There is a snail that lives amongst the thermal vents two miles beneath the surface of the Indian ocean that has developed a unique defense adaptation. Long ago it evolved the ability to take bits of iron sulfide floating around in the water and incorporate it into its shell, which effectively became iron-plated.
Crysomallon squamiferum’s researchers write in the PNAS (Proceedings of the National Academy of Sciences) report (PDF found here) that the shell is…
…advantageous for penetration resistance, energy dissipation, mitigation of fracture and crack arrest, reduction of back deflections, and resistance to bending and tensile loads.
Extended article and links abound at The Ecological Society of America Blog.