Cephalopod intelligence is a measure of the cognitive ability of the

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

of molluscs. Intelligence is generally defined as the process of acquiring, storing, retrieving, combining, comparing, and recontextualizing information and conceptual skills. Though these criteria are difficult to measure in nonhuman animals, cephalopods seem to be exceptionally intelligent invertebrates. The study of cephalopod intelligence also has an important comparative aspect in the broader understanding of animal cognition because it relies on a nervous system fundamentally different from that of

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

. In particular, the Coleoidea subclass (

cuttlefish Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of ...

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...

, and

octopuses An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish ...

) is thought to be the most intelligent

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

and an important example of advanced cognitive evolution in animals, though nautilus intelligence is also a subject of growing interest among zoologists. The scope of cephalopod intelligence and learning capability is controversial within the biological community, complicated by the inherent complexity of quantifying non-vertebrate intelligence. In spite of this, the existence of impressive

spatial learning In cognitive psychology and neuroscience, spatial memory is a form of memory responsible for the recording and recovery of information needed to plan a course to a location and to recall the location of an object or the occurrence of an event. Sp ...

capacity,

navigational Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

abilities, and

predatory Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

techniques in cephalopods is widely acknowledged.

Brain size and structure

Cephalopods have large, well-developed

brains A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

, and their brain-to-body mass ratio is the largest among the invertebrates, falling between that of

endothermic In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. p. ...

and ectothermic vertebrates. The

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...

of cephalopods is the most complex of all invertebrates. The giant

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

fibers of the cephalopod

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

have been widely used for many years as experimental material in

neurophysiology Neurophysiology is a branch of physiology and neuroscience that studies nervous system function rather than nervous system architecture. This area aids in the diagnosis and monitoring of neurological diseases. Historically, it has been dominated b ...

; their large diameter (due to lack of

myelination Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be l ...

) makes them relatively easy to study compared with other animals.

Behavior

Predation

Veined_Octopus_-_Amphioctopus_Marginatus_eating_a_Crab

Unlike most other molluscs, all cephalopods are active predators (with the possible exceptions of the

bigfin squid Bigfin squids are a group of rarely seen cephalopods with a distinctive morphology. They are placed in the genus ''Magnapinna'' and family Magnapinnidae. Although the family is known only from larval, paralarval, and juvenile specimens, some a ...

and vampire squid). Their need to locate and capture their prey has likely been the driving evolutionary force behind the development of their intelligence. Crabs, the staple food source of most octopus species, present significant challenges with their powerful pincers and their potential to exhaust the cephalopod's respiration system from a prolonged pursuit. In the face of these challenges, octopuses will instead seek out lobster traps and steal the bait inside. They are also known to climb aboard fishing boats and hide in the containers that hold dead or dying crabs. Captive cephalopods have also been known to climb out of their tanks, maneuver a distance of the lab floor, enter another aquarium to feed on the crabs, and return to their own aquariums.

Communication

Although believed to not be the most social of animals, many cephalopods are in fact highly social creatures; when isolated from their own kind, some species have been observed shoaling with fish. Cephalopods are able to communicate visually using a diverse range of signals. To produce these signals, cephalopods can vary four types of communication elements: chromatic (skin coloration), skin texture (e.g. rough or smooth), posture, and locomotion. Changes in body appearance such as these are sometimes called

polyphenism A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions. It is therefore a special case of phenotypic plasticity. There are several types of polyphen ...

. Some cephalopods are capable of rapid changes in skin colour and pattern through nervous control of chromatophores. This ability almost certainly evolved primarily for

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the ...

, but squid use color, patterns, and flashing to communicate with each other in various courtship rituals. Caribbean reef squid can even discriminate between recipients, sending one message using color patterns to a squid on their right, while they send another message to a squid on their left. The Humboldt squid shows extraordinary cooperation and communication in its hunting techniques. This is the first observation of cooperative hunting in invertebrates. It is believed that squids are slightly less intelligent than octopuses and cuttlefish; however, various species of squid are much more social and display greater social communications, etc., leading to some researchers concluding that squids are on par with dogs in terms of intelligence.

Learning

In laboratory experiments, octopuses can be readily trained to distinguish between different shapes and patterns, and one study concluded that

are capable of using

observational learning Observational learning is learning that occurs through observing the behavior of others. It is a form of social learning which takes various forms, based on various processes. In humans, this form of learning seems to not need reinforcement to oc ...

; however, this is disputed. Octopuses have also been observed in what has been described as play: repeatedly releasing bottles or toys into a circular current in their aquariums and then catching them. Cephalopods can demonstrably benefit from

environmental enrichment Environmental enrichment is the stimulation of the brain by its physical and social surroundings. Brains in richer, more stimulating environments have higher rates of synaptogenesis and more complex dendrite arbors, leading to increased brain ac ...

indicating behavioral and neuronal plasticity not exhibited by many other invertebrates. In a study on social learning, common octopuses (observers) were allowed to watch other octopuses (demonstrators) select one of two objects that differed only in color. Subsequently, the observers consistently selected the same object as did the demonstrators. Both octopuses and nautiluses are capable of vertebrate-like

Tool use

The

octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...

has repeatedly been shown to exhibit flexibility in the use of tools. At least four individuals of the

veined octopus ''Amphioctopus marginatus'', also known as the coconut octopus and veined octopus, is a medium-sized cephalopod belonging to the genus ''Amphioctopus''. It is found in tropical waters of the western Pacific Ocean. It commonly preys upon shrimp, cr ...

(''Amphioctopus marginatus'') have been observed retrieving discarded

coconut The coconut tree (''Cocos nucifera'') is a member of the palm tree family ( Arecaceae) and the only living species of the genus ''Cocos''. The term "coconut" (or the archaic "cocoanut") can refer to the whole coconut palm, the seed, or the ...

shells, manipulating them, transporting them some distance, and then reassembling them for use as shelter. It is surmised that the octopuses used bivalves for the same purpose before humans made coconut shells widely available on the sea floor. Other sea creatures construct homes in a similar manner; most

hermit crabs Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an a ...

use the discarded shells of other species for habitation, and some crabs place sea anemones on their carapaces to serve as camouflage. However, this behavior lacks the complexity of the octopus's fortress behavior, which involves picking up and carrying a tool for later use. (This argument remains contested by a number of biologists, who claim that the shells actually provide protection from bottom-dwelling predators in transport.) Octopuses have also been known to deliberately place stones, shells, and even bits of broken bottles to form walls that constrict their den openings. In laboratory studies, ''Octopus mercatoris'', a small pygmy species of octopus, has been observed to block its lair using plastic

Lego Lego ( , ; stylized as LEGO) is a line of plastic construction toys that are manufactured by The Lego Group, a privately held company based in Billund, Denmark. The company's flagship product, Lego, consists of variously colored interlocking ...

bricks.Oinuma, Colleen, (14 April 2008). "''Octopus mercatoris'' response behavior to novel objects in a laboratory setting: Evidence of play and tool use behavior?" In ''Octopus Tool Use and Play Behavior

/ref> Smaller individuals of the

common blanket octopus The common blanket octopus or violet blanket octopus (''Tremoctopus violaceus'') is a large octopus of the family Tremoctopodidae found worldwide in the epipelagic zone of warm seas. The degree of sexual dimorphism in this species is very high, wi ...

(''Tremoctopus violaceus'') hold the tentacles of the

Portuguese man o' war The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, which is ...

(whose venom they are immune to), both as means of protection and as a method of capturing prey.

Problem-solving ability

The highly sensitive suction cups and prehensile arms of octopuses, squid, and cuttlefish allow them to hold and manipulate objects. However, unlike vertebrates, the motor skills of octopuses do not seem to depend upon mapping their body within their brains, as the ability to organize complex movements is not thought to be linked to particular arms. Cephalopods can solve complex puzzles requiring pushing or pulling actions, and can also unscrew the lids of containers and open the latches on acrylic boxes in order to obtain the food inside. They can also remember solutions to puzzles and learn to solve the same puzzle presented in different configurations. File:Oktopus opening a container with screw cap 01.jpg, File:Oktopus opening a container with screw cap 02.jpg, File:Oktopus opening a container with screw cap 03.jpg, File:Oktopus opening a container with screw cap 04.jpg, Captive octopuses require stimulation or they will become lethargic; this typically takes the form of a variety of toys and puzzles. At an aquarium in Coburg, Germany, an octopus named Otto was known to juggle his fellow tank-mates around, as well as throw rocks to smash the aquarium glass. On more than one occasion, Otto even caused

short circuits A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. ...

by crawling out of his tank and shooting a jet of water at the overhead lamp. Additionally, cephalopods have been shown to have the capacity for future planning and reward processing after being tested with the

Stanford marshmallow experiment The Stanford marshmallow experiment was a study on delayed gratification in 1972 led by psychologist Walter Mischel, a professor at Stanford University. In this study, a child was offered a choice between one small but immediate reward, or two sm ...

Protective legislation

Due to their intelligence, cephalopods are commonly protected by

animal testing regulations Animal testing regulations are guidelines that permit and control the use of non-human animals for scientific experimentation. They vary greatly around the world, but most governments aim to control the number of times individual animals may be us ...

that do not usually apply to invertebrates. In the UK from 1993 to 2012, the common octopus ('' Octopus vulgaris'') was the only invertebrate protected under the Animals (Scientific Procedures) Act 1986. Cephalopods are the only invertebrates protected under the 2010

European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...

directive "on the protection of animals used for scientific purposes". In 2019, some scholars have argued for increased protections for cephalopods in the United States as well.