SPIRE INDEX AND PREFERRED SURFACE ORIENTATION IN SOME LAND SNAILS

Fourteen species of land snails [Balea perversa, Cochlodina laminata, Clausilia bidentata, Ena montana, Cochlicella acuta, Helix aspersa, Cepaea hortensis, Arianta arbustorum, C. nemoralis, Cernuella virgata, Candidula intersecta, Trichia striolata, Helicella itala, Discus rotundatus], have been tested for their preference for surfaces at 0.degree., 90.degree. or 180.degree. under laboratory conditions. They range from high-spired (height/breadth = 4.1) to discoidal forms (height/breadth = 0.4). There is a positive association of spire height with tendency to adopt the 90.degree. surface. Species of intermediate (globular) shape show less specificity for a particular surface than high- or low-spired species. The exception is H. aspersa, which behaves more like a high-spired species than like its similarity shaped relatives. The differences in preference will help to reduce interaction between co-existing species in the field.