Octopuses and squid

Cephalopod Facts

Classification:

Kingdom: Animalia

Subkingdom: Eumetazoa

Phylum: Mollusca

Class: Cephalopoda

Subclasses: Nautiloidea (nautilus), Coleoidea (octopuses and squids)

Orders:Nautilida (nautilus); Sepiida (cuttlefishes); Sepiolida, Teuthida (squids); Spirulida (spirula); Octopoda (octopuses); Vampyromorphida (vampire squid)

Suborder: Two main suborders of Octopoda—Cirrina (webbed), Incirrina (round bodied)

Geographical location: Every ocean, but mainly the Indian Ocean and the South Pacific

Habitat: The ocean floor

Gestational period: Varies by species from forty days to one year

Life span: Six months to five years for octopuses, depending on species; five years for squids; twenty-plus years for chambered nautilus

Special anatomy: Eight to ten tentacles, usually with suction cups at the end; round, sacklike bodies for octopuses

Octopuses and squid belong to the subclass Coleoidea, which is in the class Cephalopods, phylum Mollusca, which includes snails and clams. They are related to other mollusks but have no internal or external shell. There are more than one thousand species of octopuses and squid alive today. They have two eyes and eight (octopuses) to ten (some squid) tentacles that are attached directly to the head. The tentacles are covered with sucker pads that help the animal move along the ocean floor, its normal place of residence. They have the most complex brain of the invertebrates, and also have long- and short-term memories, much like vertebrates.

The genus Octopus contains several different species, which vary greatly in size. The smallest is Octopus wolfi, a species that averages less than half an inch in length. The largest species, formerly Octopus dofleini, commonly known as the giant Pacific octopus and now classified in the genus Enteroctopus as Enteroctopus dolfleini, can grow to sixteen feet in length and weigh up to three hundred pounds, with a tentacle span of thirty feet. The best known and most widely distributed species is Octopus vulgaris, a medium-sized octopus found in every ocean. This species is from two to three feet in length and lives in holes on the ocean floor. It feeds mainly on crabs, lobsters, and other crustaceans. It is very intelligent. One Japanese scientist taught an octopus how to open a sealed jar to retrieve its contents, a spiny lobster.

An octopus can change its skin color quickly when it is frightened or threatened. Its changed color provides camouflage to help it blend in with the background so that the octopus becomes almost invisible to predators. Scientists have discovered that octopuses change colors not only for defense, but also to reveal their moods and emotions. Angry members of the species turn a deep red in color, while during mating season, both males and females display stripes and colors that reflect their inner excitement. Some species squirt out clouds of a dark inky substance, which hangs in the water for several seconds. This inkblot has the same size and shape as the octopus, and while it draws the attention of the predator, the octopus escapes. When an enemy, such as a moray eel, attacks an octopus, it may lose one of its eight arms in the fight, and while the eel watches the twitching arm, the injured octopus can swim away. The tentacle grows back very quickly.

Squid are cephalopods and belong to the superorder Decabrachia (ten-armed), which has several orders and many species. They are found in every ocean and range in size from less than one inch to more than sixty-five feet in length. Adult squid of some species can race through the water at speeds of up to twenty-five miles per hour. They are aggressive hunters, equipped with two more tentacles than octopus. The squid use these extra arms to catch their food. Some squid hunt in packs and use their ability to change color to lure their prey. They are also bioluminescent, which means they can light up. Actually, bacteria living under their skin produce the light in squid that live close to the surface. Deep-water squid, on the other hand, living thousands of feet below the surface, make their own light. These species have light-producing organs called photophores that make two chemicals: a protein called luciferin and an enzyme known as luciferase. When the two chemicals are mixed, the enzyme breaks down the protein, releasing a pale, blue-green light. This is the same process used by fireflies. Some squid species can squirt out clouds of glowing bacteria when they are endangered. This light show distracts the predator and helps the squid escape.

Squid, Cuttlefish, and Nautilus

The giant squid, Architeuthus dux, is one of the largest invertebrates on Earth, each species having eyes the size of automobile headlights and weighing up to one thousand pounds; only the colossal squid, Mesonychoteuthis hamiltoni, is larger, with a maximum recorded weight of 1,091.29 pounds (495 kg). Despite their size, few observers have seen one of these animals in its natural environment. In 2006 researchers in Japan were able to capture images of a live giant squid, and a team from Japan's National Science Museum caught a live giant squid and brought it to the surface. Perhaps the major reason the giant squid has rarely been seen live is that they live so deep in the ocean. Another reason is their enormous speed and rapid acceleration. Because of this speed, they can easily evade their major predators, tuna and sharks. Some can even leave the water for short periods and glide through the air like flying fish to escape their enemies.

The cuttlefish, genus Sepia, is a cephalopod that can eject clouds of ink to confuse enemies and can swim almost as rapidly as squid. Its most remarkable characteristic, however, is its ability to change color, which biologists believe is used by the species as a method of communication. Cuttlefish can display thirty different color patterns that range from very light to very dark. They can also exhibit zebralike stripes and patterns that look like a pair of dice. They can change colors quickly to escape predators by blending into the background. Color changes are also used to attract mates and outshine rivals during courtship. Cuttlefish have ten arms or tentacles, with two longer than the other eight. Most of the time the two longer arms are tucked under their bodies, but if supper swims by, they shoot out to grab the shrimp or fish and drag it to their mouths.

Next to the octopus, the cuttlefish is probably the most intelligent invertebrate in the sea. In experiments, cuttlefish have been taught to recognize which colored disks signal food and which do not. Baby cuttlefish know from the moment of birth how and when to bury themselves in the sand, how to squirt an inky substance to confuse predators, and how to get away quickly when they encounter larger animals. The ink of the cuttlefish, which is called sepia (the genus name) was the original dark pigment used in India ink. This ink was used in quill pens in England and France in the 1600s and is still used today by artists for drawing and lettering.

The chambered nautilus, Nautilus pompilius, is one of five species in the genus Nautilus. It is a living fossil. The surviving species are found only 60 to 1,500 feet below the surface of the Indian and Pacific oceans. Five hundred million years ago, nautiloids were the masters of the sea. At that time, there were more than 2,500 species, some with straight shells and others with coiled shells like the modern nautilus. They are nocturnal feeders, coming to the surface only on moonless nights to feast on small fish and shrimp. They are the only members of the class Cephalopoda to still have an external shell. They have eighty to one hundred arms surrounding their heads. Each arm can touch and taste food. The nautilus gets its name from the thirty to thirty-eight walled chambers that are found inside its shell. The animal lives in the outermost chamber and uses the others to float in the water.

The nautilus is an endangered species, mainly because of the beauty of its shell. Philippine Island fishermen catch about five thousand living animals every year to sell to shell collectors. They are also hunted extensively off the coasts of India and Indonesia.

Growth and Reproduction

Most cephalopods, including the giant squid, grow quickly and die after a short life. The giant Pacific octopus, for example, which is only one-twentieth the size of the giant squid, lives just three to five years. It is estimated that the giant squid lives for no more than five years. This means that its growth to adulthood is extremely fast. When it is a baby, it is less than an inch long, but within three years, it has reached almost sixty feet in length. Growing at such a rapid rate requires huge amounts of food. Giant squid eat enormous quantities of fish and other squid, which they catch with the suckers on their tentacles and crush in their massive mouths.

Octopuses and squid have separate sexes and reproduce internally. In some species, modified sucker discs at the tip of one of its tentacles distinguish the male. This arm is used to remove a packet of sperm from within his body cavity and insert it into the cavity of the female. Within two months after mating, the female attaches strands of clustered eggs to the ceiling of her dwelling under the sand. The number of eggs laid varies greatly from species to species, with the common octopus laying anywhere from 200,000 to 400,000 very tiny eggs. Other species lay as few as 150 eggs. Once the eggs are laid, the mother gently caresses the eggs with her suckers to keep algae and bacteria from growing on them. She also squirts them with streams of water to keep them clean. As the baby inside the egg matures, the mother’s gentle caresses become more violent to help the developing octopus break away from its egg house. Most mothers do not eat after laying their eggs and die shortly after their eggs have hatched. Baby octopuses in species like Octopus vulgaris are carried about in water currents for about a month before they settle to the bottom, where they start to feed. Babies in other species look just like a miniature adult and immediately sink to the bottom where they start living. On average, the survival rate for a baby octopus is extremely small. Only about one or two out of 200,000 eggs will survive to become an adult.

The chambered nautilus cements its eggs to rocks or coral on the seafloor. They take almost a year to hatch. A baby nautilus is only about an inch long when it hatches from its egg case but grows into an adult quickly. It is the longest-living cephalopod, with some adults living fifteen to twenty years. Unlike the octopus, the chambered nautilus does not die immediately after reproduction.

Cephalopods make up a large part of the diet of whales, seals, fishes, and seabirds.

Cephalopod Evolution

The earliest ancestors of octopuses and squid were mollusks with thick shells that protected them from their enemies. Of the estimated one thousand species of cephalopods still living, only the chambered nautilus and cuttlefish have remnants of an internal shell. Cephalopods began losing their shells in the Triassic period, 245 to 208 million years ago. The earliest squid appeared in the Jurassic period, 208 to 144 million years ago. The oldest known octopod, Palaeoctopus newboldi, now extinct, comes from the Cretaceous period and is at least 140 million years old.

Principal Terms

Invertebrates: Animals without backbones

Tentacles: A long flexible arm or projection

Bibliography

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Nuwer, Rachel, and Sonja Anderson. "Ten Wild Facts about Octopuses: They Have Three Hearts, Big Brains and Blue Blood." Smithsonian Magazine, 13 Mar. 2024, www.smithsonianmag.com/science-nature/ten-wild-facts-about-octopuses-they-have-three-hearts-big-brains-and-blue-blood-7625828/. Accessed 3 July 2024.

"Octopuses." National Wildlife Federation, www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Octopuses. Accessed 3 July 2024.

Rosa, R., et al. “Biology and Ecology of the World’s Largest Invertebrate, the Colossal Squid (Mesonychoteuthis hamiltoni): A Short Review.” Polar Biology, vol. 40, no. 9, pp. 1871–1883, doi:10.1007/s00300-017-2104-5.

Schweid, Richard. Octopus. Reaktion Books, 2014.