Transparency in the eye region of an ostracod carapace (Macrocypridina castanea, Myodocopida)

Abstract

Many myodocopid ostracods are unusual in that they have well-developed compound eyes yet must view their environment through a shell. The cypridinid Macrocypridina castanea is relatively large among ostracods (about 5–10 mm) and is a pelagic predator. This species possess highly pigmented shells with a transparent region lying just above the eye. Here we examine the ultrastructure and transparency of this window using electron microscopy, serial-block face scanning electron microscopy and X-ray diffraction analysis and optical modelling. An internal, laminar stack was identified within the window region of the shell that formed a more regular half-wave reflector than in non-window regions, and where the distance between molecules in the chitin–protein fibrils decreases as compared to the non-window area. This results in excellent transmission properties—at around 99% transmission—for wavelengths between 350 and 630 nm due to its half-wave reflector organization. Therefore, blue light, common in the mid and deep sea, where this species inhabits, would be near-optimally transmitted as a consequence of the sub-micrometre structuring of the shell, thus optimizing the ostracod's vision. Further, pore canals were identified in the shell that may secrete substances to prevent microbial growth, and subsequently maintain transparency, on the shell surface. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’.

Biomimetic Transparent Eye Protection Inspired by an Ostracod (Crustacea) Carapace

“…Therefore the uniqueness of these species is that not only do they have compound eyes but they also possess highly transparent yet protective carapaces, through which they must see (Parker et al, 2019).…”

“…While some species of myodocopids possess transparent windows in their carapace in the regions covering the eyes only, others possess a carapace with uniform transparency (Parker et al, 2019). Parker et al (2019) discovered that the transparent properties of the carapace of the cypridinid Macrocypridina castanea were aided the carapace's thin-layered (internal laminar stack) construction ( Figure 1).…”

“…While some species of myodocopids possess transparent windows in their carapace in the regions covering the eyes only, others possess a carapace with uniform transparency (Parker et al, 2019). Parker et al (2019) discovered that the transparent properties of the carapace of the cypridinid Macrocypridina castanea were aided the carapace's thin-layered (internal laminar stack) construction ( Figure 1). The largest, laminate section of this carapace was found to be composed of a chitin-protein complex and low magnesium calcite with alternating high-low index material layers, each with an optical thickness (actual thickness multiplied by the refractive index) of ½ wavelength of blue light.…”

Establishment of long-term ostracod epidermal culture

“…The majority of myodocopid ostracods are benthic; they bury up to 1 cm depth in the sediments of the ocean floor (McKenzie et al 1999). Most myodocopid ostracods can be distinguished from other ostracods as they possess good vision with well-developed compound eyes (Parker et al 2019), up to one third of their overall body size (Parker 1998). Some myodocopids in the family Cypridinidae are known to possess transparent carapaces or transparent windows in the parts of the carapace that cover the eyes (Parker et al 2019).…”

“…Most myodocopid ostracods can be distinguished from other ostracods as they possess good vision with well-developed compound eyes (Parker et al 2019), up to one third of their overall body size (Parker 1998). Some myodocopids in the family Cypridinidae are known to possess transparent carapaces or transparent windows in the parts of the carapace that cover the eyes (Parker et al 2019). The cypridinid species used in the present study, Skogsbergia lerneri, is 2-3 mm in length and found at a depth of 1-130 m along the eastern coast of the American continents from Florida to the top of Brazil and the Caribbean islands (Kornicker 1958) and possess a carapace with uniform transparency.…”