Data from: Three-dimensional midwater camouflage from a novel two-component photonic structure in hatchetfish skin

The largest habitat by volume on Earth is the oceanic midwater, which is
also one of the least understood in terms of animal ecology. The organisms
here exhibit a spectacular array of optical adaptations for living in a
visual void that have only barely begun to be described. We describe a
complex pattern of broadband scattering from the skin of Argyropelecus
sp., a hatchetfish found in the mesopelagic zone of the world's
oceans. Hatchetfish skin superficially resembles the unpolished side of
aluminum foil, but on closer inspection contains a complex composite array
of sub-wavelength-scale dielectric structures. The superficial layer of
this array contains dielectric stacks that are rectangular in
cross-section, while the deeper layer contains dielectric bundles that are
elliptical in cross-section; the cells in both layers have their longest
dimension running parallel to the dorsal-ventral axis of the fish. Using
the finite-difference time-domain approach and photographic radiometry, we
explored the structural origins of this scattering behavior and its
environmental consequences. When the fish’s flank is illuminated from an
arbitrary incident angle, a portion of the scattered light exits in an arc
parallel to the fish's anterior-posterior axis. Simultaneously, some
incident light is also scattered downward through the complex birefringent
skin structure and exits from the ventral photophores. We show that this
complex scattering pattern will provide camouflage simultaneously against
the horizontal radially symmetric environmental light in this habitat, the
predatory bioluminescent searchlights that are ubiquitous here. The
structure also directs light incident on the flank of the fish into the
downwelling, silhouette-hiding counterillumination of the ventral
photophores.