Anatomy of Biomphalaria Boissyi as Related to Its Infection with Schistosoma Mansoni

Abstract

Among the fresh-water mollusks, planorbid snails play a significant role in the life histories of digenetic trematodes of man and livestock. Investigations of their morphology are of considerable value to both the malacologist and the parasitologist. Wright (1952) emphasized the need for studlies of internal anatomy as an aid in the identification of snail vectors of bilharziasis. Although Baker (1945) presented a most comprehensive account of planorbids, the scope of his work was so broad that phases of studies pertaining to some genera and species, such as Biomphalaria boissyi, were not taken into account. Biomphalaria was considered only in a very abbreviated way and, because of a lack of specimens, no morphological details were included. Somewhat earlier, Connolly (1925) in his discussion of the non-marine mollusca of Portuguese East Africa referred to the anatomy of Planorbis pfeifferi., which he later (1938) regarded as, Biomphalaria pfeifferi. The purpose of this paper is to consider the anatomy of the planorbid snail, Biomphalaria boissyi, the intermediate host of Schistosoma mansoni and other trematodes in Egypt, the Sudan, and other African countries. This study also illustrates the general organization of a planorbid snail. Oine objective is to provide the malacologist and the parasitologist with descriptive morphological information and as many anatomical illustrations as possible. Emphasis is placed on the position of the internal organs and their relation to one another. Particular stress is placed on anatomical information in relation to infection of B. boissyi with S. mansoni, and its bearing on snailparasite relations in general. Similar investigations were carried out by Faust and Hoffman (1934) in their studies of schistosomiasis in Puerto Rico. The systematics of the genus Biomphalaria was considered recently in an extensive study by Amberson and Schwarz (1953). They stated that the snail intermtediate host of S. mansoni in Africa is Biomphalaria alexandrina. Two subspecies were recognized: B. a. alexandrina Ehrenberg, with a northern distribution and B. a. pfeifferi Krauss with a southern distribution. However, their conclusions were based on shell characters and biological factors; they contributed no anatomical data. It is becoming increasingly evident that only after the anatomical details have beeni clarified that one could appreciate whether Biomphalaria boissyi (Potiez et Michaud, 1838) should be synonymized with B. alexandria (Ehrenberg).2