Anatomy of finfish and shellfish

Unit 13- Mollusca

13.4.6. Excretory System
It includes a kidney or renal sac consisting of three thin-walled chambers, two ventral and one mid-dorsal, which communicate with one another. The two ventral chambers open, at one end, to the exterior by renal apertures placed on renal papillae, lying one on either side of the rectum, and at the other, communicate with the pericardium by reno-pericardial apertures. Through each ventral chamber passes the corres¬ponding branchial vein, formed by the bifurcation of the vena cava. The vein is covered by excretory glandular epithelium which extracts the nitrogenous waste products from the blood. The dorsal chamber encloses the pancreatic follicles covering and opening into the ducts of the digestive gland. They are richly vascular and are said to serve an excretory function. The nitrogenous excretory substance has been detected in the cavities of the renal sac in the form of guanin which is discharged into the mantle cavity.