Cephalopods - nature’s strangest creatures?

With their alien appearance yet strangely familiar intelligence, cephalopods are easily some of the ocean’s more intriguing creatures. Ask around any dive shop and you’re sure to find someone who can recall profound, and sometimes even emotional, encounters with these truly fascinating animals. And here at ZuBlu we just can’t get enough! So we thought we’d delve a little deeper into the unusual world of cephalopods - read on to find out more.

If you haven’t seen it yet, we can only assume you’ve been living under a rock - perhaps at the bottom of the ocean alongside a friendly octopus? It’s safe to say the recent Netflix documentary took the world by storm, garnering a steady-stream of praise and recently winning an Oscar for ‘best documentary’. The film, for those that haven’t yet seen it, follows the relationship between filmmaker and freediver Craig Foster, and an inquisitive young octopus in False Bay, South Africa. Throughout their relationship, Foster learns the depths of this creature’s intelligence, discovering its natural curiosity, improvisation, and just maybe, even affection. 

Of course, many of the revelations made by Craig Foster during his year with the octopus are not altogether new. Scientists have long known the extraordinary capabilities of cephalopods, and have even used knowledge of their advanced biological and cognitive processes to help tackle complex scientific challenges. 

Well the short answer is huge amounts! But for a proper explanation, we should start with what makes cephalopods so unique. Cephalopods are a family of marine-dwelling molluscs that date back to around 485 million years ago - that’s a long time before the dinosaurs and even before sharks! Today, there are four broad types of cephalopod - octopuses, squid, cuttlefish and nautiluses. All breathe using gills and have the largest brain-to-body ratio of all invertebrates. Plus, they all have multiple arms or tentacles - and yes, there is a difference.

These creatures have so many unique physiological traits, it’s hard to know where to start... But here’s a few we find most interesting.

As we mentioned, tentacles and arms are far from the same thing, and while all cephalopods have arms, they don’t all have tentacles. Octopuses, squid and cuttlefish have eight arms - but nautiluses can have more than 90! - and both squid and cuttlefish also have two tentacles. Arms have suckers, and sometimes hooks, running along the entire underside, while tentacles are usually longer, retractable and have a flattened tip where the suckers are located. 

Cephalopods move in a variety of interesting ways. For example, cuttlefish use a pair of undulating fins to maneuver through the water, while some species such as the coconut octopus, can even walk on two ‘legs’ while using the rest to maintain their cunning disguise. But easily the most common movement among cephalopods is jet propulsion. To do this, they fill their mantle cavity - which is usually used to pass oxygenated water to the gills - with water and quickly ‘shoot’ it out of their siphon. The force of the water being ejected propels the cephalopod in the opposite direction. Although all cephalopods have this ability, the efficiency of the movement differs greatly depending on the species. 

Most cephalopods have highly complex eyes that come in a range of shapes and sizes. Octopuses have a rectangular pupil while a squid’s is circular, and cuttlefish’s are a strange w-shape. Despite the differences in appearance, cephalopod eyes are often surprisingly similar to that of a human, and could be the result of a single shared gene which can be traced back to our last common ancestor, over 500 million years ago! However, cephalopods lack the specialised receptor cells that humans use to differentiate colours. So are they all colourblind? Well maybe, but maybe not. A recent study suggests that the unique shape of their pupils may act like a prism, scattering colours into their individual wavelengths and allowing the animal to process colour in a different way. 

We’ll never truly know if what Craig Foster experienced out amongst the kelp of South Africa was genuine affection from a wild animal. But if cephalopods can feel such emotions, with a total of three hearts they’d certainly have a lot of love to give. One of these hearts is used to push oxygenated blood around the body, while the other two pass deoxygenated blood through the gills. And guess what - their blood is blue, not red. This is because, instead of the iron-based hemoglobin molecules found in human blood, cephalopods use a copper-based molecule called hemocyanin. It is believed this helps them maintain oxygen efficiency in environments of varying temperature and oxygen levels.

With the exception of the nautilus, modern cephalopods have largely freed themselves of impractical and cumbersome shells. In fact, the octopus has no bones at all, and apart from a bird-like beak, it’s almost entirely soft. Clearly, this comes in handy when squeezing into cracks among the reef, or trying to mimic the free-flowing form of floating algae. Cuttlefish and squid, on the other hand, retain a single flattened bone-like structure which is used largely for balance and buoyancy. 

And while the nautilus' shell may make it considerably less agile, it is in itself an incredible feat of evolution. The shell is actually a spiral of many individual chambers containing mixtures of gas and seawater. And, by selectively increasing or decreasing the fluid within each chamber, the nautilus is able to alter its own buoyancy as it changes depths. 

Cephalopods have a well-developed nervous system which accounts for their impressive intelligence. Their brain to body ratio is the largest of all molluscs - and while that might not sound too impressive, they can also rival some mammals. Plus, in cephalopods, the central brain is only part of the picture. Large nervous structures can also be found outside of the brain, including in each of the arms. In fact, up to 60% of an octopus's neurons can be found outside of the central brain, making things such as basic arm movements more or less autonomous.

Easily one of the most astounding of all cephalopod behaviours is the ability to change colour. Without the protection of a hard exterior shell, squid, cuttlefish and octopuses rely on sophisticated skin tissues to blend in with their surroundings and avoid detection by predators. Chromatophores are pigment-containing organs that can be dilated and contracted beneath the skin to reveal a specific amount of colour. But, the pigment within these organs is typically only red, yellow, or brown. So to create a wider range of colours, these masters of mimicry use a secondary layer of structures called iridophores. These stacks of thin cells reflect light back at different wavelengths, effectively changing the creature’s colour in the viewer’s eyes. And that’s not all! Cephalopds also use protrusions of skin known as papillae to match the texture of their surroundings and blur any identifiable edges. How cool is that?

Unsurprisingly, cunning cephalopods will often utilise several of these incredible abilities in the hunt for food. Cuttlefish are masters of distraction, dazzling their prey with raised, swaying arms and hypnotising waves of colour passing rhythmically over their body. Visual attacks like these can also be observed in octopuses, as well as ambushing, luring, stalking, and even hunting in disguise. Incredibly, cephalopods have also been documented using tools to give them a ‘leg-up’ on their prey. Pygmy squids, for example, will release ink between themselves and their prey, and then launch an attack through the darkness. 

As you’ve probably guessed by now, nothing is simple in the world of cephalopods. In fact, when it comes to these remarkable creatures, we could happily talk about them for days. Want to find your own ‘Octopus teacher’? Our team of dive travel experts know all the top destinations and best seasons for the ultimate cephalopod experience, so get in touch and start planning yours today.