A transparent squid may camouflage itself by activating specialized cells in its eyes.
Many marine creatures emit light to hide shadows that might be seen by predators below. To find out how animals control this bioluminescence, Amanda Holt and Alison Sweeney at the University of Pennsylvania in Philadelphia used transmission electron microscopy to study the eyes of the squid Galiteuthis (pictured). They found that the underside of the eye — one of the few parts of the creature that is not transparent — has fibre-like cells in a range of shapes that channel bioluminescence while leaking light at different rates.
The authors modelled how the light travels through the various cell shapes. They suggest that the squid could activate different populations of cells to vary the intensity and distribution of the light passing through them, allowing the animal to camouflage itself at any depth.