2021/09/12 by Leanne Friedrich, Wai Sze T. Lam, Friedrich, Leanne +19
Agricultural and Biological Sciences · Earth and Planetary Sciences · Environmental Science · Physics and Astronomy · #Biological Physics (physics.bio-ph) #Cephalopods and Marine Biology #Coral and Marine Ecosystems Studies #FOS: Physical sciences #Marine and coastal plant biology #Materials Science (cond-mat.mtrl-sci) #Optics (physics.optics) #cond-mat.mtrl-sci #physics.bio-ph #physics.optics
paper · pdf · doi:10.48550/arxiv.2110.15199
arxiv created 2021/09/12 · openalex publication_date 2021/09/12 · arxiv updated 2021/10/29 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The chiton Acanthopleura granulata uses aragonitic lenses embedded in its shell to focus light onto photoreceptors. Because aragonite is biaxially birefringent, the microstructure of the lens greatly impacts the optical performance. In addition, the chiton lives in the intertidal, so lenses experience two environments with different refractive indices: air and water. Using EBSD, we find that the lens is polycrystalline and contains curved grain boundaries. A combination of large, twinned grains and nanotwins ensure that the aragonitic <001> axis is consistent across the lens. However, the orientation of the <001> axis relative to the shell varies between lenses. Ray tracing simulations predict the optical performance of lenses of various microstructures in wet and dry environments. Though twinning helps to limit birefringence-induced aberrations, variations in the orientation of the <001> axis between lenses lead to variations in focal lengths between lenses and cause image doubling in some lenses. As such, the birefringence of aragonite does not help the lens to transmit focused images in both air and water.