Octopus anatomy is strikingly different from the human body, unless you’re Dr. Otto Gunther Octavius. Eight arms are the most obvious trait, but beneath the mottled skin there’s actually an array of brains, one for each tentacle. And just how many hearts does an octopus have? The answer is a surprising three, and each has an important function, so they’re not just spares.
These facts are just the tip of the iceberg for one of the more specialized creatures under the sea.
How Long Does an Octopus Live?
With such a uniqueness in octopus anatomy, you’d expect these cephalopods to live forever. Sadly, no. The usual life span in the wild is only around one to two years for most species, according to National Geographic.
The Nature Conservancy Council of Canada notes that the largest species, the Northern Giant Pacific octopus, is also the longest lived. It reaches up to around five meters in length and between 20 and 50 kilograms in weight (about 16.5 feet and between 44 and 110 pounds), and dies at around five years old, usually after mating or laying and caring for eggs.
Scientific American blogged about the loss of the National Zoo’s resident octopus, Pandora, who had been entertaining visitors in her tank for 27 months, which is quite a record for an octopus.
How Many Hearts Does an Octopus Have?
An octopus has not one, but three hearts.
Two of them — the branchial hearts — pump blood to the gills where it picks up oxygen. The third, or systemic heart, pumps the oxygenated blood around the body, fueling up the eight tentacles for whatever they and their suckers plan to do.
Octopuses are quite active as cephalopods, and it’s thought that the three hearts are necessary to maintain their power. However, when swimming, the octopus does not use its systemic heart and can tire quite easily. It creates water jets with its body mantle instead to power propulsion.
Octopus blood is blue due to the copper-based, oxygen-carrying hemocyanin it contains. Hemocyanin doesn’t carry oxygen as well as a human’s iron-based hemoglobin, and New Scientist explains this might be why octopuses need more than one heart. Unfortunately, hemocyanin doesn’t carry oxygen so well in acidic conditions. Since climate change is gradually lowering the pH of the world’s oceans, the environment here may not be ideal for octopus anatomy in the future.
Another reason for the impressive array of hearts is due to another peculiar feature of octopus anatomy: They have a mini brain in each of the eight tentacles, which helps each arm act independently with speed and sharp reflexes. A ninth brain oversees the entire nervous system and can also somewhat override the mini brain to operate each tentacle.
The brain-to-body ratio for an octopus is the largest for any invertebrate, and they have around the same number of neurons as a dog. They are known to be extremely intelligent, learning to solve puzzles in lab simulations and are also able to recognize people.
Having such a powerful and extensive nervous system takes a lot of energy, hence the three hearts to pump blood around the octopus.
Tentacles and Suckers
Tentacles, each covered in an array of powerful suckers, are used for locomotion and gathering food. Although octopuses can swim, their preferred locomotion is to crawl along the seabed. Octopuses can also use their tentacles to manipulate objects, unscrewing jars and holding food. Male octopuses use a specialized grooved tentacle called a hectocotylus to pass a spermatophore to the female during mating. The National History Museum describes how some male octopuses also leave the appendage with the female.
Octopus anatomy has inspired robot development; using biomimicry, researchers at Harvard developed a soft tentacle bot that can carefully grasp irregular objects. There have even been attempts to develop climbing robots based on their ability to grasp surfaces such as ladder rungs and rough walls.
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