The inner hinge-ligament of Pectinidae (Lamellibranchiata) is an elastic block of amorphous cross-linked protein, plasticized with water. It acts as a compression spring, and is the antagonist of the shell adductor muscle.
2. Its elasticity is shown to be rubber-like, in that the elastic restoring force is mainly due to entropy changes. Rubber-like elasticity has been demonstrated by other authors in two other proteins (elastin and resilin).
3. Pectinidae swim by rapid opening and closing of the shell. The resilience of the inner hinge-ligament of Chlamys at the frequency of the swimming movements is at least 91%.
4. The inner hinge-ligament of Pectinidae is compared with other proteins which show long-range elasticity.