There exists a snail, in hydrothermic vents in the Indian Ocean, that incorporates iron particles into its shell for extra protection.
From collision detection:
Scientists discovered Crysomallon squamiferum in 1999, but they didn’t know a whole lot about the properties of its shell until this month, when a team led by MIT scientists
decided to study it carefully. The team did a pile of spectroscopic and
microscopic measurements of the shell, poked at it with a nanoindentor,
and built a computer model of its properties to simulate how well it
would hold up under various predator attacks.
The upshot, as they write in their paper (PDF here), is that the shell is “unlike any other known natural or synthetic engineered armor.”
Part of its ability to resist damage seems to be the way the shell
deforms when it’s struck: It produces cracks that dissipate the force
of the blow, and nanoparticles that injure whatever is attacking .
Also, the post uses the phrase “Darwinian evolution crossed with Burning Man”. Win.