Structure of the Excretory System of Hawaiian Nerites (Gastropoda: Neritoidea)

Neritoidean gastropods are present in freshwater, brackish andmarine environments, which vary in salinity and exposure todehydration. In this study we examine the structure of the excretory systemof Hawaiian nerites, which indicates possible processes thatenable these gastropods to survive in a wide range of environmentsin the Hawaiian Islands. As is true of other nerites studied to date, the main excretorymechanism of Hawaiian nerites is through filtration of the bloodbetween podocytes in the auricle epicardium, resulting in productionof an ultra-filtrate, which collects in the pericardial cavity.No podocytes are present on the surface of the ventricle ofHawaiian nerites. The reno-pericardial canal conveys the urine tothe kidney, the epithelium of which is composed mainly of acidophiliccells in marine nerites. In brackish and fresh water species,baso-philic cells are present in addition to the acidophiliccells present in marine nerites. It is proposed that the basophilickidney cells allows non-marine nerites to osmoregulate and producea hyperosomotic urine at low salinities. A bladder is present,and empties into the mantle cavity near the gill by way of a ureter. (Received 26 November 1997; accepted 15 May 1998)