An analysis of water‐content regulation in osmoconforming limpets (Mollusca: Patellacea)

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Abstract
The capacity to regulate body volume is important in the ability of soft‐bodied osmoconforming marine animals to withstand osmotic stress. In the present study two intertidal limpets, Collisella digitalis and Notoacmea scutum, which differ in their tolerance of osmotic stress, are compared in their ability to regulate water content. Two direct measurements and two mathematical approaches developed by Oglesby ('75) and Machin ('75), respectively, have been used. Both species are osmoconformers over the range 500–1,500 mOs/1 but showed a slight tendency to hyporegulate Cl− and Na+ in the hemolymph. In weight and tissue hydration changes following a change in osmotic pressure of the medium, C. digitalis did not vary as widely as did N. scutum and so appears to have better control of body volume. This correlates well with the previous finding that C. digitalis tolerates a wider range of salinity than does N. scutum.