Cephalopods: Characteristics, History, and Unusual Features

Home | Category: Cephalopods (Octopus and Squid)


Orders of Cephalopods (left to right, top down
1) Loligo vulgaris
2) Eledone moschata
3) Sepia officinalis
4) Nautilus
5) Spirula spirula
6) Vampyroteuthis infernalis
7) Austrorossia mastigophora

Octopuses, squid, nautiluses, vampire squids and cuttlefish are cephalopods, a class of mollusks whose name means "head-footed." There are two subclasses of Cephalopoda: 1) chambered nautiluses, with external shells and anatomy that has remained virtually unchanged for 450 million years; and 2) coleoidea, which includes octopuses, squids and cuttlefish. The latter are soft, fleshy mollusks with their shells inside their bodies instead of outside as is the case with most mollusks.

The word “cephalopod” is derived from the Greek words for “head foot,” an apt description for animals whose eyes are situated just above their many limbs. Cephalopods are exclusively marine animals characterized by a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from primitive molluscan foot. Fishermen sometimes refer to cephalopods "inkfish" because of their ability to squirt ink.

Jennifer A. Mather wrote in Natural History magazine, “Most mollusks are clams or snails that hide within hard shells and have little brainpower. But cuttlefish, octopuses, and squid (which along with nautiluses make up the cephalopod mollusks) are nothing like their shell-bound relatives. Evolution led them to lose their protective shells, but what they gained was far more interesting: dexterous, sucker-lined arms; ever-changing camouflage skin; complex eyes; and remarkably well-developed brains and nervous systems. [Source: Jennifer A. Mather, Natural History, February 2007]

There are over 800 species of cephalopod, and new ones are being found, especially in the deep sea. Cephalopods are divided into two subclasses and five orders. Nautiluses (members of the order Nautiloidea) have more than 90 tentacles; some squid (members of orders Sepioidea and Teuthoidea) have eight arms and two tentacles; and octopus and some squid (members of orders Ocotopoidea and Vampyromorpha) have eight arms. Some like nautiluses have an exterior shell. Others, like many squid and cuttlefish, have internal shells. Many cephalopods are social creatures; when isolated from their own kind, some species have been observed shoaling with fish. [Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW), Wikipedia]

Cephalopods are of economic importance to humans. Squid and octopus are common food sources in many counties, particularly in Asia and the Mediterranean. They reproduce quickly which means that even though millions of metric tons of them are caught every year, they are not in danger of being overfished. In the past they were often caught with drift nets, which are now banned not because they caught too many squid but because they caught other animals like dolphins and sharks. In addition to this, nautilus shells are used as decorations. The internal shells of cuttlefish — cuttlebones — are sold in pet stores as a calcium source for birds. Giant squid and octopuses have been the subject and inspiration for many sea-monster stories and B-movies.

Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems


20120518-octopus _-_NOAA_Photo_Library.jpg
Cephalopods are mollusks (also spelled mollusc) — creatures with shells. There are four kinds of mollusks in the phylum, Mollusca: 1) gastropods (single shell mollusks); 2) bivalves or Pelecypoda (mollusks with two shells); 3) cephalopods (mollusks such as octopuses and squids that have internal shells); and 4) amphineura (mollusks such as chitons that have a double nerve).

The world’s first shells emerged about 500 million years ago, taking advantage of the plentiful supply of calcium in seawater. Their shells were composed of calcium carbonate (lime), which has been the source of much of the world limestone, chalk and marble. According to a 2003 paper in Science, the use of large amounts of calcium carbonate for shell-building in early years of life on earth altered the chemistry of the atmosphere to make conditions more favorable for creatures living on land.

Animals with shells have been found living in the Mariana Trench, the deepest places in the ocean, 36,201 feet (11,033 meters) below the sea surface, and 15,000 feet above sea level in the Himalayas. Darwin’s discovery that there were fossil of sea shells at 14,000 feet in the Andes helped shape of theory of evolution and understanding of geologic time.

Earliest Cephalopods

The earliest cephalopod fossil dates back 530 million to 515 million years. An estimated 11,000 extinct taxa have been described, and this occurred even though although the soft-bodied nature of cephalopods means they are not easily fossilized. It is believed that cephalopods evolved from an ancient group of gastropods. Cephalopods, represented by primitive nautiloids, were dominant during the Ordovician period (485 million to 444 million years ago). [Source: Wikipedia]

Ed Yong wrote in The Atlantic: About 530 million years ago, an ancient group of mollusks slowly modified their protective shells into buoyancy aids by filling them with gas. With this transformation, they could more easily walk along the ocean floor, and then swim over it. They were the first cephalopods. For eons, they and their descendants kept their shells. [Source: Ed Yong, The Atlantic, July 2, 2019] .

cephalopods and other creatures on an
ancient Greek fish plate
Ammonoidea (extinct Nautilus-like molluscs) arose during the late Paleozoic (541 million to -252 million years ago) and grew to large numbers during the Mesozoic (252 million to 66 million years ago). According to Animal Diversity Web: Ammonites had an external, coiled shell similar to that of Nautilus. Ammonites were very successful — scientists have described 600 genera based on shell type — but became extinct at the end of the Mesozoic. Belemnoids, which also appeared in the Mesozoic, had internal shells. They are believed to be the precursors of modern-day squid and cuttlefish. However, the ancestors of these animals may have been living before the belemnoids. [Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW)]

Tully Monsters

Tully monsters roamed The Earth's oceans 300 million years ago and left behind bizarre fossils with a rear half looking like a squid and a front half looking like a miniature blind plesiosaur, with stalked eyes coming out of the side of its body. The creature was so strange scientists debate whether or not it had a backbone and whether or not it was a mollusk, arthropod, conodont, tunicate or a worm.

Properly known as a Tullimonstrum, this soft-bodied creature lived in shallow tropical coastal waters of muddy estuaries during the Pennsylvanian geological period. A single species, T. gregarium, is known and was first discovered in 1958 in the Essex biota in the Mazon Creek fossil beds of Illinois.

Tullimonstrum probably reached lengths of up to 35 centimetres (14 inches) and, judging from the fossils, seems to have been a carnivore that hunted in the ocean’s water column or bottom.. It had a mostly cigar shaped body, with a triangular tail fin, pair of vertical, ventral fins, two long stalked eyes, and a long neck tipped with a claw-like appendage coming out of its face. The appendage has eight small sharp teeth on each "jaw", which may have been used to probe for small creatures and edible detritus in muddy sea bottom. The absence of a hard part in the fossil implies that it did not have any bones or a shell. A bizarre transverse bar-shaped structure, which terminate in two round organs containing the pigment melanin are believed have been camera-type eyes. The creature possessed structures which have been interpreted as gills, and a possible notochord or rudimentary spinal cord.

A study published on April 16, 2022 in the journal Palaeontology concluded that the Tully monster was likely an invertebrate. Live Science reported: Most recent Tully monster studies argue that it's either a vertebrate relative of modern cyclostomes (including lampreys and hagfish) in the chordate group or an unknown invertebrate. Now, researchers in Japan think they've cracked the case, with the help of a 3D laser scanner. "We believe that the mystery of it being an invertebrate or vertebrate has been solved," first author Tomoyuki Mikami, a doctoral student at the University of Tokyo and a researcher at the National Museum of Nature and Science in Tokyo, said in a statement. "Based on multiple lines of evidence, the vertebrate hypothesis of the Tully monster is untenable." [Source: Patrick Pester, Live Science, April 24, 2023]

The researchers scanned more than 150 Tully monster fossils to create color-coded 3D maps of the animal's anatomical structures. They also X-rayed one well-preserved proboscis — the claw-like appendage — to examine the creature's teeth. The results suggested that features previously used to argue Tully monsters are near cyclostomes taxonomically, including their teeth and gill pouches, were misinterpreted. The teeth analyzed in the new study had bulging bases — unlike cyclostome teeth, which are thinner at the base. The authors said what appeared to be gills was actually just segmentation in the body.

a Tully monster

Most convincing of all, the team claims, is segmentation found on the creature's head. "This characteristic is not known in any vertebrate lineage, suggesting a nonvertebrate affinity," Mikami said. Victoria McCoy, an assistant professor at the University of Wisconsin-Milwaukee, is not convinced, however. McCoy led a 2016 study placing Tully monsters near cyclosomes and a 2020 study that found Tully monster tissues were made up of proteins like those of vertebrates — and not chitin, like those of invertebrates. "It didn't change my mind about what the Tully monster was," McCoy told Live Science. "But it is new information, and that definitely advances our understanding."

Cephalopod Shed Their Shells

Ed Yong wrote in The Atlantic: About 275 million years ago, everything changed. It’s possible that competition from fast, shallow-water fish forced cephalopods to become more agile, or drove them into deeper waters where buoyant shells would have been a hindrance. For these reasons, or perhaps others, the ancestors of octopuses lost their shells entirely, while the ancestors of squid and cuttlefish internalized theirs. (The white, brittle slabs that people feed pet birds are cuttlebones, the internalized shells of cuttlefish.) [Source: Ed Yong, The Atlantic, July 2, 2019] . “Unencumbered by a shell, cephalopods became flexible in both body and mind, according to Amodio and his colleagues. They could move faster, expand into new habitats, insinuate their arms into crevices in search of prey. “This allowed them to feed on many more kinds of food, requiring more complex foraging techniques,” Amodio says. “We think this is one of the key challenges that pushed them to become smarter.”

“Losing their shells also made the cephalopods exquisitely vulnerable. One scientist described their soft, unprotected bodies as the equivalent of “rump steak, swimming around.” The rest of the ocean seemingly agrees: Almost every major group of predators eats cephalopods, including dolphins, seals, fish, seabirds, and even other cephalopods. This gantlet of threats might have fueled the evolution of the cephalopods’ amazing color-changing skin, their short life spans, and their large brains. After all, intelligence can help an otherwise defenseless creature create new defenses.

“It’s telling that the nautilus — the only living cephalopod that still has an external shell — bucks all of these trends. It lives for up to 20 years, reproducing several times during its life. It also has a much smaller brain than its shell-less relatives, and doesn’t seem to be anywhere as smart. The loss of the shell “has been linked to so many of the adaptations that make cephalopods special,” says Piero Amodio from the University of Cambridge

Cephalopod Features

Front and back of squids and octopus by Haeckel, 1904: squids: 1) Chiroteuthis Veranyi; 2) Histioteuthis Rüppellii (Histioteuthis bonnellii); 3) Pinnoctopus cordiformis (Pinnoctopus cordiformis). Octopus: Octopus vulgaris.

Cephalopods have soft bodies and don’t have any bones. Their head merges with a ring of arms or tentacles surrounding the head. The arms, tentacles, and funnel are all derivatives of the molluscan foot. Cephalopods are regarded as more developed and sophisticated than mollusks like snails, clams and oysters. In fact they are considered the most advanced and developed invertebrates (animals without backbones). They have the largest brains and nervous systems of any invertebrate and their brains are much bigger in relationship to their bodies than those of fish. Most cephalopods grow quickly, mate once and die. Most live no more than 18 months.

Cephalopods have a bird-like beak; well-developed eyes; and sucker-covered arms, or tentacles, used to catch prey, move about and transfer sperm from the male to female. The appendage at the top of their arms is not their head. It is actually a mantle that stores their organs. The horny beak lies at the center of a cephalopod’s limbs and is used for piercing and consuming food and is secreted by the walls of the buccal cavity, which contains the radula. The radula is a tongue-like belt of teeth used to rasp food items and break them into smaller pieces. Food passes through the cephalopod’s donut-shaped brain. [Source: Monterey Bay Aquarium ~]

Cephalopods propel themselves by forcing water through a tubular siphon that draws water behind the eyes and shoot it out under the head. They also have the ability to grown back their arms and tentacles and sometimes communicate by changing the shape of their arms. All cephalopods shoot out ink, which is actually a mix of ink and mucus. The ink isn't intended to hide the animal but serve as a decoy that predators attack while the cephalopod escapes.

Cephalopods like squid and octopus usually have three hearts: One systemic heart that pumps blood through the rest of the body after the hearts have pumped it to the gills, where oxygen is taken up. They also have a mantle, a bag-like sac that sits above a cephalopod’s eyes that doesn’t contain the brain but holds the animal's internal organs, including its hearts, gills, reproductive organs and ink sac.

Cephalopods typically have arms, tentacles, or a combination of the two that extend from the animals’ head. Arms differ from tentacles in that they are completely lined with suction cups. Tentacles sometimes terminate in rounded clubs with suction cups and sometimes with hooks. Tentacles are generally used to grab passing prey. An octopus has eight arms and no tentacles. Squid and cuttlefish have eight arms and two tentacles have many sticky tentacles, but no arms. ~

Cephalopod Mantle, Blood and Respiration

According to Animal Diversity Web: The mantle surrounds the visceral sac and possesses strong muscles required for contraction of the cavity and respiration. An opening in the mantle cavity serves as an inhalant aperture, whereas the funnel serves as the exhalent aperture. All cephalopods have one pair of unciliated ctenidia within the mantle cavity, with the exception of Nautilus, which has two pairs of ctenidia. The movement of water over the ctenidia is controlled by muscular contractions of the funnel or mantle wall. [Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW)]

20120518-squid Mastigoteuthis_flammea.jpg
flaming whiplash squid (Mastigoteuthis flammea)
Cephalopods are the only molluscs with a closed circulatory system. They generally have two gill hearts (also known as branchial hearts) that move blood through the capillaries of the gills. A single systemic heart then pumps the oxygenated blood through the rest of the body.Like most molluscs, cephalopods use hemocyanin, a copper-containing protein, rather than hemoglobin, to transport oxygen. As a result, their blood is colorless when deoxygenated and turns blue when bonded to oxygen. [Source: Wikipedia]

Cephalopods gills are located on the ventral surface of the mantle cavity. They absorb oxygen and exchange gases with the seawater by forcing water through their gills, which are attached to the top of the animal. Water enters the mantle cavity on the outside of the gills, after which the entrance of the mantle cavity closes. When the mantle contracts, water is forced through the gills, which lie between the mantle cavity and the funnel. The water's expulsion through the funnel can be used to power jet propulsion. Cephalopod gills are much more efficient than those of other mollusks. They are supported by a skeleton of strong fibrous protein.

Cephalopod Shells and Ink

With the exception of the nautiluses and species of octopus belonging to the suborder Cirrina,all known cephalopods have an ink sac, which can be used to expel a cloud of dark ink to confuse predators. This sac is a muscular bag which originated as an extension of the hindgut. It lies beneath the gut and opens into the anus, into which its contents — almost pure melanin — can be squirted. Its proximity to the base of the funnel means the ink can be distributed by ejected water as the cephalopod uses its jet propulsion. The ejected cloud of melanin is usually mixed, upon expulsion, with mucus, produced elsewhere in the mantle, and therefore forms a thick cloud, resulting in visual (and possibly chemosensory) impairment of the predator. Some cephalopods releases a cloud with a greater mucus content that approximates the shape of cephalopod that ejected it — strategy aimed at getting a predator to attack the ink rather than the cephalopod. The ink ejecting behavior of cephalopods gave birth to their common name of "inkfish", orginally pen-and-ink fish. [Source: Wikipedia]

body parts involved in cephalopod ink-producing

Among cephalopods, nautilus are the only ones with an external shell. Cuttlefish (sepioids) and squid (teuthiods) have reduced inner shells, while octopuses (ocotopoids) and vampyromorphans lack shells altogether. During the evolution from more conventional mollusks, many cephalopods lost or reduced their shells, replacing them with other defense mechanisms. According to the Monterey Bay Aquarium: These adaptations allow them to quickly change color, jet-propel themselves away from danger, or disappear in a cloud of ink. Cuttlefish have a hard internal shell-like structure called a cuttlebone and squid have a more flexible internal structure called a pen, both of which are used for internal support. Octopuses have no shell-like structure at all. Being without a shell has its advantages, though, when you are squeezing yourself into an inaccessible crevice to escape a predator. [Source: Monterey Bay Aquarium]

While cephalopods may look nothing like their shelled relatives, they do share several features in common: All mollusks have a mantle, which encloses the internal organs and produces the shell. The radula, the rasping tongue that scrapes food into smaller pieces, can be found inside a cephalopod’s beak and in the mouths of snails and other snail relatives. Whether for digging down into the sand and disappearing like a clam or slowly creeping along the surface like a snail, all mollusks have a foot. A cephalopod’s “foot” is modified into arms and tentacles.

Cephalopod’s Donut-Shaped Brain and Nervous System

A cephalopod’s large donut-shaped brain is located behind the eyes and donut, wrapped around the esophagus. When the animal eats the brain stretches slightly as food moves through the esophagus. Cephalopods also possess well-developed nervous systems and complex sensory organs. [Source: Monterey Bay Aquarium]

brain of a squid

Cephalopods are widely regarded as the most intelligent of the invertebrates. Their nervous system is the most complex of the invertebrates, with their brain-to-body-mass ratio falling between that of endothermic (warm-blooded) and ectothermic (cold-blooded) vertebrates. The ganglia in the cephalopod’s brain are large and close to each other, forming a large brain. Certain upper lobes within the brain serve as controls for memory and learning. Captive cephalopods — octopus — have also been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on captive crabs, and return to their own aquarium. [Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW), Wikipedia]

The cephalopod brain is protected in a cartilaginous cranium. Cephalopods also possess ganglia elsewhere within the mantle cavity linked to the brain by giant axons (nerve fibers) that are involved with muscular contraction. The giant axons of the cephalopod mantle have been widely used for many years in neuroscience experiments. Their large diameter (due to lack of myelination) makes them relatively easy to study compared with those of other animals. [Source: Wikipedia]

Cephalopod Senses

Cephalopods have advanced vision. They have statocysts which can detect gravity and possess a variety of chemical sense organs. The eyes of nautiluses are primitive and function similarly to a pinhole camera. but in other cephalopods they are highly developed and resemble vertebrate eyes with a lens, retina, and iris. These eyes are capable of forming images and distinguishing colors. [Source: Wikipedia, Animal Diversity Web (ADW)]

In vertebrate eyes on the left, the nerve fibers route before the retina, blocking some light and creating a blind spot where the fibers pass through the retina. In cephalopod eyes on the right, the nerve fibers route behind the retina, and do not block light or disrupt the retina. 1 is the retina and 2 the nerve fibers. 3 is the optic nerve. 4 is the vertebrate blind spot.

In addition to be used to grab onto prey, the cephalopod’s suction cups are also help them explore their world as they are responsible for the animal’s senses of taste and smell. Octopuses use their arms for depth perception and rely their tactile senses of smell and taste to explore their environment and seek out prey. Some squids have been shown to detect sound using their statocysts, but, in general, cephalopods are deaf. [Source: Monterey Bay Aquarium]

Most cephalopods rely on vision to detect predators and prey, and to communicate with one another. Their eyes’ performance level is about the same as the eyes of sharks. Experiments have shown that common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects. Cephalopods' eyes are good at sensing polarized light but even though many have their ability to change color, many are considered to be color blind. Their eyss are more sensitive to sensing changes brightness and pattern and light levels coming from the body. [Source: Wikipedia]

Cephalopod’s Ability to Change Their Skin Color

Many cephalopods change color to blend in with their backgrounds or to express fear, aggression and sexual excitement. Color changes are caused by chromatophores, pigments sacs situated just under the skin that suddenly swell with signals from the brain. The sacs are yellow, red, black and brown. By expanding and contracting them cephalopods can produce a variety of shades and patterns.

When camouflaging themselves, cephalopods use their chromatophores to change brightness and pattern according to the background they see, but their ability to match the specific color of a background may come from cells such as iridophores and leucophores that reflect light from the environment.

Reef cuttlefish
It appears that cephalopods don’t willfully control their color-changing. Instead, the skin seems act on its own, responding to cues that elicit a colorful response. The octopus changes skin color when they are sleeping. The ability to change colors and camouflage is critical to avoid predation. The cephalopods’ pigment-rich cells in their skin — the chromatophores — are surrounded by cells containing contractile fiber, which give cephalopods the ability to change color and patterns accurately and rapidly in response to stimuluses. Chromatophores may also respond to hormonal cues. When the contractile fibers are stimulated, they contract and expose a larger amount of color. [Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW)]

The problem with using skin colors to send messages is that predators can also pick up on them and use them to their advantage such as attacking when the cephalopods are distracted by sexual matters. Studies by Lydia Mathgar and Roger Nento of Wood Holes Institute suggest that squids — and likely cuttlefish and octopuses too — get around this problem by using communication channels that they can see but predators can’t. Cephalopods have two distinct layers of skin: an inner layer of iridophone cells that is both iridescent and reflects light and an outer layer made up of pigment organs called chromatophores. They also have a complex visual system tuned to read the skin patterns that predators can’t pick up.

Evidence of original coloration has been detected in cephalopod fossils dating as far back as the Silurian Period. These creatures had concentric stripes, which are thought to have served as camouflage. Devonian cephalopods had more complex color patterns, whose function are unknown.

Cephalopod Feeding

All cephalopods are carnivorous and have a two-part beak. Most have a radula, although it is reduced in most octopus . The strong beaks them break apart even tough muscle and some crustacean and mollusk shells. According to Animal Diversity Web: There are two pairs of salivary glands, one of which may be poisonous. The digestive tract consists of three parts: esophagus , which may contain a crop; stomach , which mashes food; and caecum , where most digestion and absorption occur. The posterior portion of the caecum contains a diverticulum that serves as an ink gland. [Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW)]

Hooded Cuttlefish
Cephalopods feed by capturing prey with their tentacles, drawing it into their mouth and taking bites from it. They have a mixture of toxic digestive juices, some of which are manufactured by symbiotic algae, which they eject from their salivary glands onto their captured prey held in their mouths. These juices separate the flesh of their prey from the bone or shell. The salivary gland has a small tooth at its end which can be poked into an organism to digest it from within. The digestive gland itself is rather short. It has four elements, with food passing through the crop, stomach and caecum before entering the intestine. Most digestion, as well as the absorption of nutrients, occurs in the digestive gland, sometimes called the liver. [Source: Wikipedia]

According to the Monterey Bay Aquarium: The feeding styles and diets of cephalopods are as varied as their lifestyles. Predators will actively hunt fish, crustaceans, and sometimes other cephalopods. Some are scavengers and even detritivores (that consume dead organic material). A squid uses its tentacles to snatch a passing fish. A cuttlefish creeping along carefully on two of its arms would potentially whip out its tentacles to catch a shrimp it had hypnotized with a flashing display of chromatophores. An octopus could plunge an arm into a crevice, taste a crab with its suction cups, and extract the delicious crustacean for dinner. A nautilus on the other hand can use its sticky tentacles to scavenge a dead fish, and a vampire squid uses a long sticky filament to catch marine snow (organic material drifting down from the surface). [Source: Monterey Bay Aquarium]

Cephalopod Movement

Cephalopods are the fastest marine invertebrates, which isn’t saying so much as its main competitors are clams, starfish, worms, coral, sea anemones and sponges. Cephalopods mainly get around by jet propulsion. According to Animal Diversity Web: To close its mantle completely, a squid fits two cartilaginous ridges on the mantle wall into two cartilaginous grooves on the opposite funnel wall; contraction of circular muscles around the mantle cavity then forces water out the funnel. The funnel can be aimed, allowing the animal to change its direction. Locomotion in other cephalopods can be accomplished by other means. Octopoids can use their arms to "walk," and sepioids and teuthoids possess lateral fins that can propel the animal. [Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW)]

Nautilus pompilius
Jet propulsion is a very energy-consuming way to travel compared to the tail propulsion used by fish and its efficiency decreases in bigger animals. The stop-start motion provided by the jets is most useful in creating bursts of high speed for capturing prey or avoiding predators. They can out-accelerate most fish. Jet propulsion is supplemented with fin motion. In the squid, the fins flap each time that a jet is released, amplifying the thrust; they are then extended between jets (presumably to avoid sinking). Movement of cephalopods is usually backward as water is forced out in a forward direction through the hyponome (the swimming funnel of a cephalopod). The direction can be controlled somewhat by pointing the hyponome in different directions. Some cephalopods accompany this expulsion of water with a gunshot-like popping noise, whose purpose is thought to be frightening away potential predators. [Source: Wikipedia]

Cephalopods employ similar methods of propulsion despite their size and age and the water environment they live in although smaller, younger ones tend to rely on jet propulsion more and their fins less while bigger ones use jet propulsion less and their fins more. Some cephalopods are able to fly through the air for distances of up to 50 meters, showing how strong jet propulsion can be. The animals spread their fins and tentacles to form wings, continues to expell water from their funnel while is in the air.and actively control lift force with body posture.

Cephalopod Reproduction and Development

Cephalopod females typically possesses a single oviduct. Male produce spermatophores that are transfered to the female's genital pore by means of a specialized arm or tentacle. In some species, a specialized arm tip — known as the hectocotylus arm — may be pinched off and left in the female's mantle cavity. Mating in some cephalopods is accompanied by courting rituals that involve color changes, body movements, or combinations of both. Cephalopods have no larval stage. Their development is directly into small versions of adults. Most cephalopods reproduce only once in a lifetime..[Source: Kristen Wheeler and Daphne G. Fautin, Animal Diversity Web (ADW)]

20120518-octopus Babyoctopus.jpg
Baby octopus
Cephalopods are a diverse group of species, but share common traits such as rapid growth rates and short life spans. It has been suggested that in order to produce the largest possible number of viable offspring, spawning events depend on the ecological environmental factors of the organism. With the exception of octopuses, most of cephalopods do not provide parental care to their offspring. Spawning time and spawning vary among marine species and can be related to temperature. The breeding period can last from several days to a month.[Source: Wikipedia]

Cephalopod life cycles can be affected by various environmental conditions. Cephalopod embryo development can be influenced salinity, oxygen saturation, temperature, pollution and light intensity. These factors also play an important role the hatching success of embryos. Food can also affect the reproductive cycle of cephalopods. Low food availability can influence the timing of spawning as well as growth.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated April 2023

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