Rhachistia braunsi (von Martens, 1869)

Rowson, B, Warren, B. H. & Ngereza, C. F., 2010, Terrestrial molluscs of Pemba Island, Zanzibar, Tanzania, and its status as an " oceanic " island, ZooKeys 70, pp. 1-39 : 14

8. Rhachistia braunsi (von Martens, 1869) Fig. 28

Buliminus (Rhachis) von Martens 1869: 150

Notes.

All Pemba material appears to be conspecific. Across sites, shells reach only c14mm when adult, and are very thin, not glossy, with faint and irregular spiral and radial striae. One or more brown spiral bands per whorl are present on a weak yellow background, some individuals having a few additional weak brown spots. In several individuals the apex is dark. Multi-banded forms match what ( Verdcourt (1961, 2006) calls Rhachidina braunsi var. quadricingulata (E. A. Smith, 1890), described from lowland Tanzania. All the Pemba material is here referred to braunsi, whose varieties we consider only colour forms. Voeltzkow’s (1923) record of " Rachis brauensis Mart." (sic) probably refers to Rhachistia braunsi from Fundu I. (Haas, 1929). The genus is here given as Rhachistia rather than Rhachidina (see Solem 1959, Mordan 1992, Herbert and Kilburn 2004).

There is a hypothesis that Bulimus histrio L. Pfeiffer, 1854, described from the New Hebrides, is a synonym of Rhachistia braunsi . Solem (1964) cited Verdcourt (1961) as confirming a suggestion in Solem (1959) that braunsi and histrio were synonyms, thus proving that histrio was an early anthropogenic introduction from East Africa. Though not quite correct (the name braunsi did not appear in Solem 1959) this was followed by other workers in the region (e.g. Starmühlner 1970) and there is now a consensus that the Australasian populations originated in East Africa (e.g. Stanisic 1998, Herbert and Kilburn 2004). However, ( Verdcourt (1961, 1983, 2006) remained ambiguous about placing the two in synonymy and objected that the colour pattern in Solem’s (1959) black and white picture of a type of Rhachistia histrio had not yet been noticed among East African species. He also noted the existence of other, earlier names. Our material is available should anyone be in a position to resolve this debate.