Octopus Vs Squid: Differences and Similarities

An octopus vs squid has been a frequently sought comparison. The octopus is quite different from a squid even though they belong to the same class- Cephalopoda.  Cephalopoda is a class of marine mollusks that include snails, nautilus, octopus as well as squid.

However, cephalopods have similar features such as symmetrical bodies, prominent heads, absence of vertebrae, and arms or tentacles extending from their bodies. Though the octopus and squid are quite different from snails and nautilus. This is because they evolved to have bodies that don’t require the use of a hard shell for protection. Hence, they resulted in other adaptations that they developed such as the ability to camouflage, strong flexible arms, and heightened intelligence.

An octopus is different from a squid
An Octopus
Squids are different from octopuses
Squids

Ranging from the tropics to the temperate zones, squids and octopuses are found in salty water. As oceans have become polluted and less conducive, several marine populations have declined over the years. However, despite this challenge, the population of cephalopods has increased rapidly. This is because cephalopods such as octopus and squid possess certain biological traits that enable them to adapt quickly to a changing environment. Such traits include a short lifespan, rapid growth, and flexible development. Hence, cephalopods are sometimes referred to as the “weeds of the sea”.

Globally, in the ocean, there are about 300 species of octopus and nearly 300 species of squid. Octopus and squids are both marine invertebrate organisms. They may be both cephalopods but differ in their physical appearance, habitat, and behavior. Here, in this article, we will be highlighting and discussing the differences and similarities between octopus and squid as we compare them.

Differences between Octopus and Squid

  1. The head of an octopus vs the head of a squid is rounded in shape compared to the triangular head of the squid.
  2. Squids have two fins on their heads, whereas octopuses do not.
  3. Octopuses do not possess any internal structure, whereas squids have a backbone-like structure called a pen.
  4. An octopus has eight arms while the squid has eight arms and two tentacles.
  5. Squids tend to be bigger than octopuses in size.
  6. The squid lives in the open ocean while octopuses prefer the seafloor.
  7. During reproduction, the female octopuses take care of their eggs by guarding and aerating them. Squids do not render such parental care.
  8. An octopus catches its prey with its arms whereas the squid uses its tentacles to catch its prey.
  9. When feeding, the octopus makes use of venom and salivary enzymes on their prey before eating. Squids on the other hand use their radula and eat their prey in chunks.
  10. Squids are more social than octopuses.
  11. Octopuses tend to be more intelligent than squids.
  • Octopus vs squid: How they look

Head

One of the physical differences between an octopus and a squid is the structure of their head. The head of an octopus is round in shape whereas, a squid head is more triangular.

On the head of a squid are two fins that are attached to each side. An octopus, however, does not have these fins. As the squid swims the fins aid the squid in navigating its direction. At the top of the head are the complex eyes of an octopus with rectangular pupils. Whereas, the complex eyes of a squid are set in the sides of the head with circular pupils.

Body

Another difference in an octopus and squid’s appearance is their body form. Octopuses have saccular bodies whereas, squid’s bodies are elongated and tubular. Moreso, the body of a squid is strengthened by a backbone-like structure compared to an octopus. Thus, the body of an octopus is more flexible than a squid’s body for them to be able to squeeze into small spaces.

The octopus has its mantle behind its head and opposite its arm. Then, the main body mass in a squid is enclosed in the mantle. Along each side of the squid’s mantle are two swimming fins. However, it is important to note that these fins are not the main source of ambulation in most squid species.

Skeletal structure

The octopus does not have a stiff bone in their bodies. This is why they are able to squeeze themselves through small and tight gaps. Squid, on the other hand, has a stiffer structure known as a pen or gladius. This structure serves as a flexible backbone that runs along the squid’s mantle. It is made of chitin which is the same material that makes up an insects’ exoskeleton. The pen act as an attachment point for certain muscles that the squid uses for locomotion. Also, it stabilizes the squid while it swims.

The octopus, however, does not possess such an internal structure. As octopuses have no internal skeleton, their bodies are very soft compared to squid. However, the only hard part of an octopus is its beak. This beak is made of chitin and the octopus uses it to eat its prey.

Appendages

Another common and significant difference between an octopus and a squid is the number of protrusions that each animal has. An octopus is distinct from a squid by having eight arms, whereas a squid has ten of these appendages.

An octopus has eight arms that possess one or two rows of suckers that have no hooks or sucker rings. Whereas, a squid has eight arms and two tentacles, that have hooks and suckers or sucker rings. Eight of the appendages of the squid are classified as arms and two are classified as tentacles. In a squid, 2 of the 10 arms it possesses have developed into long slender tentacles with expanded ends. It has four rows of suckers with hooks and sucker rings. Thus, the squid has both arms and tentacles, which have hooks and suckers.

However, the difference between a tentacle and an arm is the suckers along the length of each appendage. These suckers cover an arm throughout its underside, whereas suckers are only at the tip of a tentacle. Thus, the octopus only has eight arms covered in suckers whereas, a squid has eight arms and two longer tentacles. The squid uses the tentacles to catch fish and shrimp in open-ocean waters. Moreso, the arms of an octopus are more flexible than the suid’s arms. This is why octopuses can use their arms to walk, handle objects, and manipulate their environment.

Octopus vs squid: Size

How are the octopus and the squid different in size? Generally, squids are bigger than octopuses.

As a matter of fact, squids in terms of total length, mantle length, and mass are the largest living cephalopods. The colossal squid (Mesonychoteuthis hamiltoni) is the largest species by at least two of these measures. They reach an estimate of 9.8 ft ( 3 m) in mantle length and about 33 ft (10 m) in total length. Also, this species is the largest of all extant invertebrates as they weigh as much as 495 kg.

However, another squid approaches these dimensions. This is the giant squid of the genus Architeuthis. The females of these squids weigh up to 275 kg. Their mantle length is about 7.9 ft (2.4 m) with a total length of as much as 49 ft (15 m ). Thus, they are likely the longest of all cephalopods.

The two largest octopus species are the giant pacific octopus (Enteroctopus dofleini) and the seven-arm octopus (Haliphron atlanticus). These two octopus species can both exceed 70 kg and the giant pacific octopus has a maximum total length of more than 20 ft (6m). Also, cirrate (finned) octopuses can reach a large size. The largest captured specimen is a Cirrothauma magna. It had a total length of 5.6 ft and a mantle length of 33 in. However, observations suggest that these species can exceed 13 ft.

Classification

The octopus and squid may belong to the same phylum and class but have other different classification hierarchies. Here is the classification of an octopus vs a squid.

  • Octopus

  • Kingdom- Animalia
  • Phylum- Mollusca
  • Class- Cephalopoda
  • Order- Octopoda
  • Family- Octopodidae
  • Subfamily- Octopodinae
  • Genus- Octopus
  • Squid

  • Kingdom- Animalia
  • Phylum- Mollusca
  • Class- Cephalopoda
  • Subclass- Coleoidea
  • Superorder- Decapodiformes
  • Orders- Myopsida, Oegopsida, Sepiida, Spirulida, Teuthida

Habitat

Generally, a squid inhabits the open ocean whereas, an octopus live usually in the cervices of the seafloor. These two animals live in saltwater, ranging from the tropics to more temperate zones.

The octopus would prefer to live in dens on the seafloor, ranging from the shallow waters to the deep. Some even inhabit bottles or other materials that happen to be at the bottom of the ocean floor. Squids, on the other hand, prefer living in the open ocean, ranging from the shallow coast to the deep depths of the sea.

The habitat of the squid is almost every saltwater body and some of the freshwater. Whereas, octopuses are barely seen in freshwater. Octopus species live in diverse regions of the sea as well as, pelagic water, coral reefs, and the ocean floor.

Feeding habit

Octopus vs Squid: What do they eat?

Generally, an octopus feeds on crustaceans from the ocean floor whereas, the squid usually eat small fish and shrimps in the water column.

Squids are carnivorous and feed basically on crabs, fishes, shrimps, and even squid. They are seen as assault predators as they can be very discreet when sneaking up on their prey to catch it before it escapes.

The bottom-dwelling octopus, on the other hand, feeds on crabs, polychaete worms, whelks, and clams. Whereas, the open-ocean octopuses feed more on fish, prawns, and other cephalopods. Also, Giant octopuses are known to kill and feed on some species of sharks.

What is the difference between an octopus and a squid in how they hunt their prey and eat?

There is a difference in how an octopus hunts compared to a squid. Several squid species hunt in groups whereas, octopuses are solitary hunters. The squid hunts in groups in order to coordinate their movement for a maximum catch.

Also, the way they feed differs. Usually, an octopus grabs its prey with its arms. Then, pierce through the shell or skin of the prey to inject a paralyzing venom. This venom weakens the muscles of the prey and causes paralysis. The octopus then releases salivary enzymes and makes the prey softer and easier to be removed from the shell. Thus, the octopus crushes it in its mouth.

However, this is different with squids. To catch their prey, the squid makes use of its two specialized tentacles. The flesh of the prey is then torn into bits. They make use of a beak-like structure called a radula to cut into the flesh of the prey. Using their beaks, squids scrape the meat into their mouths and eats the prey in chunks. The radula at the mouth of the squid has several rows of teeth that enable the squid to grind the meat before ingesting it.

Reproduction

The reproduction processes in an octopus differ from that of a squid.

In octopuses, the male makes use of a specialized arm called the hectocotylus to transfer sperm. The spermatophores are transferred into the buccal cavity of the female. However, the female octopus lays a group of eggs in strings. She lays them on the roof of her den and guards them till they hatch. While guarding her eggs, the female octopuses usually clean and aerate the eggs with water expelled from her siphon. It might take 30 days or more for the eggs to hatch, depending on the species. She may even build a wall of rocks to seal off the den and remains in the den until she dies. After the eggs have hatched, the female octopus dies afterward.

On the other hand, squids mate in large groups. During the mating period, large groups of female and male squids come together. They swim in a circle and after some time, two squids are seen swimming together. These two are the squids that will breed. After mating, the female squid lays her eggs attaching their eggs to static structures such as rocks, ocean floor, seaweed, or coral reefs. However, unlike the female octopuses, squids don’t invest in their young ones. She doesn’t wait around the eggs to hatch as she leaves after laying them. However, she may hide them from predators and leave. These eggs hatch on their own and try to make it in the open sea. The majority of squids and octopuses die after reproducing.

Lifespan

Generally, octopuses are shorter-lived with a lifespan of 6 months – 3 years, whereas squids can live for 9 months – 5 years. Shortly after mating, the male octopuses and squids usually die. However, there is an exception with the giant Pacific octopus as it can live up to five years under certain circumstances.

Social structures

The social structure of an octopus is quite different from that of a squid. An octopus is a solitary animal compared to squids that can live in schools or independently.

Generally, octopuses have been observed to be solitary animals as they do not live in groups. Likewise, few squid species are solitary but most of them live in groups. Thus, they travel the ocean in schools.

Octopus vs squid intelligence

When comparing intelligence, it is said that squids are slightly less intelligent than octopuses and cuttlefish. Though several species of squid are much more social and exhibit greater social communications. As a result, some researchers concluded that in terms of intelligence, they are on par with dogs.

Octopuses, on the other hand, are highly intelligent. Among cephalopods, only octopuses, as well as nautiluses, are capable of vertebrate-like spatial learning. Moreso, scientists have discovered that they can navigate their way through mazes. Also, octopi have been seen solving problems quickly and having at least short-term memories of those solutions.

Furthermore, octopuses have been observed in their aquarium in a play behavior where they release bottles or toys repeatedly into a circular current and then catch them. Tool use has been observed in these animals. A typical example is seen in the veined octopus that gathers discarded coconut shells to build a shelter.

Harvesting

Even in fishing, the harvesting of these animals differs. For octopuses, fishers catch them by using weighted chains that drag along the ocean floor. Thus, scaring the octopi into a net. Another fishing technique used for octopuses involves lowering traps and pots knowing that the octopuses will use them as shelters. Also, spearfishing and drift fishing is practiced.

For squids, they are caught by fishers with jigging. This involves them shining bright lights and dropping lines into the water with special lures. These special lures are called jigs. These jigs jerk up and down. Thus, attracting the squids to the light and movement. However, fishers recently started using large seine nets that encircle the squids. Thereby, forming pockets and trapping the squids.

Octopus vs Squid: Similarities

Heart

The number of hearts of an octopus vs a squid is the same. They both have three hearts each. One of the hearts- the systematic heart is dedicated to the circulation of blood around the body. Whereas, the two auxiliary hearts (branchial hearts) pumps blood through each of the two gills.

Blood

The blood (hemolymph) of an octopus and a squid contains a copper-rich protein known as hemocyanin. This hemocyanin, however, is more efficient at transporting oxygen molecules in cold waters with low oxygen levels. Therefore, it is actually ideal for the octopuses and squid in the ocean.

The hemocyanin when compared with hemoglobin transports oxygen more efficiently in cold waters with low oxygen conditions than hemoglobin. Hemocyanin is dissolved in the plasma. This gives the blood of an octopus and squid a bluish color. Thus, the blood of an octopus and squid is blue because the hemocyanin that carries oxygen around their body contains copper instead of iron. However, if their blood becomes deoxygenated, like when they die, the blue color fades out as the blood turns clear.

Locomotion

An octopus and squid both move by jet propulsion. This involves drawing water into a muscular sac in the mantle cavity that surrounds their bodies. Then, they expel the water out through a narrow siphon.

The octopus and squid can swim in any direction. Squids, however, use the fins located on their heads to propel themselves when they swim at low speeds. They are stabilized by these fins when moving slowly. However, the fins wrap around the body when squids move quickly, by way of jet propulsion. Most octopuses, as adults do not have fins, although some deepwater octopuses are exceptions.

Defense

Camouflage

Octopuses and squid can change color for camouflage and signaling. Some species of octopuses and squids are even bioluminescent as they use their light for counter-illumination camouflage.  They have specialized skin cells to camouflage. These animals camouflage to escape predators.

The octopus and squid have developed pigment-bearing cells (chromatophores) that contain yellow, red, orange, brown, or black pigments. Also, reflective iridophores are another color-changing cells in octopuses and squids. This color-changing or camouflage ability is also used amongst these animals to communicate with one another or warn other of their species.

Octopus vs Squid Ink

When threatened, both species- octopus and squid can expel clouds of ink into the water to quickly escape a predator.

The ink sac of these animals is close enough to the funnel so that with a water jet, they can shoot out the ink. However,  the ink passes through glands that mix it with mucus. Thus, it forms a thick dark blob that allows an octopus or squid to escape their predator. The black color of the ink is a result of melanin which is the main pigment.

Similarities of Octopus and Squid

  1. Octopuses and squids are both mollusks and invertebrates.
  2. They both have 3 hearts and blue blood.
  3. These cephalopods can both camouflage and use cloud ink as a defense mechanism against predators.
  4. They both move by using jet propulsion.

Octopus vs Squid taste

The taste of octopus meat vs that of a squid has been compared a lot. Octopus meat is chewy with a really good taste. The taste of an octopus doesn’t taste fishy and is distinct from a squid taste. However, some people think the meat of octopus and squid tastes the same. The fact is, a squid meat taste is more like a mild flavor that is somewhat reminiscent of shellfish. Whereas, the meat of an octopus tastes like that of chicken or pork. The good thing, however, about the meat of an octopus is that it easily absorbs the flavor of what it is cooked in. Compared to squid meat, it is more tender and juicier. Although, cooking octopus meat or squid meat can be tricky as both need to be cooked either slowly or quickly.

Octopus vs Squid: Fight

Between an octopus and squid, which is likely to win in a fight comparison?

There are speculations that the squid is more likely to win. This assumption and comparison are based on the strength, size, and weight of these animals. Squids tend to be bigger than octopuses and even weigh more. Moreso, they can be more aggressive than octopuses. An octopus may be a good swimmer but it is not a ferocious attacker like a squid.

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