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cephalopod
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{{Automatic taxobox| taxon=Cephalopoda
Late Cambrianearliest=CambrianLate Cambrian – Present{{The Mollusca>volume=11}}}}| image=Squid komodo.jpg| image_caption=Bigfin reef squid(Sepioteuthis lessoniana)Georges Cuvier>Cuvier, 1797Class (biology)>Subclasses| subdivision= }}A cephalopod ({{IPAc-en|ˈ|s|ɛ|f|ə|l|ə|p|ɒ|d|,_|ˈ|k|ɛ|f|-}}) is any member of the molluscan class Cephalopoda (Greek plural , {{transl|grc|kephalópoda}}; "head-feet"{{Source?|Is neuter plural also attested in ancient Greek.|date=July 2019}}) such as a squid, octopus, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Ammonoidea (ammonites) and Belemnoidea (belemnites).

Distribution

{{multiple image
| align =right
| footer =Left: A pair of Sepia officinalis in shallow waterRight: Benthoctopus sp. on the Davidson Seamount at 2,422 m depth
| image1 =Sepia officinalis Linnaeus, 1758 .jpg
| width1 =220
| image2 =Benthoctopus sp.jpg
| width2 =190
}}There are over 800 extant species of cephalopod,WEB,weblink Welcome to CephBase, CephBase, 29 January 2016, although new species continue to be described. An estimated 11,000 extinct taxa have been described, although the soft-bodied nature of cephalopods means they are not easily fossilised.{{The Mollusca|volume=12}}Cephalopods are found in all the oceans of Earth. None of them can tolerate freshwater, but the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water.JOURNAL, Bartol, I. K., Mann, R., Vecchione, M., 2002, Distribution of the euryhaline squid Lolliguncula brevis in Chesapeake Bay: effects of selected abiotic factors, Marine Ecology Progress Series, 226, 235–247, 10.3354/meps226235, 2002MEPS..226..235B, Cephalopods are thought to be unable to live in freshwater due to multiple biochemical constraints, and in their +400 million year existence have never ventured into fully freshwater habitats.WEB,weblink Are there any freshwater cephalopods?, ABC Science, 16 January 2013, Cephalopods occupy most of the depth of the ocean, from the abyssal plain to the sea surface. Their diversity is greatest near the equator (~40 species retrieved in nets at 11°N by a diversity study) and decreases towards the poles (~5 species captured at 60°N).

Biology

Nervous system and behavior

{{See also|Cephalopod intelligence|squid giant axon|squid giant synapse|cephalopod aggression}}{{multiple image
| align =right
| footer =Left: An octopus opening a container with a screw capRight: Hawaiian bobtail squid, Euprymna scolopes, burying itself in the sand, leaving only the eyes exposed
| image1 =Oktopus opening a container with screw cap 01.jpg
| width1 =179
| image2 =Euprymna_scolopes_(Bobtail_squid)_behavior.jpg
| width2 =202
}}Cephalopods are widely regarded as the most intelligent of the invertebrates, and have well developed senses and large brains (larger than those of gastropods).BOOK, Tricarico, E., Amodio, P., Ponte, G., Fiorito, G., 2014, Cognition and recognition in the cephalopod mollusc Octopus vulgaris: coordinating interaction with environment and conspecifics, Witzany, G., Biocommunication of Animals, Springer, 337–349, 978-94-007-7413-1, The nervous system of cephalopods is the most complex of the invertebratesBOOK,weblink The cephalopod nervous system: What evolution has made of the molluscan design, B. U., Budelmann, The nervous systems of invertebrates: An evolutionary and comparative approach, 978-3-7643-5076-5, O., Breidbach, W., Kutsch, 1995, and their brain-to-body-mass ratio falls between that of endothermic and ectothermic vertebrates.{{Rp|14}} Captive cephalopods have also been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on the crabs, and return to their own aquarium.Raven, Peter et al. (2003). Biology, p. 669. McGraw-Hill Education, New York. {{ISBN|9780073383071}}.The brain is protected in a cartilaginous cranium. The giant nerve fibers of the cephalopod mantle have been widely used for many years as experimental material in neurophysiology; their large diameter (due to lack of myelination) makes them relatively easy to study compared with other animals.JOURNAL, I., Tasaki, T., Takenaka, Resting and action potential of squid giant axons intracellularly perfused with sodium-rich solutions, Proceedings of the National Academy of Sciences of the United States of America, 50, 4, 619–626, 1963, 10.1073/pnas.50.4.619, 14077488, 221236, 1963PNAS...50..619T, Many cephalopods are social creatures; when isolated from their own kind, some species have been observed shoaling with fish.JOURNAL, A., Cephalopods and fish: the limits of convergence, Biological Reviews, 47, 2, Packard, 241–307, 1972, 10.1111/j.1469-185X.1972.tb00975.x, Some cephalopods are able to fly through the air for distances of up to 50 m. While cephalopods are not particularly aerodynamic, they achieve these impressive ranges by jet-propulsion; water continues to be expelled from the funnel while the organism is in the air.JOURNAL, Macia, Silvia, Robinson, Michael P., Craze, Paul, Dalton, Robert, Thomas, James D., New observations on airborne jet propulsion (flight) in squid, with a review of previous reports, 10.1093/mollus/70.3.297, Journal of Molluscan Studies, 70, 3, 297–299, 2004, The animals spread their fins and tentacles to form wings and actively control lift force with body posture.JOURNAL, Muramatsu, K., Yamamoto, J., Abe, T., Sekiguchi, K., Hoshi, N., Sakurai, Y., 2013, Oceanic squid do fly, Marine Biology, 160, 5, 1171–1175, 10.1007/s00227-013-2169-9, One species, Todarodes pacificus, has been observed spreading tentacles in a flat fan shape with a mucus film between the individual tentaclesWEB,weblink Scientists Unravel Mystery of Flying Squid, 20 February 2013, Ocean Views, National Geographic, while another, Sepioteuthis sepioidea, has been observed putting the tentacles in a circular arrangement.JOURNAL, Jabr, Ferris, 2 August 2010, Fact or Fiction: Can a Squid Fly out of Water?, Scientific American,weblink

Senses

Cephalopods have advanced vision, can detect gravity with statocysts, and have a variety of chemical sense organs.{{Rp|34}} Octopuses use their arms to explore their environment and can use them for depth perception.

Vision

File:Nautilus pompilius (head).jpg|thumb|right|250px|The primitive nautilus eye functions similarly to a pinhole camerapinhole camera(File:Sepia eyelid shape.theora.ogv|thumb|right|250px|The W-shaped pupil of the cuttlefish expanding when the lights are turned off)Most cephalopods rely on vision to detect predators and prey, and to communicate with one another.JOURNAL, J. M., D. J., Eernisse, Charting Evolution's Trajectory: Using Molluscan Eye Diversity to Understand Parallel and Convergent Evolution, Serb, Evolution: Education and Outreach, 1, 4, 439–447, 2008, 10.1007/s12052-008-0084-1, Consequently, cephalopod vision is acute: training experiments have shown that the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects. The morphological construction gives cephalopod eyes the same performance as sharks'; however, their construction differs, as cephalopods lack a cornea, and have an everted retina. Cephalopods' eyes are also sensitive to the plane of polarization of light.JOURNAL, Part M, Chapter 4: Physiology of Coleoids, Treatise Online, Martin J., Wells, Lawrence, Kansas, USA,weblink
doi=10.17161/to.v0i0.4226, {{paywall}} Unlike many other cephalopods, nautiluses do not have good vision; their eye structure is highly developed, but lacks a solid lens. They have a simple "pinhole" eye through which water can pass. Instead of vision, the animal is thought to use olfaction as the primary sense for foraging, as well as locating or identifying potential mates.(File:Cuttlefish eye.jpg|thumb|250px|A cuttlefish with W-shaped pupils which may help them discriminate colors.)Surprisingly, given their ability to change color, all octopodes and most cephalopodsBOOK, Messenger, John B., Roger T., Hanlon, Cephalopod Behaviour, Cambridge University Press, 1998, Cambridge, 17–21, 978-0-521-64583-6, are considered to be color blind. Coleoid cephalopods (octopus, squid, cuttlefish) have a single photoreceptor type and lack the ability to determine color by comparing detected photon intensity across multiple spectral channels. When camouflaging themselves, they 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.Hanlon and Messenger, 68. They also produce visual pigments throughout their body, and may sense light levels directly from their body.JOURNAL, Mäthger, L., Roberts, S., Hanlon, R., Evidence for distributed light sensing in the skin of cuttlefish, Sepia officinalis, Biology Letters, 6, 5, 600–603, 2010, 20392722, 2936158, 10.1098/rsbl.2010.0223, Evidence of color vision has been found in the sparkling enope squid (Watasenia scintillans),JOURNAL, Michinomae, M., Masuda, H., Seidou, M., Kito, Y., Structural basis for wavelength discrimination in the banked retina of the firefly squid Watasenia scintillans, Journal of Experimental Biology, 193, 1, 1–12, 1994, 9317205, which achieves color vision by the use of three distinct retinal molecules (A1, sensitive to red; A2, to purple, and A4, to yellow?) which bind to its opsin.JOURNAL, Seidou, M., Sugahara, M., Uchiyama, H., Hiraki, K., Hamanaka, T., Michinomae, M., Yoshihara, K., Kito, Y., On the three visual pigments in the retina of the firefly squid, Watasenia scintillans, Journal of Comparative Physiology A, 166, 6, 1990, 10.1007/BF00187321, In 2015, a novel mechanism for spectral discrimination in cephalopods was described. This relies on the exploitation of chromatic aberration (wavelength-dependence of focal length). Numerical modeling shows that chromatic aberration can yield useful chromatic information through the dependence of image acuity on accommodation. The unusual off-axis slit and annular pupil shapes in cephalopods enhance this ability.BIORXIV, Stubbs, A. L., Stubbs, C. W., 2015, A novel mechanism for color vision: Pupil shape and chromatic aberration can provide spectral discrimination for 'color blind' organisms, 017756,

Photoreception

In 2015, molecular evidence was published indicating that cephalopod chromatophores are photosensitive; reverse transcription polymerase chain reactions (RT-PCR) revealed transcripts encoding rhodopsin and retinochrome within the retinas and skin of the longfin inshore squid (Doryteuthis pealeii), and the common cuttlefish (Sepia officinalis) and broadclub cuttlefish (Sepia latimanus). The authors claim this is the first evidence that cephalopod dermal tissues may possess the required combination of molecules to respond to light.JOURNAL, Kingston, A. C., Kuzirian, A. M., Hanlon, R. T., Cronin, T. W., 2015, Visual phototransduction components in cephalopod chromatophores suggest dermal photoreception, Journal of Experimental Biology, 218, 10, 1596–1602, 10.1242/jeb.117945, 25994635,

Hearing

Some squids have been shown to detect sound using their statocysts.NEWS,weblink BBC News, The cephalopods can hear you, 2009-06-15, 2010-04-28,

Use of light

missing image!
- Cuttlefish color.jpg -
This broadclub cuttlefish (Sepia latimanus) can change from camouflage tans and browns (top) to yellow with dark highlights (bottom) in less than a second.
{{further|Counter-illumination}}Most cephalopods possess an assemblage of skin components that interact with light. These may include iridophores, leucophores, chromatophores and (in some species) photophores. Chromatophores are colored pigment cells that expand and contract in accordance to produce color and pattern which they can use in a startling array of fashions. As well as providing camouflage with their background, some cephalopods bioluminesce, shining light downwards to disguise their shadows from any predators that may lurk below. The bioluminescence is produced by bacterial symbionts; the host cephalopod is able to detect the light produced by these organisms.JOURNAL, Tong, D., Rozas, S., H., Oakley, Colley, Mcfall-Ngai, Mitchell, J., J., J., Evidence for light perception in a bioluminescent organ, Proceedings of the National Academy of Sciences of the United States of America, 106, 24, 9836–9841, Jun 2009, 0027-8424, 19509343, 2700988, 10.1073/pnas.0904571106, 2009PNAS..106.9836T, Bioluminescence may also be used to entice prey, and some species use colorful displays to impress mates, startle predators, or even communicate with one another.

Coloration

{{further|Animal coloration|Category:Animals that can change color}}Cephalopods can change their colors and patterns in milliseconds, whether for signalling (both within the species and for warning) or active camouflage, as their chromatophores are expanded or contracted."integument (mollusks)."Encyclopædia Britannica. 2009. Encyclopædia Britannica 2006 Ultimate Reference Suite DVD Although color changes appear to rely primarily on vision input, there is evidence that skin cells, specifically chromatophores, can detect light and adjust to light conditions independently of the eyes.JOURNAL, Ramirez, M. D., Oakley, T. H, Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides, Journal of Experimental Biology, 2015, 218, 10, 1513–1520, 10.1242/jeb.110908, 25994633,weblink 4448664, Coloration is typically stronger in near-shore species than those living in the open ocean, whose functions tend to be restricted to disruptive camouflage.{{Rp|2}} Most octopuses mimic select structures in their field of view rather than becoming a composite color of their full background.JOURNAL, Josef, Noam, Amodio, Piero, Fiorito, Graziano, Shashar, Nadav, 2012-05-23, Camouflaging in a Complex Environment—Octopuses Use Specific Features of Their Surroundings for Background Matching, PLOS ONE, 7, 5, e37579, 10.1371/journal.pone.0037579, 1932-6203, 3359305, 22649542, 2012PLoSO...737579J, Evidence of original coloration has been detected in cephalopod fossils dating as far back as the Silurian; these orthoconic individuals bore concentric stripes, which are thought to have served as camouflage.JOURNAL, Minute Silurian oncocerid nautiloids with unusual color patterns, Manda, Štěpán, Turek, Vojtěch, Acta Palaeontologica Polonica, 54, 3, 2009, 503–512, 10.4202/app.2008.0062, Devonian cephalopods bear more complex color patterns, of unknown function.JOURNAL, Colour patterns in Early Devonian cephalopods from the Barrandian Area: Taphonomy and taxonomy, Vojtěch, Turek, 54, 3, 2009, 491–502, 10.4202/app.2007.0064, Acta Palaeontologica Polonica,

Ink

With the exception of the Nautilidae and the species of octopus belonging to the suborder Cirrina,BOOK, Roger T., Hanlon, John B., Messenger, Cephalopod Behaviour, 2, Cambridge University Press, 1999, 978-0-521-64583-6, all known cephalopods have an ink sac, which can be used to expel a cloud of dark ink to confuse predators.BOOK, 978-0-632-06048-1, Peter, Boyle, Paul, Rodhouse, 2004, Blackwell,weblink 10.1002/9780470995310.ch2, Cephalopods : ecology and fisheries, 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, like a smokescreen. However, a more sophisticated behavior has been observed, in which the cephalopod releases a cloud, with a greater mucus content, that approximately resembles the cephalopod that released it (this decoy is referred to as a Pseudomorph). This strategy often results in the predator attacking the pseudomorph, rather than its rapidly departing prey. For more information, see Inking behaviors.The ink sac of cephalopods has led to a common name of "inkfish",DICTIONARY, inkfish,weblink Merriam-Webster, 1 February 2018, formerly the pen-and-ink fish.BOOK, Bickerdyke, John, Sea Fishing, 1895, Longmans, Green, and Co., London, 114,weblink the common squid or calamary (Loligo vulgaris). It is sometimes called the pen-and-ink fish, on account of its ink bag, and the delicate elongated shell which is found within it., {{multiple image|direction=vertical|align= right|width= 250|image1= Chtenopteryx sicula2 - from Commons.jpg|caption1= Viscera of Chtenopteryx sicula|image2= Ocythoe tuberculata viscera - from Commons.jpg|caption2= Viscera of Ocythoe tuberculata}}

Circulatory system

Cephalopods are the only mollusks with a closed circulatory system. Coleoids 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.JOURNAL, Wells, M.J., Nervous control of the heartbeat in octopus, Journal of Experimental Biology, 85, 1, 111–28, 1 April 1980,weblink 7373208, 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 exposed to air.JOURNAL, Ghiretti-Magaldi, A., The Pre-history of Hemocyanin. The Discovery of Copper in the Blood of Molluscs, Cellular and Molecular Life Sciences, 48, 10, 971–972, October 1992, 10.1007/BF01919143,

Respiration

Cephalopods exchange gases with the seawater by forcing water through their gills, which are attached to the roof of the organism.{{Rp|488}} Water enters the mantle cavity on the outside of the gills, and 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. The gills, which are much more efficient than those of other mollusks, are attached to the ventral surface of the mantle cavity.JOURNAL, Electron Microscopical and Histochemical Studies of Differentiation and Function of the Cephalopod Gill (Sepia Officinalis L.), 10.1007/BF00993999, 1979, Zoomorphologie, 93, 3, 193–207, Schipp, Rudolf, Mollenhauer, Stephan, Boletzky, Sigurd, There is a trade-off with gill size regarding lifestyle. To achieve fast speeds, gills need to be small – water will be passed through them quickly when energy is needed, compensating for their small size. However, organisms which spend most of their time moving slowly along the bottom do not naturally pass much water through their cavity for locomotion; thus they have larger gills, along with complex systems to ensure that water is constantly washing through their gills, even when the organism is stationary. The water flow is controlled by contractions of the radial and circular mantle cavity muscles.JOURNAL,weblink 1994, Journal of Experimental Biology, 153–165, 194, On the respiratory flow in the cuttlefish Sepia Officinalis, Q., Bone, E. R., Brown, G., Travers, 1, 9317534, The gills of cephalopods are supported by a skeleton of robust fibrous proteins; the lack of mucopolysaccharides distinguishes this matrix from cartilage.JOURNAL, 10.1016/j.zool.2008.01.003, 18722759, 2009, Cole, A., Hall, B.
volume=112 pages=2–15, Zoology, See alsoweblink The gills are also thought to be involved in excretion, with NH4+ being swapped with K+ from the seawater.

Locomotion and buoyancy

missing image!
- Octopus3.jpg -
Octopuses swim headfirst, with arms trailing behind
While most cephalopods can move by jet propulsion, this is a very energy-consuming way to travel compared to the tail propulsion used by fish. The efficiency of a propellor-driven waterjet (i.e. Froude efficiency) is greater than a rocket.JOURNAL, Anderson, E.
, Demont, M., The mechanics of locomotion in the squid Loligo pealei: Locomotory function and unsteady hydrodynamics of the jet and intramantle pressure, Journal of Experimental Biology, 203, 18, 2851–2863, 2000, 10952883,weblink The relative efficiency of jet propulsion decreases further as animal size increases; paralarvae are far more efficient than juvenile and adult individuals.JOURNAL, Bartol, I. K., Krueger, P. S., Thompson, J. T., Stewart, W. J., Swimming dynamics and propulsive efficiency of squids throughout ontogeny, 10.1093/icb/icn043, Integrative and Comparative Biology, 48, 6, 720–733, 2008, 21669828, Since the Paleozoic era, as competition with fish produced an environment where efficient motion was crucial to survival, jet propulsion has taken a back role, with fins and tentacles used to maintain a steady velocity.
Whilst jet propulsion is never the sole mode of locomotion,{{rp|208}} the stop-start motion provided by the jets continues to be useful for providing bursts of high speed – not least when capturing prey or avoiding predators. Indeed, it makes cephalopods the fastest marine invertebrates,BOOK, 978-0-19-852761-9, Marion, Nixon, J. Z., Young, 2003, Oxford University Press, New York, The Brains and Lives of Cephalopods, {{Rp|Preface}}and they can out-accelerate most fish.BOOK, Squid as Experimental Animals, Daniel L., Gilbert, William J., Adelman, John M., Arnold, illustrated, Springer, 1990, 978-0-306-43513-3,weblink The jet 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).Oxygenated water is taken into the mantle cavity to the gills and through muscular contraction of this cavity, the spent water is expelled through the hyponome, created by a fold in the mantle. The size difference between the posterior and anterior ends of this organ control the speed of the jet the organism can produce.JOURNAL, 10.1007/s00227-001-0772-7, Quantification of ontogenetic discontinuities in three species of oegopsid squids using model II piecewise linear regression, 2002, Shea, E., Vecchione, M., Marine Biology, 140, 5, 971–979, The velocity of the organism can be accurately predicted for a given mass and morphology of animal.JOURNAL, A study in jet propulsion: an analysis of the motion of the squid, Loligo vulgaris,weblink Journal of Experimental Biology, 56, 155–165, 1972, W., Johnson, P. D., Soden, E. R., Trueman, February 1972, Motion of the cephalopods is usually backward as water is forced out anteriorly through the hyponome, but direction can be controlled somewhat by pointing it in different directions.{{sfnp|Campbell|Reece|Mitchell|1999|p=612}} Some cephalopods accompany this expulsion of water with a gunshot-like popping noise, thought to function to frighten away potential predators.JOURNAL, 10.1017/S0025315407058225, A new noise detected in the ocean, 2007, Guerra, A., Martinell, X., González, A. F., Vecchione, M., Gracia, J., Martinell, J., Journal of the Marine Biological Association of the United Kingdom, 87, 5, 1255–1256, 10261/27009, Cephalopods employ a similar method of propulsion despite their increasing size (as they grow) changing the dynamics of the water in which they find themselves. Thus their paralarvae do not extensively use their fins (which are less efficient at low Reynolds numbers) and primarily use their jets to propel themselves upwards, whereas large adult cephalopods tend to swim less efficiently and with more reliance on their fins.
missing image!
- Nautilus front.jpg -
Nautilus belauensis seen from the front, showing the opening of the hyponome
Early cephalopods are thought to have produced jets by drawing their body into their shells, as Nautilus does today.JOURNAL, Jet Propulsion and the Evolution of the Cephalopods
volume=49 date= July 1991 last1=Wells last2=O'Dor Nautilus is also capable of creating a jet by undulations of its funnel; this slower flow of water is more suited to the extraction of oxygen from the water. The jet velocity in Nautilus is much slower than in coleoids, but less musculature and energy is involved in its production.10.1016/S0016-6995(06)80360-8 YEAR=1993 FIRST1=J., JR. VOLUME=26 PAGES=49–61, Jet thrust in cephalopods is controlled primarily by the maximum diameter of the funnel orifice (or, perhaps, the average diameter of the funnel){{RpLAST2=HOAR YEAR=2000 JOURNAL=ICES JOURNAL OF MARINE SCIENCE PAGES=8–14 TITLE=THE FORCES ACTING ON SWIMMING SQUID JOURNAL=JOURNAL OF EXPERIMENTAL BIOLOGY PAGES=421–442, 1988, Water refills the cavity by entering not only through the orifices, but also through the funnel. Squid can expel up to 94% of the fluid within their cavity in a single jet thrust. To accommodate the rapid changes in water intake and expulsion, the orifices are highly flexible and can change their size by a factor of twenty; the funnel radius, conversely, changes only by a factor of around 1.5.Some octopus species are also able to walk along the seabed. Squids and cuttlefish can move short distances in any direction by rippling of a flap of muscle around the mantle.While most cephalopods float (i.e. are neutrally buoyant or nearly so; in fact most cephalopods are about 2–3% denser than seawater), they achieve this in different ways.{{The Mollusca|chapter=11: Evolution of Buoyancy and Locomotion in recent cephalopods|volume=12}}Some, such as Nautilus, allow gas to diffuse into the gap between the mantle and the shell; others allow purer water to ooze from their kidneys, forcing out denser salt water from the body cavity; others, like some fish, accumulate oils in the liver; and some octopuses have a gelatinous body with lighter chlorine ions replacing sulfate in the body chemistry.The Macrotritopus defilippi, or the sand-dwelling octopus, was seen mimicking both the coloration and the swimming movements of the sand-dwelling flounder Bothus lunatus to avoid predators. The octopuses were able to flatten their bodies and put their arms back to appear the same as the flounders as well as move with the same speed and movements.JOURNAL, Hanlon, Roger T., Watson, Anya C., Barbosa, Alexandra, 2010-02-01, A 'Mimic Octopus' in the Atlantic: Flatfish Mimicry and Camouflage by Macrotritopus defilippi, The Biological Bulletin, 218, 1, 15–24, 10.1086/BBLv218n1p15, 20203250, 0006-3185, 1912/4811, Females of two species, Ocythoe tuberculata and Haliphron atlanticus, have evolved a true swim bladder.The argonaut shell: Gas-mediated buoyancy control in a pelagic octopus

Shell

{{See also|Cirrate shell|Cuttlebone|Gladius (cephalopod)|Mollusc shell}}{{multiple image|direction=vertical|width=220|image1=Spirula spirula.jpg|caption1=Cross section of Spirula spirula, showing the position of the shell inside the mantle|image2=Herklots 1859 I 2 Sepia officinalis - schelp.jpg|caption2=Cuttlebone of Sepia officinalis|image3=Sepioteuthis lessoniana gladius.jpg|caption3=Gladius of Sepioteuthis lessoniana}}Nautiluses are the only extant cephalopods with a true external shell. However, all molluscan shells are formed from the ectoderm (outer layer of the embryo); in cuttlefish (Sepia spp.), for example, an invagination of the ectoderm forms during the embryonic period, resulting in a shell (cuttlebone) that is internal in the adult.JOURNAL, Baratte, S., Andouche, A., Bonnaud, L., Engrailed in cephalopods: a key gene related to the emergence of morphological novelties, Development Genes and Evolution, 217, 5, 353–362, 2007, 17394016, 10.1007/s00427-007-0147-2, The same is true of the chitinous gladius of squid and octopuses.JOURNAL, 10.1016/j.geobios.2003.01.009, 'Nude ammonoids': a challenge to cephalopod phylogeny?, 'Ammonoïdes nus': un défi pour la phylogénie des céphalopodes ?, 2004, von Boletzky, S., Geobios, 37, 117–118, Cirrate octopods have arch-shaped cartilaginous fin supports,BOOK,weblink 288, Oceanography and Marine Biology: An Annual Review, R. N., Gibson, R. J. A., Atkinson, J. D. M., Gordon, CRC Press, 2006, 978-1420006391, which are sometimes referred to as a "shell vestige" or "gladius".JOURNAL, 1983, 10.1098/rstb.1983.0021, Cirrothauma murrayi Chun, a finned octopod, Aldred, R. G., Nixon, M., Young, J. Z., Philosophical Transactions of the Royal Society B: Biological Sciences, 301, 1103, 1–54, 1983RSPTB.301....1A, The Incirrina have either a pair of rod-shaped stylets or no vestige of an internal shell,JOURNAL, Fuchs, D., Ifrim, C., Stinnesbeck, W., 2008, A new Palaeoctopus (Cephalopoda: Coleoidea) from the Late Cretaceous of Vallecillo, north-eastern Mexico, and implications for the evolution of Octopoda, Palaeontology, 51, 5, 1129–1139, 10.1111/j.1475-4983.2008.00797.x, and some squid also lack a gladius.JOURNAL, The terminal spine of sepiolid hatchlings: its development and functional morphology (Mollusca, Cephalopoda), von Boletzky, Sigurd, Bulletin of Marine Science, July 1991, 107–112, 49, The shelled coleoids do not form a clade or even a paraphyletic group. The Spirula shell begins as an organic structure, and is then very rapidly mineralized.JOURNAL, 10.1007/s10347-005-0054-9, Spirula – a window to the embryonic development of ammonoids? Morphological and molecular indications for a palaeontological hypothesis, 2005, Warnke, K., Keupp, H., Facies, 51, 1–4, 60–65, Shells that are "lost" may be lost by resorption of the calcium carbonate component.JOURNAL, A., Beran, M., Molluscan shell evolution with review of shell calcification hypothesis, 154, Comparative Biochemistry and Physiology B, 351–371, 3, Smrz, I., Furuhashi, 2009, 19665573, T., Schwarzinger, Miksik, C., 10.1016/j.cbpb.2009.07.011, Females of the octopus genus Argonauta secrete a specialized paper-thin egg case in which they reside, and this is popularly regarded as a "shell", although it is not attached to the body of the animal and has a separate evolutionary origin.The largest group of shelled cephalopods, the ammonites, are extinct, but their shells are very common as fossils.The deposition of carbonate, leading to a mineralized shell, appears to be related to the acidity of the organic shell matrix (see Mollusc shell); shell-forming cephalopods have an acidic matrix, whereas the gladius of squid has a basic matrix.JOURNAL, 1996, Dauphin, Y., The organic matrix of coleoid cephalopod shells: molecular weights and isoelectric properties of the soluble matrix in relation to biomineralization processes, Marine Biology, 125, 3, 525–529, 10.1007/BF00353265, 2019-08-19, The basic arrangement of the cephalopod outer wall is: an outer (spherulitic) prismatic layer, a laminar (nacreous) layer and an inner prismatic layer. The thickness of every layer depends on the taxa.BOOK, Les subdivisions majeures de la classe des céphalopodes : bases de la systématique actuelle : apport de l'analyse microstructurale, Dauphin, Y., 1983, These Doct. Etat, Université Paris Sud, 972899981, In modern cephalopods, the Ca carbonate is aragonite. As for other mollusc shells or coral skeletons, the smallest visible units are irregular rounded granules.JOURNAL, Dauphin, Y., 2001, Nanostructures de la nacre des tests de céphalopodes actuels, Paläontologische Zeitschrift, 75, 1, 113–122, 10.1007/bf03022601, 0031-0220, {{multiple image
| align =left
| footer =Left: A giant squid found in Logy Bay, Newfoundland, in 1873. The two long feeding tentacles are visible on the extreme left and right.Right: Detail of the tentacular club of Abraliopsis morisi
| image1 =Logy bay giant squid 1873.png
| width1 =220
| image2 =Tentacule Abraliopsis morisi.jpg
| width2 =133
}}

Head appendages

Cephalopods, as the name implies, have muscular appendages extending from their heads and surrounding their mouths. These are used in feeding, mobility, and even reproduction. In coleoids they number eight or ten. Decapods such as cuttlefish and squid have five pairs. The longer two, termed tentacles, are actively involved in capturing prey;{{Rp|225}} they can lengthen rapidly (in as little as 15 milliseconds{{Rp|225}}). In giant squid they may reach a length of 8 metres. They may terminate in a broadened, sucker-coated club.{{Rp|225}} The shorter four pairs are termed arms, and are involved in holding and manipulating the captured organism.{{Rp|225}} They too have suckers, on the side closest to the mouth; these help to hold onto the prey.{{Rp|226}} Octopods only have four pairs of sucker-coated arms, as the name suggests, though developmental abnormalities can modify the number of arms expressed.JOURNAL, Toll, R. B., Binger, L. C., Arm anomalies: Cases of supernumerary development and bilateral agenesis of arm pairs in Octopoda (Mollusca, Cephalopoda), Zoomorphology, 110, 6, 313–316, 1991, 10.1007/BF01668021, The tentacle consists of a thick central nerve cord (which must be thick to allow each sucker to be controlled independently)BOOK, 1912, Anatomy of the Common Squid, surrounded by circular and radial muscles. Because the volume of the tentacle remains constant, contracting the circular muscles decreases the radius and permits the rapid increase in length. Typically a 70% lengthening is achieved by decreasing the width by 23%.{{Rp|227}} The shorter arms lack this capability.The size of the tentacle is related to the size of the buccal cavity; larger, stronger tentacles can hold prey as small bites are taken from it; with more numerous, smaller tentacles, prey is swallowed whole, so the mouth cavity must be larger.Nixon 1988 in JOURNAL, M. G. E., J., Allocrioceras from the Cenomanian (mid-Cretaceous) of the Lebanon and its bearing on the palaeobiological interpretation of heteromorphic ammonites, Wippich, Palaeontology, 47, 5, 1093–1107, 2004, 10.1111/j.0031-0239.2004.00408.x, Lehmann, Externally shelled nautilids (Nautilus and Allonautilus) have on the order of 90 finger-like appendages, termed tentacles, which lack suckers but are sticky instead, and are partly retractable.

Feeding

File:Architeuthis beak.jpg|thumb|The two-part beak of the giant squidgiant squidAll living cephalopods have a two-part beak;{{Rp|7}} most have a radula, although it is reduced in most octopus and absent altogether in Spirula.{{Rp|7}}{{The Mollusca|volume=12|chapter=5}}{{rp|110}} They 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. Nutrients and waste materials are exchanged between the gut and the digestive gland through a pair of connections linking the gland to the junction of the stomach and caecum. Cells in the digestive gland directly release pigmented excretory chemicals into the lumen of the gut, which are then bound with mucus passed through the anus as long dark strings, ejected with the aid of exhaled water from the funnel. Cephalopods tend to concentrate ingested heavy metals in their body tissue.C.Michael Hogan. 2011. Celtic Sea. eds. P.Saundry & C.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC.

Radula

{{See also|Radula#In cephalopods}}File:Veined Octopus - Amphioctopus Marginatus eating a Crab.jpg|thumb|Amphioctopus marginatusAmphioctopus marginatusThe cephalopod radula consists of multiple symmetrical rows of up to nine teeth{{tolweb|2035|title=Cephalopod radula |first1=Richard E. |last1=Young |first2=Michael |last2=Vecchione |first3=Katharina M. |last3=Mangold}} – thirteen in fossil classes.JOURNAL, 10.1111/j.1469-7998.1995.tb01785.x, A nomenclature for the radula of the Cephalopoda (Mollusca) – living and fossil, 1995, Nixon, M., Journal of Zoology, 236, 73–81, The organ is reduced or even vestigial in certain octopus species and is absent in Spirula. The teeth may be homodont (i.e. similar in form across a row), heterodont (otherwise), or ctenodont (comb-like). Their height, width and number of cusps is variable between species. The pattern of teeth repeats, but each row may not be identical to the last; in the octopus, for instance, the sequence repeats every five rows.{{rp|79}}Cephalopod radulae are known from fossil deposits dating back to the Ordovician.JOURNAL, Gabbott, S. E., Orthoconic cephalopods and associated fauna from the late Ordovician Soom Shale Lagerstatte, South Africa, Palaeontology, 42, 123–148, 1999, 10.1111/1475-4983.00065, They are usually preserved within the cephalopod's body chamber, commonly in conjunction with the mandibles; but this need not always be the case;BOOK,weblink Cephalopods present and past: new insights and fresh perspectives, Springer, 978-1-4020-6461-6, Landman, Neil H., Davis, Richard Arnold, Mapes, Royal H., 2007, many radulae are preserved in a range of settings in the Mason Creek.BOOK, Richardson & ..., 1977, Fossils of the Mason Creek, Radulae are usually difficult to detect, even when they are preserved in fossils, as the rock must weather and crack in exactly the right fashion to expose them; for instance, radulae have only been found in nine of the 43 ammonite genera,JOURNAL, Kruta, I., Landman, N., Rouget, I., Cecca, F., Tafforeau, P., The role of ammonites in the Mesozoic marine food web revealed by jaw preservation, 10.1126/science.1198793, Science, 331, 6013, 70–72, 2011, 21212354, 2011Sci...331...70K, {{Clarify|date=March 2011}} and they are rarer still in non-ammonoid forms: only three pre-Mesozoic species possess one.

Excretory system

Most cephalopods possess a single pair of large nephridia. Filtered nitrogenous waste is produced in the pericardial cavity of the branchial hearts, each of which is connected to a nephridium by a narrow canal. The canal delivers the excreta to a bladder-like renal sac, and also resorbs excess water from the filtrate. Several outgrowths of the lateral vena cava project into the renal sac, continuously inflating and deflating as the branchial hearts beat. This action helps to pump the secreted waste into the sacs, to be released into the mantle cavity through a pore.BOOK, Barnes, Robert D., 1982, Invertebrate Zoology, Holt-Saunders International, Philadelphia, PA, 450–460, 978-0-03-056747-6, Nautilus, unusually, possesses four nephridia, none of which are connected to the pericardial cavities.The incorporation of ammonia is important for shell formation in terrestrial molluscs and other non-molluscan lineages.JOURNAL, 30155937, 461–469, Ammonia Volatilization and Absorption by Terrestrial Gastropods_ a Comparison between Shelled and Shell-Less Species, Physiological Zoology, 52, 4, 1979, Loest, R. A., 10.1086/physzool.52.4.30155937, Because protein (i.e. flesh) is a major constituent of the cephalopod diet, large amounts of ammonium ions are produced as waste. The main organs involved with the release of this excess ammonium are the gills.JOURNAL, 10.1080/10236249409378907, Ammonia production in cephalopods, physiological and evolutionary aspects, 1994, Boucher-Rodoni, R., Mangold, K., Marine and Freshwater Behaviour and Physiology, 25, 1–3, 53–60, The rate of release is lowest in the shelled cephalopods Nautilus and Sepia as a result of their using nitrogen to fill their shells with gas to increase buoyancy. Other cephalopods use ammonium in a similar way, storing the ions (as ammonium chloride) to reduce their overall density and increase buoyancy.

Reproduction and life cycle

File:Papierboot Argonauta 200705181139.jpg|220px|thumb|Female Argonauta argoArgonauta argoFile:Ocythoe tuberculata hectocotylus - from Commons.jpg|220px|thumb|Detail of the hectocotylus of Ocythoe tuberculataOcythoe tuberculataFile: Onykia ingens with non-erect penis.jpg|250px|thumb|A dissected male specimen of Onykia ingensOnykia ingens(File: Onykia ingens with erect penis.jpg|250px|thumb|A specimen of the same species exhibiting an elongation of the penis to 67 cm in length)Cephalopods are a diverse group of species, but share common life history traits, for example, they have a rapid growth rate and short life spans.BOOK, Vidal, Erica A. G., Advances in Cephalopod Science: Biology, Ecology, Cultivation and Fisheries., Stearns (1992) suggested that in order to produce the largest possible number of viable offspring, spawning events depend on the ecological environmental factors of the organism. The majority of cephalopods do not provide parental care to their offspring, except, for example, octopus, which helps this organism increase the survival rate of their offspring. Marine species' life cycles are affected by various environmental conditions.JOURNAL, Rodrigues, M., Guerra, Troncoso, The embryonic phase and its implication in the hatchling size and condition of Atlantic bobtail squid Sepiola Atlantica, Helgoland Marine Research, 65, 2, 211–216, 10.1007/s10152-010-0217-0, 2010, 2011HMR....65..211R, The development of a cephalopod embryo can be greatly affected by temperature, oxygen saturation, pollution, light intensity, and salinity. These factors are important to the rate of embryonic development and the success of hatching of the embryos. Food availability also plays an important role in the reproductive cycle of cephalopods. A limitation of food influences the timing of spawning along with their function and growth. Spawning time and spawning vary among marine species; it's correlated with temperature, though cephalopods in shallow water spawn in cold months so that the offspring would hatch at warmer temperatures. Breeding can last from several days to a month.

Sexual maturity

Cephalopods that are sexually mature and of adult size begin spawning and reproducing. After the transfer of genetic material to the following generation, the adult cephalopods then die. Sexual maturation in male and female cephalopods can be observed internally by the enlargement of gonads and accessory glands.JOURNAL, Arkhipkin, A. I., Reproductive system structure, development and function in cephalopods with a new general scale for maturity stages, Journal of Northwest Atlantic Fishery Science, 1992, 12, 63–74, 10.2960/j.v12.a7, Mating would be a poor indicator of sexual maturation in females; they can receive sperm when not fully reproductively mature and store them until they are ready to fertilize the eggs. Males are more aggressive in their pre-mating competition when in the presence of immature females than when competing for a sexually mature female.JOURNAL, Mohanty, Sobhi, Ojanguren, Alfredo F., Fuiman, Lee A., 2014-07-01, Aggressive male mating behavior depends on female maturity in Octopus bimaculoides, Marine Biology, 161, 7, 1521–1530, 10.1007/s00227-014-2437-3, 0025-3162, Most cephalopod males develop a hectocotylus, an arm tip which is capable of transferring their spermatozoa into the female mantel cavity. Though not all species use a hectocotylus; for example, the adult nautilus releases a spadix.JOURNAL, Saunders, W. B, Spinosa, C., Sexual dimorphism in Nautilus from Palau, Paleobiology, 1978, 4, 3, 349–358, 10.1017/S0094837300006047, An indication of sexual maturity of females is the development of brachial photophores to attract mates.JOURNAL, Young, R. B., A Systematic Approach to Planning Occupational Programs, Community College Review, 1975, 19–25, 10.1177/009155217500300204, 3, 2,

Fertilization

Cephalopods are not broadcast spawners. During the process of fertilization, the females use sperm provided by the male via external fertilization. Internal fertilization is seen only in octopodes. The initiation of copulation begins when the male catches a female and wraps his arm around her, either in a "male to female neck" position or mouth to mouth position, depending on the species. The males then initiate the process of fertilization by contracting their mantle several times to release the spermatozoa.JOURNAL, Squires, Z. E, Norman, M. D, Stuart-Fox, D., Mating behaviour and general spawning patterns of the southern dumpling squid Euprymna tasmanica, Journal of Molluscan Studies, 2013, 79, 3, 263–269, 10.1093/mollus/eyt025, Cephalopods often mate several times, which influences males to mate longer with females that have previously, nearly tripling the number of contractions of the mantle. To ensure the fertilization of the eggs, female cephalopods release a sperm-attracting peptide through the gelatinous layers of the egg to direct the spermatozoa. Female cephalopods lay eggs in clutches; each egg is composed of a protective coat to ensure the safety of the developing embryo when released into the water column. Reproductive strategies differ between cephalopod species. In giant Pacific octopus, large eggs are laid in a den; it will often take several days to lay all of them. Once the eggs are released and attached to a sheltered substrate, the females then die, making them semelparous. In some species of cephalopods, egg clutches are anchored to substrates by a mucilaginous adhesive substance. These eggs are swelled with perivitelline fluid (PVF), a hypertonic fluid that prevents premature hatching.JOURNAL, Marthy, H. J., Hauser, R, Scholl, A., Natural tranquilizer in cephalopod eggs, Nature, 1976, Fertilized egg clusters are neutrally buoyant depending on the depth that they were laid, but can also be found in substrates such as sand, a matrix of corals, or seaweed. Because these species do not provide parental care for their offspring, egg capsules can be injected with ink by the female in order to camouflage the embryos from predators.

Male–male competition

Most cephalopods engage in aggressive sex: a protein in the male capsule sheath stimulates this behavior. They also engage in male–male aggression, where larger males tend to win the interactions. When a female is near, the males charge one another continuously and flail their arms. If neither male backs away, the arms extend to the back, exposing the mouth, followed by the biting of arm tips.JOURNAL, Norman, M. D., Lu, C. C., Redescription of the southern dumpling squid Euprymna tasmanica and a revision of the genus Euprymna (Cephalopoda: Sepiolidae), Journal of the Marine Biological Association of the United Kingdom, 1997, 77, 4, 1109–1137, 10.1017/s0025315400038662, During mate competition males also participate in a technique called flushing. This technique is used by the second male attempting to mate with a female. Flushing removes spermatophores in the buccal cavity that was placed there by the first mate by forcing water into the cavity. Another behavior that males engage in is sneaker mating or mimicry – smaller males adjust their behavior to that of a female in order to reduce aggression. By using this technique, they are able to fertilize the eggs while the larger male is distracted by a different male. During this process, the sneaker males quickly insert drop-like sperm into the seminal receptacle.JOURNAL, Iwata, Y., Ito, K., Sakurai, Y., Effect of low temperature on mating behavior of squid Loligo bleekeri, Fisheries Science, 2008, 74, 6, 1345–1347, 10.1111/j.1444-2906.2008.01664.x,

Mate choice

Mate choice is seen in cuttlefish species, where females prefer some males over others, though characteristics of the preferred males are unknown. A hypothesis states that females reject males by olfactory cues rather than visual cues. Several cephalopod species are polyandrous- accepting and storing multiple male spermatophores, which has been identified by DNA fingerprinting. Females are no longer receptive to mating attempts when holding their eggs in their arms. Females can store sperm in two places (1) the buccal cavity where recently mated males place their spermatophores, and (2) the internal sperm-storage receptacles where sperm packages from previous males are stored. Spermatophore storage results in sperm competition; which states that the female controls which mate fertilizes the eggs. In order to reduce this sort of competition, males develop agonistic behaviors like mate guarding and flushing. The Hapalochlaena lunulata, or the blue-ringed octopus, is unable to distinguish between males and females and readily mates with both.JOURNAL, Cheng, Mary W., Caldwell, Roy L., July 2000, Sex identification and mating in the blue-ringed octopus, Hapalochlaena lunulata, Animal Behaviour, 60, 1, 27–33, 10.1006/anbe.2000.1447, 10924200, 0003-3472,

Sexual dimorphism

In a variety of marine organisms, it is seen that females are larger in size compared to the males in some closely related species. In some lineages, such as the blanket octopus, males become structurally smaller and smaller resembling a term, "dwarfism" dwarf males usually occurs at low densities.BOOK, Fairbairn, D., Blanket Octopus: Drifting Females and Dwarf Males, Odd couples: Extraordinary differences between the sexes in the animal kingdom, 2013, Princeton University Press, 104–115, The blanket octopus male is an example of sexual-evolutionary dwarfism; females grow 10,000 to 40,000 times larger than the males and the sex ratio between males and females can be distinguished right after hatching of the eggs.(File:SquidEggCases-MontereryAquarium-April2-07.png|thumb|left|Egg cases laid by a female squid)

Embryology

Cephalopod eggs span a large range of sizes, from 1 to 30 mm in diameter. The fertilised ovum initially divides to produce a disc of germinal cells at one pole, with the yolk remaining at the opposite pole. The germinal disc grows to envelop and eventually absorb the yolk, forming the embryo. The tentacles and arms first appear at the hind part of the body, where the foot would be in other molluscs, and only later migrate towards the head.JOURNAL, Sasaki, S., Vecchione, T., Kasugai, Moritaki, T., Agata, T., M., K., Evolution of the cephalopod head complex by assembly of multiple molluscan body parts: Evidence from Nautilus embryonic development, Journal of Morphology, 269, 1, 1–17, Jan 2008, 17654542, Shigeno, 10.1002/jmor.10564, The funnel of cephalopods develops on the top of their head, whereas the mouth develops on the opposite surface.BOOK, 978-0-306-43513-3, Daniel L., Gilbert, William J., Adelman, John M., Arnold, 1990, Plenum Press, New York, Squid as experimental animals,weblink {{Rp|86}} The early embryological stages are reminiscent of ancestral gastropods and extant Monoplacophora.The shells develop from the ectoderm as an organic framework which is subsequently mineralized. In Sepia, which has an internal shell, the ectoderm forms an invagination whose pore is sealed off before this organic framework is deposited.

Development

missing image!
- Chtenopteryx sicula paralarvae - from Commons.jpg -
Chtenopteryx sicula paralarvae. Left: Two very young paralarvae. The circular tentacular clubs bear approximately 20 irregularly arranged suckers. Two chromatophores are present on each side of the mantle. Centre: Ventral, dorsal and side views of a more advanced paralarva. An equatorial circulet of seven large yellow-brown chromatophores is present on the mantle. Posteriorly the expanded vanes of the gladius are visible in the dorsal view. Right: Ventral and dorsal views of a very advanced paralarva.
{{multiple image
| align =right
| footer =Left: Immature specimens of Chiroteuthis veranyi. In this paralarval form, known as the doratopsis stage, the pen is longer than the mantle and 'neck' combined
Right: A mature Chiroteuthis veranyi. This species has some of the longest tentacles in proportion to its size of any known cephalopod.
| image1 =Chiroteuthis veranyi immature.jpg
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}}The length of time before hatching is highly variable; smaller eggs in warmer waters are the fastest to hatch, and newborns can emerge after as little as a few days. Larger eggs in colder waters can develop for over a year before hatching.BOOK, 12846042, 978-0-12-026144-4, 2003
first1=S., Biology of early life stages in cephalopod molluscs, 44, 143–203, 10.1016/S0065-2881(03)44003-0, Advances in Marine Biology, The process from spawning to hatching follows a similar trajectory in all species, the main variable being the amount of yolk available to the young and when it is absorbed by the embryo.Unlike most other mollusks, cephalopods do not have a morphologically distinct larval stage. Instead, the juveniles are known as paralarvae. They quickly learn how to hunt, using encounters with prey to refine their strategies.Growth in juveniles is usually allometric, whilst adult growth is isometric.JOURNAL, Understanding the process of growth in cephalopodsissue=4first=Natalie A.pages=379–386doi=10.1071/MF03147,

Evolution

The traditional view of cephalopod evolution holds that they evolved in the Late Cambrian from a monoplacophoran-like ancestorJOURNAL, Lemche, H., Wingstrand, K. G.,weblink Link to free full text + plates, 1959, The anatomy of Neopilina galatheae Lemche, 1957 (Mollusca, Tryblidiacea), Galathea Report, 3, 9–73, with a curved, tapering shell,JOURNAL,weblink Link to free full text + plates, Wingstrand, K. G., 1985, On the anatomy and relationships of Recent Monoplacophora, Galathea Report, 16, 7–94, which was closely related to the gastropods (snails).BOOK, 10.1002/9780470995310.ch3, 9780470995310, Cephalopods, 2005, Boyle, Origin and Evolution, P., Rodhouse, P., 36, The similarity of the early shelled cephalopod Plectronoceras to some gastropods was used in support of this view. The development of a siphuncle would have allowed the shells of these early forms to become gas-filled (thus buoyant) in order to support them and keep the shells upright while the animal crawled along the floor, and separated the true cephalopods from putative ancestors such as Knightoconus, which lacked a siphuncle. Neutral or positive buoyancy (i.e. the ability to float) would have come later, followed by swimming in the Plectronocerida and eventually jet propulsion in more derived cephalopods.JOURNAL, Kröger, B. R., Some Lesser Known Features of the Ancient Cephalopod Order Ellesmerocerida (Nautiloidea, Cephalopoda), 2007, Palaeontology, 50, 3, 565–572, 10.1111/j.1475-4983.2007.00644.x, However, some morphological evidence is difficult to reconcile with this view, and the redescription of Nectocaris pteryx, which did not have a shell and appeared to possess jet propulsion in the manner of "derived" cephalopods, complicated the question of the order in which cephalopod features developed – provided Nectocaris is a cephalopod at all.JOURNAL, Primitive soft-bodied cephalopods from the Cambrian, Smith, Martin R., Caron, Jean-Bernard, 2010, Nature, 427–428, 465, 20505713, 7297, 10.1038/465427a, 2010Natur.465..427B, Early cephalopods were likely predators near the top of the food chain. After the late Cambrian extinction led to the disappearance of many Anomalocaridids, predatory niches became available for other animals.BOOK, Jain, Sreepat, Fundamentals of Invertebrate Palaeontology: Macrofossils,weblink 2016, Springer, 978-81-322-3658-0, 73, During the Ordovician period the primitive cephalopods underwent pulses of diversificationJOURNAL, Yun-bai, B., Y. B., Pulsed cephalopod diversification during the Ordovician, Palaeogeography, Palaeoclimatology, Palaeoecology, 273, 1–2, 174–201, 2009, Kröger, 10.1016/j.palaeo.2008.12.015, 2009PPP...273..174K, to become diverse and dominant in the Paleozoic and Mesozoic seas.JOURNAL, Dzik, J., 1981, Origin of the Cephalopoda, Acta Palaeontologica Polonica, 26, 2, 161–191,weblink In the Early Palaeozoic, their range was far more restricted than today; they were mainly constrained to sublittoral regions of shallow shelves of the low latitudes, and usually occurred in association with thrombolites.JOURNAL, 2009, The origin and initial rise of pelagic cephalopods in the Ordovician, PLOS ONE, 4, 9, e7262, 10.1371/journal.pone.0007262, 19789709, 2749442, Kröger, B. R., Servais, T., Zhang, Y., Kosnik, M., 2009PLoSO...4.7262K, A more pelagic habit was gradually adopted as the Ordovician progressed. Deep-water cephalopods, whilst rare, have been found in the Lower Ordovician – but only in high-latitude waters.The mid-Ordovician saw the first cephalopods with septa strong enough to cope with the pressures associated with deeper water, and could inhabit depths greater than 100–200 m. The direction of shell coiling would prove to be crucial to the future success of the lineages; endogastric coiling would only permit large size to be attained with a straight shell, whereas exogastric coiling – initially rather rare – permitted the spirals familiar from the fossil record to develop, with their corresponding large size and diversity.JOURNAL, C. H., The nautiloid cephalopods: a strange success: President's anniversary address 1986, Journal of the Geological Society, 144, 1, Holland, 1–15, 1987, 10.1144/gsjgs.144.1.0001, 1987JGSoc.144....1H, (Endogastric mean the shell is curved so as the ventral or lower side is longitudinally concave (belly in); exogastric means the shell is curved so as the ventral side is longitudinally convex (belly out) allowing the funnel to be pointed backward beneath the shell.)File:1212amma.jpg|thumb|left|upright=1.2|An ammonoidammonoidThe ancestors of coleoids (including most modern cephalopods) and the ancestors of the modern nautilus, had diverged by the Floian Age of the Early Ordovician Period, over 470 million years ago.JOURNAL, Kröger, Björn
, 2006, Early growth-stages and classification of orthoceridan cephalopods of the Darriwillian (Middle Ordovician) of Baltoscandia, Lethaia, 39, 2, 129–139, 10.1080/00241160600623749, The Bactritida, a Silurian–Triassic group of orthocones, are widely held to be paraphyletic to the coleoids and ammonoids, that is, the latter groups arose from within the Bactritida.JOURNAL, The evolution of coleoid cephalopods and their present biodiversity and ecology, Young, R. E., Vecchione, M., Donovan, D. T., South African Journal of Marine Science, 20, 1, 1998, 393–420, 10.2989/025776198784126287, {{rp|393}} An increase in the diversity of the coleoids and ammonoids is observed around the start of the Devonian period and corresponds with a profound increase in fish diversity. This could represent the origin of the two derived groups.
Unlike most modern cephalopods, most ancient varieties had protective shells. These shells at first were conical but later developed into curved nautiloid shapes seen in modern nautilus species.Competitive pressure from fish is thought to have forced the shelled forms into deeper water, which provided an evolutionary pressure towards shell loss and gave rise to the modern coleoids, a change which led to greater metabolic costs associated with the loss of buoyancy, but which allowed them to recolonize shallow waters.{{Rp|36}} However, some of the straight-shelled nautiloids evolved into belemnites, out of which some evolved into squid and cuttlefish.{{Verify source|date=November 2008}} The loss of the shell may also have resulted from evolutionary pressure to increase maneuverability, resulting in a more fish-like habit.{{Rp|289}}There has been debate on the embryological origin of cephalopod appendages.BOOK, Cephalopods – Present and Past, Tanabe, K., Tokai University Press, 2008, Tokyo, {{page needed|date=December 2017}} Until the mid-twentieth century, the "Arms as Head" hypothesis was widely recognized. In this theory, the arms and tentacles of cephalopods look similar to the head appendages of gastropods, suggesting that they might be homologous structures. Cephalopod appendages surround the mouth, so logically they could be derived from embryonic head tissues.JOURNAL, Basil, Jennifer, Bahctinova, Irina, Kuroiwa, Kristine, Lee, Nandi, Mims, Desiree, Preis, Michael, Soucier, Christian, 2005-09-01, The function of the rhinophore and the tentacles of Nautilus pompilius L. (Cephalopoda, Nautiloidea) in orientation to odor, Marine and Freshwater Behaviour and Physiology, 38, 3, 209–221, 10.1080/10236240500310096, However, the "Arms as Foot" hypothesis, proposed by Adolf Naef in 1928, has increasingly been favoured; for example, fate mapping of limb buds in the chambered nautilus indicates that limb buds originate from "foot" embryonic tissues.JOURNAL, Shigeno, Shuichi, Sasaki, Takenori, Moritaki, Takeya, Kasugai, Takashi, Vecchione, Michael, Agata, Kiyokazu, January 2008, Evolution of the cephalopod head complex by assembly of multiple molluscan body parts: Evidence from Nautilus embryonic development, Journal of Morphology, 269, 1, 1–17, 10.1002/jmor.10564, 17654542,

Phylogeny

The approximate consensus of extant cephalopod phylogeny, after Strugnell et al. 2007, is shown in the cladogram. Mineralized taxa are in bold. The attachment of the clade including Sepia and Spirula is unclear; either of the points marked with an asterisk may represent the root of this clade.{{clade|1=
{{clade|1=Nautilus (File:Nautilus Palau.JPG|70px)
| label1=Nautiloids
| label2=Coleoids
| 2 =
{{clade | 1= Basal octopods (e.g. Argonauta) (File:Papierboot Argonauta 200705181139.jpg|70px)
| 2 =
{{clade | 1= Vampyroteuthis (File:Vampire des abysses.jpg|70px)
| 2 =
{{clade | 1= Heteroteuthis (bobtail squid) (File:Heteroteuthis hawaiiensis1.jpg|90px)
| label2=*
| 2 =
{{clade | 1={{clade
|Sepia (cuttlefish) (File:Sepia officinalis 2.jpg|70px)
|Idiosepius
}}
| 2 =
{{clade | 1=Sepioteuthis (File:アオリイカ-Sepioteuthis lessoniana.jpg|70px)
| 2 =
{{clade | 1=Spirula (File:Spirula spirula illustration.jpg|70px)
| 2=Certain squid (e.g. Bathyteuthis) (File:Bathyteuthisabyssicola.jpg|90px)
| label2=*
}}
}}
}}
}}
}}
}}
}}
}}
The internal phylogeny of the cephalopods is difficult to constrain; many molecular techniques have been adopted, but the results produced are conflicting.JOURNAL, 10.1093/mollus/eym038, Molecular phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) inferred from three mitochondrial and six nuclear loci: a comparison of alignment, implied alignment and analysis methods, 2007, Strugnell, J., Nishiguchi, M. K., Journal of Molluscan Studies, 73, 4, 399–410, JOURNAL, Strugnell, J., Norman, M., Jackson, J., Drummond, A., Cooper, A., Molecular phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) using a multigene approach; the effect of data partitioning on resolving phylogenies in a Bayesian framework, Molecular Phylogenetics and Evolution, 37, 2, 426–441, 2005, 15935706, 10.1016/j.ympev.2005.03.020, Nautilus tends to be considered an outgroup, with Vampyroteuthis forming an outgroup to other squid; however in one analysis the nautiloids, octopus and teuthids plot as a polytomy. Some molecular phylogenies do not recover the mineralized coleoids (Spirula, Sepia, and Metasepia) as a clade; however, others do recover this more parsimonious-seeming clade, with Spirula as a sister group to Sepia and Metasepia in a clade that had probably diverged before the end of the Triassic.JOURNAL, Cooper, A. J., A., Cladistics, 89–96, 22, Drummond, J., 2006, Divergence time estimates for major cephalopod groups: evidence from multiple genes, Strugnell, J., Jackson, 10.1111/j.1096-0031.2006.00086.x, JOURNAL, 10.1093/oxfordjournals.molbev.a026419, 10958852, 2000, Carlini, D. B., Reece, K. S., Graves, J. E., Actin gene family evolution and the phylogeny of coleoid cephalopods (Mollusca: Cephalopoda), 17, 9, 1353–1370, Molecular Biology and Evolution, Molecular estimates for clade divergence vary. One 'statistically robust' estimate has Nautilus diverging from Octopus at {{Ma|415|error=24}}.JOURNAL, 10.1007/s00239-005-0160-x, 16501879, 2006, Bergmann, S., Lieb, B., Ruth, P., Markl, J., The hemocyanin from a living fossil, the cephalopod Nautilus pompilius: protein structure, gene organization, and evolution, 62, 3, 362–374, Journal of Molecular Evolution, 2006JMolE..62..362B,

Taxonomy

File:Nautilus pompilius 3.jpg|thumb|230px|Chambered nautilusChambered nautilusFile:Sepia officinalis (aquarium).jpg|thumb|230px|Common cuttlefishCommon cuttlefish
missing image!
- Sepiola atlantica.jpg -
Atlantic bobtail (Sepiola atlantica)
missing image!
- Loligo vulgaris.jpg -
European squid (Loligo vulgaris)
missing image!
- Octopus vulgaris2.jpg -
Common octopus (Octopus vulgaris)
The classification presented here, for recent cephalopods, follows largely from Current Classification of Recent Cephalopoda (May 2001), for fossil cephalopods takes from Arkell et al. 1957, Teichert and Moore 1964, Teichert 1988, and others. The three subclasses are traditional, corresponding to the three orders of cephalopods recognized by Bather.JOURNAL
, Bather, F.A., 1888b
, Professor Blake and Shell-Growth in Cephalopoda
, Annals and Magazine of Natural History
, 1, 6, 6, 421–426
,weblink 10.1080/00222938809460761
, Class Cephalopoda († indicates extinct groups) Order Spirulida: Ram's horn squid Order Sepiida: cuttlefish Order Sepiolida: pygmy, bobtail and bottletail squid Order Teuthida: squid Family † Trachyteuthididae Order Vampyromorphida: Vampire squid Order Octopoda: octopus Order † BoletzkyidaOther classifications differ, primarily in how the various decapod orders are related, and whether they should be orders or families.

Suprafamilial classification of the Treatise

This is the older classification that combines those found in parts K and L of the Treatise on Invertebrate Paleontology, which forms the basis for and is retained in large part by classifications that have come later.Nautiloids in general (Teichert and Moore, 1964) sequence as given.
Subclass † Endoceratoidea. Not used by Flower, e.g. Flower and Kummel 1950, interjocerids included in the Endocerida.
Order † Endocerida Order † Intejocerida
Subclass † Actinoceratoidea Not used by Flower, ibid
Order † Actinocerida
Subclass Nautiloidea Nautiloidea in the restricted sense.
Order † Ellesmerocerida Plectronocerida subsequently split off as separate order. Order † Orthocerida Includes orthocerids and pseudorthocerids Order † Ascocerida Order † Oncocerida Order † Discosorida Order † Tarphycerida Order † Barrandeocerida A polyphyletic group now included in the Tarphycerida Order Nautilida
Subclass † Bactritoidea
Order † Bactritida
Paleozoic Ammonoidea (Miller, Furnish and Schindewolf, 1957)
Suborder † Anarcestina Suborder † Clymeniina Suborder † Goniatitina Suborder † Prolecanitina
Mesozoic Ammonoidea (Arkel et al., 1957)
Suborder † Ceratitina Suborder † Phylloceratina Suborder † Lytoceratina Suborder † Ammonitina
Subsequent revisions include the establishment of three Upper Cambrian orders, the Plectronocerida, Protactinocerida, and Yanhecerida; separation of the pseudorthocerids as the Pseudorthocerida, and elevating orthoceratid as the Subclass Orthoceratoidea.

Shevyrev classification

Shevyrev (2005) suggested a division into eight subclasses, mostly comprising the more diverse and numerous fossil forms,JOURNAL
, Shevyrev
, A. A.
, 2005
, The Cephalopod Macrosystem: A Historical Review, the Present State of Knowledge, and Unsolved Problems: 1. Major Features and Overall Classification of Cephalopod Mollusks
, Paleontological Journal
, 39, 6, 606–614, Translated from Paleontologicheskii Zhurnal No. 6, 2005, 33–42.
JOURNAL
, Shevyrev
, A. A.
, 2006
, The cephalopod macrosystem; a historical review, the present state of knowledge, and unsolved problems; 2, Classification of nautiloid cephalopods
, Paleontological Journal
, 40
, 1
, 46–54
, 10.1134/S0031030106010059
,
although this classification has been criticized as arbitrary.WEB, Kroger, B., Peer review in the Russian 'Paleontological Journal',weblink dead,weblink" title="web.archive.org/web/20090831224201weblink">weblink 2009-08-31,
File:Ammonites 180308.jpg|thumb|Various species of ammoniteammoniteFile:Ostenoteuthis siroi.JPG|thumb|Holotype of Ostenoteuthis siroi from family OstenoteuthidaeOstenoteuthidaeFile:Fossil-Belemnoidea-complete.jpg|thumb|A fossilised belemnitebelemniteClass Cephalopoda JOURNAL
, Bather, F.A.
, 1888a
, Shell-growth in Cephalopoda (Siphonopoda)
, Annals and Magazine of Natural History
, 1, 4
, 6, 298–310
,weblink
, 10.1080/00222938809460727
,

Cladistic classification

missing image!
- Vampylarge.JPG -
Pyritized fossil of Vampyronassa rhodanica, a vampyromorphid from the Lower Callovian ({{Ma|Callovian}})
Another recent system divides all cephalopods into two clades. One includes nautilus and most fossil nautiloids. The other clade (Neocephalopoda or Angusteradulata) is closer to modern coleoids, and includes belemnoids, ammonoids, and many orthocerid families. There are also stem group cephalopods of the traditional Ellesmerocerida that belong to neither clade.JOURNAL
, Berthold, Thomas, Engeser, Theo, 1987
, Phylogenetic analysis and systematization of the Cephalopoda (Mollusca)
, Verhandlungen Naturwissenschaftlichen Vereins in Hamburg
, 29, 187–220
, WEB,weblink Fossil Nautiloidea Page, Engeser, Theo, 1997,weblink" title="web.archive.org/web/20060925110442weblink">weblink 2006-09-25, The coleoids, despite some doubts,{{Rp|289}} appear from molecular data to be monophyletic.JOURNAL, 10.1111/j.1096-0031.2004.00032.x, A combined approach to the phylogeny of Cephalopoda (Mollusca), 2004, Lindgren, A. R., Giribet, G., Nishiguchi, M. K., Cladistics, 20, 5, 454–486, 10.1.1.693.2026,

In culture

{{further|Cephalopods in popular culture}}File:Colossal octopus by Pierre Denys de Montfort.jpg|thumb|upright|left|Pen and wash drawing of an imagined colossal octopus attacking a ship, by the malacologist Pierre de MontfortPierre de MontfortAncient seafaring people were aware of cephalopods, as evidenced by artworks such as a stone carving found in the archaeological recovery from Bronze Age Minoan Crete at Knossos (1900 – 1100 BC) has a depiction of a fisherman carrying an octopus.WEB, Hogan, C. Michael, 22 December 2007,weblink Knossos fieldnotes, The Modern Antiquarian, The terrifyingly powerful Gorgon of Greek mythology may have been inspired by the octopus or squid, the octopus's body representing the severed head of Medusa, the beak as the protruding tongue and fangs, and its tentacles as the snakes.BOOK, {{google books, y, OnHO4orvz18C, | title=Medusa: Solving the Mystery of the Gorgon | last=Wilk | first=Stephen R. | date=2000 | publisher=Oxford University Press | isbn=978-0-19-988773-6}}File:NROL-39 Patch.jpg|thumb|The NROL-39 mission patch, depicting the alt=A mission badge of an octopus spanning the world against a starry background, labelled "NROL-39" and "Nothing is beyond our reach"The Kraken are legendary sea monsters of giant proportions said to dwell off the coasts of Norway and Greenland, usually portrayed in art as giant cephalopods attacking ships. Linnaeus included it in the first edition of his 1735 Systema Naturae.WEB, {{google books, y, WfQTAAAAQAAJ, 82, | title=Caroli Linnaei Systema naturae sistens regna tria naturae | work=google.com}}BOOK, Edward, Smedley, Hugh James, Rose, Henry John, Rose, Encyclopaedia Metropolitana, Or, Universal Dictionary of Knowledge: Comprising the Twofold Advantage of a Philosophical and an Alphabetical Arrangement, with Appropriate Engravings, {{google books, y, 3X1GAQAAIAAJ, 255, |year=1845|publisher=B. Fellowes|pages=255–}} A Hawaiian creation myth says that the present cosmos is the last of a series which arose in stages from the ruins of the previous universe. In this account, the octopus is the lone survivor of the previous, alien universe.BOOK, 9, Dixon, Roland Burrage, Roland Burrage Dixon, Oceanic, The Mythology of All Races, {{google books, y, gLIIAQAAIAAJ&pg=PP2, | date=1916 | publisher=Marshall Jones Company | pages=2–}} The Akkorokamui is a gigantic tentacled monster from Ainu folklore.BOOK, Batchelor, John, The Ainu and Their Folklore, London, The Religious Tract Society, 1901, A battle with an octopus plays a significant role in Victor Hugo's book Travailleurs de la mer (Toilers of the Sea), relating to his time in exile on Guernsey.EB1911, Octopus, Ian Fleming's 1966 short story collection Octopussy and The Living Daylights, and the 1983 James Bond film were partly inspired by Hugo's book.JOURNAL, Cohen-Vrignaud, Gerard, On Octopussies, or the Anatomy of Female Power, Differences, 2012, 23, 2, 32–61, 10.1215/10407391-1533520, Japanese erotic art, shunga, includes ukiyo-e woodblock prints such as Katsushika Hokusai's 1814 print Tako to ama (The Dream of the Fisherman's Wife), in which an ama diver is sexually intertwined with a large and a small octopus.BOOK, Sointu, Fritze, Saara, Suojoki, Forbidden Images: Erotic Art from Japan's Edo Period, {{google books, y, QRtmAAAACAAJ, 23, |year=2000|publisher=Helsingin kaupungin taidemuseo|isbn=978-951-8965-54-4| language=Finnish | pages=23–28 }}BOOK, Japanese Erotic Fantasies: Sexual Imagery of the Edo Period, Uhlenbeck, Chris, Margarita Winkel, Ellis Tinios, Amy Reigle Newland, 2005, Hotei, 978-90-74822-66-4, 161, The print is a forerunner of tentacle erotica.BOOK, Briel, Holger, 2010, The Roving Eye Meets Traveling Pictures: The Field of Vision and the Global Rise of Adult Manga, Berninger, Mark, Ecke, Jochen, Haberkorn, Gideon, Comics As a Nexus of Cultures: Essays on the Interplay of Media, Disciplines, {{google books, y, e-aWWTZeergC, 203, | publisher=McFarland | isbn=978-0-7864-3987-4 | page=203}} The biologist P. Z. Myers noted in his science blog, Pharyngula, that octopuses appear in "extraordinary" graphic illustrations involving women, tentacles, and bare breasts.WEB, Myers, P. Z., PZ Myers, Extraordinary Octopus Illustrations,weblink Pharyngula, 18 March 2017, 17 May 2017, WEB, Myers, P. Z., PZ Myers, Definitely not safe for work,weblink Pharyngula, 18 March 2017, 29 October 2006, Since it has numerous arms emanating from a common center, the octopus is often used as a symbol for a powerful and manipulative organization, usually negatively.WEB, Smith, S.,weblink Why Mark Zuckerberg Octopus Cartoon Evokes 'Nazi Propaganda,' German Paper Apologizes, iMediaEthics, 26 February 2010, 31 May 2017,

See also

{{Wikipedia books|Cephalopoda}}

References

{{Reflist}}

Further reading

  • JOURNAL, 10.1134/S0031030108110014, Cephalopods in the marine ecosystems of the Paleozoic, 2008


, Barskov, I. S., M. S., Boiko, V. A., Konovalova, T. B., Leonova, S. V., Nikolaeva, Paleontological Journal
, 42, 1167–1284, 11, A comprehensive overview of Paleozoic cephalopods.
  • BOOK, Campbell, Neil A., Reece, Jane B., Mitchell, Lawrence G., Biology, fifth edition, Addison Wesley Longman, Inc., Menlo Park, California, 1999, 978-0-8053-6566-5, harv,
  • Felley, J., Vecchione, M., Roper, C. F. E., Sweeney, M. & Christensen, T., 2001–2003: Current Classification of Recent Cephalopoda. National Museum of Natural History: Department of Systematic Biology: Invertebrate Zoology: Cephalopods
  • N. Joan Abbott, Roddy Williamson, Linda Maddock. Cephalopod Neurobiology. Oxford University Press, 1995. {{ISBN|0-19-854790-0}}
  • Marion Nixon & John Z. Young. The brains and lives of Cephalopods. Oxford University Press, 2003. {{ISBN|0-19-852761-6}}
  • Hanlon, Roger T. & John B. Messenger. Cephalopod Behaviour. Cambridge University Press, 1996. {{ISBN|0-521-42083-0}}
  • Martin Stevens & Sami Merilaita. Animal camouflage: mechanisms and function. Cambridge University Press, 2011. {{ISBN|0-521-19911-5}}
  • JOURNAL, Rodhouse, P. G., Nigmatullin, Ch. M., Role as Consumers, Philosophical Transactions of the Royal Society B: Biological Sciences, 1996, 351, 1343, 1003–1022, 10.1098/rstb.1996.0090,
  • Classification key to modern cephalopods:weblink

External links

{{Wikispecies|Cephalopoda}}{{EB1911 poster|Cephalopoda}} {{Commons category|position=left|Cephalopoda|Cephalopoda}}{{Mollusc}}{{taxonbar|from=Q128257}}{{Authority control}}


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