Euopisthobranchs: Excretory System

Abstract

As in other gastropods, in euopisthobranchs the pericardial cavity that surrounds the heart is spatially and functionally connected to the excretory system, forming the renopericardial system. Podocytes or podocyte‐like cells of the auricular epicardium and pericardium wall mediate selective fluid transfer from the circulatory system into the pericardium. Therefore, the fluid inside the pericardium is primary urine. Functionally and structurally, the renopericardial consists of three sections, i.e. (i) podocytes of the atrial and pericardial wall serve in ultrafiltration, (ii) a ciliated renopericardial duct transports the ultrafiltrate into the kidney, and (iii) and unciliated kidney that modifies the ultrafiltrate. The kidney cells are highly vesiculated, unciliated cells with basal infolds indicative for transcytosis across the epithelium. In small euopisthobranch species, the kidney is basically a simple duct, in larger species, like in those of the genus Aplysia , the kidney consists of large, branched, anatomizing, and intertwined ducts. The modified primary urine is released to the exterior via a short ciliated duct that terminates in the nephropore.