Cephalopod Curiosities

Nela Kolčáková

            Octopus is a fascinating animal. It has stunning camouflage abilities, a complex nervous system, and a visual system which might have even better design than our own. However, the first and perhaps unexpected problem that one must tackle when trying to talk about the octopus is the plural form of the word. Is it octopi, octopuses or octopodes?

            The word “octopus” has Greek origins. It is a combination of the roots oktō meaning “eight” and pous meaning “foot”. Since some words that come from Greek or Latin keep their ancient plural form in English, like criterion – criteria or thesis – theses, it would be reasonable to assume octopus would be the same. Using the Greek grammar rules, the correct pluralization of octopus should be “octopodes”. However, the word “octopus” did not come directly from Greek. It actually came to English from Modern Latin. That adds a bit of weight to the argument that the plural of octopus should be “octopi”, similar to cactus – cacti or thesaurus – thesauri. And at last but not least, octopus is now a word in English, so English rules can be applied to it, which is the reasoning behind the plural “octopuses”. In the end, there is no organisation which dictates the norms of English, and major dictionaries disagree on which forms are correct and which are incorrect, so it is largely left to personal choice. The safest bet is “octopuses” because everyone will definitely understand it. However, if you ever want to sound fancy or start a long debate about etymology, you can try using “octopodes”.

            Moving on from the linguistic aspect of octopuses to the more physiological ones, there are many fun facts pertaining to these magnificent molluscs. Take their cardiovascular system, for example. They have a closed circulatory system, just like us but if you have seen Finding Dory, you may know that octopuses have three hearts. One of the hearts is called systemic and it is the main heart that pumps the blood around the body to the organs. The other two hearts are branchial hearts, and they help pump the blood through the gills. However, there is more to the octopus’s hearts. The systemic heart does not function while the octopus is swimming, so the cephalopod can only swim for short distances and it prefers crawling. Nevertheless, crawling does sound like a rather unrefined term to refer to a creature that has blue blood. Indeed, many molluscs, octopuses included, have hemocyanin with copper instead of haemoglobin with iron in their blood. This gives the blood a blueish hue rather than the red we are used to in humans. It is beneficial for octopuses to have hemocyanin, because it is better for transporting oxygen in cold environments. So, since octopuses are blue-blooded and hence of noble origin, it might be more appropriate to say that this creature elegantly perambulates along the seafloor.

Octopuses are also known for their camouflage abilities. It is natural to imagine that the main use of these abilities is hiding from predators and prey. However, cephalopods use them to communicate with each other as well. They can completely change their skin colour and skin texture in a matter of seconds. This is possible thanks to various types of specialised cells with pigments (chromatophores) and with abilities to reflect light (iridophores), and the papillae on the skin of the octopus. These papillae can change their shape, which helps smoothen or roughen the skin. Another factor contributing to the camouflage is the unique way the octopus’s nervous system is structured. Its brain has a central part, which contains around 10 % of all the neurons present in the body, and two large optical lobes containing about 30 %. The remaining 60 % of the neurons are in the skin and in the tentacles, which gives octopuses precise control over them. On the whole, octopus’s nervous system is much less centralised than our own, because each tentacle has its own cluster of neurons – a ganglion – which acts something like a substitute for a brain and the spinal cord, allowing the tentacles to move independently of each other. The huge range of movement that octopuses display is even more impressive because they are invertebrates. They have no bones or joints hence they can bend their tentacles in any direction.

            Another interesting thing about the octopus are its eyes. Humans have very complex camera-type eyes. Surprisingly enough, cephalopods have camera-type eyes too. In the human eye, the retina – where the cells detecting light and colours are – is inverted, which means that the light-detecting cells aren’t facing the opening of the eye. This makes connecting the optic nerve to the retina a bit more complicated since it creates a blind spot. Octopuses do not have an inverted retina and thus have no need for a blind spot. Some might say that the octopuses evolved better eyes than humans. However, there is a catch. Since octopuses have only one type of light receptor, they are thought to be colour-blind. How can they change colours so expertly to blend in with their surroundings, then? No one really knows yet, but there are some theories. For example, cephalopods have very weirdly shaped pupils. Octopuses´ pupils generally have a rectangular shape, but cuttlefish and squids can have U-shaped or W-shaped pupils. It is thought that the wide pupils boost the effect of chromatic aberration and allow the cephalopods to detect colours in a different way than humans do.

            The research about octopuses has various practical uses, for example in robotics or artificial intelligence. There are many other things we do not know about these fascinating creatures yet, but based on what we have seen so far, any further discoveries are bound to be breathtakingly amazing.


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Sanders, R. (2016, July 5). Weird pupils let octopuses see their colorful gardens. Berkeley Newsnews.berkeley.edu/2016/07/05/weird-pupils-let-octopuses-see-their-colorful-gardens/