Squid is any of a number of soft-bodied marine animals that have 8 or 10 limbs around the mouth. Squids are invertebrates, or animals that lack a backbone. They belong to a group of invertebrates called cephalopods, which also includes octopuses, nautiluses, and cuttlefish. Squids live in all seas and at all depths.
The body of a squid
has two fins, one on each side of the tail. In most squid species (kinds), the head is surrounded by eight arms and two often longer limbs called tentacles. The arms and tentacles possess rows of suckers. Instead of bones, the animal has a pen (reduced shell) inside its body. Squids range in length from less than 1 foot (0.3 meters) to about 60 feet (18 meters), including the tentacles.
A squid’s head has two well-developed eyes, a pair of powerful beaklike jaws, and a toothed structure called a radula. The radula assists the jaws in tearing up food, and it also helps move the food into the digestive system. A muscular, tubelike structure called the mantle forms the main part of the body. Attached to the body below the head is a smaller tubelike structure called the funnel. A squid propels itself through the water by filling its mantle with water and then forcing the water back out through the funnel. Squids also have three hearts—a main systemic heart and two additional branchial hearts. The branchial hearts supply blood to the animal’s gills.
The life of a squid.
Many types of squids live close to the ocean surface or near shores. Coral reefs house some of the most colorful varieties. Other types inhabit the dark, cold waters of the deep sea. Some species have structures called photophores, which emit light. Scientists do not completely understand the function of photophores, but a squid may use them for signaling other squids, luring prey, or scaring away predators.
A squid’s diet consists of various sea animals, including fish, shellfish, and plankton. Squids often catch their prey by attacking with sudden bursts of speed. They then hold onto the prey using the suckers on their arms and tentacles. Many squids also have glands that emit a poison for stunning prey.
Numerous animals eat squids, including toothed whales, seals, sharks, and bony fishes. Squids avoid these animals in a variety of ways. For example, all squids have an ink sac that spurts out a dark fluid when the squid flees from a predator. This fluid may conceal the squid as it escapes. Many species can also escape danger by rapidly changing color. Skin cells called chromatophores contain a colored pigment. When a squid is threatened, these cells contract or expand to produce sudden color changes. Such color changes can either startle the predator or enable the squid to hide by blending into its environment.
Squids have large brains and often exhibit complex behaviors. Many types swim in large groups. To attract females or ward off rivals, male squids sometimes change color and wave their arms as a form of display.
The number of eggs produced by females varies from a few dozen to many thousands. Newborn squids resemble miniature versions of the adults. Squids generally do not live long. Lifespans typically range from a few months to a few years.
Kinds of squids.
Some of the best-known squids live in shallow waters near coasts. The Caribbean reef squid, for example, inhabits coral reefs throughout the Caribbean Sea. This small squid grows to about 12 inches (30 centimeters) long. It feeds on crustaceans and small fish.
Two related species, the longfin inshore squid and the veined squid, rank among the most commercially important types. People around the world eat them and use them as fish bait. Longfin inshore squids inhabit the western Atlantic Ocean from Newfoundland to Venezuela. Veined squids live in eastern Atlantic waters and the Mediterranean Sea. Both species gather in shallow coastal areas to breed and lay eggs. They range from 15 to 36 inches (38 to 91 centimeters) long.
Many squids inhabit deep ocean waters around the world. Scientists know little about most of these animals, which have rarely been seen alive. Deep-sea squids include the huge colossal squids and giant squids, which may reach about 60 feet (18 meters) in length. Giant squids probably eat other mollusks, including squids, as well as fish.
In the late 1980’s, scientists discovered an unusual deep-sea squid. Sometimes called the longarm squid, it has 10 extremely long, threadlike arms of equal size. The arms bend to create elbowlike forms. Nearly all other squids possess eight arms and two tentacles. The long-arm squid also has two huge fins that flap as the animal moves. The total length of this creature probably reaches 10 to 20 feet (3 to 6 meters).
Squids and people.
Squids have captured people’s imaginations for centuries. Many seafaring cultures, such as those of Japan and Polynesia, created stories of large sea monsters that probably represented squids. Such cultures often prized squids as a source of food. Today, squids play an important role in the fishing industry worldwide, both as food and as bait.
Scientists from a variety of fields study squids. Researchers analyze the nervous systems of squids to learn more about how the human nervous system functions. Biologists and deep-sea explorers continue to discover new squid species.
