In the ever-evolving arms race of the deep sea, camouflage is the name of the game.
Other than making yourself attractive to a potential mate, most sea creatures rate being invisible to predators as a high priority.
Now a marine expert has discovered a unique octopus and squid that can change camouflage at will.
The Japetella heathi octopus and the Onychoteuthis banksii squid share the ability to change from a transparent state to an opaque red colour.
Both states are enough to baffle all comers in the mid-level ocean - where the sun's rays barely penetrate.
At a level of 2,000 to 3,000 feet below the surface, most predators spy the silhouette of their prey from underneath - against the lighter backdrop above.
In this case, it pays to be transparent, which is the default state of the octopus and squid.
Sharp-eyed predators would be able to see both creature's eyes and guts - which for obvious reasons cannot be transparent.
But the octopus and squid have evolved so that both their eyes and guts are reflective - further cutting down their silhouette.
With silhouette spotters out of the way, the only thing to worry about is happening upon a hungry 'searchlight' fish, such as the angler fish.
These amazing creatures use 'bioluminescence' to light up the darkness around them - both luring curious fish and exposing others.
The reflective eyes and guts of the octopus and squid would clearly give their location away.
So the Japetella heathi and the Onychoteuthis banksii turn an opaque red colour - effectively making them invisible in the deep.
Duke University post-doctoral researcher Sarah Zylinski said both species instantly turn on skin pigments, called chromatophores, to achiefve the opaque colour.
During experiments in 2010, Dr Zylinski shined blue-filtered LED light on specimens of both creatures to watch them rapidly go from clear to opaque.
She noted that when the light was removed they immediately reverted to transparent.
Further tests this year, Dr Zylinski found that both species reflected twice as much light in their transparent state as in the opaque state.
She said shallow-water cephalopods will change their body patterns for a shadow or shape passing overhead, but deeper water animals do not.
Both the Japetella heathi and Onychoteuthis banksii tracked the movement of probes and objects moving around them, but stayed transparent.
It was only when they were exposed to light, an unusual phenomenon in the depths, that they went opaque.
Dr Zylinski said: 'Smaller young animals are found higher in the water column and have fewer chromatophores, so they are more reliant on transparency, which makes sense because there won't be predators using searchlights there.'
But the mature adults have a higher density of chromatophores, making them potentially more opaque, and they can be found in deeper waters where bioluminescence becomes the dominant light source.
