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144. Day Octopus (Octopus cyanea) (arm movement)



Subject:

Inside the hull of a small wreck, a Day Octopus (Octopus cyanea) is wriggling its arms (octopuses have eight arms, not tentacles). Their soft and highly movable arms are covered on the inside with rows of suckers that can feel, taste, and smell the octopus’ surroundings. Each octopus has around 280 of these suckers per arm, making it a total of 2.240 suckers or so in total.


Believe it or not, there is no scientific name for an octopus's suckers; they are just called “suckers”. However, the different parts of these suckers do have complicated scientific names. The soft, squishy part of the sucker that is most visible is the infundibulum and is surrounded on the edge by a mucus-like rim called the epithelium. In the centre of the infundibulum is a round cavity known as the acetabulum. Each sucker is attached to the arm by a muscular base that can rotate the sucker in any direction and elongate it to almost the double of its normal length.


The arms of an octopus can be compared to a Swiss Army knife. These multifunctional limbs are used for many different things. Besides being the octopus’s main sensory apparatus, the arms are also used for all kinds of locomotion, camouflage and mimicry, hunting, and even mating.


Each arm is controlled by an independent mini-brain. These mini-brains are clusters of nerve cells controlled, in turn, by the large central brain. Octopuses are extremely intelligent creatures and have an IQ that can be compared to that of a dog. They are masters at solving problems and have the capacity for solution thinking.


Some octopus species are also capable of using autotomy. Autotomy or self-amputation is the behaviour whereby an animal discards a body part in an attempt to escape a predator. When under attack, the octopus can shed one of its arms, similar to what a lizard may do with its tail. The arm will wriggle independently for a period long enough to fool the attacker while the octopus makes a hasty escape. The octopus has the capacity to regenerate its discarded arm. The newly regenerated arm, which can take up to 100 to 130 days to complete, is as perfect as its previous discarded one.


One of the male octopus's arms is used to store and transfer spermatophores to the female. This is done by the third arm on the right side, called the hectotylus. This specialised arm has its final 10cm/4inch or so modified into a reproductive organ.


Technique:

The movement of these arms happens completely silently underwater. Underwater video equipment records sounds on a dive; however, the recorded sounds are mainly the diver’s breath (which we can classify as noise) and the more subtle sounds are most of the time inaudible.


The slimy movement sound was added in post-production to make this underwater scene more realistic. Sounds and music enhance the storytelling aspect in underwater videos. They can add depth and emotion to a scene, help to create the right atmosphere, emphasise the mood of the story being told, and make the viewing experience more impactful.


More on this topic:

For a more in-depth description about the octopus' colour changing ability please go to our vlog post 133 or click on this link: https://www.beyondscuba.com/post/day-octopus-changes-rapidly-of-colour

For a more in-depth description about autotomy please go to our vlog post 15 or click on this link: https://www.beyondscuba.com/post/decoy-defence


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