Ultrastructure and Mineral Composition of Bathymodiolus Shell From Wocan-1 Hydrothermal Vent, Northwest Indian Ocean

The Mussel organisms from the sulfide hydrothermal field of the mid-ocean ridge can virtually record the ecological environment information around the region. However, the distribution characteristics, ultrastructure and genesis of the minerals of the shells are not well studied. A mount of mussels were first collected from the Wocan-1 hydrothermal field in the Northwest Indian Ocean, by the Manned deep-sea submersible (JIAOLONG) in 2017, which were ideal samples for investigating this scientific issue. The mussel, deep-sea Bathymodiolus of the Indian Ocean (Bathymodiolus marisindicus), is analysed by the Scanning electron microscope, Laser Raman spectroscopy, and Fourier transform infrared spectrum for their natural cross-section morphology, and mineral component. The results show that the longitudinal growth of the Bathymodiolus shell includes periostracum, prism layer,transition layer, aragonite slate layer and myostracum from the outer to the inner. In the fibrous prismatic prism layer of the shell, the c-axis cross-section of the prism is irregular, and the width of the calcite prism perpendicular to a-axis is about 818 similar to 960 nm, and it is nearly 45 degrees oblique with the aragonite layer, and there are interlaced calcite prisms. The shape of the transition layer of the shell is extremely irregular, and it continues the growth orientation of the prismatic layer showing a trend of transition from the prismatic to the slate of aragonite. The aragonite layer has a lamellar structure, and it's about 205 similar to 1 260 nm in thickness. In the aragonite layer of the Bathymodiolus shell of the Wocan-1 hydrothermal vent, the thickness of the aragonite tablets of the same region is the same, but the thickness of the tablet of different regions is different. The myostracum has a simple prismatic ultrastructure, which is overlaid by both prismatic and nacre layers (aragonite lamellar layer). Spectral analysis shows that the minerals of the nacre and prism layers of the Bathymodiolus shell are inorganic aragonite with relatively high crystallinity and biogenic calcite,respectively. The morphology characteristics, mineral components, and genesis of the Bathymodiolus shell analyzed in the study can provide a potential example for studying the hydrothermal field's mollusk shell formation mechanism and bioinduced mineralization process.