EFFECT OF DESICCATION ON THE WATER ECONOMY OF TERRESTRIAL GASTROPODS OF DIFFERENT PHYLOGENETIC ORIGINS - A PROSOBRANCH (POMATIAS-GLAUCUS) AND 2 PULMONATES (SPHINCTEROCHILA-CARIOSA AND HELIX-ENGADDENSIS)

This study compares the water relations and resistance to desiccation in three species of land snails of different phylogenetic origins: the prosobranch Pomatias glaucus and the pulmonates Helix engaddensis and Sphincterochila cariosa. All three species are understone-dwellers of the Mediterranean climatic zone of Israel. S. cariosa was the most re sistant and P. glaucus the least resistant to desiccation. The total m ass loss during desiccation in S. cariosa is 5 times lower than in the other two species. It was also the only species that maintained its s oft body water content during desiccation and the only one that secret ed a calcareous epiphragm. H. engaddensis has a relatively large water content and thus can sustain a large water loss. I suggest that the s usceptability of P. glaucus to desiccation is probably related to its phylogenetic origin and that the operculum does not constitute a signi ficant barrier to water loss.