The structure of the dorsal body wall of the starfish Echinaster spinulosus was studied using polarized light microscopy of frozen tissues, scanning electron microscopy and histology. The collagen fibres of the body wall form a three-dimensional orthogonal web. Voids in the web contain ossicles and papulae. The orthogonal web delivers dimensional stability but allows shear necessary for ray torsion. The ossicles and fibres interact to load the fibres in tension and the ossicles in compression. Strain rates of the dorsal body wall were measured on live animals during typical movements. Uniaxial tension tests of the body wall yielded Young's moduli of 267 MPa (longitudinal), 249 MPa (transverse) and 353 MPa (bias); curves were essentially linear. The body wall was approximately linearly viscoelastic and showed hysteresis at 0.01 Hz. Stress relaxation over five decades of time (in seconds) yielded relaxation spectra with peaks in relaxation time at 2.96-3.35, depending on test direction. Stress relaxation caused the connective tissue to soften. The surface of fractured stress-relaxed tissue revealed wispy, dissociated fibril tufts, whereas unrelaxed fractures produced blunt-ended fibre bundles. Neural control was necessary for body wall integrity.
In the field: an interview with Martha Muñoz
Martha Muñoz is an Assistant Professor at Yale University, investigating the evolutionary biology of anole lizards and lungless salamanders. In our new Conversation, she talks about her fieldwork in Indonesia, Costa Rica, the Dominican Republic and the Appalachian Mountains, including a death-defying dash to the top of a mountain through an approaching hurricane.
Graham Scott in conversation with Big Biology
Graham Scott talks to Big Biology about the oxygen cascade in mice living on mountaintops, extreme environments for such small organisms. In this JEB-sponsored episode, they discuss the concept of symmorphosis and the evolution of the oxygen cascade.
Trap-jaw ants coordinate tendon and exoskeleton for perfect mandible arc
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Trap-jaw ants run the risk of tearing themselves apart when they fire off their mandibles, but Greg Sutton & co have discovered that the ants simultaneously push and pull the mandibles using energy stored in a head tendon and their exoskeleton to drive the jaws in a perfect arc.
Hearing without a tympanic ear
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In their Review, Grace Capshaw, Jakob Christensen-Dalsgaard and Catherine Carr explore the mechanisms of hearing in extant atympanate vertebrates and the implications for the early evolution of tympanate hearing.
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