Osmoregulation and Excretion in Prosobranch Gastropods Part I: Physiology and Biochemistry

Abstract

INTRODUCTIONThe mechanisms of excretion in molluscs were reviewed by Potts (1967), and those specific to gastropods by Potts (1975), but reviews of osmoregulation in invertebrates have usually taken a broad view and dealt with a number of phyla. This review, which is presented in two parts, attempts to summarize current knowledge concerning both excretion and osmoregulation in prosobranch gastropods.Prosobranch gastropods have colonized a very wide range of habitats, from the sea and brackish waters to fresh water and parts of the land. Their degree of tolerance of changes in external conditions is therefore immensely varied. Some marine species are closely confined to normal sea water, while estuarine species such as Assiminea grayana Fleming can tolerate a range from fresh water to twice the concentration of sea water (Seelemann, 1968b;Little & Andrews, 1977). Freshwater species also show great diversity: Valvata piscinalis (Miiller) and V. cristata Miiller are found in waters with as little calcium as 0.13 mM 1~', whereas others such as V. macrostoma Morch require at least 0.5 mM 1~' (Boycott, 1936). On land, most prosobranchs are restricted to humid, calcium-rich environments, but although none lives in deserts as do some pulmonates, many tropical species of Pomatiasidae are found on dry limestone cliffs.This variation in tolerance must also be considered with reference to the diversity of structural organization. Scattered information is available for more than 25 different families, including members of all the prosobranch orders, so that it is not surprising to find quite a degree of variation. To avoid confusion, the species and families referred to are set out in Table 1.