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

ABSTRACT

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 resistant and P. glaucus the least resistant to desiccation. The total mass 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 soft body water content during desiccation and the only one that secreted a calcareous epiphragm. H. engaddensis has a relatively large water content and thus can sustain a large water loss. I suggest that the susceptability of P. glaucus to desiccation is probably related to its phylogenetic origin and that the operculum does not constitute a significant barrier to water loss.