First published online October 17, 2008
Journal of Experimental Biology 211, 3421-3432 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020479
To bend a coralline: effect of joint morphology on flexibility and stress amplification in an articulated calcified seaweed
Patrick T. Martone* and
Mark W. Denny
Hopkins Marine Station of Stanford University, Pacific Grove, CA 93950,
USA
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Fig. 1. (A) The articulated coralline Calliarthron cheilosporioides,
including (B) long-section and (C) cross-section diagrams of genicula (yellow)
and intergenicula (pink). Dimensions are genicular length  ,
intergenicular length L, intergenicular lip length x,
intergenicular radius y and genicular radii r1
and r2. Genicula are shown in yellow; intergenicula are
shown in pink.
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Fig. 4. Comparison of bending model predictions and observed frond deflections for
two representative fronds and three applied forces.
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Fig. 5. Effect of varying genicular dimensions on frond deflection. (A) Genicular
length, , (B) genicular radii r1 and
r2, (C) intergenicular lip length x, (D)
intergenicular length L, (E) intergenicular radius y and (F)
tensile modulus, Et.
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Fig. 6. Effect of varying genicular dimensions on the maximum stress within first
genicula (triangles) and the deflection angle of whole fronds (circles).
x-axes represent percentage change in (A) genicular length ,
(B) genicular radii r1 and r2, (C)
intergenicular lip length x, (D) intergenicular length L,
(E) intergenicular radius y and (F) tensile modulus
Et. Note that axes have differing scales.
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Fig. 7. Effect of varying genicular dimensions on the ratio of flexibility (a
presumed benefit) to stress (a presumed cost). Adjustments to genicular
dimensions that increased the flexibility:stress ratio were considered net
benefits for articulated fronds. Symbols represent changes in genicular radii
(black circles), genicular length (black triangles), intergenicular lip length
(black squares), intergenicular length (gray circles), tensile modulus (gray
triangles) and intergenicular radius (gray squares).
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Fig. A2. Diagram of cross-sectioned geniculum indicating how polar coordinates were
calculated for each elliptical geniculum. Genicular tissue is shown in yellow;
intergenicular tissue is shown in pink; A is the unstretched
genicular cross-sectional area; r1 and
r2 are genicular radii; (a,b) are
coordinate positions along the periphery of the elliptical geniculum; and
 is the angle relative to the geniculum center.
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Fig. A4. Diagram of bending geniculum in long-section (A) and cross-section (B)
precisely when intergenicula make contact. Genicular tissue is shown in
yellow; intergenicular tissue is shown in pink. Contact angle (2β) can be
calculated from genicular dimensions.
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Fig. A5. Diagram of bending geniculum in long-section (A) and cross-section (B)
after intergenicula make contact. Genicular tissue is shown in yellow;
intergenicular tissue is shown in pink; k is half the new length of
genicular tissue.
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© The Company of Biologists Ltd 2008
i,
bending angle 
i and length of distal intergeniculum
Li are indexed for each geniculum no. i, numbered
from the base (see Appendix A for details).
–
) curve of
Calliarthron geniculum. Tensile modulus was calculated from the slope
of the linear regression.
is the perpendicular distance of the
neutral axis from the genicular midline; and x is the intergenicular
lip length.