Assertion: gastropod's shell | /r/HasAspect | three layers
Facets:
value: for extra strength
type: PURPOSE
Source sentences:
text: The shell has three layers for extra strength: a tough outer layer, a chalky middle layer, and a shiny inner layer, next to the animal’s skin.
text: They are the only known animals to incorporate iron sulfides into their bodies, and their unique shells have three layers to sustain them against threats such as a dissolving shell or being hunted by crabs.