There’s a reason why squids and octopuses are often confused with each other. For one, they are both classified as cephalopods, with heads and arms that they use for swimming and catching prey. But while they may resemble each other, they do have their physical differences and unique hunting methods, not to mention habitat preferences.
So what is the difference between a squid and an octopus? Let’s find out below.
Squid vs Octopus
To help you understand squids and octopuses better, we’ll describe their differences and similarities when it comes to biological classification, anatomy, size, lifespan, habitat, and hunting behavior.
Both squids and octopuses are cephalopods, which means “head-footed” as they have no real feet and their head is their most prominent feature. They’re also both invertebrates and mollusks, and they both have eight arms. And, unlike other mollusks, neither one has a shell.
Squids and octopuses are built similarly, but you can tell they’re different creatures just from their appearance. The octopus has a round head and eight arms that radiate from it like the spokes of a wheel. The squid has a triangular head, eight arms in the rear, two extra long tentacles, a long body, and a bony plate called a “pen” that’s a vestigial remnant of its mollusk shell.
You’ll also notice that a squid has two fins on their head, while the octopus has no fins at all—except for some deep-water species like the Dumbo octopus, which was named for the ear-like fins on its head that resemble the large, floppy ears of Disney’s Dumbo (the elephant).
Both squids and octopuses have suckers on their arms, but the two extra tentacles on squids are equipped with specialized hooks and sucker rings with teeth attached.
Interestingly, both have squirt ink and copper in their blood. The copper is what helps transport oxygen within the animals’ bodies and makes their blood blue.
Many believe squids are the much smaller kind. Surprisingly, squids normally grow between 60 centimeters to nearly 20 meters long—although the smallest species of squid, the sepiolid, is under an inch long. Octopuses, on the other hand, only grow anywhere between 1 centimeter to 9 meters.
Another key difference between squids and octopuses is their life expectancy. Considering their size, both have a pretty decent lifespan. Squids normally live between 9 months to 5 years, while octopuses can survive anywhere between 1 to 3 years.
Squids can be found in various areas of the open sea, from shallower waters to the darker depths of the ocean. On the other hand, octopuses prefer the seafloor level, whether it be shallow or deep waters. In fact, this is why you’ll find octopuses living in rubbish that have sunk to the bottom of the ocean floor.
Due to their anatomical differences, their hunting techniques can vary. Squids swim in the open ocean in groups and use their two extra tentacles with sucker rings to give them a little extra reach and help catch fish and shrimp, which they’ll then eat in chunks.
Octopus, on the other hand, stay on the seafloor and eat bottom-dwelling crustaceans, because their soft bodies make them vulnerable to predation. They grab, pierce, and inject poison into their prey to paralyze it. They will then dissolve and loosen the prey’s meat using their saliva before ripping it apart using their beak and mouth.
Comparison Table: Key Differences Between Squid and Octopus
|Plural||Squid (collective); Squids (2 or more species)||Octopodes; Octopi; Octopuses|
|Found in||Saltwater, open ocean||Saltwater, dens of the seafloor|
|Nature||Solitary or living in schools||Solitary by nature|
|Anatomy||Mantle, head, 2 fins, 8 arms, 2 tentacles with hooks and sucker rings||Mantle, head, 8 arms with 1 or 2 rows of suckers without hooks|
|Shell||Has a bony structure called a pen, which serves as its flexible backbone||None|
|Fins||2 on their head||None, except for rare few found in deep water|
|Size||Up to 60cm (average squid); 13 to 20m (giant squid)||1cm to more than 5m|
|Life Span||9 months to 5 years||1 to 3 years|
|Hunting Behavior||Catches food with two long tentacles and eats in chunks||Grabs and pierces into prey to inject paralyzing venom, dissolves and loosens meat with saliva, rips prey apart using beak and mouth|
|Food Source||Fish and Shrimp||Bottom-dwelling crustaceans|