VARIATION IN SNAIL SPECIES WIDESPREAD ON PORTO SANTO, MADEIRAN ARCHIPELAGO

Shell variation has been studied in two widespread land snailsfrom Porto Santo, Madeiran archipelago: the helicid speciesor species complex Heterostoma paupercula (Lowe) and the clausiliidspecies Boett-geria lowei Albers. Samples were collected fromthe mainland and the offshore islets from sea level to the highestaltitude. Shell size, colour and presence or absence of penstometeeth were scored in H. paupercula and some individuals weredissected to examine genitalia. Shell size and rib number werescored in B. lowei. In B. lowei size declines and rib number increases with altitude.In H. paupercula samples from sandy locations have a largershell size and a higher frequency of pale colour than thosefrom non-sandy locations. On average, sandy sites have a loweraltitude than non-sandy ones, however, so that these two variablesare confounded. The survey shows that shell characters of akind used in taxonomy are subject to variation associated withecology, this must be borne in mind when assessing present-daytaxa and morphological change through the fossil sequence. Thedata for H. paupercula support the conclusion that it is a singlespecies variable in shell characters and polymorphic for hemiphally. ⁴Present address for Gao Gaixt Biology Department, Shanxi EducationalCollege, Taiyuan, Shanxi, P.R.China (Received 27 February 1995; accepted 27 August 1995)