AQUATIC SNAILS OF THE BULINUS-AFRICANUS GROUP IN ZAMBIA IDENTIFIED ACCORDING TO MORPHOMETRY AND ENZYMES

The Bulinus africanus species group (Planorbidae) of freshwater snails has been reported to be represented in Zambia by two species, B. afri canus (Krauss) and B. globosus (Morelet), both named as intermediate h osts for Schistosoma haematobium. Uncertainty in identification of the se snails from morphology led to the present investigation, combining morphometry (shell and copulatory organ) with enzyme analysis. Observa tions of both kinds were made usually on the same individual snails, f rom collecting sites mostly in the Lusaka area or at Lake Kariba. Part icular attention was given to the proportional relationship between th e penis sheath and the preputium of the copulatory organ, a character used previously to distinguish B. africanus from B. globosus in south- eastern Africa. The enzyme profile MDH-1, AcP-2, PGD-1 and PGM-2 was c ommon to all snails examined from 25 populations; GPI and HBDH were po lymorphic. The enzyme data indicate that the samples represent a singl e species. Shell characters varied continuously. The copulatory organ was generally of the form known for B. globosus. Although the copulato ry organ of a few individuals had proportions overlapping the range re ported for B. africanus, the present variation was continuous and was not bimodal. It is concluded that all these specimens are conspecific and may be identified as B. globosus. Previous identifications of B. a fricanus from Zambia appear to need substantiation and it seems that i f this species is present at all in the sampled areas, it must be unco mmon. It is relevant in regard to possible strain differences within S . haematobium in Zambia, that our observations indicate that only a si ngle species of intermediate host is involved in transmission.