Core–shell nanospheres behind the blue eyes of the bay scallop Argopecten irradians. Issue 159 (23rd October 2019)

• Record Type: Journal Article
• Authors: Harris, Olivia K.; Kingston, Alexandra C. N.; Wolfe, Caitlin S.; Ghoshroy, Soumitra; Johnsen, Sönke; Speiser, Daniel I.
• Is Part Of: Journal of the Royal Society interface. Volume 16:Issue 159(2019)
• Publication Date: 2019-10-23
• Subjects: biophotonics -- iridescence -- optics -- scattering -- structural colour -- visual ecology; Physical sciences -- Research -- Periodicals; Life sciences -- Research -- Periodicals; Interdisciplinary research -- Periodicals; 570.5
• DOI: 10.1098/rsif.2019.0383
• Languages: English
• ISSNs: 1742-5689

Abstract

Abstract : The bay scallop Argopecten irradians (Mollusca: Bivalvia) has dozens of iridescent blue eyes that focus light using mirror-based optics. Here, we test the hypothesis that these eyes appear blue because of photonic nanostructures that preferentially scatter short-wavelength light. Using transmission electron microscopy, we found that the epithelial cells covering the eyes of A. irradians have three distinct layers: an outer layer of microvilli, a middle layer of random close-packed nanospheres and an inner layer of pigment granules. The nanospheres are approximately 180 nm in diameter and consist of electron-dense cores approximately 140 nm in diameter surrounded by less electron-dense shells 20 nm thick. They are packed at a volume density of approximately 60% and energy-dispersive X-ray spectroscopy indicates that they are not mineralized. Optical modelling revealed that the nanospheres are an ideal size for producing angle-weighted scattering that is bright and blue. A comparative perspective supports our hypothesis: epithelial cells from the black eyes of the sea scallop Placopecten magellanicus have an outer layer of microvilli and an inner layer of pigment granules but lack a layer of nanospheres between them. We speculate that light-scattering nanospheres help to prevent UV wavelengths from damaging the internal structures of the eyes of A. irradians and other blue-eyed scallops.