Cephalopod intelligence has an important comparative aspect in the understanding of intelligence because it relies on a nervous system fundamentally different from that of vertebrates. The cephalopod class of molluscs, particularly the Coleoidea subclass (cuttlefish, squid, and octopuses), are considered the most intelligent invertebrates and an important example of advanced cognitive evolution in animals.
The scope of cephalopod intelligence is controversial, complicated by the challenges of studying these elusive and fundamentally different creatures. Classical conditioning of cephalopods has been reported, and one study (Fiorito and Scotto, 1992) even concluded that octopuses practice observational learning. However, the latter idea is disputed by some, and doubt has been shed on some other reported capabilities. In any case, impressive spatial learning capacity, navigational abilities, and predatory techniques remain beyond question.
Unlike most other molluscs, all cephalopods are active predators (with the possible exception of the bigfin squid and vampire squid). Their requirement to locate and capture their prey has been a probable driving force behind the development of their intelligence, uniquely advanced in their phylum.
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 prize inside. They are also known to climb aboard fishing boats and hide in the containers that hold dead or dying crabs.
Dexterity, an ability essential for tool use and manipulation, is also found in cephalopods. The highly sensitive suction cups and prehensile arms of octopuses, squid, and cuttlefish are as effective at holding and manipulating objects as the human hand. 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.
An octopus at the Sea Star Aquarium in Coburg named Otto was known to juggle his fellow tankmates around, as well as throwing rocks and smashing the aquarium glass. On more than one occasion he even caused short circuits by crawling out of his tank and shooting a jet of water at the overhead lamp.
Another example of cephalopod intelligence is the communication that takes place between the more social species of squid. Some cephalopods are capable of rapid changes in skin color and pattern through nervous control of chromatophores. This ability almost certainly evolved primarily for camouflage, but squid use color, patterns, and flashing to communicate with one another in various courtship rituals. Caribbean Reef Squid can send one message via color patterns to a squid on their right, while they send another message to a squid on their left.
The octopus is one of the prime examples of an invertebrate animal which has repeatedly been shown to exhibit flexibility in its use of tools. At least four specimens of the Veined Octopus (Amphioctopus marginatus) have been witnessed retrieving discarded coconut shells, manipulating them, transporting them some distance, and then reassembling them to use as a shelter. It is surmised that the octopuses originally used bivalves for the same purpose, before humans made coconut shells widely available on the sea floor. Most hermit crabs use discarded shells of other species for habitation and other crabs choose sea anemones to cultivate on their carapaces as camouflage; numerous insects use rocks, sand, leaves and so on as building materials; however, none of this behavior compares to the complexity of the octopus's fortress behavior, which involves picking up and carrying a tool to use later on.
Nautiluses are much closer to the first cephalopods that appeared about 500 million years ago than the early modern cephalopods that appeared maybe 150 million years later. They have a seemingly simple brain, not the large complex brains of octopuses and squid, and had long been assumed to lack intelligence. But the cephalopod nervous system is quite different from that of other animals, and recent experiments have shown not only memory, but a changing response to the same event over time.
In a study in 2008, a group of nautiluses (N. pompilius) were given food as a bright blue light flashed until they began to associate the light with food, extending their tentacles every time the blue light was flashed. The blue light was again flashed without the food 3 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, and 24 hours later. The nautiluses continued to respond to the blue light for up to 30 minutes after the experiment. An hour later they showed no reaction to the blue light. However, between 6 and 12 hours after the training, they again responded to the blue light. The researchers concluded that nautiluses had memory capabilities similar to the "short-term" and "long-term memories" of the more advanced cephalopods, despite having different brain structures. However the long-term memory capability of nautiluses was much shorter than that of other cephalopods. The nautiluses completely forgot the earlier training 24 hours later, in contrast to octopuses, for example, which can remember conditioning for weeks afterwards. While this may simply be the result of the conditioning procedure being suboptimal for sustaining long-term memories in nautiluses, the study nevertheless demonstrated that scientists may have previously underestimated the memory capabilities of nautiluses.
- "Cephalopod intelligence" in The Encyclopedia of Astrobiology, Astronomy, and Spaceflight.
- "Observational Learning in Octopus vulgaris" by Graziano Fiorito and Pietro Scotto
- "What is this octopus thinking?" by Garry Hamilton
- Is the octopus really the invertebrate intellect of the sea? by Doug Stewart. In: National Wildlife. Feb/Mar 1997, vol.35 no.2
- Behold the Humboldt squid. Tim Zimmermann, Outside Magazine, July 2006.
- Cousteau, Jacques Yves (1978). Octopus and Squid: The Soft Intelligence
- Zullo, L; Sumbre, G; Agnisola, C; Flash, T; Hochner, B. (2009). "Nonsomatotopic organization of the higher motor centers in octopus". Curr Biol 19 (19): 1632–6. doi:10.1016/j.cub.2009.07.067. PMID 19765993.
- "Otto the Octopus wreaks havoc"
- Cloney, R.A.; Florey, E. (1968). "Ultrastructure of cephalopod chromatophore organs". Z Zellforsch Mikrosk Anat 89 (2): 250–280. doi:10.1007/BF00347297. PMID 5700268.
- Brown, C; Garwood, M. P.; Williamson, J. E. (2012). "It pays to cheat: Tactical deception in a cephalopod social signalling system". Biology Letters 8 (5): 729–32. doi:10.1098/rsbl.2012.0435. PMC 3440998. PMID 22764112.
- "''Sepioteuthis sepioidea'', Caribbean Reef squid". The Cephalopod Page. Retrieved 2010-01-20.
- Byrne, R.A., U. Griebel, J.B. Wood & J.A. Mather 2003. PDF (3.86 MB) Berliner Geowissenschaftliche Abhandlungen 3: 29–35.
- Finn, J. K.; Tregenza, T.; Tregenza, N. (2009). "Defensive tool use in a coconut-carrying octopus". Current Biology 19 (23): R1069–R1070. doi:10.1016/j.cub.2009.10.052. PMID 20064403.
- Morelle, Rebecca (2009-12-14). "Octopus snatches coconut and runs". BBC News. Retrieved 2010-01-20.
- "Coconut shelter: evidence of tool use by octopuses | EduTube Educational Videos". Edutube.org. 2009-12-14. Retrieved 2010-01-20.
- NOVA: Kings of camoflauge. Film Finance Corporation Australia Limited & Kaufmann Productions; WGBH. 2007.
- Ewen Callaway (2 June 2008). "Simple-Minded Nautilus Shows Flash of Memory". New Scientist. Retrieved 7 March 2012.
- Kathryn Phillips (15 June 2008). "Living Fossil Memories". Inside JEB 211 (12): iii. doi:10.1242/jeb.020370.
- Robyn Crook & Jennifer Basil (2008). "A biphasic memory curve in the chambered nautilus, Nautilus pompilius L. (Cephalopoda: Nautiloidea)". The Journal of Experimental Biology 211 (12): 1992–1998. doi:10.1242/jeb.018531.
- So you think you're smarter than a cephalopod? by Wendy Williams, At the Smithsonian's Ocean Portal.
- What behavior can we expect of octopuses? by Dr. Jennifer Mather, Department of Psychology and Neuroscience, University of Lethbridge and Roland C. Anderson, The Seattle Aquarium.
- Is the octopus really the invertebrate intellect of the sea? by Doug Stewart. In: National Wildlife. Feb/Mar 1997, vol.35 no.2.
- Giant Octopus — Mighty but Secretive Denizen of the Deep from the National Zoo in Washington D.C.
- Living Fossils Have Long- And Short-term Memory Despite Lacking Brain Structures Of Modern Cephalopods
- M.J. Wells (1962). Brain and Behaviour in Cephalopods. Heinemann.
- Roger T. Hanlon & John B. Messenger (1996). Cephalopod Behaviour. Cambridge University Press. ISBN 0-521-42083-0.
- Marion Nixon and John Z. Young (2003). The Brains and Livees of Cephalopods. Oxford University Press.
- Binyamin Hochner; Tal Shomrat & Graziano Fiorito (June 1, 2006). "The Octopus: A Model for a Comparative Analysis of the Evolution of Learning and Memory Mechanisms". The Biol. Bull. 210 (3): 308–817. PMID 16801504.
- Octopuses are Smart Suckers!? By Dr. Jennifer Mather, Department of Psychology and Neuroscience, University of Lethbridge and Roland C. Anderson, The Seattle Aquarium
- Through the Eye of an Octopus, by Eric Scigliano, Discover Magazine, October 1, 2003.
- The Diversity and Evolution of Invertebrate Nervous Systems Set Institute. Retrieved 12 December 2014.