Oral water ingestion in the pulmonate freshwater snail, Lymnaea stagnalis

In Lymnaea stagnalis, oral uptake of ambient medium was studied using Cr-51-ethylenediaminetetraacetic acid. In normal snails Cr-ethylenediaminetetraacetic acid uptake showed two components: a high uptake rate within the first hour followed by moderate uptake proportional with time. The tracer accumulated mainly in the digestive system. All animals showed initial, transient uptake. Moderate uptake proportional with time did not occur in snails in which the buccal ganglia had been extirpated, in which both the buccal ganglia had been extirpated and the oesophagus was sectioned, or in snails provided with an oesophageal fistula. These snails did not accumulate tracer in the intestinal system. This type of tracer accumulation clearly represented oral ingestion of surrounding water. The oral water ingestion rate ranged from 8 to 12 mu l . h(-1). g(-1). Assuming complete absorption, this accounts for 20-30% of the urine production rate. At low external concentrations the contribution of oral water ingestion to Na+ balance is negligible. However, its importance will grow with increasing external concentrations and becomes a major factor at higher concentrations. The ingestion rate increased almost sixfold when starving snails were allowed to feed. It is suggested that oral water ingestion is a consequence of making bite cycles and swallowing.