WATER-BALANCE AND RESISTANCE TO DESICCATION IN ROCK-DWELLING SNAILS

We have examined the resistance to desiccation among rock-dwelling lan d snails of various phylogenetic groups: Cristataria genezarethana (Cl ausiliidae), Rupestrella rhodia (Chondrinidae) and Levantina caesarean a (Helicidae), all from the same location in Israel. L. caesareana was the most resistant and R. rhodia the least resistant to desiccation a nd C. genezarethana was of intermediate resistance. Differences in the rates of water loss during desiccation were determined mainly by rate of water loss during the first 2 days of desiccation. The high rates of water loss in rock-dwelling species exceed those of other snails in the Mediterranean habitat of Israel. However, snails collected in the field at the end of aestivation were in only a mild state of dehydrat ion, suggesting that the rocky habitat protects its occupants against desiccation. We also suggest that among the rock-dwelling species, the protective role of the rock is more important in the more evolutionar ily primitive genera (the chondrinid Rupestrella and the clausiliid Cr istataria) and that physiological capacities are more effective in the more highly evolved helicid Levantina.