Molecular secrets of the “iron-plated snail”



Life isn’t easy for the “scaly-foot gastropod”. This humble snail lives in hydrothermal vent fields two miles deep in the Indian ocean, and is surrounded by vicious predators. For example, there’s the “cone snail”, which stabs at its victims with a harpoon-style tooth as a precursor to injecting them with paralyzing venom. Then there’s the Brachyuran crab, which has been known to squeeze its prey for three days in an attempt to kill it. Yowsa.

Ah, but the scaly-foot gastropod has its own tricks. To fight back, it long ago evolved a particularly cool defense structure: It takes the grains of iron sulfide floating in the water around it and incorporates it into the outer layer of its shell. It it thus an “iron-plated snail”.

Oh yes way. 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 it:

Within the indent region, consolidation of the granular structure is observed within and around the indent. Localized microfractures exhibit tortuous, branched, and noncontinuous pathways, as well as jagged crack fronts resulting from separation of granules, all of which are beneficial for energy dissipation and preventing catastrophic brittle fracture. Such microfracture modes may serve as a sacrificial mechanism. Upon indentation, inelastic deformation will be localized in the softer organic material between the granule interfaces, which allows for intergranular displacement and friction while simultaneously being compressed down into the softer ML. Shear of iron sulfide nanoparticles against the indenter surface is expected, in particular since penetrating attacks take place off-angle rather than directly on top of the shell apex, and can be facilitated by intergranular displacements during yielding of the OL. This provides a potential grinding abrasion and wear mechanism to deform and blunt the indenter (since biological penetrating threats are in reality deformable as well) that will continue throughout the entire indentation process.

Beyond awesome. This is Darwinian evolution mixed with, like, Burning Man.

Being scientists of biomimicry, the authors surmise that if it were possible to reverse-engineer the entire shell — it’s not just the outer iron layer that’s cool; there are also two inner layers with gooey nougat that are equally important in defending the snail — they could produce superstrong materials for military defense and “load-bearing”.

Fair enough. But personally I’m satisfied just to have more pure science that proves, yet again, the inexhaustible Weirdness Of The Briny Deep.

Iron snails, people! Iron snails.



(Thanks to the Eco Tone blog for alerting me to this one!)

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