What if you live in a world where you’re able to be weightless all day and supported by a cocoon of water? Do you NEED bones? Nope. So, do octopus have bones? They have ZERO bones, and yet they still have structure to them. How do they manage to be anything more than a blob? Let’s take a look at how octopuses maintain their shape and have lived a happy bone-free life in the ocean!
To perform all these activities, an octopus’s 8 important appendages must be flexible, muscular, and rigid!
… But how are they able to be ridged without bones or a spine?
Does an octopus have a skeleton?
An octopus skeleton is essentially made up of water, and it’s all thanks to their hydrostatic skeleton!
With the help of the dense muscles that make up their arms, they pressurize water inside their bodies, allowing them to keep their shape. All an octopus has to do is flex to make its arm rigid!
By controlling the pressure that they exert on the water inside their bodies, they can make their arm like jelly to get through nooks and crannies in rocks and then stiffen up to grab hold of a prey item.
Unlike bone structures with rigid skeletal elements, the octopus can:
- Shorten at MULTIPLE locations simultaneously!
🐙 Fun Fact 🐙
What’s cool is that it’s not only the arms of the octopus that consists of muscular hydrostats… it’s basically the ENTIRE octopus.
Muscular-hydrostatic support is used to:
- Create pressure in the suckers
- Support and create a movement of the beaks
- Provide muscular action for the mantle during respiration and jet propulsion
- Provide support and muscular action to a variety of other structures and organs!
Just out for a stroll…
Octopuses also use their unique skeleton to push heavy objects away and carry objects around for protection by rising up and “stilt walking.”
The Coconut Octopus is capable of bipedal movement, which means ‘walking’ on two arms with a ‘rolling gait’, although sometimes they’ll use three or four. The behavior above is known as “the moving rock” trick, where an octopus will keep most of its arms tucked in close to its body and glide across the ocean floor.
While the hydrostatic skeleton is the most prevalent skeletal form amongst invertebrates, it is also found in vertebrates. An elephant’s trunk and your tongue are also examples of a hydrostatic skeletal system at work!
Note: Learn more about this amazing system and all the cool stuff octopuses can do with their arms.
🐙 Fun Fact 🐙
Invertebrates all over the world have nifty ways of keeping their body shape without the help of bones.
Lobsters and crabs have exoskeletons made from chitin that they need to molt out of to grow. Jellyfish are made up of a literal jelly-like substance called mesoglea, and sea sponges are a dense network of fibers made out of collagen.
Why do octopuses need no bones?
Octopuses don’t really have the need for the structural support of bones because many live in complex environments or habitats with lots of holes and crevices. It serves them better to be super flexible in many ways!
An octopus can fit into small spaces, squeeze through tiny openings and cracks and hide in areas that would be inaccessible to most predators, which are vertebrates.
Octopuses seem to have infinite degrees of freedom by being flexible enough to squeeze their whole body into impossibly tiny spaces! How tiny? National Geographic observed a 600lb octopus squeezing through a hole the size of a quarter— isn’t that nuts?!
While it’s handy to be crazy flexible, it also makes you a squishy treat, so octopuses rely on natural structures of the ocean for protection, such as rocks, corals, and for some species, shells, and coconuts.
They also have fantastic camouflage skills to pull out of their bag of tricks as well.
Are there any hard parts on an octopus?
YES, but they aren’t bones!
Octopuses have a hard beak, surrounded by muscles called a buccal mass which they use to crush their food. It is primarily made from chitin (lobsters and crab exoskeletons are made of the same thing!), and it’s similar to the cartilage that makes up our fingernails.
A study of Humboldt squid beaks found they contain 4 key elements:
- Dark pigment
The base of the beak is mostly made of water, with levels of protein increasing near the stabbing beak end, making it the stiffest portion of the beak.
Makes sense, right?!
You would want the part of your mouth meant to shred crab meat fish flesh and crack into clam/crab shells to be the toughest.
With no bones to leave behind, are there any octopus fossils?
Again, the answer is YES!
Soft tissue does not preserve well, so the cephalopod fossil record is primarily made up of ancestors who had external shells like the ammonites and nautiloids (the nautilus is the only living relative from that group!).
While squid and cuttlefish still have internal shells, many octopuses have lost theirs completely, which makes finding fossils of them incredibly unique!
The latest octopus fossil found!
Just recently, a 330-million-year-old, well-preserved TEN-armed octopus fossil was found in Montana. This exciting discovery pushed back the time frame of when vampyropods (an ancient cephalopod group to which octopus belonged) appeared in the ocean by 82 MILLION years.
This means octopuses were around BEFORE the dinosaurs!!!
We know they’ve been planning world domination for a while, but maybe they’re closer than we realize! It’s so impressive because the last fossilized octopus was found in 1982 in France and was ‘only’ 165-million-year-old.
This fossil is also the first vampyropod fossil that has 10 arms instead of the usual 8 that we see in today’s octopus.
I know what you’re thinking… wouldn’t they be related to squid then? Not necessarily – if you consider our elusive vampire squid who falls within the vampyropod group and has 8 arms AND 2 filaments they use for feeding.
Note: Check out this post to find out more about all the cephalopod tentacle and arm configurations!
So… do octopus have bones?
Bones aren’t the only shape creator in town! Depending on where you live and what you do, bones can be a completely overrated and unnecessary body part.
If you want to educate yourself some more about all sorts of different cephalopods, take a look at our encyclopedia. Or, what we call it, our Octopedia!
Connect with other octopus lovers via the OctoNation Facebook group, OctopusFanClub.com! Make sure to follow us on Facebook and Instagram to keep up to date with the conservation, education, and ongoing research of cephalopods.
More Posts To Read:
- 8 Octopus Facts (You’ve Probably Never Heard Of)!
- How Do Octopus Mate?
- Cuttlefish Quidditch: Learn About Cuttlefish Migration!
- A Dreaming Octopus? Let’s Look At Cephalopod Sleep Cycles!
- 7 Jaw-Dropping Caribbean Reef Octopus Facts
Corinne is a biologist with 10 years of experience in the fields of marine and wildlife biology. She has a Master’s degree in marine science from the University of Auckland and throughout her career has worked on multiple international marine conservation projects as an environmental consultant. She is an avid scuba diver, underwater photographer, and loves to share random facts about sea creatures with anyone who will listen. Based in Japan, Corinne currently works in medical research and scientific freelance writing!