Fine structure of the Polian vesicle in the holothurians Eupentacta fraudatrix and Cucumaria japonica

摘要

The wall of the Polian vesicle is composed of three layers: the innermost is the water vascular mesothelium, the connective tissue layer is subjacent to this, and outermost is the perivisceral mesothelium. Both mesothelia are typical pseudstratified myoepithelia composed of peritoneal and myoepithelial cells. Numerous myocytes of the water vascular mesothelium constitute a powerful circular musculature. In the perivisceral mesothelium, the myocytes are much less abundant and lie parallel to the axis of the organ thereby forming a longitudinal musculature. The contractile system of the Polian vesicle is innervated by a basiepithelial plexus associated with the perivisceral mesothelium. In the water vascular mesothelium, neither neuronal perikarya nor processes were found.