The Evolution of Kidney Function in the Neritacea (gastropoda, Prosobranchia)

Gastropod molluscs of the superfamily Neritacea (or order Neritacea: see Morton & Yonge, 1964) are found in marine, freshwater and terrestrial environments; but despite these wide differences in habitat the general anatomical organization is similar in all the members of the group. In particular the organization of the renal system appears to be very similar in marine and freshwater species, and to be not greatly altered in the terrestrial forms. This is surprising in a group subjected to the apparently different problems posed by life in these various environments. The family Neritidae contains many tropical marine forms, e.g. Nerita spp., and freshwater species which are also found in temperate zones, e.g. the European species Theodoxus fluviatilis. The terrestrial forms are all tropical and form the family Helicinidae. Very little is known about this family at present, except for an anatomical account (Bourne, 1911). They inhabit damp tropical forests and are often associated with a limestone substrate, although the family as a whole is not confined to limestone areas. The present paper investigates some of the functions of the kidneys of marine, freshwater and terrestrial species with respect to salt and water balance. Some discussion is given concerning the route by which the Helicinidae have colonized land.