OBSERVATIONS ON SHELL MORPHOLOGY, ENZYMES AND RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) IN BULINUS-AFRICANUS GROUP SNAILS (GASTROPODA, PLANORBIDAE) IN ZANZIBAR

The taxonomic status of Bulinus globosus and B. nasutus as separate sp ecies remains unclear, especially in areas of East Africa where their distribution overlaps. In order to throw further light on this questio n, a study was carried out on snails collected from the islands Unguja and Pemba, collectively known as Zanzibar, which lie in the Indian Oc ean close to mainland Africa. In total, 169 snails from 22 sample site s were characterised by three methods: morphometric analysis of 15 she ll measurements, enzyme analysis involving three enzyme systems and an alysis with random amplified polymorphic DNA (RAPD). Enzyme analyses i ndicated that both B. nasutus and B. globosus were present on each isl and and their distribution was allopatric. Shell variation was conside rable but did not clearly differentiate these taxa. Similarly, RAPD an alysis indicated substantial genetic variation within and between samp les: more often than not, no two RAPD profiles were identical within t he sample. On Pemba, B. globosus is more widely dispersed than B. nasu tus which is confined to the eastern coast of the central region. On U nguja, B. globosus is found in more northern areas than B. nasutus.