The glass squid is a master of luminous disguise. Unlike the many species that use bioluminescence as an attention-grabbing beacon, this animal uses light as a cloak to evade prying eyes.
Aside from its opaque eyes and the polka dot-like chromatophores (pigmented cells that aid in camouflage) that cover its body, the glass squid is completely transparent. The chromatophores are not an issue, but the opaque color of its eyes can be a dead giveaway. Many species hunt for prey by scanning the water column above them, looking for any telltale silhouettes that might signal the presence of their next meal.
To confound its potential predators, the glass squid makes use of two U-shaped light-emitting photophores located at the base of its eyes: the lights cancel out the shadows cast by the opaque eyes. The effect of this strategy, called counterillumination, is to break up the squid's silhouette by mimicking the intensity and color of downwelling light from the surface.