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Journal of Experimental Biology 57,205-215 (1972)
Published by Company of Biologists 1972

Osmotic and Ionic Regulation in a Terrestrial Snail, Pomatias Elegans (Gastropoda, Prosobranchia) With a Note on Some Tropical Pomatiasidae

T. J. RUMSEY ¹

¹ Department of Zoology, University of Bristol, Bristol BS8 1 UG

1. The haemolymph concentration in the pomatiasids is higher than in any other terrestrial gastropods so far studied.

2. P. elegans shows a yearly cycle of haemolymph concentration, showing maximum values in January and February 1971, and June and July 1971. Minimal values were obtained between March and May 1971.

3. The concentration of calcium in the haemolymph (especially of Pomatias) is high, a value of 20.2 mM/l being obtained for one group of Pomatias. This reflects their dependence on calcareous soils for survival.

4. Haemolymph and urine are isosmotic and isoionic.

5. The mantle fluid is generally less concentrated than the haemolymph and urine, ionic reabsorption presumably occurring over the mantle epithelium. Potassium, calcium and magnesium ions are selectively reabsorbed.

6. The highest haemolymph concentrations in pomatiasids were found in animals that inhabited areas with the least rainfall, and vice versa.

7. During inactivity the percentage ionic composition of the haemolymph of P. elegans altered as the O.P. increased. Sodium decreased, magnesium increased, and bicarbonate decreased. It is suggested that the fall in bicarbonate concentration is due to a change in the buffering capacity of the haemolymph.