Shell Microstructure Protects From Compression

Biological Strategy

Queen conch

AskNature Team

Image: G. P. Schmahl / NOAA / CC BY - Creative Commons Attribution alone

Prevent Buckling

When a living system undergoes compression to the extent that it causes structural damage, it results in buckling. For example, if a person pushes down on the top or the side of a paper cup, the cup’s wall will eventually give way, or buckle. Although a living system could add material to strengthen a structure, this requires expending precious energy. Instead, it must use energy and materials conservatively to avoid buckling, strengthening structures through careful placement of materials to resist, absorb, or deflect compressive forces. For example, instead of one long, tubular stem, some plants like bamboo have stronger nodes scattered along their stems. When compressed, these nodes keep the round stems from taking on an oval shape that weakens the structure and could result in buckling.

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Prevent Deformation

When a living system undergoes compression, tension, shear, bending, or twisting, its internal inter-molecular forces can often resist these forces and even change shape temporarily, returning to the original shape when the forces stop. However, if the force is too strong or lasts too long, permanent deformation or structural failure can occur, resulting in death. Therefore, living systems have strategies to resist deformation or help ensure limited deformation. For example, bones have thin crystals and proteinaceous fibers that provide strength and flexibility, protecting them from forces that would otherwise cause deformation on a daily basis.

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Gastropods

Class Gastropoda (“stomach-foot”): Snails and slugs

There are at least 40,000 known species of gastropod, with many more yet to be discovered, making it the largest class of mollusks. These animals exhibit torsion, meaning their internal organs are twisted 180° during development. The majority of gastropods have shells, and most open up on the right side. The largest gastropods are the size of a small child (3 feet, or 1 meter) while the smallest are barely visible to the naked eye.

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The shell of the conch survives compression and three-point bending due to lath-like aragonite crystals that form a microlayer.

The conch shell is known for its highly organized shape, but it is not the organization alone that makes these special animals. The shell of a conch has a microstructure made up of a cross-lamellar matrix consisting of lath-like aragonite crystals. It is this structure that creates the hard shell and provides such strong mechanical responses for a shell under compressive forces. In a sea full of predators this shell provides the animal with its only protection. Such unique design would prove useful for materials used in high impact or high compressive situations.