ABSTRACT
The classification of gastropod molluscs is in a continuing state of revision and it will be some time before a system comes to be generally agreed for the groups of higher rank (Haszprunar, 1988; Ponder, 1988a). Gastropods have been divided commonly into two major groups, the Streptoneura (including those known as the Prosobranchia or prosobranchs) and the Euthyneura (pulmonates and opisthobranchs). The freshwater gastropods of Africa are either prosobranchs (socalled because they have a comb-like gill, the ctenidium, situated within the mantle cavity and in front of the heart) or pulmonates (lacking a gill, the mantle cavity serving as an air-breathing organ; treated in Chapter 4).
