Evolution
Biomphalaria snail shells
Biomphalaria snails have a long evolutionary history, stretching back almost 100 million years to the New World, where fossil forms have been found. Molecular analyses also trace evolution of the genus to ancestors of extant South American species.
B. choanomphala is thought to be a relatively young species.
It is believed that between 2 to 3 million years ago (though reports vary widely in their estimates), Biomphalaria snails crossed the Atlantic and became established in West Africa, giving rise to a new species which probably resembled modern B. camerunensis or B. pfeifferi.
This then radiated eastwards throughout the complex. A modern species called B. angulosa is probably the basal species for what became the Nilotic species complex.
Nilotic species complex
- contains B. choanomphala and its sister species:
- B. sudanica
- B. alexandrina
- species are all endemic to the Nile and/or its headwaters in the Lake Victorian basin and surrounding lakes
The recent evolutionary history of this Nilotic group is less clear, as the 3 species are so genetically similar. Hopefully current molecular research, when combined with traditional taxonomic tools such as morphological analysis, will shed light on this question.