STRENGTH AND DESIGN OF SHELLS OF THE TWO ECOLOGICALLY DISTINCT BARNACLES, BALANUS BALANUS AND SEMIBALANUS (BALANUS) BALANOIDES (CIRRIPEDIA)

¹ Department of Zoology, Duke University, Durham, North Carolina, 27706, U.S.A.
² Department of Biology, University of York, York, YO1 5DD, England, U.K.

1. The shells of specimens of Semibalanus balanoides and Balanus balanus were loaded in compression. For shells of similar mass or pseudovolume (1 b h), B. balanus was about four times as strong as S. balanoides.

2. The morphology of the shell plates and their junctions is described. The shell of B. balanus is mechanically superior to that of S. balanoides in its possession of a calcified basis, well developed radii and in its general workmanship.

3. Neither the microstructure nor the microhardness of the shell plates gives significant indications that differences in material properties could account for the differences in strength observed.

4. It is suggested that S. balanoides has a life history with a short life expectancy which makes it important to reproduce early in life and that, compared with B. balanus, neatness of shell construction and, hence, shell strength is sacrificed to speed in the process.

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