Ventral Photophores and Counterillumination

Counterillumination or countershading is a unique antipredatory behavior common to midwater cephalopods, decapod crustaceans and fishes. Counterillumination camouflages an animal being viewed from below by mimicking the downwelling light and reducing their dark silhouette. All squid that use this method have photophores on the ventral surface of their mantle. This technique is dependant upon bioluminescence for it to be effective; a transparent body often is not sufficient. It is important to note that counterillumination is only feasible in areas where the bioluminescent pattern is believable. Too close to the surface, and the altered silhouette will be too dark. Too deep into the bathypelagic zone, and illumination will be too bright and could potentially attract predators (Jones 2004).