Comparative Functional Morphology of the Bivalve Excretory System

Abstract

Combining injection techniques with ultrastructural observations, and relating these findings to the more traditional physiological and morphological studies have shed new light onthe excretory mechanisms underlying the processes of ultrafiltration, secretion and reabsorption in some bivalve molluscs. These basic processes are further elucidated by comparing normal excretory tissues with those in bivalves that have been subjected to stress by pollutants in either the natural environment or under laboratory experimentation. The process of ultrafiltration is size and charge dependent and occurs at the filtration barrier at the base of the podocytesin the pericardial gland. Primary urine may be modified by secretion (primarily from the kidney cells but also from the podocytes), reabsorbtion in the kidney, and by the addition of hemocytes passing from blood spaces through the epithelium into the lumen of the kidney. Numerous concrements (granules, concretions and membranes) that result from lysosomal activities inthe podocytes, kidney cells and hemocytes along with the fluid are excreted into the mantle cavity