The Glass Octopus reaches 11 cm (4.3 in) in mantle length and 45 cm (18 in) when you include the tentacles. They live in tropical and subtropical waters across the world at depths between 165 and 1,690 metres (540 and 5,550 feet). This is the Twilight Zone, where the Sun's light is reduced to a blue haze. Transparency therefore is a supreme camouflage if you can manage it.