Studies on the distribution pattern, submergence, salinity tolerance and desiccation limit of a salt marsh snail Pythia plicata were carried out. The survey of this snails from February 1984 to January 1985 revealed that the percentage of occurrence was high in place where there is a thick vegetation and low salinity and low where there is less vegetation and high salinity. In general the areas of mangroves near the freshwater connection is distributed with this snail and the areas of more neritic influence or in the seaward side these snails are less in their occurrence. When the submergence and salinity tolerance was tested in 12 different salinities from 2.2 to 30.4 ppt, the snails survived for 3 days in lower and higher salinities but 5 days in medium salinities. Mortality of 20% after 24 hours, 50 to 75% after 48 hours and 70 to 90% after 96 hours were recorded in the 12 salinities tested. It is evident that P.plicata has a tolerence in varying salinities with a preference towards low salinities. Fifty per cent mortality due to desiccation was noted after 9 days at room temperature (27 to 30' C).

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