Squid eyes and camouflage
Cephalopods possess a sophisticated array of mechanisms to achieve camouflage in dynamic underwater environments. While active mechanisms such as chromatophore patterning and body posturing are well known, passive mechanisms such as manipulating light with highly evolved reflectors may also play an important role.
Using transparency and reflection, animals residing in the ocean’s featureless midwater environment can make themselves nearly invisible to potential predators. Since the pelagic light field in regions of the ocean with asymptotic light regimes is roughly cylindrical, radiance matching can be an effective strategy for reflective camouflage; if an animal can perfectly reflect, with the same intensity and spectral composition, light radiating from behind a viewer, this reflectance will also match the light radiating from behind the animal, and the animal will remain inconspicuous on its background.
Well, the case is that has been demonstrated that the silvery reflective tissue surrounding the eyes of squid in the family Loliginidae appears to have several novel optical features contributing to camouflage from lateral-looking predators in shallow and midwater pelagic environments.
This silvery covering consists of packed spindle-shaped cells that achieve broadband visible reflectance by creating a large range of layer thicknesses. The silvery covering of the squid eye apparently matches the background radiance of the water column in which the animal is immersed, thereby hiding the retina by creating the illusion of transparency.
Reference: [Holt et al., 2011]
Photo credit: ©Courtney Platt | Caribbean reef squid, Sepioteuthis sepioidea (Teuthida - Loliginidae) at Grand Cayman.