The exotic fresh-water snail Helisoma duryi (Wetherby, 1879) (Planorbidae) In Southern Africa

INTRODUCTION Van Bruggen (1974) discussed the identity of specimens of the North American pulmonate genus Helisoma Swainson, 1840 (Mollusca: Planorbidae) from three localities in southern Africa. He identified Helisoma (Seminolina) cf. duryi seminole Pilsbry, 1934, from a farm dam in South West Africa and Helisoma (?Pierosoma) sp. from an artificial pond at Mandini in Zululand (recorded as Helisoma sp. by Brown, 1967) and from Cape Point on the Cape Peninsula. These identifications were based on shell characters since only dry material was available. Snails belonging to Helisoma have been collected by the present author from two additional localities and are examined below. Both these populations occur(red) in the suburban areas of major South African cities. The five widely separated localities are shown in fig. 1. Live Helisoma were collected in June 1969 from fish ponds in the rosarium in Jan van Riebeeck Park (26°07'S 28°01'E) in the Johannesburg suburb of Emmarentia. The snails were plentiful here, as was another exotic, Physa acuta (Draparnaud). Unfortunately the soft parts of these Helisoma were not kept and the population had disappeared by 1 November 1974 when the author paid a return visit. It is possible that the population was elminated by cleaning of the ponds during the intervening five and a half years. In February 1973 Mr. B. Campbell of the Zoology Department, University of Cape Town, sent the author a collection of Gastropoda amongst which were three specimens of Helisoma collected on 25 March 1972 from marginal grass of the partly canalized Liesbeeck River in the Cape Tow