Glowing photophores are visible on this midwater squid (Abralia veranyi) viewed from below at low light levels. We think of light as a way to see in the dark. But many species use it to help them hide. This adaptation is called counterillumination. Seen from below, an animal might stand out as a dark shape against the brighter water above. By glowing on its underside, it can blend in. Watch a video of scientists describing their encounters with bioluminescent animals in the deep sea.