During the day, cuttlefish on spawning grounds move about the ocean floor in plain view. Males wave their arms in aggressive bouts (left), and both genders engage in conspicuous sexual signaling. In another sunlit setting, a cuttlefish guards its mate (middle). As reported in the April 2007 issue of The American Naturalist, however, Roger T. Hanlon and colleagues at the Marine Biological Laboratory in Woods Hole, Mass., have found that such activities cease after nightfall. Furthermore, the invertebrates assume disruptive, mottled or uniform camouflage patterns, as seen in a nighttime image of a cuttlefish among seafloor vegetation (right). Courtesy of Roger T. Hanlon. It is thought that cuttlefish show diverse cryptic coloration patterns to avoid predators, which have evolved to possess acute vision under dark conditions. The complex behavior of the animals points also to their own excellent eyesight and to the efficiency of their visual system. In this study, mottled and disruptive patterns, or a combination of the two, were most common and afforded the cuttlefish near invisibility in exposed areas after dusk. Even during the daytime, when faced with a group of dolphins, stingrays or other predators, the creatures were observed to descend rapidly to the substrate and to camouflage themselves.