Squid

There are about 300 different species of squid. They are found in all of the oceans throughout the world, including in the freezing cold Antarctic waters. They eat a range of different foods, including tiny animals such as krill, some fish, and even each other. Most squid species live less than 1-2 years, though some larger deep-sea species may live several years, but rarely more than 5. Although they have some things in common with octopuses, a squid and an octopus are completely different animals.

5 Amazing Squid Facts

• Some squid have special cells in their skin that allow them to change colors.
• Most squids have 8 arms and two longer tentacles.
• Squid have tough beaks that they use to kill and eat their prey.
• Many squids that live in deep water have bioluminescent organs that show through their skin.
• Squids are one of the few animals that have multiple hearts. In total, squids have three hearts.

Classification and Scientific Name

All squid are cephalopods, which means they are members of the scientific class Cephalopoda, along with octopuses and cuttlefish. The class name comes from the Greek words for head and foot. They are members of the superorder Decapodiformes, which is derived from the Greek words for 10 feet. Squids belong to the order Teuthida, a term that comes from the Greek word for fierce.

Appearance and Behavior

Squids can look different from one another, depending on the species, but in general, all squid have an elongated, tubular body called the mantle, which ends at a somewhat flattened head. On either side of the mantle are fins that aid the squid in moving through the water. Depending on the species, these fins can be quite large, running the full length of the mantle, or very small, located just at one end. A squid also has relatively large eyes, one on either side of its head, that provide a wide field of vision.

At the lower end of the squid’s body are the arms and tentacles, attached to the head. Each of the arms has suckers on it, as do the tentacles. The suckers of some squids are also armed with sharp hooks that allow them to grip their prey tightly. Squid do not have a skeleton as we do, but they have a chitinous internal structure called a gladius or pen.

The shape of the squid allows it to slip quickly through the water. When swimming slowly, it uses its fins for propulsion, but if the squid is in a hurry, it moves by taking in water through its mantle and then squirting it out through its siphon, jet-propelling it through the water. The siphon can be moved to point in any direction, allowing the squid to quickly move in whichever way it chooses.

Squids are usually black, white, brown, or gray, but many of them can change their appearance at will. The Humboldt squid, for example, can flash red and white, and other squids can match their color to their surroundings or display a colorful pattern on their bodies. They can use color to signal to other squid or to help camouflage themselves to avoid predators.

Deep-sea squid often have bioluminescent organs, and these lighted body parts can be seen from outside the animal. Typically, squid can squirt a cloud of ink when they feel threatened. The ink hides them and gives them time to escape to safety. A notable exception to this is the vampire squid, which squirts a sticky, bioluminescent cloud into the water that glows for about 10 minutes, giving the vampire squid time to get away.

Squid come in many different sizes. The heaviest squid on record was a colossal squid discovered in New Zealand in 2007. This huge animal weighed more than 1,000 pounds (453.6 kg), almost as heavy as a grizzly bear. The longest scientifically confirmed giant squid was about 43 feet (13 meters) long, though unverified reports suggest they may reach greater lengths. Most squid are much smaller, with the average being about 2 feet (60 cm) long, the size of an average man. The smallest squid known is the Southern pygmy squid, which is practically invisible at only ¾ of an inch (1.6 cm) long.

Squids tend to live alone, but they do sometimes gather in groups, and some of them have even been known to hunt cooperatively, similar to the way a pack of wolves hunts. When they do gather, a group of squid is called either a shoal or a squad, with the exception of the giant squid. A group of giant squid is called a school.

History and Evolution

Squid are believed to have evolved from shelled cephalopod ancestors over 400 million years ago, with modern squid lineages diverging much later. Even more interesting, it may appear that they also evolved from a prehistoric snail. It may raise the question of where the snail shell disappeared, but the remainder of shells, or hints of them, are found in other animals with common ancestry. They are like little clues to investigating the family trees of the past for animal species. From such evolutionary evidence, you can see that the cuttlefish has what is called the cuttlebone, which is a leftover clue of having a shell. Nautiluses also have internal and external examples of the remaining shell.

Another fascinating feature of squid evolution is how they came to have eight arms and two tentacles. Scientists have found evidence that the arms and tentacles of squid are derived from the molluscan foot, similar to other cephalopods. Squids have amazingly adapted and evolved their singular foot to become what we know them to be today.

Types of Squid

There are hundreds of different types of squid across the world. These are just a few of them.

• Colossal Squid (Mesonychoteuthis hamiltoni): The Colossal Squid is incredibly large, with a weight of at least 1,091 pounds and a length estimated at 14 feet. This size makes the colossal squid the largest squid in the world. Colossal squid are believed to be ambush predators and use bioluminescence to attract their prey. These squid are believed to primarily inhabit the Southern Ocean, circumferential to Antarctica, up to 13,000 feet deep. Because they live at such extraordinary depths, much is left to be learned about these creatures.
• Vampire Squid (Vampyroteuthis infernalis): The Vampire Squid usually exists in the deep sea and uses bioluminescent organs and oxygen metabolism to survive parts of the sea that have extremely low levels of oxygen. This sea creature resembles both a squid and an octopus. However, it is neither of the two. ‘It has eight arms and two thin retractile filaments, rather than true tentacles. The vampire squid’s name comes from its dark color and the skin that connects its multiple arms, forming a cape-like structure. Vampire squids have two filaments. However, these sea creatures are only able to extend one filament that helps these fish overcome energy deficiencies in areas where the concentration of oxygen is low.
• Humboldt Squid (Dosidicus gigas): The Humboldt Squid, often called the jumbo squid, can grow up to 110 pounds with a maximum length of up to 7 feet. This squid is found in the eastern Pacific Ocean and is the largest of the flying squid. They are most often found in large shoals of about 1,200 individuals and live at depths between 660 and 12,300 feet. They can swim up to 15 miles per hour and are vicious predators. They primarily feed on other mollusks, small fish, and crustaceans, but are also frequent cannibals. In pursuit of prey, Humboldt squid chase down and attack using their barbed tentacle suckers. They then tear apart the prey’s flesh with their razor-sharp, parrot-like beak. Each sucker has a ring of sharp teeth, and the squid’s beak can easily tear tough tissue. There have been verified reports of human attacks, primarily on deep-sea divers.
• Bigfin Reef Squid (Sepioteuthis lessoniana): The Bigfin Reef Squid, also known as the glitter squid or oval squid, belongs to the loliginid squid family Loliginidae. They get their name from the large oval fin connected to the mantle. Although they rank as a medium-sized species and only measure around 1.5 to 13 inches long, they grow faster than almost any other large marine invertebrate. They engage in elaborate mating displays and live relatively short lives, with a maximum age of just 315 days. 
• Giant Squid (Architeuthis dux): The Giant Squid is estimated to weigh up to 606 pounds and is capable of reaching lengths between 39 and 43 feet, making it the longest squid in the world. Giant squid inhabit the deep-sea between an estimated 989 and 3,280 feet and have therefore been incredibly hard to study. Very few have been studied alive, and most of what is known about them comes from studying carcasses that have washed up onto beaches. The giant squid’s diet consists of deep-sea fish species and other smaller squid. The giant squid is a solitary hunter and catches its prey using two tentacles with barbed suckers.
• Heterololigo Squid (Heterololigo bleekeri): The Heterololigo Squid is a genus with only one species. It is known for its short tentacles and only lives for about one year. Japanese fisherman catch these off their coasts.
• Swordtip Squid (Uroteuthis edulis): The Swordtip Squid is commonly caught in the southern East China Sea. They have a lifespan of just nine months and spend most of this time migrating based on sea temperatures.

Habitat

Squids are found in oceans all around the world. Not all species live in all parts of the world. Some squid prefer warmer, tropical waters, while others thrive in the cold seas where krill and other food can be found, but as a species, they can be found almost everywhere.

Unlike octopuses, which live in nooks in rocks and coral reefs, squid are free-swimming and do not seek a place to call home, though some of them do live near the ocean floor, which helps to hide them from their enemies.

Diet

For the most part, squid eat fish such as orange roughy, lantern fish, and hoki, along with other sea creatures such as oysters, crabs, and shrimp. Squids are also cannibals and will happily devour another squid, even of their own species, if they are hungry. The size of the prey depends on the size of the squid.

Humboldt squid are well-known for their aggressive nature, and they will consume anything they can catch. There have even been tales of shoals of them attacking and eating fishermen who are unlucky enough to fall into the water when the squid is present.

The vampire squid is different from most other squids because it doesn’t catch and eat live food, nor does it drink blood, as its name might suggest. Instead, it floats through the water waiting to catch detritus that falls through the water. This is made up of tiny dead animals and fecal pellets from other creatures. This squid then rolls everything it has caught into a ball and sticks it together with mucus, then eats the ball it has made.

Predators and Threats

Because squid comes in a huge range of sizes and is found almost everywhere, many types of animals eat squid. Small squid are eaten by almost any kind of predator imaginable, but their main predators are penguins, seals, sharks such as the grey reef shark, whales such as the sperm whale, and humans.

Despite being a popular prey item, squid remains plentiful in the wild. According to the International Union for the Conservation of Nature (IUCN), squid is classified as having a status of Least Concern, which means that there are no immediate threats to squid known to exist, and their numbers in the wild are plentiful.

At least some types of squid can regenerate their tentacles, so if one is lost in an attack by a predator or in some other way, the squid can eventually replace the lost part. Scientists do not believe that squids can regenerate their arms. Only their longer tentacles appear to have the ability to regrow.

Human Consumption

In general, squid is a source of food for human beings, and is under threat from overfishing. Squid is consumed as a cultural staple in places like Japan, where it is included in sushi cuisine. In Western culture, it is referred to by the Italian term calamari, served stuffed, as sliced rings, or as flat pieces.

Areas where squid is caught include the North Pacific, the Mediterranean, the East Coast of the U.S., and the Northeast Atlantic. It’s beneficial to humans for the vitamins and nutrients it contains, namely copper, manganese, zinc, selenium, vitamin B12, and riboflavin.

Reproduction, Babies, and Lifespan

Because there are so many different species of squid, some variation exists in how they reproduce and how long they live. Typically, squids mate in large groups and reproduce when the male places sperm into the female’s mantle. She can then store the sperm until she is ready to use it. When it is time, the female uses the sperm to fertilize her eggs, and she will then lay her eggs on the ocean floor or attach them to seaweed. She will not care for them any further.

When the eggs hatch, the babies usually look like tiny copies of the adults and are known as paralarvae. They will grow and change as they mature, ultimately becoming squid that can care for themselves. The little squid absorbs their egg yolk initially, and this feeds them until they can catch food for themselves.

The lifespan of a squid is somewhat uncertain, but scientists think that most squids don’t live longer than 5 years in the wild, and many don’t survive even that long. The exception to this is the larger squid that lives deep in the ocean, some of which have been known to live up to 15 years. Most species die after reproducing.

Population

The total population of all of the varieties of squid is impossible to know, but they number in the millions. The IUCN lists them as being of least concern, which means that squid are not considered threatened or endangered in any way. A drop in the squid population could spell disaster for many other species, as so many creatures depend on the squid for survival. One sperm whale, for example, can eat up to 800 squid in a single day, and elephant seals may consume large numbers of squid as an essential part of their diet.