Octopuses are marine invertebrates, classified as cephalopods, known for their intelligence and problem-solving abilities. As aquatic animals, they efficiently manage breathing and chemical sensing, leading many to wonder if they use structures comparable to a mammal’s nose. Their unique biological systems for acquiring oxygen and navigating their world reveal a physiology far different from land-based organisms.
The Anatomical Reality
Octopuses do not have a nose, nostrils, or any dedicated nasal cavity structure resembling those found in terrestrial vertebrates. Their anatomy is fundamentally different, lacking a central facial organ for breathing or smelling. The functions a nose performs in mammals are instead distributed across several specialized organs. These cephalopods rely on distinct, separate mechanisms for gas exchange and chemical detection, reflecting their evolutionary path as aquatic mollusks.
Respiration: Breathing Without Lungs
The octopus draws oxygen from the water using a pair of feathery gills housed within the muscular mantle cavity. To breathe, the octopus draws seawater into the mantle cavity through an aperture near its head. Muscular contractions then force this water across the gill filaments.
As the water passes over the gills, dissolved oxygen diffuses into the bloodstream, and carbon dioxide diffuses out. This gas exchange is efficient because the octopus has two branchial hearts, which pump blood through the gills to maximize oxygen uptake. The oxygenated blood then returns to a third, systemic heart, which circulates it to the rest of the body.
The deoxygenated water is expelled forcefully through the siphon or funnel, which also serves for jet propulsion. Octopuses also respire through their skin via cutaneous respiration, which accounts for a significant portion of their total oxygen intake.
Chemoreception: The Sense of Smell
Octopuses perceive the chemical landscape of their environment through specialized receptors on their arms and suckers. Their eight arms are lined with hundreds of suckers, and each is equipped with chemoreceptors that allow the octopus to “taste” what it touches. This powerful “touch-taste” sense allows them to explore and identify objects and potential threats.
These sensory cells function as a contact-dependent chemosensory system, detecting molecules that do not easily dissolve in water. They can detect terpenoids, often released by marine invertebrates as defense signals. The arms can use these receptors to make independent decisions without constant input from the brain. Octopuses also possess chemosensory pits on the skin of their mantle that detect scents from a distance.