The mollusc, known as the scaly-foot gastropod, has been known for about a decade. It was discovered living in the deep sea near the Kairei Indian hydrothermal vent field on the Central Indian Ridge. The natural environment for the animal is harsh. There are extremes of temperatures, high pressures and high acidity levels that can easily damage shells of calcium carbonate. Brachyuran crabs live in the vicinity and these "are known to compress gastropod mollusc shells between their chela" with loads of up to 60N.
"To understand how the valiant gastropod holds up to these trials, Christine Ortiz of MIT and her colleagues used nanoscale experiments and computer simulations to dig in to the shell's structure. Many other species' shells exhibit what Ortiz calls "mechanical property amplification," in which the whole material is hundreds of times stronger than the sum of its parts."
The scaly-foot gastropod uses a unique trilayered shell to protect itself from hazards. (Image credit: Anders Waren, Swedish Museum of Natural History. Source here)
Most exoskeletal structures are technically known as multilayered composites. The parameters are the layer thicknesses, the nano- and microstructure of each layer, the number of layers, the sequence of layers, etc. Each species appears to have its own resultant profile.
"Design, inspired by nature, of engineering materials with robust and multifunctional mechanical properties [i.e., those which sustain a variety of loading conditions] is a topic of major technological interest in a variety of civilian and defense applications. Here, we identify the design principles of the shell of a gastropod mollusc from a deep-sea hydrothermal vent [order Neomphalina, family Peltospiridae, species Crysomallon squamiferum]. This system has a trilayered structure unlike any other known mollusc or any other known natural armor, with a relatively thick compliant organic layer embedded between two stiffer mineralized layers, an outer iron sulfide-based layer and an inner calcified shell."
The outer layer is about 30 micrometres thick and is mineralised: it contains iron sulphide particles (greigite, Fe2S4). This gastropod is the only metazoan known to employ iron sulphide as a skeletal material. The middle layer is about 150 micrometres thick and is thought to be the periostracum (the template for shell mineralization, providing protection against corrosive and dissolutive marine environments, and also chemical protection from boring organisms). The inner layer is composed of aragonite that is itself layered:
"[It] possesses a gradient layer [. . .] with a typical crossed lamellar layer (CLL) microstructure (approximately 50 [micro]m thick), followed by a relatively thick layer also with a CLL microstructure (approximately 200 [micro]m thick, followed by a thin prismatic layer (PL) on the inner surface of the shell (approximately 1.5 [micro]m thick)."
This structure has been studied empirically and modelled. Simulations were performed to understand how the shell responds to impacts and applied loads. There are too many details to document here.
"It is interesting to see how C. squamiferum has created these additional different protection mechanism compared to other gastropod molluscs by using materials plentiful and specific to the deep-sea hydrothermal vent environment, i.e., vent fluids rich in dissolved sulfides and metals.
The design principles of the trilayered shell of C. squamiferum exhibit many aspects that are different from the highly calcified shells of typical gastropod molluscs or any other natural armor. Each material layer serves distinct and multifunctional roles leading to many advantages."
Design principles have emerged from this research. The authors have found new design features leading to enhanced functional performance. "Each material layer serves distinct and multifunctional roles leading to many advantages". They point out that design principles are extremely important because there are so many variables: "The design space for synthetic multilayered structural composites for protective applications is enormous". The great merit of biological systems is that they provide a chart to steer through this space. However, the authors attribute design in biological systems to an "evolutionary process".
"Biological systems, such as the one described here, greatly reduce the engineering design space since efficient threat-protection design concepts have emerged through the lengthy evolutionary process that fulfill the necessary functions and constraints."
The problem with this evolutionary framework is that it has no empirical validity. We have no warrant for explaining design principles via evolutionary processes. The authors explain that they do not know whether the observed design "represents an advanced functional adaptation as an antipredatory response or an exaptation (i.e., a trait that evolved to serve one function, but subsequently and simultaneously may serve other functions)". This comment is, unfortunately, entirely typical of the culture prevailing in science produced by philosophical materialism. Evolutionists have supreme confidence in their theoretical framework, but do not seem to see the need to constrain theory by reference to empirical data. Observed adaptations do not demonstrate the emergence of design concepts. The only sources of design concepts that we know of are intelligent agents. Replacing the culture of materialism by one that integrates information inputs with physics and chemistry is long overdue.
With this alternative culture, paragraphs like the following take on a new richness of meaning:
"In particular, the efficient natural armor structural system described here sustains both mechanical loading, as well as thermal fluctuations with inherent mechanisms to prevent catastrophic failure. The multimaterial, trilayer design and advantageous curved geometry enables structural stiffening, reduction of radial displacements, penetration resistance, and stability during thermal impulses even with the presence of large mismatches between constituent materials. Trilayered sandwich composite designs have had limited use in military applications, and the concepts reported here could lead to bioinspired improvements and broader applicability and improved performance for human, vehicle, and structural armor."
Protection mechanisms of the iron-plated armor of a deep-sea hydrothermal vent gastropod
Haimin Yao, Ming Dao, Timothy Imholt, Jamie Huang, Kevin Wheeler, Alejandro Bonilla, Subra Suresh, and Christine Ortiz
Proceedings of the National Academy of Sciences, January 19, 2010, vol. 107, no. 3, 987-992 | doi:10.1073/pnas.0912988107
Abstract: Biological exoskeletons, in particular those with unusually robust and multifunctional properties, hold enormous potential for the development of improved load-bearing and protective engineering materials. Here, we report new materials and mechanical design principles of the iron-plated multilayered structure of the natural armor of Crysomallon squamiferum, a recently discovered gastropod mollusc from the Kairei Indian hydrothermal vent field, which is unlike any other known natural or synthetic engineered armor. We have determined through nanoscale experiments and computational simulations of a predatory attack that the specific combination of different materials, microstructures, interfacial geometries, gradation, and layering are advantageous for penetration resistance, energy dissipation, mitigation of fracture and crack arrest, reduction of back deflections, and resistance to bending and tensile loads. The structure-property-performance relationships described are expected to be of technological interest for a variety of civilian and defense applications.
Grossman, L. Snail In Shining Armor, Science News, February 13th, 2010; Vol.177 #4 (p. 13)
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