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Abstract
The variation in tenacity of single tube feet from three sea urchin species with contrasted habitats was assessed and correlated with the ultrastructure of their adhesive secretory granules. The tube feet of Arbacia lixula and Sphaerechinus granularis have larger discs and more complex adhesive granules than those of Paracentrotus lividus, but A. lixula attaches to glass with significantly lower tenacity (0.05 – 0.09 MPa) than the other two species (0.10 – 0.20 and 0.11 – 0.29 MPa, respectively). However, the estimated maximal attachment force one tube foot can produce is similar for all three species investigated. No clear relationship between tube foot size, tenacity, adhesive secretory granule ultrastructure and species habitat can therefore be established. For P. lividus the tenacity of single tube foot discs on four different smooth substrata was also compared, which showed that both the total surface energy and the ratio of polar to non-polar forces at the surface influence tube foot attachment strength. This influence of the surface characteristics of the substratum appears to affect the cohesiveness of the adhesive secretion more than its adhesiveness.
Acknowledgements
We thank the Director and staff of the Observatoire Océanologique Arago at Banyuls-sur-mer (France) for providing facilities, and P. Postiau for technical assistance. R.S. benefitted from a doctoral grant of the Foundation for Science and Technology of Portugal (SFRH/BD/4832/2001). P.F. is Research Associate of the National Fund for Scientific Research of Belgium (FNRS). This study is a contribution from the “Centre Interuniversitaire de Biologie Marine” (CIBIM; http://www.ulb.ac.be/sciences/biomar/html/adherence.html).
