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217. Day Octopus (Octopus cyanea) (breathing mechanism)


A Day Octopus (Octopus cyanea) is partially hidden between boulders on a Mauritian reef.

The behaviour of this octopus is not very interesting, but by doing almost nothing, at least nothing observable, the camera catches the octopus’ interesting breathing mechanism.

Octopuses, like most living things, submerged or not, need oxygen to live. Just like most underwater animals, the octopus extracts this oxygen through gills. The cephalopod’s gills are located inside the animal’s mantle cavity. The scientific name for an octopus’ gills is ctenidia. The mantle opening pumps water into the cavity, and the capillaries in the feathery filaments of the gills extract the oxygen from the seawater and release the carbon dioxide. Unlike mammals that use haemoglobin to absorb the oxygen and carbon dioxide and carry it through the bloodstream, octopuses, like most gastropods, use haemocyanin.

Haemocyanin has a bluish colour, tinting the octopus’ blood blue.

Two of the octopus’ three hearts, also called “branchial hearts,” pump the oxygen-poor blood to the gills; then the oxygen-rich blood is pumped via the main heart, also called the “systemic heart,” to the rest of the cephalopod's body. Each gill has its own branchial heart. Every several breaths, the octopus squeezes the accumulated water, now poor in oxygen, through its siphon out of its mantle cavity into the ocean, deflating its mantle cavity. This siphon is a hollow muscular structure near the base of the octopus’ mantle. Forceful squeezes can also be used to create a jet-like propulsion.

Octopuses use ink as a defence mechanism to fend off potential predators. The ink is produced and released from ink sacs that are located between the animal’s gills. The black ink, which mainly consists of melanin, is squeezed out of the mantle cavity and dispersed with the aid of the siphon, usually combined with a strong propulsion to escape and confuse the eventual predator. Most cephalopod species produce ink with the exception of all nautilus species and deep-sea octopuses. There is another gastropod species that can produce ink; the sea hares (Aplysia species), a large opisthobranch mollusk.

Besides breathing through its gills, the octopus also breathes through its skin in a process called cutaneous respiration. The needed oxygen is absorbed by its skin and directly delivered to the bloodstream, where it’s transported to the rest of its body.

Besides being a great organ for respiration, the octopus’ skin is also used as a tool for camouflage. The octopus’ skin contains chromatophores that have the ability to change colour and papillae that can change the skin structure. Colour changing is explained in great detail in our vlog post 133.


The sound emitted by the octopus was not recorded by the underwater video equipment. It was either very subtle or the breathing did not produce any audible sounds. The only noise in the video was the release of bubbles resulting from the underwater videographer’s breathing through a regulator. This noise was removed and replaced by sound effects to accentuate the breathing mechanism of this octopus.

To retain the viewer’s attention, I opted not to add any background music (there is no music anyway under water) but subtle ambient underwater sounds to create a specific atmosphere for this short underwater video.

Filming location:

This short underwater videoclip has been filmed in Mauritius 🇲🇺

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