The Iron Snail

The Iron Snail
The Scaly-foot gastropod was discovered in 2001.
The snail's foot is very unusual in that it is armored with iron-mineral scales. It is protected by scale-shaped sclerites composed of iron
sulphides greigite and pyrite. No other animal is known to use iron sulfides in this way.

The snail's shell is also unusual. The shell structure is composed of three layers.
The outer layer is about 30 μm thick, and is made of iron sulphides, containing greigite Fe3S4. This makes this gastropod the only metazoan known so far that employs this material in its skeleton.

The middle shell layer is organic, and is also the thickest of the three (about 150 μm). It is comparable to the periostracum, a thin protein coating found on other snail shells.
The innermost layer is made of aragonite, a form of calcium carbonate that is commonly found both in the shells of mollusks and in various corals.

Each layer contributes to the effectiveness of the snail's shell in different ways. The middle organic layer appears to absorb the mechanical strain and energy generated by a squeezing attack (as by the claws of a crab), making the shell much tougher. The organic layer also acts to dissipate heat.

Sources and further reading:
http://www.thefeaturedcreature.com/2013/11/scaly-foot-gastropod-the-snail-with-an-iron-fist-foot.html
http://en.wikipedia.org/wiki/Scaly-foot_gastropod

Image: http://www.zoo.ox.ac.uk/group/oceans/people/CC.html