Despite opportunities for radiation provided by spatio-
temporal isolation, the basic morphological plan of pulmonate
snails has remained conservative. In consequence of the
resulting dearth of morphological characters and their
plasticity, there is a case for using biochemical characters
such as exogenous chemicals released by the snails (e.g. amino
acids) and their chemoreception niche as taxonomic aids to
classify snails of medical importance. As these same
chemicals are used by snails to distinguish conspecifics they
could also be used as 'environmental antibodies in controlled
release formulations (CRF's) designed to remove target snails
in a specific, cost-effective and ecologically acceptable
manner.
The snails, surface-living bacteria, algae and macrophytic
plants are considered as co-evolved, interactive modular
systems with strong mutualistic elements. Recently,
anthropogenic perturbations such as deforestation, and damming
of flowing waters, have benefited these modules whereas others
such as river canalization, acid deposition, accumulation of
pesticide residues and eutrophication have harmed them.
Research is needed to elucidate the factors which limit the
growth of snails in primitive habitats, uninfluenced by man,
as well as in those subject to harmful anthropogenic factors.
The understanding thus gained could be applied to develop
cost-effective primary health care strategies to reduce or
prevent transmission of schistosomiasis and other water
related diseases.