Structure of the excretory system of Hawaiian nerites (Gastropoda: Neritoidea)

Abstract

Neritoidean gastropods are present in freshwater, brackish and marine environments, which vary in salinity and exposure to dehydration. In this study we examine the structure of the excretory system of Hawaiian nerites, which indicates possible processes that enable these gastropods to survive in a wide range of environments in the Hawaiian Islands. As is true of other nerites studied to date, the main excretory mechanism of Hawaiian nerites is through filtration of the blood between podocytes in the auricle epicardium, resulting in production of an ultra-filtrate, which collects in the pericardial cavity. No podocytes are present on the surface of the ventricle of Hawaiian nerites. The reno-pericardial canal conveys the urine to the kidney, the epithelium of which is composed mainly of acidophilic cells in marine nerites. In brackish and fresh water species, basophilic cells are present in addition to the acidophilic cells present in marine nerites. It is proposed that the basophilic kidney cells allows non-marine nerites to osmoregulate and produce a hyperosomotic urine at low salinities. A bladder is present, and empties into the mantle cavity near the gill by way of a ureter.