Incidence and persistence of reversed-coiling in Quaternary land snails

This paper reviews evidence for the incidence and persistence of reversed-coiling in different species of land snail based on studies of Quaternary sequences in Britain, Ireland and Siberia. Most sequences lack evidence for reversed-coiling but the relative proportions of dextral and sinistral specimens are presented for a few that do. Such data are reported for thirteen specimens belonging to seven species from seven sites in Britain and Ireland, mostly calcareous tufas of Holocene age. Sinistral specimens of Acicula fusca were recovered from three different sites but reversed-coiled specimens of other species were confined to single localities. The frequencies of reversed-coiling in most European samples are generally extremely low (zero to <1%) and relatively short-lived, although reversed-coiled specimens were recovered from adjacent stratigraphical horizons at three of the sites reported here. This situation contrasts with a Holocene floodplain sequence in Siberia, where sinistral specimens of Cochlicopa occurred in 12/18 samples, with a mean frequency of 9.8% (38/385) for the whole profile. Not only are the frequencies of reversed-coiling much higher than in most European sites but it appears to have persisted for much longer, indeed for much of the last 6000 14C yr BP. Reasons for this unusual situation are discussed. A plea is made for more assiduous recording of reversed-coiled specimens from Quaternary sequences.