Brachiopods are in fact small marine creatures that look a bit like mollusks, but are not actually closely related with them. An African brachiopod, known as Discinisca tenuis, has a particularly interesting feature: its protective outer shell is soft and pliable in water, but becomes hard when dry.
In a recent study, an international team of scientists used a process called cryotomography to analyze some of those shells, which are about half a millimeter thick. The shells were found to have a brick-wall-like structure, in which the "bricks" are nanocrystals of a fluorapatite mineral (similar to our tooth enamel), while the "mortar" that joins the bricks is made of molecules. organic compounds such as chitin and various proteins.
(Photo: Brookhaven National Laboratory) When that mortar is dry, it holds the bricks together rigidly and inflexible. Once the mortar gets wet, however, it quickly becomes soft, allowing the bricks to slide back and forth against each other. A network of pores inside the shell helps guide the water into the mortar, facilitating the process.
This quality is believed to help groups of Discinisca tenuis to survive in their habitat. When creatures are exposed to the air during low tides, their shells harden to offer protection from predators and the elements. When submerged, however, their shells soften so that adjacent brachiopods don't harm each other as they sway back and forth between the waves.
Scientists hope that technology inspired by this mechanism may one day be used in applications such as adaptive sports helmets and other protective clothing.