Functions
Figure 1. Shows the anatomy of the Crabs
Exoskeleton Composite Material
Helge Fabritius revealed that there are other compositions contained in the crab shell. The crab shell shows region with low calcium content while containing large quantity of magnesium. They also reveal areas with hardly any magnesium. Magnesium atoms in calcium carbonate crystal cause irregularities in the crystal structure, thus increasing the stiffness of the mineral which in turn hardened the crab carapace [5].
The author also demonstrated that the claws have high mineral content as it need to withstand particularly strong forces. However, carapace contains fewer minerals making it less heavy. There are more resilient compounds in carapace to form a thicker shell.
Carapace Geometry
While the results of this study may or may not be applicable to the rainbow crabs, but it shows how the carapace geometry is influenced to favor certain dimensions in order to cope with functional groups (male or female) and sites conditions.
Mechanism
References
[2] Madigan, M., Martinko, J. and Parker, J. (2000). Brock biology of microorganisms. 1st ed. Upper Saddle River, NJ: Prentice Hall.
[3] The composition of the exoskeletons of large arthropods: example of two crustaceas: The American lobster Homarus americanus and the edible crab Cancer pagurus. (2007). Thermochimica Acta, [online] 463(1-2), p.2. Available at: http://www.mpie.de/index.php?id=2836.
[4] P.-Y. Chen, A. Y.-M. Lin, J. McKittrick, and M. A. Meyers, "Structure and mechanical properties of crab exoskeletons," Acta Biomaterialia, vol. 4, pp. 587-596, 5// 2008.
[5] A. STIRN. 10 May 2014). Bionanocomposites. MATERIALS & TECHNOLOGY.
[6] (2014, May). Rainbow Land Crab. Available: http://www.exotic-pets.co.uk/rainbow-land-crab.html
[7] A. T. Souza, M. I. Ilarri, J. Campos, J. C. Marques, and I. Martins, "Differences in the neighborhood: Structural variations in the carapace of shore crabs Carcinus maenas (Decapoda: Portunidae)," Estuarine, Coastal and Shelf Science, vol. 95, pp. 424-430, 12/20/ 2011.
[8] Chen, Bin; Yin, Dagang; Chen, Xi; Yuan, Quan; Zhang, Zhiling, "Nanostructural Mechanism of Toughness of Crab Carapace", Journal of Computational and Theoretical Nanoscience, Volume 10, Number 6, June 2013, pp. 1436-1440(5)