ULTRASTRUCTURE OF THE HEART AND EXCRETORY SYSTEM OF MYTILUS-EDULIS (L)

The morphology and ultrastructure of the heart and excretory system of the marine lamellibranch bivalve mollusc, Mytilus edulis (L.) are described. This paper supports the view that ultrafiltration of the blood occurs in the pericardial cavity. The auricles, pericardial glands and afferent oblique veins contain podocytes which are usually ascribed to the specific function of ultrafiltration. These cells are absent in the ventricle. The pericardial cavity communicates with the exterior via a very short (ca. 1-2 mm) renal tubule. The kidney comprises of a series of highly branched diverticula of this tubule and displays little or no structural differences throughout the organ. The kidney cells form a single layered columnar epithelium with a brush border, basal nuclei, infolded basal membranes and are characterized by the presence of many membrane-limited granules occupying as much as 20 % of the cell volume. These granules and those of the podocytes are subsequently shed into the lumen of the kidney tubule and are excreted in the urine which is therefore largely paniculate. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.