I photographed these cuttlefish mating while diving off Lady Elliot Island. There was a big group of them but this couple was not shy. Cuttlefish are marine animals of the order Sepiida and, despite their name, are not fish but molluscs. They have a remarkable ability to rapidly alter their skin colour at will, to communicate with other cuttlefish and to camouflage themselves from predators.
Lady Elliot Island, off Queensland coast
Canon G10, 28mm lens, 1/250, f2.8, ISO 80, underwater flash