circular muscle, and introvert circular muscle retractors are now fully contracted and located within the trunk.