The scaly-foot gastropod (*Chrysomallon squamiferum*), a hydrothermal vent snail, possesses a unique shell structure composed of three distinct layers. The outermost layer is reinforced with iron sulfides, primarily greigite, which gives the shell a metallic appearance and magnetic properties. The middle layer consists of a spongy organic structure that acts as a shock absorber against mechanical attacks from predators. The innermost layer is made of aragonite, a common form of calcium carbonate. While researchers initially hypothesized that the iron-rich outer layer serves as a defense against chemical toxicity, recent studies demonstrate that its primary function is mechanical, dispersing the energy of crushing attacks from crabs and other predators by cracking along microscopic lines without compromising the underlying structural layers.
Based on the text, what is true of the outermost layer of the scaly-foot gastropod's shell?
- AIt is composed of a spongy organic structure that functions as a shock absorber.
- BIt was proven by recent studies to serve as the snail’s primary defense against chemical toxicity.
- Its primary purpose is to disperse the force of physical attacks through microscopic fractures.Answer
- DIt is constructed from aragonite to give the shell its magnetic properties.