Abstract
In the developing pluteus larva of S. purpuratus, the initial morphogenetic event in the formation of a functional gut is the appearance of two constrictions in the archenteron. These two constrictions become the cardiac and pyloric sphincters. During the 2 h in which the constrictions form, the sphincter cells change from cuboidal to wedge-shaped, and the apical ends of the sphincter cells develop an electron-dense region in which microfilaments can be resolved. Constriction of the archenteron was reversibly inhibited by cytochalasin B, although cytochalasin B had no effect once the constrictions had fully formed. Neither the electron-dense region nor the microfilaments were observed after cytochalasin B treatment. It is suggested that sphincter formation is initially accomplished by a microfilament-mediated contraction of the apical ends of the sphincter cells, which changes their shape and constricts the archenteron.

This publication has 19 references indexed in Scilit: