The ultrastructure of the heart and kidney of the pilid gastropod mollusc Marisa cornuarietis, with special reference to filtration throughout the Architaenioglossa

Transmission and scanning electron micrographs of the heart and kidney of Marisa cornuarietis (L.) reveal that the auricle is largely responsible for filtration supplemented to a small extent by the ventricle. The epicardial cells of the auricle are specialized to allow the escape of a filtrate of the blood, but do not bear any resemblance to podocytes. The posterior part of the kidney is lined by a characteristic renal epithelium excreting uric acid and resorbing glucose whilst the anterior part has an epithelium specialized for active transport of ions. A possible mechanism for filtration is suggested, and the functional significance of the structural variations in the heart and kidney of pilids, viviparids and cyclophorids is discussed.