Cephalopoda

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(Class Cephalopoda: modifications)
(Biology: Pachydiscus seppenradensis is Parapuzosia seppenradensis)
 
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==Biology==
==Biology==
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The name Cephalopoda literally means "head feet" which refers to the cluster of [[arm]]s and/or [[tentacle]]s that project forward from the head, surrounding the mouth.  The group includes living [[Coleoidea|coleoids]] (squid, octopods, and cuttlefish) and ''[[Nautilus]]'', and a large number of ancient (mostly [[Paleozoic]] and [[Mesozoic]]) forms.  All are active marine predators (although some early types were drifters), able to swim swiftly, and easily competing with fish in the marine habitat.  There are 650 living species, but more than 7,500 fossil forms are known (and as in all cases like this this number is obviously a gross underestimate of the real number of cephalopod species that have ever lived through the [[Phanerozoic]] time).  Like fish they are equipped with highly developed eyes and other sense organs, include both active swimmers and bottom-dwellers, and in many cases have a streamlined body for more efficient locomotion.  Swimming is by rapidly expelling water from the [[mantle cavity]].  The water is forced out through a funnel or [[siphon]] - the [[hyponome]] - actually a tube-like flap of modified foot, thus driving the animal in the opposite direction.  This is the key to the so-called "jet-propulsion" of these animals   The funnel is highly maneuverable and can be directed in any direction, allowing motion backwards or forwards.  However, the fastest movement is backward escape swimming, with powerful contractions of the mantle ejecting water through the forward facing funnel.  A cloud of "ink" can also be ejected as a sort of underwater smoke screen to hide the fleeing animal.
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The name Cephalopoda literally means "head feet" which refers to the cluster of [[arm]]s and/or [[tentacle]]s that project forward from the head, surrounding the mouth.  The group includes living [[Coleoidea|coleoids]] (squid, octopods, and cuttlefish) and ''[[Nautilus]]'', and a large number of ancient (mostly [[Paleozoic]] and [[Mesozoic]]) forms.  All are active marine predators (although some early types were drifters), able to swim swiftly, and easily competing with fish in the marine habitat.  There are 650 living species, but more than 7,500 fossil forms are known (and as in all cases like this this number is obviously a gross underestimate of the real number of cephalopod species that have ever lived through the [[Phanerozoic]] time).  Like fish they are equipped with highly developed eyes and other sense organs, include both active swimmers and bottom-dwellers, and in many cases have a streamlined body for more efficient locomotion.  Swimming is by rapidly expelling water from the [[mantle cavity]].  The water is forced out through a funnel or [[siphon]], knows as the hyponome, thus driving the animal in the opposite direction.  This is the key to the so-called "jet-propulsion" of these animals. The funnel is highly maneuverable and can be directed in almost any direction, allowing motion backwards or forwards.  However, the fastest movement is backward escape swimming, with powerful contractions of the mantle ejecting water through the forward facing funnel.  A cloud of "ink" can also be ejected as a sort of underwater smoke screen to hide the fleeing animal.
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All cephalopods are carnivorous, feeding primarily on fish, other [[Mollusca|mollusks]], [[Crustacea]], and worms.  The head projects into a crown of prehensile tentacles - ranging from 8 in the octopus to 80 or 90 in the living nautilus. These tentacles are actually a specialized form of the standard molluscan foot, and used for grasping prey. Once the prey is snared it is bitten with strong beak-like jaws and pulled into the mouth by the [[radula]].
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All cephalopods are carnivorous, feeding primarily on fish, other [[Mollusca|mollusks]], [[Crustacea|crustaceans]], and worms.  The head projects into a crown of prehensile arms ranging from 8 in octopus to about 90 in the living nautilus. Cephalopod arms, or tentacles, and used for grasping prey, are a specialized development of the basic molluscan foot. Once the prey is snared it is bitten with strong beak-like jaws and pulled into the mouth by the [[radula]].
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Cephalopods are quite large by molluscan standards (most species being between 6 and 70 cm including tentacles), with the giants of the group - such as the modern day ''[[Architeuthis]]'', the giant squid, with a body length (including tentacles) of up to 20 meters, the Ordovician [[Endocerida|endocerid]] [[Nautiloidea|nautiloid]] ''[[Cameroceras]]'', with a straight shell up to 10 metres in length, and the Cretaceous [[Ammonoidea|ammonoid]] ''[[Pachydiscus seppenradensis]]'', with a coiled shell 3 metres in diameter - the largest invertebrates ever to live, with weights of one to two tons.  Such giant cephalopods play or played a similar ecological role of top predator to that of [[Devonian]] [[Arthrodira|arthrodire]] [[Placodermi|placoderms]], [[Mesozoic]] [[pliosaur]]s and [[Cenozoic]] [[Odontoceti|toothed whales]].
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Cephalopods are quite large by molluscan standards (most species being between 6 and 70 cm including tentacles), with the giants of the group - such as the modern day ''[[Architeuthis]]'', the giant squid, with a body length (including tentacles) of up to 20 meters, the Ordovician orthoconic [[Endocerida|endocerid]] ''[[Cameroceras]]'', with a straight shell up to 10 metres in length, and the Cretaceous [[Ammonoidea|ammonoid]] ''[[Parapuzosia seppenradensis]]'', with a coiled shell 3 metres in diameter - the largest invertebrates ever to live, with weights of one to two tons.  Such giant cephalopods play or played a similar ecological role of top predator to that of Devonian [[Arthrodira]], Mesozoic [[pliosaur]]s, and Cenozoic [[Odontoceti|toothed whales]].
Cephalopods have a highly developed nervous system, unequalled among the invertebrates, and correlated with locomotor dexterity and carnivorous lifestyle (predators generally always have larger brains than prey animals).  There is a high level of cephalization (development and concentration of sensory and neural centers in the head).  The nerve ganglia are concentrated and more or less fused to form a brain that encircles the esophagus. A bundle of giant nerve fibres tied to the [[mantle]] give them very rapid reflexes.  They are visual creatures, changing colour to express mood.  The eyes of the [[Coleoidea]] are very elaborate, with a retinal structure remarkably like that found in vertebrates.  The eye of the giant squid is the largest of any animal - 40 cm across. Nautiloids have smaller and more primitive eyes.
Cephalopods have a highly developed nervous system, unequalled among the invertebrates, and correlated with locomotor dexterity and carnivorous lifestyle (predators generally always have larger brains than prey animals).  There is a high level of cephalization (development and concentration of sensory and neural centers in the head).  The nerve ganglia are concentrated and more or less fused to form a brain that encircles the esophagus. A bundle of giant nerve fibres tied to the [[mantle]] give them very rapid reflexes.  They are visual creatures, changing colour to express mood.  The eyes of the [[Coleoidea]] are very elaborate, with a retinal structure remarkably like that found in vertebrates.  The eye of the giant squid is the largest of any animal - 40 cm across. Nautiloids have smaller and more primitive eyes.
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While there is general agreement regarding classification of recent cephalopods, mostly coleoids, based on soft part anatomical features, classification of extinct fossil forms based on such criteria is impossible other than for a few inferences that night be drawn from preserved muscle attachment scars, preserved radula, tentacle imprints, and isolated body impressions. Shell based features on the other hand provide the basis for a reliable, phylogenetically plausible  and generally accepted classification of extinct forms.   
While there is general agreement regarding classification of recent cephalopods, mostly coleoids, based on soft part anatomical features, classification of extinct fossil forms based on such criteria is impossible other than for a few inferences that night be drawn from preserved muscle attachment scars, preserved radula, tentacle imprints, and isolated body impressions. Shell based features on the other hand provide the basis for a reliable, phylogenetically plausible  and generally accepted classification of extinct forms.   
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====Palcephalopoda-Neocephalopoda ====
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'''Palcephalopoda-Neocephalopoda'''
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The Palcephalopoda-Neocephalopoda distinction is based on essential differences between the living nautiloid genera, ''Nautilus'' and ''Allonautilus'', and the huge variety of living coleoids. Living nautiloides are tetrabranchiate (have 4 gills in 2 pairs), are lateradulate (13 elements per radular row), and produce multiple batches of well develovoped offspring from large yolk-rich eggs. The have an external shell, retained from their ancestors but have mutliple finger-like protractable tentacles, probably a derived character. Also their eyes have no lens but operate like a pin-hole camera, again apparently primitive,  Coleoids are dibranchiate (have 2 gills), are angusteradulate (9 elements per radular row) and in general produce a single batch of numerous planctonic offspring before dying. They lack an external shell, a obvious derived character but have 8 or 10 muscular suckered and/or hooked tentacles which seems to be a retained primitive trait. On the other hand coleoids have well developed eyes with lenses, sometimes covered by a corneal membrane.
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The <u>Palcephalopoda-Neocephalopoda</u> distinction is based on essential differences between the living nautiloid genera, ''Nautilus'' and ''Allonautilus'', and the huge variety of living coleoids. Living nautiloides are tetrabranchiate (have 4 gills in 2 pairs), are lateradulate (13 elements per radular row), and produce multiple batches of well develovoped offspring from large yolk-rich eggs. The have an external shell, retained from their ancestors but have mutliple finger-like protractable tentacles, probably a derived character. Also their eyes have no lens but operate like a pin-hole camera, again apparently primitive,  Coleoids are dibranchiate (have 2 gills), are angusteradulate (9 elements per radular row) and in general produce a single batch of numerous planctonic offspring before dying. They lack an external shell, a obvious derived character but have 8 or 10 muscular suckered and/or hooked tentacles which seems to be a retained primitive trait. On the other hand coleoids have well developed eyes with lenses, sometimes covered by a corneal membrane.
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The extent to which these distinctions can be extrapolated into fossil forms is questionable and subject to individual interpretation. Ammonoids for example are thought to be more closely related to coleoids than to nautiloids on the basis of being angueratulate (with 9 radular elements like coleoids) from the few radula found, in spite of having an external shell, and are therefor considered neocephalopods. Paleozoic orthocerids are considered neocephalopods because their protoconch is like that of ammonoids in spite of having an obviously nautiloid phragmocone.
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The extent to which these distinctions can be extrapolated into fossil forms is questionable and subject to individual interpretation. Ammonoids for example are thought to be more closely related to coleoids than to nautiloids on the basis of being angueradulate (with 9 radular elements like coleoids) from the few radula found, in spite of having an external shell, and are therefor considered neocephalopods. Paleozoic orthocerids are considered neocephalopods because their protoconch is like that of ammonoids in spite of having an obviously nautiloid phragmocone.
==== Alternative Taxonomies====
==== Alternative Taxonomies====
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The following basically follows Teichert (1988) with the Palcephalopoda/Neocephalopoda hypothesis incorporated; except that Teichert's two Subclasses '''Endoceratoidea''' and '''Actinoceratoidea''' have been discarded, since the two orders [[Endocerida]] and [[Actinocerida]] are probably not so distinct from their contemporaries as to justify such a high taxonomic ranking.
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:'''An Infraclass based taxonomy'''
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'''Infraclass unnamed''' ("Ellesmeroceroidea"? or several infraclasses?)
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The following basically follows Teichert (1988) except that Teichert's two Subclasses Endoceratoidea and Actinoceratoidea have been discarded, since the two orders [[Endocerida]] and [[Actinocerida]] are not so distinct from their contemporaries as to justify such a high taxonomic ranking.
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  Order [[Plectronocerida]] Flower, 1964
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  Order [[Yanhecerida]] Chen & Qi, 1979 (or included in Plectronocerida or Ellesmerocerida?)
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  Order [[Protactinocerida]] Chen & Qi, 1979 (or included in Plectronocerida or Ellesmerocerida?)
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  Order [[Ellesmerocerida]] Flower, 1950
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  Order [[Endocerida]] Teichert, 1933
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  Order [[Intejocerida]] Balashov, 1960 (or included in Endocerida?)
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  Order [[Discosorida]] Flower, 1950
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  Order [[Actinocerida]] Teichert, 1933
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  Order [[Pseudorthocerida]]
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'''Infraclass Nautiloidea''' Agassiz, 1947 (= Nautiloidea "sensu stricto")
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'''Infraclass unnamed''' ("Ellesmeroceroidea"? or several infraclasses?)<br>
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  Order [[Tarphycerida]] Flower, 1950
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:Order [[Plectronocerida]] Flower, 1964.
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    Suborder [[Tarphycerina]] Flower, 1950
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:Order [[Yanhecerida]] Chen & Qi, 1979.(or included in Plectronocerida?)
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    Suborder [[Barrandeocerina]] Flower
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:Order [[Protactinocerida]] Chen & Qi, 1979.(or included in Plectronocerida?)
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  Order [[Oncocerida]] Flower, 1950
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:Order [[Ellesmerocerida]] Flower, 1950.
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  Order [[Nautilida]] Agassiz, 1847
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:Order [[Endocerida]] Teichert, 1933.
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:Order [[Intejocerida]] Balashov, 1960. (or included in Endocerida?)
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:Order [[Discosorida]] Flower, 1950  
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:Order [[Actinocerida]] Teichert, 1933
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:Order [[Pseudorthocerida]]
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'''Infraclass Nautiloidea''' Agassiz, 1947<br> (Superorder Nautilitoidea, Wade)<br>
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:Order [[Tarphycerida]] Flower, 1950.
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::Suborder [[Tarphycerina]] Flower, 1950.
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::Suborder [[Barrandeocerina]] Flower, 1950.
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:Order [[Oncocerida]] Flower, 1950.
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:Order [[Nautilida]] Agassiz, 1847.
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'''Infraclass Orthoceratoidea''' Kuhn, 1940
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'''Infraclass Orthoceratoidea''' Kuhn, 1940
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  Order [[Orthocerida]] Kuhn, 1940  
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(Orthoceratoidea Wade, in part)<br>
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  Order [[Ascocerida]] Kuhn, 1949  
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:Order [[Orthocerida]] Kuhn, 1940.
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:Order [[Ascocerida]] Kuhn, 1949.
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'''Infraclass Ammonoidea''' Agassiz, 1947
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'''Infraclass Ammonoidea''' Agassiz, 1947<br>
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  Order [[Bactritida]] Shimanskiy  
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(=Subclass [[Ammonoidea]])
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  Order [[Anarcestida]] Miller & Furnish 1954  
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:Order [[Bactritida]] Shimanskiy  
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  Order [[Goniatitida]] Hyatt 1884  
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:Order [[Anarcestida]] Miller & Furnish 1954  
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  Order [[Clymeniida]] Wedekind 1927  
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:Order [[Goniatitida]] Hyatt 1884  
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  Order [[Prolecanitida]] Miller & Furnish 1954  
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:Order [[Clymeniida]] Wedekind 1927  
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  Order [[Ceratitida]] Hyatt 1884  
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:Order [[Prolecanitida]] Miller & Furnish 1954  
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  Order [[Phyllocerida]] Kuhn, 1940  
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:Order [[Ceratitida]] Hyatt 1884  
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  Order [[Lytocerida]] Hyatt 1889  
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:Order [[Phyllocerida]] Kuhn, 1940  
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  Order [[Ammonitida]] Agassiz 1847  
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:Order [[Lytocerida]] Hyatt 1889  
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  Order [[Ancylocerida]] Wedman 1966  
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:Order [[Ammonitida]] Agassiz 1847  
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:Order [[Ancylocerida]] Wedman 1966  
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'''Infraclass Coleoidea''' Bather, 1888
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'''Infraclass Coleoidea''' Bather, 1888 <br>
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  Order [[Boletzkiyida]] Bandel, Reitner & Stürmer 1983
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(=Subclass [[Coleoidea]])
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  Order [[Aulococerida]] Wedman 1966
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:Order [[Aulococerida]] Wedman 1966
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  Order [[Belemnitida]] Zittel 1885
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:Order [[Boletzkiyida]] Bandel, Reitner & Stürmer 1983
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  Order [[Phragmoteuthida]] Jeletzky 1964
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:Order [[Belemnitida]] Zittel 1885
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  Order [[Teuthida]] Naef 1916
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:Order [[Belemnoteuthida]] Stolley 1919
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  Order [[Belemnoteuthida]] Stolley 1919
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:Order [[Phragmoteuthida]] Jeletzky 1964
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  Order [[Sepiida]] Naef 1916
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:Order [[Teuthida]] Naef 1916
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  Order [[Vampyromorpha]] Grimpe 1917
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:Order [[Sepiida]] Naef 1916
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  Order [[Octopodida]] Leach 1818
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:Order [[Octopodida]] Leach 1818
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:Order [[Vampyromorpha]] Grimpe 1917 (or in Octopodida)
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==[[Cephalopoda phylogeny|Evolutionary History]]==
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:'''Superordinal Classification''' from Wade, 1988.
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>Group (Subclass) '''Nautiloidea'''
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Superorder [[Plectronoceratoidea]]
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: Order: [[Plectronocerida]]
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: Order: [[Yanhecerida]] (or in Plectronocerida)
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: Order: [[Protactinocerida]] (or in Plectronocerida)
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: Order: [[Ellesmerocerida]].
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Superorder Endoceratoidea, = Order: [[Endocerida]]
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Superorder Actinoceratoidea, = Order: [[Actinocerida]]
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Superorder Discosoroidea, = Order: [[Discosorida]]
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Superorder [[Orthoceratoidea]]
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: Order: [[Orthocerida]]
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: Order: [[Pseudorthocerida]]
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: Order: [[Ascocerida]]
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Superorder [[Nautilitoidea]]
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: Order: [[Tarphycerida]]
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: Order: [[Oncocerida]]
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: Order: [[Nautilida]]
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>Group (subclass '''Dibranchia''')
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Superorder [[Bactritoidea]]
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: Order: [[Bactritida]]
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: Order: [[Aulococerida]]
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: Order: [[Spirulida]]
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Superorder [[Ammonoidea|Ammonitoidea]]
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(= subclass Ammonoidea, see for content)
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Superorder [[Coleoidea]]
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(= subclass Coleoidea)
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: Order: [[Belemnitida]]
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: Order: [[Phragmoteuthid]]
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: Order: [[Sepiida]]
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: Order: [[Teuthida]]
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: Order: [[Octopoda]]
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====[[Cephalopoda phylogeny|Evolutionary History]]====
==''References'' ==
==''References'' ==
Teichert,Curt 1988. "Main Features of Cephalopod Evolution", pp.19-20, in ''The Mollusca'' vol.12, ''Paleontology and Neontology of Cephalopods'', ed. by M.R. Clarke & E.R. Trueman, Academic Press, Harcourt Brace Jovanovich
Teichert,Curt 1988. "Main Features of Cephalopod Evolution", pp.19-20, in ''The Mollusca'' vol.12, ''Paleontology and Neontology of Cephalopods'', ed. by M.R. Clarke & E.R. Trueman, Academic Press, Harcourt Brace Jovanovich
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'''Credits'''   
'''Credits'''   
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© M. Alan Kazlev 1998-2002 with revisions by John M 2010.
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© M. Alan Kazlev 1998-2002 with revisions by John M 2010-2011.

Latest revision as of 11:56, 12 September 2014

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