Mechanical properties of sea-urchin lantern muscles: a comparative investigation of intact muscle groups in Paracentrotus lividus (Lam.) and Stylocidaris affinis (Phil.) (Echinodermata, Echinoidea) |
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Authors: | I C Wilkie M D Candia Carnevali F Andrietti |
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Institution: | (1) Department of Biological Sciences, Glasgow Caledonian University, 70 Cowcaddens Road, Glasgow G4 0BA, Scotland, Tel.: +44-141 331-3207, Fax: +44-141 331-3208, e-mail: i.wilkie@gcal.ac.uk, GB;(2) Dipartimento di Biologia “Luigi Gorini”, Università degli Studi di Milano, 26 Via Celoria, I-20133 Milano, Italy, IT |
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Abstract: | The jaw apparatus, or lantern, of sea-urchins contains five pairs of retractor and protractor muscles which are responsible
for lantern displacement. Using intact retractor or protractor groups, the force-length relations of these muscles were compared
in two taxonomically distant species, Paracentrotus lividus and Stylocidaris affinis. The total contractile forces generated by the muscles can be resolved into vertical and horizontal components. It was found
that the vertical component of the retractors is maximal at a lantern position which is significantly lower (i.e. more protruded)
in Paracentrotus than in Stylocidaris. Total forces generated by the retractors were in both species maximal at or above the lantern `resting positions'. In Paracentrotus alone, the total force-displacement curves tended to be bimodal. It is hypothesized that the retractors of Paracentrotus contain two populations of muscle fibres, one adapted for jaw opening and one for lantern retraction. No significant differences
in the properties of the protractors of the two species could be identified. The lantern of Paracentrotus is more mobile than that of Stylocidaris and is able to exploit a wider range of food sources. This investigation has shown that the force-length relations of the
lantern muscles match their differing working conditions.
Accepted: 3 November 1997 |
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Keywords: | Echinodermata Echinoidea Lantern of Aristotle Muscle mechanics Force-length relations |
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