Nephridopore

Low power transmission electron micrograph of a transverse section
accross the floor of the kidney sac illustrating the location of the
three main epithelial types associated with the kidney surfaces. 
Large blocks of muscle in the lips forming the nephridopore control the
contractions of the sphincter and the movements of fluids between the
lumen of the kidney sac and the pallial cavity.

     ce    =   ciliated epithelium 
     cv    =   connective tissue vesicular cells
     kl    =   lumen of kidney sac 
     ko    =   opening of kidney
      m    =   muscle blocks
     me    =   mantle epithelium 
     re    =   renal epithelium 

     Scale bar represents 10 micrometers