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Squid vs. Octopus: Similarities And Differences Explained

If you ever interchange squid vs. octopus, you are not alone. Both ocean dwellers, these fascinating creatures have eight arms, shade-shifting skin, and a unique head shape. One of them has the unique ability to produce ink which they spew on the paths of their predators. 

They are also closely related since they belong to the group Cephalopoda (which is a group of mollusks that also includes snails and nautilus). While they share remarkable similarities, some distinct features can help you recognize the difference between octopus and squid. 

Read on as we look at the physical, biological, and behavioral distinctions between the octopus and squid. 

Related Read: Squid Facts, Octopus Facts, Alpaca vs. Llama, Tortoise vs. Turtle.

Squid vs. Octopus: Classification

squid and octopus side by side
Squid (Photo by Dan Hershman on Wikimedia Commons licensed under CC BY 2.0 (Cropped from original)), Octopus (Photo by Pia B on Pexels.)

The squid and octopus are marine animals and mollusks belonging to the same group/ family called the Cephalopoda and the Phylum Mollusca. Other mollusks in this family include nautiluses and cuttlefish. 

These two Cephalopods go their separate ways at their orders. Octopuses belong to the Octopoda. The squid belongs to a super order called Decapodiformes (derived from a Greek word that means “10-legged”). 

Below the super order, Decapodiformes is the order called Teuthida. Teuthida has suborders called Myopsida and Oegopsida.

Squids under the Myopsida order are covered-eyed squid species, while squids under the Oegopsida are open-eyed squid species. We have 300 octopus species and 300 squid species.

Squids and Octopuses: Physical Characteristics 

Octopus
Octopus, Photo: iStock.

As we mentioned earlier, it can get tricky to distinguish between the octopus vs. squid. However, some features can make it easy to distinguish between both animals. 

Let's look at some physical differences between the octopus vs. squid: 

Size 

The body sizes of squids and octopuses vary. You can find squids and octopuses from less than an inch to over 40 feet in length. The Giant Squid can grow to around 33-43 feet. The largest living cephalopod is the Giant Squid, which has a recorded length of 43 feet. On the other hand, the largest octopus species is the Giant Pacific Octopus, which is only around 16 feet.

The smallest known squid species is the Southern Pygmy squid, which is under an inch, and the smallest octopus is the Star-Sucker Pygmy, which is around 2 inches.

Eight arms

Octopuses have eight arms covered with sucker rings which they use to smell, grip, and taste. Octopuses have one of the most flexible arms they can use on the ocean floor.

The squid, on the other hand, also has eight arms, each covered with sucker rings. However, they have two tentacles covered with muscular hooks or sucker rings, depending on the species. These two tentacles are longer than their other eight arms, and they use these long tentacles to capture prey. So, the limbs of octopuses are called arms (not tentacles), while squids have eight arms and two longer tentacles. 

Head shape 

One unique characteristic that can help you differentiate the average squid from the octopus is the shape of their heads. Octopuses have a rounded head, while squids have a triangular head with two fins located on either side of their triangular-shaped head. 

The two fins look like wings, which they use to move around the open ocean. Most octopuses only have a round head with no fins except some deep water species like the Dumbo octopus. 

Octopuses typically move around by jet propulsion. 

Anatomy 

Looking at the anatomy of both squids and octopuses, octopuses have no internal skeleton and have soft bodies. But the octopus has a beak, the only hard part of its body. This beak is made of chitin, which they use to catch fish and other prey. 

On the other hand, a squid’s body has a hard internal shell called a Pen. Both the squid and octopus have three hearts, two of which pump blood through their gills. The third heart circulates blood throughout their bodies. 

Squids and Octopuses: Reproduction 

Squid
Squid, Photo by harum.koh on Wikimedia Commons CC BY-SA 2.0 (Cropped from original).

Squids mate in large groups and attach their eggs to the ocean floor, coral reef, rocks, or any fixed structure. Both parents don’t take care of their young but let the eggs hatch and let them find their way in the world. 

On the other hand, male octopuses use a specialized arm called the hectocotylus. They use this specialized arm to transfer sperm to the mantle cavity of the female1. The female octopus then lays eggs in strings, which they guard until they hatch. Depending on the octopus, this can be anywhere from a month to a year. 

The females may build protection like a wall of rocks around the eggs and remain there till the eggs hatch. 

The male octopuses and squids experience a period of decline after mating and eventually die. When they die, their bodies return to the food web, providing food for their young and other animals. 

Most squids have a shorter lifespan than octopuses, living anywhere from one to three years. On the other hand, octopuses live between one to five years.

Squids and Octopuses: Habitat                                   

Squids and octopuses prefer salty, warm water and can be found in different oceans worldwide. 

Most octopuses stick their arms to the ocean floor, propelling themselves to the top by jet propulsion. Octopuses tend to hide away in the deep, dark crevices of the ocean when they are not hunting for bottom-dwelling crustaceans. 

The most common octopus (Octopus vulgaris) is found in the Mediterranean Sea and Atlantic Ocean. 

On the other hand, squids live in the open ocean, where they can find their favorite foods, which include shrimp and small fish.  

Squids and Octopuses: Locomotion and Social Structure  

Squid
Squid, Photo by Betty Wills on Wikimedia Commons licensed under CC BY-SA 4.0 (Cropped from original).

Both octopuses and squids move around by what we already identified as jet propulsion. They suck in water into their muscular sac located in their mantle cavity and expel the water quickly. This lets them propel themselves higher, quickly altering their course and direction. 

However, squids have fins on their mantle, which they use to move themselves when swimming at low speeds. These fins help to stabilize them as they swim and wrap themselves when they propel themselves with jet propulsion2. Octopuses typically don't have fins, but some other octopuses, like the Dumbo octopus, do. 

Regarding social structure, octopuses are solitary animals, and you will typically find them across the ocean floor close to their den. Squids are also solitary creatures; most species swim and fill their belly with small fish. However, some squid species are very social. You will typically find them moving around in large groups. 

Squids and Octopuses: How they catch prey 

Octopus
Octopus, Photo by Elias Levy on Wikimedia Commons licensed under CC BY 2.0 (Cropped from original).

Octopuses use their eight limbs for catching prey and walking around on the seafloor. They also use their arms to manipulate objects around them. 

Since they mostly dwell at the bottom of the oceans, octopuses feed on crustaceans like clams, crabs, and lobsters. Octopuses inject paralyzing venom into the shells of their prey. Then, they release enzymes that loosen meat from the inner shell of the prey. 

On the other hand, squids use their long tentacles to capture fish and shrimp, tearing their flesh into bits and scraping them into their mouths. 

Squids and Octopuses: Defense Mechanism 

Sharks, whales, fish, and even humans feed on the octopus and squid. So, how do these creatures defend themselves from predators? 

When squids are threatened, they release black squid ink, destabilizing the predator and allowing the squid to dash for it. All squid species carry an ink sac, which they spray on their predator when they feel in danger3.

On the other hand, the octopus has no inks but can easily camouflage into rocks5, coral reefs, and other objects thanks to their ability to change the color of their skin. This happens thanks to the chromatophores on the octopus’s skin. 

Squid vs Octopus: Food & Fishing 

Squid
Squid, Photo by Rickard Zerpe on Wikimedia Commons CC BY-SA 2.0 (Cropped from original).

Commercial fishing is one of the biggest threats to the squid and octopus. Many fishermen trawl for these creatures using weighted chains, lowering traps, and spearfishing. Both are eaten as food in various cultures all over the world. 

All parts of the squid, including the tentacles, arms, and ink, are edible except for the beak. Fried squid rings and arms are common in Chinese and Southeast Asian cultures. In the Mediterranean, people serve squid with other dishes like pasta, soups, and risotto. 

The octopus is common in countries like Japan and South Korea. In fact, some small octopuses are sometimes eaten alive in countries like South Korea. 

Squid vs. Octopus: Population & Growth

Octopus
Octopus, Photo by Anneli Salo on Wikimedia Commons licensed under CC BY-SA 3.0 (Cropped from original).

Interestingly, only a few species of squid and octopus are endangered, threatened, or vulnerable. Squids and octopuses are among the few creatures experiencing population growth due to climate change. 

As a result of rising temperatures in the ocean, the warm salty water causes the rapid growth and development of the octopus and squid4. This causes them to breed and grow into maturity.

On the flip side, both creatures are voracious predators, which means this rapid population could lead to a decline in the type of fishes they feed on. 

Final thoughts on squids and octopuses 

So there we have it. Squids and octopuses are unique creatures that appear very similar. While both come from the same family, they have other specific features, such as how they eat, where they live, their physical features, and more, making them distinct. 

You can go through this article and find out how these creatures differ from one another. 

1

Huffard, Christine & Caldwell, Roy & Boneka, Farnis. (2010). Male-Male and Male-Female Aggression May Influence Mating Associations in Wild Octopuses (Abdopus aculeatus). Journal of comparative psychology (Washington, D.C. : 1983). 124. 38-46. 10.1037/a0017230.

2

Bartol, I. K., Krueger, P. S., Thompson, J. T., & Stewart, W. J. (2008). Swimming dynamics and propulsive efficiency of squids throughout ontogeny. Integrative and Comparative Biology, 48(6), 720-733.

3

Derby, C.D. Cephalopod Ink: Production, Chemistry, Functions and ApplicationsMar. Drugs 2014, 12, 2700-2730.

4

Doubleday, Z. A., Prowse, T. a. A., Arkhipkin, A. I., Pierce, G. J., Semmens, J. M., Steer, M. A., Leporati, S. C., Lourenço, S., Quetglas, A., Sauer, W. H. H., & Gillanders, B. M. (2016). Global proliferation of cephalopods. Current Biology, 26(10), R406–R407.

5

Alleva, Enrico & Tramacere, Antonella & Manciocco, Arianna. (2011). A catalogue of body patterning in cephalopoda. Annali dell'Istituto Superiore di Sanità. 47. 475-475.

By Jennifer Okafor, BSc.

Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.

Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.

Squid Photo by George Berninger Jr. on Wikimedia Commons licensed under CC BY-SA 3.0 (Cropped from original) and Octopus Photo by Riccardo Marchegiani on Pexels
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