Octopus vs Squid

Do you know the differences between these clever creatures?

We describe them as strange, smart, fascinating, and amazing. Squid and octopuses are unique invertebrates because of their eight arms (squid also have two long tentacles, for ten limbs total) and their highly developed nervous systems. They belong to the kingdom Animalia and are in the phylum Mollusca. Over 289 species of octopuses and 300 species of squid live in our oceans worldwide. Let’s take a close look at these incredible animals.

A common octopus. Octopus vulgaris
A common octopus. Octopus vulgaris. Credit: Wikimedia/Albert Kok
A shoal of squid. Loligo vulgaris, Credit: flickr.com/Museos Científicos Coruñeses

Table of Contents

Is it an octopus or a squid? Physical differences to remember

Octopuses and squid are marine animals belonging to the scientific class of Cephalopoda. Cephalopoda comes from the Greek plural (κεφαλόποδες, kephalópodes) which means “head feet.” Squid and octopuses have arms connected to their heads, so they belong in this scientific classification.

The suckers of an octopus
The suckers of an octopus. Serena Repice Lentini, Credit: unsplash.com/Serena Repice Lentini

It’s commonly known that an octopus has eight arms—the word “octopus” means “eight feet”! But did you know these arms have rows of suckers underneath them? An octopus may have as many as 280 suckers on each arm. The flexible arms give the octopus the ability to walk, handle food, and attach itself to rocks or coral.


The head of an octopus is round, and its body is called a mantle. The mantle contains the animal’s organs. Its stomach, gills, ink sac, reproductive organs, and intestines are located here. The octopus has three hearts. Yes, three! Even more astonishing, the octopus has nine, count them, nine brains! The mantle also contains the liver and kidneys. Octopuses have a beak, which is used to chop food into smaller pieces.


Octopuses come in a variety of sizes, from the tiny Octopus wolfi which is about an inch long (2.5 cm) to the Pacific octopus (Enteroctopus dofleini) that measures 16 feet (5 m). A common octopus (Octopus vulgaris) can range from 12 to 36 inches long (30.5 to 91.4 cm).


Unlike an octopus, a squid has a triangular head. It has eight arms that are located on the head and circle the mouth. A squid also has two tentacles that are used primarily for grabbing and holding prey. Squids have hooks, suckers, or sucker rings on their arms. A Caribbean reef squid (Sepioteuthis sepioidea) uses suckers on its tentacles to capture its prey. A colossal squid (Mesonychoteuthis hamiltoni) has hooks on its arms to snag its food.

Caribbean reef squid
Caribbean reef squid. Sepioteuthis sepioidea., Credit: Wikimedia/Jan Derk

Like the octopus, the squid’s mantle contains a stomach, gills, digestive organs, ink sac, and reproductive organs. Comparable to the octopus, a squid has three hearts and nine brains. Two fins, located on the mantle of the squid, aid in movement. The chitin beak on the squid helps break apart prey.


Squid come in diverse sizes, with the Southern pygmy squid (Idiosepius notoides) measuring 0.629 inches (1.6 cm) to the Antarctic squid (Mesonychoteuthis hamiltoni) measuring a whopping 39 feet (11.8872 m).

Habitats of squid and octopuses

Octopuses are found in the world’s oceans. They survive in both warm and cold oceans. They conceal themselves under rocks and in coral, making a den. Octopuses live in their den for around fourteen days and then head off to find a new place. They tolerate depths up to 2,000 m (6,600 ft) but also live in shallow water.


Like octopuses, squid live in the world’s oceans, usually in shallow waters and up to a depth of 3000 m (9800 ft). Some species live in hydrothermal vents deep in the ocean. Squid swim constantly, and are pelagic, meaning they are found in the upper layers of the open sea.

How do squid and octopuses move?

An octopus swims quickly by using jet propulsion. This action helps it escape sneaky predators. How does it work? It pulls water into its muscular mantle and forces the water out through the siphon. The octopus then swims backwards through the water, like an exploding rocket. An octopus walks with its arms on the seabed or on a beach if it gets caught in a low tide.

Octopus in sand. Barcelona Spain
Octopus in sand. Barcelona Spain, Credit: pexels.com/Alexinphotography World

Squid also use jet propulsion to speed through the water. Like the octopus, the water is drawn up into the squid’s siphon and forced out for locomotion. Squid use their jet propulsion to accelerate toward prey, and their fins to steer.


Both the octopus and the squid can change directions by changing the position of their siphon. They speed up and slow down by changing the force of water pushed through the siphon.

How do squid and octopuses catch prey?

Octopuses use their excellent vision and sense of touch to catch prey. An octopus searches for food by poking its arms into rocks and crevices. Once it locates the food, it uses its arms to grab the prey and wrap it up, preventing escape. An octopus kills its prey by injecting toxins into them through its beak. It can drill into a clam by using the hard beak to reach the food. An octopuses’ amazing arms have sensory endings that allow it to “taste” food. Octopuses consume clams, mussels, lobsters, crab, and fish. They also eat snails and sea slugs.


The diet of squid consists of clams, oysters, fish, shrimp, and crabs. A small squid will feed on plankton. Large squid will feast on herring, eel, cod, and fish. A giant squid will eat shark and deep-sea fish. A squid shoots out its two tentacles to grab its prey. The tentacles’ hooks prevent the prey from escaping. It will devour its food by crushing and chopping it with its beak.

How do they escape predators?

Squid and octopuses have unique adaptations for survival. Both have ink glands that produce ink, which they use for defense. The ink is stored in an ink sac until they need to protect themselves from enemies.


Squid have the remarkable ability to escape predators by releasing a cloud of blue-black ink. This ink is released through their rectum with a jet stream of water. The ink prevents the predator from finding the squid, giving it time to swim away.


An octopus uses black ink to obscure a predator’s view by ejecting the ink with a burst of water. For example, if a crab is sneaking up to eat an octopus’ eggs, the octopus releases the ink.


Another defense mechanism of these creatures is the ability to camouflage themselves. Their skin contains color changing cells called chromatophores. These cells have a small sac of pigment that holds black, brown, red, orange, or yellow colors. When the sacs are stretched and relaxed, the colors become brighter or darker allowing the animals to blend into their surroundings.

How do squid and octopuses reproduce?

First, a male and female octopus find a safe area to sit by each other. Next, the male uses a specialized arm called a hectocotylus to transfer sperm to the female. He mates only once, then dies. He stops eating, and death can occur quickly in fourteen days or after several months.


The female octopus lays her eggs in her den. She lays anywhere from 30,000 eggs up to 100,000 eggs. She protects them with dedication until they hatch, fending off predators. While guarding the eggs, she stops eating, and does not leave them to hunt. She passes away after all the eggs are hatched

Giant Pacific octopus’ eggs
Giant Pacific octopus’ eggs, Credit: fisheries.noaa.gov

A male squid gives a sperm packet, called a spermatophore, to a female using the hectocotylus. The female stores the sperm inside her body or on her arms. When she is ready to release her eggs, the sperm and eggs mix in a jelly-like substance. Incredibly, she holds this mass in her arms until the eggs are all fertilized. A mass can contain 3,000 or more eggs. The eggs are released into the water and hatch in about two weeks. Neither parent stays nearby to protect the juvenile squid.


Pen: The pen of the squid is considered an internalized shell, like the mineralized external shells of other mollusks. Pens are commonly transparent, tough, and flexible. The pen protects internal organs and is a place where muscles attach.


Mantle: The main part of a cephalopod’s body containing all the organs. It is the pocket of skin that covers the body.


Siphon: A tube-like structure through which water (or, more rarely, air) flows.


Beak: A structure used to cut and crush prey. It’s made from a hard substance called chitin.


Pelagic: Inhabiting the upper layers of the open sea


Camouflage: A defense tactic on which organisms blend in with their surroundings


Chromatophore: A cell that contains pigment


Hectocotylus: A modified arm used by male octopuses and some other cephalopods to transfer sperm to the female.


Adaptation: Any heritable trait that helps an organism, such as a plant or animal, survive and reproduce in its environment


Hydrothermal vents: Naturally-forming structures found in the ocean that usually occur where tectonic plates are moving apart. Ocean water gets heated to extreme temperatures when seeping through the Earth’s crust.


Spermatophore: A capsule surrounding a mass of spermatozoa, produced by the male of various animal species, and transferred to the female

Readability: 68.6


Flesch Kincaid Grade Level: 6.4

Scales, Helen. What is the difference between a squid and an octopus? August 13, 2022



What’s the Difference? Octopus vs Squid



Squid vs Octopus. https://www.diffen.com/difference/Octopus_vs_Squid


Arnst, John. What’s the Difference Between Arms and Tentacles? January 24, 2022. https://www.livescience.com/difference-arms-tentacles


Reddy, Deepthi. Squid Tentacles. How Many Do They Have and What Purpose Do They Serve? November 09, 2021.



Octopus Habitat. https://octopusworlds.com/octopus-habitat/


How Does an Octopus Change Its Colour and Shape? July 23, 2021



Sranko, George. Why Do Male Octopuses Die After Mating? https://biogeoplanet.com/why-octopuses-die-after-mating/


Squid Watching Over Eggs. https://ocean.si.edu/ocean-life/invertebrates/squid-watching-over-eggs

Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.

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  • Lisa Endicott

    My passion for science is rooted in my love and curiosity for nature and animals. I have successfully taught biology, health and English as a Second Language classes for 27 years in Madison, Wisconsin. I earned degrees in Biology and Life Science education along with a Masters in reading education from the University of Wisconsin, La Crosse. I completed my English as a Second Language certificate at the University of Wisconsin, Madison. I find teaching most rewarding when students dig deeper into lessons to answer their own questions. I am excited to write for Smore Science to share the extraordinary world of science. Young women, you belong in STEM careers. We need your voices and your talents. Embrace risks and challenge yourselves.