Baby Skeleton Devil With Eyes That Squirt Out Goo

A highly intelligent group of ocean dwelling house creatures, the living cephalopods include the eight-armed octopuses, the 10-armed squids and cuttlefishes, and the shelled chambered nautiluses. Early in their development, cephalopods relied on the sturdy protection of shells, but over time many eventually lost the outer shell and instead relied on new adaptations like heightened intelligence, a talent for hiding, and strong, flexible artillery. The largest—the giant squid—measures longer than a school bus, while the smallest ones—like the pygmy squid and California lilliput octopus—could sit on the tip of your finger. Cephalopods have long fascinated humans and were frequently mentioned by Aristotle, and this fascination shows no signs of diminishing today.

Anatomy, Diversity, and Evolution

Anatomy

Cephalopod literally means "caput pes" in Greek, a reference to the way the cephalopod's head connects to its many arms. The basic cephalopod body plan includes ii optics, a mantle, a funnel (likewise called a siphon), and at least eight arms. Some have hard, internal structures, like the cuttlebone in the cuttlefish and the pen in the squid, that evolved from the hard, outer shells of their ancestors, but in many octopuses the difficult structure is completely lost. Just the chambered nautiluses accept an external crush.

Giant squid have eight arms but use their two long feeding tentacles to seize prey. (Smithsonian Establishment)

Arms, Tentacles, and Suckers

Octopus have eight artillery while squid and cuttlefish have eight arms plus 2 other specialized arms, called tentacles. The tentacles are adapted to snatch prey from farther away through their ability to extend and retract. Both the arms and tentacles are equipped with powerful suckers that can function like suction cups. The suckers in some squids are transformed into sharp hooks to amend grasp their prey, making squid a formidable underwater predator. The sucker rings of squids are equanimous of "suckerin" proteins that are similar in strength and construction to the protein found in spider'southward silk.

The tentacles and suckers of squid come in many shapes and sizes. At the acme is the Pacific flight squid, in the centre is the bending squid, and at the lesser is the ram's horn squid. (A. Pollock and Ewald Rübsamen via Wikimedia Commons)

With viii sucker lined arms and in some cases a pair of tentacles, a cephalopod can maintain a pretty tight grip. But how a cephalopod maintains that grip differs between squid and octopus. Squid use their suckers primarily for grabbing food. The cup-shaped sucker connects to the squid arm or tentacle via a thin stem. Once the strong, circular surface of the sucker comes in contact with the prey, a tug from the stalk decreases the pressure level within the sucker cavity, creating a sticky seal.

(Analogy by Gabby Wharton)

An octopus is a bit more dexterous than a squid, and uses its artillery for a variety of tasks including walking and handling objects. Upon coming in contact with an object, similar a tasty crab or rocky ledge, the sucker surface creates a seal with the object. Trapped within the sucker cavity, the water has nowhere to go as the sucker muscles contract. The muscle wrinkle causes water pressure inside the sucker crenel to drop and the college pressure of the surrounding open up sea forces the sucker surface against its chosen target, creating a stiff hold. Inspired past the force and suction mechanism of octopus suckers, scientists are using them as models for medical adhesives and zipper in robots.

The nautilus boasts an amazing 90 plus arms. These arms lack suckers but are lined with sticky grooves that help them grab prey.

Sight

Cephalopods are famous for their eyes. In some cephalopods the eyes are equally complex as the man eye, and the eye of the giant squid is enormous. Most cephalopod eyes, like human eyes, contain an iris, pupil, lens, and in some cases, a cornea. Octopus, squid, cuttlefish, and nautilus all take differently shaped pupils— an octopus has a rectangular student, a cuttlefish has a w-shaped pupil, and a squid's pupil is circular. Only the nautilus has a comparatively basic eye beefcake, relying on a pinhole student without a lens. They are able to dilate and constrict their pupils in varying light intensities and can probably distinguish very uncomplicated visual cues.

Octopus, squid, cuttlefish, and nautilus all have differently shaped pupils— an octopus has a rectangular pupil. (Greg McFall, NOAA)

The rest of the cephalopods have complicated eyes. Even more than remarkably, the circuitous eyes of humans and cephalopods are surprisingly similar in design considering the two evolved independently. A report by scientists at the Nagahama Institute of Bio-Scientific discipline and Technology found that this similarity is due to one shared cistron, Pax6, traced back to our last mutual ancestor, more than 500 1000000 years ago. The factor is considered a master control gene—meaning it orchestrates how to brand an eye (like an educational activity manual) rather than constructing the individual building blocks.

Despite the complexity of their eyes, cephalopods are virtually probable colorblind. The ability to run across color relies on specialized receptor cells. In animals and humans these cells are called cones, a distinction from the light sensitive cells called rods. Humans take three different types of cones: one that detects reddish wavelengths of lite, ane that detects bluish, and one that detects green. In combination, these cones permit united states of america to see a wide breadth of color hues. Only cephalopods only have ane type of photoreceptor prison cell, rendering information technology colorblind.

Or perhaps not! A recent report suggests that the strange shape of their pupils may allow some cephalopods to distinguish colors in a unique way.  The unusual shape may act somewhat like a prism, scattering the various colors that make upward white calorie-free into their individual wavelengths. In one case the low-cal has been divided, a cephalopod tin then focus the individual colors onto its light-sensitive retina past a subtle change in the distance between the lens and retina. This method would have quite a bit of processing power compared to a multi-cone eye and can help explain why a cephalopod has such a large brain.

A cuttlefish student is in the form of a "Westward." (Steve McNicholas Flickr)

Cuttlefish eyes are especially notable among cephalopods. Cuttlefish are the most talented at discerning differences in polarized light, a feat that human eyes are unable to reach (humans perceive polarized light as a glare). For animals that can run into it, polarization adds an actress dimension to an paradigm, like to the addition of color to a blackness and white photo.  Natural light from the sun, or an incandescent light bulb, is unpolarized, meaning its energy radiates in all directions. Only when light reflects off of a surface the light energy may be stripped down to just one management—this is polarized light. The angle of polarized low-cal varies depending on the surface it bounces off of—this is what a cuttlefish tin discern. A cuttlefish tin can await at polarized light and notice within one caste the difference in that light'southward energy direction.

Propulsion and Move

A cephalopod gets effectually past using several different methods. In general, they apply jet propulsion—strong muscles fill the mantle miscarry h2o from the drapery crenel through the funnel and propel the creature in the opposite direction. Bottom-dwelling house octopuses commonly apply jet propulsion just equally a ways of escape, instead relying on their artillery to walk beyond the ocean floor—a few species fifty-fifty walk on ii arms. A 2005 study found that the coconut octopus and the algae octopus tiptoe astern on two artillery, a method that allows them to maintain their ambiguous cover-up while crawling. For hovering, cephalopods have a couple of different strategies.  Cuttlefish and a few squid species either undulate their fins to hover. Others produce and shop an ammonium-based chemic that makes them neutrally buoyant.

This common octopus ( Octopus vulgaris ) shows off its funnel, which it uses to propel itself through the water (and as well expel waste). (Wikimedia user Beckmannjan)

The nautilus has a specialized system for movement and buoyancy that takes advantage of the compressible nature of gas. Within the crush of a nautilus are chambers of gas that it uses like a flotation device.  The nautilus' buoyancy is dependent upon a consistent volume of the gas within the crush, which becomes a bit tricky when you consider that at deeper depths the surrounding ocean pressure squeezes the gas pocket and at shallower depths it lets the gas expand. But the nautilus uses its chambered shell like a submarine's anchor organisation to pass fluid and gas betwixt the chambers to adjust the internal shell pressure and proceed the gas a consistent book as it swims between varying bounding main depths.

The "Dense octopod" swims by moving its fins and pulsing its webbed arms. (©1999 MBARI)

Named for its visual likeness to the truthful nautilus, the paper nautilus or argonaut is actually an octopus, and the females live in a cardboard structure. A female argonaut secretes an egg case that not just looks similar a nautilus beat simply also is used to help with buoyancy. At the ocean surface the octopus traps air within its papery beat and so propels itself underwater. At a certain depth, the compressed air pocket counterbalances the octopus' weight, rendering it neutrally buoyant. The uncanny similarity betwixt the argonaut egg casing and the nautilus' shell signal it may be an example of convergent evolution.

Circulatory System

Cephalopods have a lot of center—three hearts to be verbal. The 2 branchial hearts push oxygen-depleted blood through the gills while the systemic center pumps the oxygenated claret throughout the torso.

For cephalopods, the term "blue bloods" takes a more than literal meaning than the medieval reference to dignity—their blood is actually blue. While humans and other animals rely on an iron-based oxygen transport system, cephalopods evolved a copper-based system, which is the source of the blueish color (similar to horseshoe crabs). The copper-based molecule in a cephalopod's claret is called hemocyanin, which binds to oxygen to acquit it throughout the torso and power muscles. It has a significantly lower oxygen binding ability when compared to atomic number 26-based hemoglobin, though a study of an Antarctic octopus, Pareledone charcoti, suggests the hemocyanin system helps cephalopods maintain efficient oxygen send in environments of varying temperature and oxygen level. Hemocyanin is most efficient in cold water but loses its concur on oxygen in more than acidic h2o suggesting that as oceans get warmer and more acidic due to climate change, cephalopods may struggle to circulate enough oxygen through their bloodstream.

The nautilus often encounters areas of low oxygen when it travels to depths of around 2,300 feet (700 thousand) and will lower its metabolic rate and siphon off pocket-size amounts of oxygen from its chambered shells in social club to survive.  It is also highly efficient at jet propulsion, more and then than even the squid, and is able to utilise upward to 75 percent of the free energy information technology transfers to the water to motility. This becomes highly advantageous when conserving oxygen is important.

A cephalopod, like this cuttlefish, has blue blood. (Erwin Poliakoff, Flickr)

Diverseness

The cephalopods are a diverse class of mollusks (a group that besides includes snails and bivalves) that emerged during an explosion of creature diversity in the oceans during the Cambrian period, over 500 million years ago (mya). Today, scientists divide the living cephalopods into three groups, chosen superorders. However, many details of cephalopod evolutionary classification continue to change as scientists detect new clues from genetic testing and newly discovered fossils. Below we've outlined the iii major superorders with some of the groups they contain according to the latest information.

The cephalopods are a diverse class of mollusks. Today, scientists divide the living cephalopods into three groups, called superorders. Many details of cephalopod evolutionary nomenclature proceed to change as scientists find new clues from genetic testing and newly discovered fossils.

(Created by Ashley Gallagher for the Ocean Portal)

Octopodiforms- The 8-armed cephalopods

• Octopus - There are roughly 300 species of octopuses pond around in the ocean today, though the exact number is continuously changing as new species are discovered. During NOAA's 2016 Okeanos mission scientists discovered the "Casper" octopus in the central Pacific Ocean in waters around 13,000 anxiety (4,000 meters) deep. Near octopuses spend the majority of their time living on the ocean floor. They are also lone creatures and adopt to live alone in a den, notwithstanding, the gloomy octopus is an exception and will congregate in underwater cities like the ones researchers nicknamed Octlantis and Octopolis. Most people are familiar with octopuses in the Incirrata grouping. They have soft bodies and no internal vanquish (or in some species 2 minor rods made of cartilage), which allows them to squeeze their bodies through unimaginably tight spaces. The Cirrata, like the dumbo octopus, are abyssal dwellers and have an internal cartilage shell, two fins on the sides of the body, and finger-like strands between their suckers called cirri.

A abyssal octopus, the dumbo octopus uses its ear-like fins to bladder in the water column. When observed in 2014 during NOAA'south Okeanos Explorer's Gulf of Mexico expedition, this dumbo had a never before seen coiled leg body posture. (NOAA)

• Vampire "Squid" (Vampyroteuthis infernalis)- Opposite to its proper noun, the vampire squid is actually more than closely related to the octopuses. Although its name translates to "the vampire squid from hell," these cephalopods are far from dangerous, as they actually eat globe-trotting particles called "marine snow" with ii, thread-similar filaments (that are modified arms). Like many deep-body of water dwellers, their bodies are covered with light organs, and they can turn almost within out by wrapping the arms around the body when they are disturbed. Their internal shell has evolved into a sparse, broad plate similar to a squid's pen.

Decapodiforms- The ten-armed cephalopods

• Cuttlefish - More than 90 species of cuttlefish live in tropical and temperate waters off of Europe, Asia, Africa and Commonwealth of australia. They are predominantly seafloor dwellers and can be establish in sandy, muddied or rocky habitats. While most species alive betwixt seven and 800 anxiety (2 and 250 meters) a few can survive at depths near 3,300 feet (yard meters). They rely on a cuttlebone—an internal, modified calcareous trounce with several chambers that help the cuttlefish maintain buoyancy. Scientists once believed cuttlefish were a completely separate lineage from other x-armed cephalopods, however, recent genetic studies show that cuttlefish are evolutionarily amongst the groups of squid.

A reaper cuttlefish is a color changing wizard, however, it often prefers a deep carmine or mauve color. (Pecker, Flickr)

• Squid – The squids are divided into quite a few groups, with over 300 species worldwide. Some live in shallow waters while others travel to depths over 16,000 feet (5,000 meters). While most squids tend to live lone lives, others congregate in schools of millions. Many squids are voracious predators. The Humboldt squid is a specially fearsome predator that uses the toothed sucker rings to grab its prey. Squids have a stiff back up structure chosen a pen (also called a gladius) that runs the length of the mantle and is fabricated of chitin. The giant squid is the largest cephalopod, the longest ever recorded measured about 43 feet (13 meters) long.
• Ram's Horn Squid - The ram's horn squid is the just living cephalopod within the spirula family, which is unique because of the internal, coiled vanquish that is collected by beachcombers. The animal lives betwixt one,000 and 5,700 feet (300 and 1,750 meters) in tropical and subtropical waters around the world. A large light organ sits at the end of its body, though its function remains a mystery. Also mysterious is how it is related to the other squids.

While virtually squid have a flattened shell remnant called a pen, the ram'southward horn squid has an internal coiled shell that they use to control buoyancy like the nautilus. (Ewald Rübsamen from Dice Cephalopoden)

Nautiloids-

• Nautilus - The only representatives of the early, shelled cephalopods that notwithstanding exist today areNautilus and the closely relatedAllonautilus (for simplicity hither, they will both be collectively referred to as nautiluses). Nautiluses live in an external, coiled beat. The beat has many chambers, and equally the nautilus grows information technology adds sequentially larger chambers. The largest and newest sleeping accommodation is where the animal lives and the smaller chambers are used like submarine ballast tanks to regulate buoyancy. A newly hatched nautilus will only have four chambers simply past the fourth dimension they are adults they average effectually xxx. There are 7 recognized species within the nautilus family.  They live in the southwestern Pacific Ocean, the Philippines, Indonesia and around Australia where they eat crab, shrimp, fish and the bodies of dead animals. High demand for nautilus shells in the beat and jewelry trade is causing business over possible extinction. The crusty nautilus species was observed live in 2015 for the kickoff time in 30 years.

Evolution

Cephalopod Ancestors

While today's cephalopods are well-nigh notable for their many arms and soft bodies, aboriginal cephalopods are generally known from their shells because they are well preserved equally fossils. Like the living nautilus, a fossil cephalopod vanquish has two distinguishing characteristics: a series of chambers divided by walls but connected by an internal tube. The barriers that carve up the chambers are called septa and the internal tissue tube is called the siphuncle.

A cantankerous-section of a nautilus shell is not only beautiful, it also is a cracking instance of the chambered cephalopod shell. The projections splitting each bedchamber are the siphuncle tubes that let gas and liquid to be transferred from chamber to sleeping room. (Jitze Couperus, Flickr)

There are many more species of fossil cephalopods (17,000) than living ones (about 800) and some of the most important groups in the past take no living descendants. The earliest ancestors of today'southward cephalopods appear in the fossil record effectually 530 mya, at a fourth dimension of intense animal diversification during the Early Cambrian. Early cephalopods probably diverged from the monoplacophorans, a group of bottom-dwelling molluscs with tall, slightly curved, conical shells. The commencement of these early on cephalopod ancestors is likely Tannuella, a mollusk with a chambered shell. However, the first confirmed cephalopod fossil is the Plectronoceras, noted by the presence of a siphuncle used for control of buoyancy. Information technology is likely the conquering of buoyancy that spurred diversification from these ancestral molluscs, since cephalopods were freed from a bottom-abode being and could explore the open h2o cavalcade.

Past the Ordovician, a period that began roughly 500 mya, a great diversity of cephalopod shells emerged. The stout, slightly curved shell shapes of the late Cambrian evolved into a variety of shapes that included coils, straight cones and domes. These shapes added benefits that expanded the cephalopod's habitat from its ancestral shallow and warm waters.

Throughout much of the cephalopod's ancestry, the coiled shell evolved time and time again from a direct shell. A coiled shape strengthens the crush, increases maneuverability, increases the ability to cut through the h2o, and lowers the energy required to maintain buoyancy. Cephalopods dominated the seas for roughly 360 million years, and information technology wasn't until the end of the Cretaceous at effectually 66 mya that fishes and marine mammals started to take over. The sluggish and armored cephalopods were probable no match for the new, swift swimmers. Not only were they competing for the same food sources, they were also likely a great snack. These fast swimmers flourished following the loss of dinosaurs during the KT mass extinction roughly 66 mya. Remarkably, coiled cephalopods in the nautiloid group survived the extinction, but the coiled ammonites did not fare so well. Some scientists argue that the acidic body of water waters post-obit the extinction-causing meteor crash dissolved the delicate shells of infant ammonites that lived nigh the ocean surface, and the deeper dwelling cephalopods remained out of harms fashion. Today but eight species of cephalopods with coiled shells remain – the seven nautilus species and the ram's horn squid.

An octopus fossil from the Cretaceous that was discovered in Lebanese republic. (Chip Clark, Smithsonian, National Museum of Natural History)

With a lineage that extends to around 530 mya, it should be no surprise that the cephalopod family unit tree is pretty complicated. There are so many lineages and types of fossils that even cephalopod specialists oftentimes debate how they are related. Below, are a few of the best-known groups of ancient cephalopods.

The Nautiloids
The Nautiloids are one of the oldest groups of cephalopods, emerging at the stop of the Cambrian roughly 500 mya. Throughout time, over 10,000 different species swam in the ocean, though today only the seven species of chambered nautiluses remain. Though the earliest nautiloids had direct shells, past the Ordovician, which began roughly 500 mya, their shells began to diversify, some condign gently curved and others coiling. Ane way scientists distinguish the nautiloid fossils from their coiled cousins the ammonoids by looking at the siphuncle. In the nautiloids information technology is found direct down the middle of the chambers while in the ammonoids information technology hugs the outer trounce wall.

The Ammonoids
Ammonoids are a group of extinct, coiled cephalopods that swam in the sea betwixt 420 and 66 mya between the Devonian and Cretaceous. The name ammonite comes from the Greek reference to the Egyptian god Amun, whose head was framed by spiraling ram's horns. Some were as small as a thumbnail while the largest measured over 8 feet (2.v meters) in diameter, taller than the average, grown human being. Ammonoids too differed from the nautiloids in that the septa dividing the shell chamber joined the outer crush wall in intricate, undulating edges. The septa-beat out edge is chosen a suture, and as the ammonoids evolved the suture became increasingly intricate. This complexity may have helped with buoyancy command, while the more than bones sutures of early on ammonoids helped withstand the force per unit area of deep water. It is possible that early ammonoids lived in deep water and over time they moved into shallower waters.

Like the modern nautilus, this extinct relative of modern squid had a protective trounce. (Mary Parrish/Smithsonian Establishment)

The Belemnites
The belemnites swam in the ocean from the finish of the Triassic to the Cretaceous roughly 245 to 66 mya and are i of the more than studied straight-shelled cephalopods. They are also the fossil group near closely related to today'south squid and octopus.  Based upon a few, rare soft-body fossils, they were squid-like and relied on jet-propulsion, with a straight internal shell and a pair of triangular fins. All the same, well-nigh of what we know nearly them comes from their shells—near belemnites had a solid tip beyond the chambered shell called a rostrum that was easily fossilized. Belemnites were tasty meals for sharks and icthyosaurs. Many shark fossils contain the arm hooks of belemnites in their stomachs, but the noticeably absent rostrum is presumed to be too difficult to assimilate and most likely was regurgitated.

There are many more species of fossil cephalopods (17,000) than living ones (most 800) and some of the near important groups in the past take no living descendants.While today'southward cephalopods are most notable for their many arms and soft bodies, ancient cephalopods are mostly known from their shells considering they are well preserved as fossils.

(Created by Ashley Gallagher for the Ocean Portal)

Behavior and Environmental

Beliefs

Intelligence

Octopus are famous for their sophisticated intelligence; some scientists even argue that cephalopods were the kickoff intelligent beings on the planet. They are able to untie knots, open up jars, and toddler proof cases, and are mostly expert escape artists. There is increasing evidence that cephalopods accept unique personalities—one octopus may be shy and reclusive, another curious and playful, or maybe mischievous and cranky. Maybe, beingness defenseless, with soft bodies and living in a competitive surroundings with stronger, more agile bony fish led them to evolve especially abrupt minds for problem-solving.

Intelligence requires big brains. A cephalopod brain is divided into many different sections called lobes. The squid Loligo has at least 30 different lobes. The lobes are specialized centers that, amidst other things, process data from the eyes, control cover-up, and store memories. Though structured similarly to other mollusks, a cephalopod nervous arrangement far surpasses the nervous systems of their closest molluscan relatives—the California sea slug has about xviii,000 neurons while the common octopus, Octopus vulgaris, has roughly 200 1000000 neurons in its brain. Humans have many more, but nether 100 billion, but a cephalopod is on par with dogs and some monkeys since they also acquit virtually two-thirds of their neurons in their arms, non their head. Different humans and other mammals, the cephalopod brain volition grow one and a half times its original size from the moment of nascence to adulthood.

A veined octopus sits inside a vacant bivalve shell, which information technology uses as a portable shelter, in the Philippines. This is ane of the few examples—if not the only example—of tool use in invertebrates. (Jeffrey de Guzman/Nature'southward Best Photography)

With intelligence comes the ability to acquire. Scientists first realized cephalopods had a talent for learning after the publication of a groundbreaking study by a German researcher named Jakob von Uexkull in 1905. Uexkull starved a grouping of octopuses for fifteen days and then presented them with hermit venereal carrying anemones on their shells. The famished octopuses readily attacked the hermit crabs, though after a few stings from the anemones they presently avoided the crabs altogether. It was clear octopuses were cleverer than once believed and, as a event, scientists in the early 1900s began testing the limits of a cephalopod's learning capacity.

Early studies plant an octopus can be trained to perform specific behaviors using food rewards and shock punishments, showing they are capable of making associations. When presented with a foreign simply harmless object they volition initially explore and investigate, just afterwards consecutive introductions, they speedily lose interest, a sign they remember the object and its now unremarkable nature.

TED-Ed, Cláudio L. Guerra

Surprisingly, though, octopuses are not the best when it comes to tackling mazes—they fail to even think a simple sequence of turns. However, in one experiment, the species Octopus maya quickly learned whether to take a right or left in a simple "T" maze to escape the dry maze and discover their reward—the reprieve of a seawater tank. Levers are as well tricky for octopuses and, for the nearly part, tests trying to teach octopuses to feed themselves using a lever machinery have been unsuccessful.

It may come as a bit of a surprise that although they are reclusive and lonely creatures, octopuses may exist able to learn from 1 some other. In a 1992 study, scientists trained a grouping of octopuses to discriminate between two colored balls. Choosing a cherry ball elicited a tasty snack while choosing a white ball elicited an unpleasant shock. Equally this group of octopuses learned to associate color with reward and penalization, a second group of octopuses was allowed to discover from split tanks. Adjacent, these observers were given the selection—blood-red or white. Without reward or penalization, the second group chose the red ball more quickly than the initial group.

Playing behavior is also attributed to intelligent organisms like mammals and some birds, but recent studies suggest octopuses may besides similar to accept a little fun. A 1999 study at the Seattle Aquarium found that two of ten octopuses squirted water at weighted pill bottles, pushing the bottles against a filter current. Afterward waiting for them to float back the octopuses squirted them once more, almost similar bouncing a basketball game. A 2006 report suggested that octopuses volition play with blocks as well.

Masters of Disguise

Sometimes referred to as the chameleons of the sea, a cephalopod can change the colour and texture of its skin in the blink of an center. Some apply this skill to blend into their surroundings every bit masters of disguise, while others purposefully stand out with a flashy display. They modify texture by controlling the size of projections on their skin (chosen papillae), creating surfaces ranging from small bumps to tall spikes. A 2018 study on cuttlefish plant that once the papillae extend they become locked in place, enabling the cuttlefish to effortlessly agree their textured disguise while expending minimal energy. The colour transformations are made possible by thousands of paint-filled cells that dot the entire body, called chromatophores.

Within each chromatophore is an elastic, paint-filled sac that is continued and controlled by several muscles and nerves. When the muscles contract the sack expands, revealing vibrant pigments—reds, browns, and yellows. When the muscles relax, the sack shrinks dorsum down, hiding the pigment. Some cephalopods also have iridophores and leucophores, which add to the complexity of the skin's color. The iridophores lie directly beneath the chromatophores and are responsible for displays of metal greens, blues, aureate, and silver. Leucophores, as well known as "white spots," scatter and reverberate all light from the environment and are believed to aid in camouflage.

This day octopus ( Octopus cyanea ) has shaped itself like algae or some coral so hide from predators or stalk prey. (Flickr user Pudekamp)

In combination, these color and texture irresolute techniques let a cephalopod to mimic near any background. Experiments past Roger Hanlon show cuttlefish expertly mimicking mottled textures, stripes, spots, and a blackness and white checkerboard!

Sure cephalopods have fifty-fifty mastered the power to impersonate other animals, a self-defence force tactic called mimicry. The mimic octopus is the height of shape-shifting wizardry. Information technology appears to imitate up to fifteen dissimilar animals (that nosotros know of). Faced with a pesky damselfish it buries six of its arms in the sand leaving just two strategically placed and colored to look like the venomous banded sea snake (a predator of the fish). It tin can besides cruise along the sand similar a flat, banded sole fish or swim upwardly in the water column like the venomous, spiny lionfish. The pharaoh cuttlefish's chosen disguise is just as impressive—it can mimic the color, beliefs and shape of a hermit crab.

Scientific discipline Friday

Bioluminescence

ome cephalopods have i more trick upwards their sleeves when irresolute color. It's called bioluminescence, which is the creation of calorie-free in specialized calorie-free organs called photophores. Lite is created through a chemic reaction that produces light energy in the torso of the animal, similar to how fireflies flash on a hot summer nighttime.  A catalyst called luciferase sets off the light producing substance called luciferin. The result is an eerie glow, startling flash, or syncopated blinking.

Bioluminescence serves more than than just a pretty brandish. The concentration of photophores on the lesser side of some squid suggests the light is used equally a camouflage technique chosen counterillumination; the bright light protects the squid from lurking predators below by allowing it to blend in with low-cal coming from the surface of the h2o. But for the cephalopods that want to stand out, light is used to lure prey or wink equally a warning for predators. The dazzling calorie-free displays of the firefly squid during mating season off the coast of Nippon are quite the sight to encounter at night, though scientists are unclear whether the purpose of the light is to concenter mates, deter predators, or something still to be discovered.

One of the about heady light displays is performed by the vampire squid. Deep ocean dwellers, vampire squid rely on iii types of light organs. Each of the viii arms is tipped with several uncomplicated light organs, tiny photophores dot the pare, and a tertiary, more complex pair of lite organs with photoreceptors sit near the fins. When startled, luminescent clouds of fungus are emitted from the arm-tip light organs, leading scientists to think the glowing display is a defense mechanism.

Ed Yong, PBS Digital Studies

While some cephalopods, similar the vampire squid, are able to produce light on their own, for others lighting upwards requires a bit of help. The bobtail squid relies on a bacterium called Vibrio fischeri, and volition selectively allow this bacterium to grow inside its photophores. At birth, a immature bobtail squid lacks the bioluminescent bacteria and must find the light producing microbes in the water cavalcade. At this stage of life, the squid's light organ is not fully adult simply pocket-size hairs forth the photophore sweep the bacteria closer, and a molecular deterrent prohibits all bacteria except Vibrio fischeri from entering. One time one bacterium successfully enters the photophore it multiplies by the hundreds of thousands, a colonization that spurs the full development of the photophore. Without the bacteria the bobtail squid's photophore will not develop, rendering the light organ useless as a cloaking device. Vibrio fischeri is a mutual bioluminescence partner with some other cephalopods that owe their glowing skills to the microbe.

Inking

"When the Sepia is frightened and in terror, it produces this blackness and muddiness in the water, as it were a shield held in front of the torso."—Aristotle,The History of Animals, Book Four (ca. 350 BC). Translated past Arthur Leslie Peck and Edward Seymour Forster.Aristotle XII: Parts of Animals Motion of Animals, Progression of Animals (1937).

In a stressful situation, a cephalopod has one terminal defence force tactic. Almost all cephalopods take an ink sac, a bladder that can suddenly release a plume of dumbo, black ink. The ink is a mix of 2 secretions—a melanin-based chemical from the ink gland that gives information technology the dark hue and a thick mucus from the animal's funnel organ. Another compound in the ink, chosen tyrosinase, is a potent irritant that can disrupt a predator's smell and taste, besides equally cause blindness. When startled or attacked by a predator the ink jet works similar a smokescreen, a distraction, or a cephalopod look-a-like that the predator attacks instead which allows the real cephalopod to make a quick escape.

A humboldt squid (Dosidicus gigas) releases a cloud of ink at nighttime in Mexico'due south Sea of Cortez. (Brian Skerry, National Geographic)

The ink can as well act as a warning cue to other cephalopods. In the presence of ink the California market place squid will begin to swim, and the Caribbean reef squid will initiate camouflage coloring. The Japanese pygmy squid has figured out how to use ink to hunt for shrimp, rather than just hide from predators. It squirts a few quick puffs in the management of the shrimp and then darts through the ink to grab its meal. The ink is potentially used as a way to both hibernate from the prey and to distract the shrimp from noticing the incoming assault.

Reproduction

For most cephalopods, sexual activity is a one time in a lifetime event—both the male and female person die soon afterward mating. A male sometimes initiates the interaction with a courtship display meant to attract and woo the female person, though for near octopuses there is picayune foreplay. If successful, the male volition use his hectocotylus, a specialized arm, to deposit sperm packets chosen spermatophores on or in the female.

Two California market squids (Loligo opalescens) mate in the waters off of California's Channel Islands. While spawning, the males' arms blush red as he embraces the female; a alert to other competing males to back-off. (© Brian Skerry, www.brianskerry.com)

The story of how the proper name hectocotylus came to exist is a tale of mistaken identity. In 1829, the famous naturalist George Cuvier identified an odd "organism" inside the mantle of a female newspaper nautilus (which, to make matters even more than disruptive is, in fact, an octopus) and idea it was a new parasitic worm which he called the hectocotylus. Turns out, it was really a male person cephalopod arm, but the name stuck. In the paper nautilus, the hectocotylus detaches completely during sex and remains inside the female person—this is what Cuvier mistook equally a worm. Fertilization varies from species to species and in some cases the female holds on to the hectocotylus in a specialized pouch and fertilizes the eggs as she lays them.

In some squid and cuttlefish, mating occurs in mass gatherings and the males compete for access to the female equally she spawns. In the European squid, Loligo vulgaris, smaller males will brim around the edges of the spawning ground and display patterns similar to a female, rather than claiming the ascendant male. Once a female begins to spawn, a small-scale male volition dart in and quickly mate with her, a beliefs that has earned them the name "sneaker" males.

Two squids tending to egg casings. (Josh Cummings, Flickr)

If a female octopus lives nearly the ocean floor, once her eggs are fertilized, she volition lookout out a shelter to lay her eggs and adhere them to the ceiling or walls in long strings.  She'll forgo eating and instead spend her time fanning the eggs with water to keep them clean and protect them from predators. While most octopus mothers spend less than a few months watching over their brood, ane deep-body of water octopus, Graneledone boreopacifica, holds the record for the longest time spent watching over her eggs—over four and a half years! The long egg evolution fourth dimension is almost likely a response to the relatively cold environment of the deep sea. For some squids that live in the open up sea, the eggs are spawned in gelatinous masses that then migrate within the water cavalcade. The discovery of a mass squid graveyard off the declension of California indicates that once the female squid successfully reproduce, they die and sink to the bottom of the body of water to over 3,300 feet (one,000 m) where they become nutrient for abyssal scavengers.

Upon hatching, the tiny, baby cephalopods get planktonic, meaning they alive in the h2o column. Many hatchlings are already expert predators and will actively pursue prey. Lilliputian is known virtually the early on life stages of specific species due to difficulties in identifying the very small young.

Ecology

In the Food Web

A cephalopod is a strategic and cunning predator. They've evolved to go proficient stalkers, ambushers, and masters of disguise. They also aren't very picky—a cephalopod can swallow anything (also plants) from crustaceans to fish, bivalves, jellyfish, and fifty-fifty other cephalopods. Divers know that a telltale sign of an octopus den is a collection of empty crab shells littered on a rocky bottom.

Carnivorous predators, all cephalopods have evolved special tools to help consume their prey. They rely on a precipitous pecker that chops their prey into bite-size pieces. Within the nib, a tongue-similar radula is lined with tiny teeth which can push button food downwards into the digestive tract or human action like a drill to bore holes in shellfish. In many cephalopods, not just the notoriously deadly blue ringed octopus, a salivary gland produces a paralyzing toxin that immobilizes and digests prey upon existence bitten. The cephalopod esophagus runs through the brain, requiring food to be sufficiently pulverized so it can fit through the narrow infinite. The digestive tract also includes a stomach, which farther mashes the food, and a caecum where some nutrients are absorbed.

An illustration of an octopus snagging a repast. (Charles Livingston Bull, Library of Congress)

Often, cephalopods are voracious consumers. A study of the California 2-spot octopus found that an 80 percent turn down in the octopus population spurred a 500 percentage explosion of their prey populations, gastropods (snails and slugs) and hermit crabs. In the English language Channel, unseasonably warm waters in 1900 and again in 1950 acquired an "octopus plague" in which Octopus vulgaris, an uncommon species in the area, became so abundant that they consumed much of the shellfish. The Western Evening Herald of Plymouth, United Kingdom wrote in 1899, "they take quite ruined the fisheries, and many men have laid upwards their boats in despair. They devour everything, even crabs, and lobsters, and oysters, and all shellfish."

Some oceanic cephalopods participate in daily movements, called diel vertical migrations. The embrace of night allows them to hunt at the surface without the threat of predators seeing them. In one case the dominicus comes up they make their way down to deeper, darker water.

The circles on this piece of sperm whale peel are behemothic squid sucker marks. (In Smithsonian Report 1916)

Although a formidable predator in its own right, the soft bodies of squid, octopus, and cuttlefish are delectable meals for other predators. Moray eels relish eating octopuses arm by arm and dolphins will toss and thrash an octopus against the water's surface in an endeavor to stun them prior to eating. Birds too swallow cephalopods. Albatrosses will plunge upward to 32 feet (x meters) deep to snatch a squid beneath the waves. Scientists often discover the tough beaks of squid and octopus in the stomachs of sperm whales and seals. Sperm whales that wash aground can fifty-fifty have large sucker scars along their torso, indicating the whales engage in epic battles with giant squid while eating them.

Human Use and Conservation

Fisheries

People accept enjoyed eating cephalopods since ancient times. According to Paul Bartsch, Curator of Mollusks at the Smithsonian Museum of National History in the early 1900s, the Greeks and Romans considered all kinds of octopus to exist a delicacy. In Rome, they would stuff the cavity within the torso total of spices, cut off the arms, and bake it in a pie. During preparation, chefs refused to use atomic number 26 knives claiming that the metal left an unsavory gustatory modality and would instead employ special bamboo knives. The Greeks, too, enjoyed octopus, and often sent 1 as a gift to parents the fifth day after a child was born, the naming day. One comedic Greek story tells the tale of Philoxenus of Cythera, a specially greedy homo. One dark, Philoxenus desired an elaborate meal, which subsequently included a massive, three-pes octopus every bit its main dish. Upon consuming all 8 arms by himself, the man savage ill and required the attention of a doctor. But the doctor's prognosis was non good—Philoxenus was told he merely had hours to live. Resigning himself to his fate, he decided to finish off the rest of the meal claiming, "he left nothing on the world which seemed to him worthy of regret."

Recently captured octopus hang to dry in Hellenic republic. (edar via Pixabay)

In many places effectually the world, octopus, squid, and cuttlefish are common bill of fare items at the dinner table. Over 4 million metric tons of cephalopods are fished from the body of water every year, the same weight as 27,000 adult whales. Squids brand upward a good chunk of the catch, accounting for about 75 percent of that total. In several areas like the Gulf of Thailand, evidence of squid fishing can even be seen from the international space station. Squid fishermen string hundreds of bright lights from their boats at dark to attract plankton, a powerful lure for squid that follow their prey to the surface where they are and so caught past the fisherman. Just octopuses and cuttlefishes are likewise culinary favorites. A 2011 Un Food and Agriculture Organization report establish that roughly 351,000 metric tons of octopus were fished the previous year, and in contempo years cuttlefishes have had similar totals. Cephalopod ink itself is the featured ingredient in Italian risotto nero and Spanish arroz negro. In Asia where at that place is a prominent cephalopod fishery, the ink is also used in traditional medicine, having exhibited antimicrobial backdrop. There is also great involvement in its use in anticancer drug development.

A nighttime view of the Gulf of Thailand from the International Space Station. (NASA, ISS)

Cephalopods reproduce quickly and so overfishing is often less of a problem than information technology is with finfishes.  Nevertheless, the giant cuttlefish (Sepia apama) experienced a significant decline in numbers during the 1990s. These cuttlefish are quite famous for their almanac breeding aggregations off the declension of Commonwealth of australia in the Spencer Gulf, a phenomenon that attracts scientists, filmmakers, tourists, and fishermen. Cuttlefish meat is as well a popular dish and although it is still unclear what is the exact cause of the population decline, exploitation of the easy to find cuttlefish is potentially a contributor. Local divers recall how in an area that once saw thousands of the cuttlefish, people are now thrilled to encounter a couple hundred. One 2008 study found a 57 percent reduction in the Spencer Gulf population between 2001 and 2008. Another 2013 Due south Commonwealth of australia Enquiry and Development Institute written report shows similar data. The Signal Lowly spawning aggregation, too off the coast of Commonwealth of australia, went from 183,000 cuttlefish in 1999 to 18,530 in 2012. In 2014, cuttlefish fishing was banned from the area and there is promise that the stricter regulations will help them rebound.

Vanquish Merchandise

The pearly white inner crush of the nautilus, chosen the nacre, is an admired and sought-afterward material. The increased harvest of nautilus for their shells has caused concern among scientists. The U.s. imported roughly 579,000 shells between 2005 and 2008, mostly to make jewelry. The shells are sometimes molded into balls and marketed every bit Osmeña pearl (a reference to the Philippine Osmeña dynasty) and are popular materials for earrings, bracelets and necklaces. Nautilus population numbers are mostly unknown, and for now, scientists are relying on anecdotal information on fishing catches to guess their decline.

The pearly nacre of a nautilus shell is sought after for jewelry. (Lisa Ann Yount, Flickr )

Fishermen in the remote islands of the Philippines employ dugout canoes and pull the nautilus traps upward past hand. In the early 2000s on the Philippine island of Bohol, fishermen caught up to 200 nautilus a twenty-four hours, but now they may only pull up a few. When fishing dries upward in one area the shell buyers move and the fishermen usually follow. Now scientists and governments are coordinating to attempt and save this ancient animal. An international proposal drafted by the U.South., Bharat, Palau and Fiji urged the protection of nautiluses nether the Convention of International Trade in Endangered Species (CITES), and in 2016 information technology was accustomed. Starting in January 2017, the international merchandise of nautilus shells had to be accompanied by a CITES permit. A National Oceanic and Atmospheric Assistants funded project is currently trying to find out how many of these animals are left in the waters of American Samoa and Fiji.

Cephalopods and Science

Embedded in the pall of every cephalopod is big neuron called the giant axon. Up to a millimeter in diameter, it is visible to the naked eye, making information technology a prime candidate for scientific experimentation. Aided by this axon, in 1939, scientists Alan Hodgkin and Andrew Huxley fabricated a monumental discovery near the mechanism of neuron signaling. The scientists were able to insert an electrode into the axon and tape an action potential, the electrical impulse that is passed from one neuron to another like a baton in a relay race. The discovery was such a awe-inspiring leap in the field of neuroscience that the responsible scientists were awarded a Nobel prize for Physiology or Medicine.

Odd Genetics

A 2017 written report found that development occurs in cephalopods differently than in whatever other organism (that nosotros know of). In general, evolution occurs through a serial of incremental changes in the DNA code—a mutation occurs in Dna, which then is transcribed in the instructional RNA, which then tells the prison cell how to build an altered poly peptide. Just cephalopods have constitute a manner to hijack that organisation and instead edit the RNA. Since DNA codes for the RNA editing proteins, an RNA editing system requires that the underlying Dna remain consistent through time. That may put a wrench in previous estimates of the cephalopod's evolutionary age. Combined with fossil data, scientists determine how old in geological time an organism is past looking at the number of mutations in a Dna sequence. If cephalopods use RNA editing instead, this aging organisation won't work and ancestral lineages may demand to be revised to place them in the proper timeframe. Next, researchers plan to dive into why cephalopods evolved such a unique organization of accommodation.

Cultural Connections

Human fascination with cephalopods began thousands of years ago. Images of octopuses announced on pottery dated from 2000 BCE during the Minoan period and there's even an Egyptian hieroglyphic in the shape of a squid.

For hundreds of years seafarers have regarded octopus and squid with trepidation, fearfulness, and awe—feelings that inspired many stories, like twenty,000 Leagues Under the Sea, that depict squid every bit terrifying beasts. Many other stories, movies, and artwork describe octopuses and squid as fearsome monsters. Just almost of the myths and legends are just that—stories with little basis in fact. Today, characters like Dr. Octavius in "Spiderman" and Ursula in "The Petty Mermaid" follow the evil monster tradition.

A Roman mosaic in Pompeii from the 'House of the Dancing Faun'. (Naples National Archaeological Museum, Public Domain)

Fossilized cephalopod shells were quite a mystery to people during ancient times, and are the source of several fantastical tales. In the 600s, the town of Whitby in North Yorkshire, England believed ammonite fossils were snakes turned to stone, and artists often carved a ophidian caput at the end of the vanquish. The town glaze of arms includes three of these "snakestones." The bullet shape of the belemnite rostrum caused the ancient Greeks to believe the fossils were thrown from the heavens in thunderstorms, a story that earned them the name "thunderbolts." They besides plow up in Greek sociology and are chosen "Devil's fingers."

This "snakehead" is from the Yorkshire coast of England. The ammonite fossil is the source of many tales near snakes turned to stone.

(James St. John, Flickr)

In Greco-Roman times the ink of a cuttlefish was a popular medium for painting, cartoon, and writing. Called sepia—the scientific name for cuttlefish—the coloring was a distinctive reddish-brown that could exist diluted to create a wide range of brownish hues. Some of the first paper photographs popularized in the 1860s had a similar color and the term was transferred to describe photographs also. However, the photo color was from the chemical deposition of albumen, an egg white base that binded with a silver solution, rather than actual cuttlefish ink. Today, the sepia filter is common in digital photograph editing.

When it comes to sports traditions, hockey has a few of the nearly elaborate, 1 of which includes an octopus. In 1952, during the playoffs, two Ruby-red Wings fans threw an octopus onto the ice. Each tentacle represented one of the eight wins (two best-of-vii series) needed to secure the Stanley Cup, a feat the Carmine Wings went on to consummate. Today, fans remember the "Legend of the Octopus" and go on to throw octopuses onto the ice during a game. Traditional etiquette requires that the octopus exist boiled (to get rid of slime) and exist thrown simply afterwards a Crimson Fly goal.

In the 1960s the Puget Sound Mudsharks dive social club hosted an annual Earth Octopus Wrestling Championship in Tacoma, Washington. Divers would pry the giant Pacific octopuses from their lair and then take them to the beach to be weighed. Many people marveled at the calmness of the octopus while they were kept in aquariums on the beach. After the winner was named the octopuses were released back into the ocean.

This octopus lure called a leho he`e is a tool of trickery. The octopus is attracted to the beautiful cowrie shell and the promise of a tasty meal but upon assail they are scooped upwards past Hawaiian fisherman. The lures are hung to 480-720 feet (146.4-219.half-dozen m) and shaken up and down to entice the octopus. Not only did fishermen catch octopus for food, the practice was also a sport for the elite. (Smithsonian Collections)

Finally, is it octopi or octopuses—how do yous know which one is correct? You may accept noticed that throughout this website the plural of octopus is octopuses. Grammarians accept been debating the plurality of octopus since the give-and-take emerged in the English language in the 1700s. The answer lies in the origin of the give-and-take, which stems from the Ancient Greek oktṓpous, not a Latin word as many mistakenly presume when they use the word octopi. Every bit a Greek word, the plural should exist octopodes, but as Merriam Webster points out, whenever a foreign word is assimilated into the English language it assumes the English plurality—so octopuses it is. Then once more, using the discussion octopodes is technically also correct, but nosotros don't suggest whipping it out in casual conversation unless you wish to spur a grammatical debate. Avoiding the confusion altogether, some scientists refer to all viii armed cephalopods as octopods, reserving the term octopus for merely those within the genus Octopus.

At the Smithsonian

Functioning Calamari

Travel to the Smithsonian's National Museum of Natural History Sant Sea Hall and you will find the largest cephalopod species in the world. Ii giant squid are displayed at the museum, the larger of the two measured 36 feet (eleven meters) when alive and was probably about 2-3 years old when it became caught in a fisherman's net off the coast of Spain. Transporting such a big specimen required the help of the U.S. Navy and the U.S. Air Strength and fifty-fifty warranted a special code name—Operation Calamari. The squids are two of only well-nigh a dozen behemothic squids on display at museums around the globe.

Larn more than virtually the giant squid on our giant squid web page, including how the giant squid was finally captured on camera.

This female behemothic squid is the larger of two on display in the Smithsonian'south Sant Ocean Hall. (Don Hurlbert/Smithsonian Institution)

Collections

The Smithsonian's National Museum of Natural History has one of the most various collections of squids and octopuses found in the world. The National Cephalopod Collection totals about 200,000 preserved specimens that were collected from around the globe and includes the holotypes for 164 cephalopod species, of which 66 are squid species. Holotypes are the specimens that are used by scientists to formally describe and proper noun a new species.

Squid expert Dr. Clyde Roper examines specimens in the Smithsonian collection. (Chip Clark/Smithsonian Institution)

Additional Resources

Websites:
Tree of Life - Bones overview of cephalopods
University of California Museum of Paleontology- The Cephalopoda
The British Geological Lodge- Information about extinct cephalopods
The University of Michigan Museum of Zoology- Creature Diverseness Web with background information on Cephalopoda

News Articles:
Curiouser and Curiouser--Octopus'south Evolution Is Even Stranger Than Thought- Scientific American
Loving the Chambered Nautilus to Decease- The New York Times
A Dolphin's Recipe for Octopus -The New York Times
Polarized Brandish Sheds Lite on Octopus and Cuttlefish Vision-and Cover-up - Scientific American
Octlantis is a Just-Discovered Underwater City Engineered by Octopuses - Quartz
The Cuttlefish, a Main of Cover-up, Reveals a New Fox - The New York Times

Books:
20,000 Leagues Under the Body of water- past Jules Verne
Kraken - by Wendy Williams
The Soul of an Octopus - by Sy Montgomery
Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness - by Peter Godfrey-Smith
Squid Empire - by Danna Staaf

April 2018

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Source: http://ocean.si.edu/ocean-life/invertebrates/cephalopods

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