Unique Characteristics of the Exoskeleton of Bythograeid Crab, Austinograea rodriguezensis in the Indian Ocean Hydrothermal Vent (Onnuri Vent Field).

The Indian Ocean hydrothermal vent is a region where a new oceanic crust is formed by magma at the interface of the deep-sea bed over 2000 m in depth. Here we examined for the first time the exoskeleton structure and mechanical properties of the bythograeid crab Austinograea Rodriguezensis living in hydrothermal vents. Scanning electron microscope and energy dispersive x-ray were used for structural analysis, and a nanoindentation system was used for mechanical analysis. The exoskeleton was divided into four layers: epicuticle, exocuticle, endocuticle, and membrane. The thickness of each layer was different from that of other crustaceans previously reported. Additionally, the number of constituent elements, composition ratio, and hardness of each layer were unique among previously studied crabs. This observation indicates that those characteristics might have evolved for creatures with a hard exoskeleton living in the deep-sea hydrothermal vent.