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The Function of the Operculum of Thais lapillus (L.) in Resisting Desiccation and Predation

Janet S. Gibson
Journal of Animal Ecology
Vol. 39, No. 1 (Feb., 1970), pp. 159-168
DOI: 10.2307/2893
Stable URL: http://www.jstor.org/stable/2893
Page Count: 10
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Function of the Operculum of Thais lapillus (L.) in Resisting Desiccation and Predation
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Abstract

(1) The resistance to desiccation of Thais lapillus (L.) was investigated at temperatures of 14-40 degrees C and relative humidities of 0, 50 and 100%. Median lethal times were found for each combination of temperature and humidity investigated and used to construct a contour diagram representing the desiccation properties of Thais. It was concluded that elevated temperature rather than desiccation would be likely to cause natural mortality. (2) The rate of water loss was studied simultaneously in four groups of whelks, those with large opercula, small opercula and without opercula, and a randomly selected group in the normal position, foot down. Another randomly selected group was studied in the upturned position. An inverse relationship was found between rate of water loss and ratio of operculum to aperture length in the first four groups but the fifth group showed the greatest water loss, indicating that the position of the aperture in relation to the substrate had a greater influence than the size of the operculum. Desiccation resistance was not considered to be the primary function of the operculum of T. lapillus. (3) In choice experiments offering equal numbers of whelks with and without opercula, it was found that Carcinus maenas (L.) was able to prey more successfully on those without opercula. The function of the operculum in Thais lapillus was concluded to be chiefly a protection against predation.

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