Anal uptake of water in terrestrial pulmonate snails

Summary The uptake of water was examined in 35 central European terrestrial pulmonate snail species from 15 families (Table 1) by giving the inactive, withdrawn animals dyed water and observing its bulk flow microscopically.During emergence, 32 of the species studied normally take up water through the pneumostome. A rectal pump (Figs. 1 and 2) rapidly conveys this water through the anus into the gut and stomach.In 7 species, anal water-uptake during emergence was quantified and found to be equivalent to 20–40% of the total body water of the inactive snails before water uptake (Table 2).After emergence, the rectal pump allows re-uptake of urine from the ureter or the lung cativity into the alimentary tract.The anal mechanism permits rapid uptake of large quantities of water into an extrasomal compartment. This helps terrestrial pulmonate snails to exploit short wet spells and presumably helps to stabilize blood concentration during activity under dry conditions.