First rule of the sea: if it has more arms than you, leave it alone.
There is a group of creatures that is armed to the hilt with smoke screens, poisonous saliva and jet-powered escape systems. But all these spy-movie gadgets are nothing compared to their ultimate secret weapon: they can change their colour and texture to match any environment, making them virtually invisible.
Welcome to the world of octopuses, cuttlefish and squid - the ultimate masters of disguise. Their diversity is nothing short of staggering, with sizes ranging from the mere 3cm of the southern pygmy squid to the whopping 18m of the colossal squid. They're found worldwide in oceans from frozen seas or dark inky depths to the shallows of tropical reefs. If it's salty, chances are you'll find them.
These creatures belong to a class of animals called cephalopods, relatives of snails and slugs, although their intelligence and mobility is far superior. The name essentially means 'head-foot' in Greek, a reference to the characteristic arms that encircle the sack-like head.
With no bones, spines or armoured exterior to protect them in an ocean filled with hungry creatures, they've had to develop some innovative survival strategies. For over 500 million years they've fine-tuned tactics to avoid being seen and, more importantly, being eaten.
The primary form of defence is to disappear by changing colour and blending in with the background. This ability is unrivalled in the animal kingdom and makes the chameleon look like an amateur. It's a case of 'now you see me, now you don't'. What makes this even more remarkable is that they're colour-blind.
Their secret is skin deep, literally. Two layers of specialised cells in their skin hold the key. The bottom layer consists of iridescent reflecting cells that produce blue, green and red. In the top layer, little bags of coloured pigment called chromatophores are controlled by muscles. When contracted, the muscles pull the sac open, revealing the colourful pigment inside. These bags of pigment are densely packed, with up to 200 in a patch of skin the size of a pencil tip. Scientists estimate there are around 20 million of these little bags of pigment beneath their skin.
Imagine the processing power needed to coordinate all of these cells at once. It's not surprising then that, as a result, they have a large brain-to-body ratio - the only similarity they share with humans.
They're like swimming TV screens, but far more interesting to watch. Many species of octopus and cuttlefish even change the texture of their skin for added effect. These incredible survival strategies are used in camouflage, communication and courtship.
Trickery and deception
Camouflage is a clever survival strategy as it minimises the risk of confrontation, physical damage and potential loss of limbs. This group of underwater aliens disappears into the background by taking on the colours of their surroundings in an instant. Colour changes also work to break up the body outline, confusing predators even more. Some species also modify their body postures, flattening themselves out or holding their arms in certain positions so they appear to be a part of the scenery. This helps them avoid the mouths of hungry hunters such as birds, whales, dolphins, seals and fish.
It also works in reverse, allowing them to sneak up on unsuspecting fish, crab, shrimp and small sharks. The element of surprise, coupled with eight sucker-covered arms - and a pair of shooting tentacles in squid and cuttlefish - is usually a fatal combination for potential prey. Their victims are devoured with a bird-like beak and digested through the middle of their doughnut-shaped brain. Nothing about these animals is normal. It's so effective, their own relatives (who they've been known to eat) don't see it coming until it's too late.
If the camouflage strategy fails, some cuttles go to the opposite extreme, putting on a dazzling light show by quickly expanding and contracting their coloured bags of pigment. The result is a pulsating display of stripes across their body and arms, a strategy thought to mesmerise prey before striking.
The southern dumpling squid has even more tricks up its tentacles. As a night dweller it actively harvests bacteria to help it blend into the surroundings. By day, this little squid is disguised under a cloak of sand, which renders it almost invisible. If discovered, it sheds the cloak in one go, creating a brilliant decoy. By night, it uses the light-emitting bacteria it has captured, which allows the squid to light up like a starry sky, confusing any predators from below.
Colour, and the way in which it is used in the animal kingdom, can also communicate a variety of information about the animal. Being bright and bold generally serves as a warning to would-be predators that the animal is toxic to eat.
Enter the blue-ringed octopus, one of the world's deadliest animals. Preferring to stay incognito or concealed under shell rubble and rocks during the day, this neon night stalker displays its mood with vibrant blue rings as a warning to would-be predators if threatened. It also has toxic saliva capable of paralysing prey many times its size.
Unlike the blue-ringed octopus, whose colour advertises its potency, some species use colour as a bluff. The aptly named striped pyjama squid, with its bold black and white stripes, screams 'I'm poisonous'. To make it even more convincing, when threatened, they'll stretch out their arms to look bigger, just to get the message across. Mind you, they're only a few centimetres long.
The mimic octopus takes the concept of 'pretence' to another level. Found on the open sand and mud flats of Indonesia and Papua New Guinea, this charismatic octopus impersonates the most deadly animals on the reef. Included in its repertoire is the ability to transform into the shape of poisonous flounders, lionfish and sea snakes.
Colours can also be used in courtship, and nothing says 'I love you' more than the flashing of dramatic colours across your body... well, for this group of eight-armed lovers, anyway. It's a visual signpost that signals to the opposite sex 'I'd like to make babies with you, how about it?' But mating can make these soft-bodied animals vulnerable, so some octopuses have developed what can only be described as a 'split-colour personality' to cope.
Males will display dazzling colours on one side of their body to seduce the ladies, yet remain camouflaged on the other side. This ensures they don't attract the attention of any potential predators or rival males while they're doing their thing. Now that's some impressive multi-tasking for any male, regardless of the species.
When it comes to finding love, some giant cuttlefish will simply pretend they're the opposite sex. Sound strange? It is, but it works a treat for smaller male giant cuttles that can't compete with muscles. The scene is like any typical high school movie, except acted out in the sea. You have the bulky males, who get all the girls, and the scrawny males, who float on the sideline watching in envy. But, equipped with their colour-changing super powers, smaller males are able to take on the colour patterns and postures of the females. In their new disguise they sneak past the big males, who are too busy competing with each other for the females to notice. In a fairy-tale-ending for the underdog - or 'under-cuttle' in this case - the male then makes out with the cuttle cutie of his dreams.
This is just a small sample of the incredible diversity of octopuses, squid and cuttles that are found jetting around our oceans and how colour can conquer all. It reads like something from a circus side-show with mimics, impersonators, cross-dressers and magicians in invisible cloaks. Without a doubt, they're some of the most impressive animals on the planet and there is nothing normal about them, which makes them so fascinating.
What is even more exciting is that, as we continue to explore new areas of the ocean and look at it like never before, there's bound to be many more weird and wonderful species waiting to be discovered.
No doubt there are thousands more sitting right in front of our eyes - we just can't see them. So next time you're swimming in the sea or roaming around a rock pool, look a little closer. That piece of floating seaweed or rock might not be what it seems...