Abstract
WHILE investigating the physiological aspects of the distribution of two species of the marine gastropod Bullia, one of us (A.C.B.) discovered that these snails can crawl only between certain limits of salinity. As the salinity of the sea-water is decreased by the addition of distilled water, movements become more and more restricted, eventually resulting in the total loss of locomotory powers while the animal becomes distended due to the osmotic inflow of water. Providing that dilution is accomplished reasonably slowly (taking 60 min. or more) the foot is not retracted at any stage, while the excitability of the muscles is greatly reduced or disappears completely. The animal remains motionless with stiff, swollen tissues. For Bullia digitalis Meuschen, this critical salinity lies in the region of 1.8 per cent, while in the case of B. laevissima (Gmelin) it is about 2.35 per cent. Loss of locomotory powers due to decreased salinity has previously been noted for some rocky-shore gastropods by Broekhuysen1 and Brown2. The phenomenon resembles the loss of contractility in vertebrate skeletal muscle subjected to ‘water rigour’. However, in Bullia the process is completely reversible. The snails can be kept for some hours at these reduced salinities without apparent ill-effect ; when returned to fresh, undiluted sea-water they soon recover and behave normally.
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References
Broekhuysen, G. J., Trans. Roy. Soc. S. Afr., 28, 255 (1940).
Brown, A. C., Portugal Acta Biol. (in the press).
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KRIJGSMAN, B., BROWN, A. ‘Water Rigour’ as an Aid when Operating on Marine Gastropoda. Nature 187, 69 (1960). https://doi.org/10.1038/187069a0
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DOI: https://doi.org/10.1038/187069a0
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